YuriiS's questions

我有这个任务：

我得到一个书名列表作为输入。分发书籍，使每个书架上的书籍数量大致相同。书籍应按字母顺序从第一个书架到最后一个书架排序。架子的数量是恒定的 5 件。归还整理在书架上的书籍

private static List<ArrayList<Book>> getShelvesOfBooks(List<Book> books){

        List<Book> sortedBooks = books.stream()
                                .sorted(Comparator.comparing(Book::getName))
                                .collect(Collectors.toList());

        List<ArrayList<Book>> shelves = new ArrayList<>();
        ArrayList<Book> shelf1 = new ArrayList<>();
        ArrayList<Book> shelf2 = new ArrayList<>();
        ArrayList<Book> shelf3 = new ArrayList<>();
        ArrayList<Book> shelf4 = new ArrayList<>();
        ArrayList<Book> shelf5 = new ArrayList<>();

        for (int i = 0; i < sortedBooks.size(); i++) {
            if (i % 5 == 0){
                shelf1.add(sortedBooks.get(i));
            }
            if (i % 5 == 1){
                shelf2.add(sortedBooks.get(i));

            }
            if (i % 5 == 2){
                shelf3.add(sortedBooks.get(i));

            }
            if (i % 5 == 3){
                shelf4.add(sortedBooks.get(i));

            }
            if (i % 5 == 4){
                shelf5.add(sortedBooks.get(i));

            }
        }

        shelves.add(shelf1);
        shelves.add(shelf2);
        shelves.add(shelf3);
        shelves.add(shelf4);
        shelves.add(shelf5);

        return shelves;
    }

在这种情况下，书籍按字母顺序排序，但最终以错误的顺序出现在书架上。

shelf1 = [Book[name='Java в действии'], Book[name='Повесть о настоящем человеке']]
shelf2 = [Book[name='Аэропорт'], Book[name='Сказки']]
shelf3 = [Book[name='Война и мир'], Book[name='Собака Баскервилей']]
shelf4 = [Book[name='Игра престолов'], Book[name='Том Сойер']]
shelf5 = [Book[name='Мастер и Маргарита'], Book[name='Цитадель']]

排序后如何下订单

shelf1 = [Book[name='Java в действии'], [name='Аэропорт']]
shelf2 = [Book[name='Война и мир'], Book[name='Игра престолов']]
shelf3 = [Book[name='Мастер и Маргарита'], Book[name='Повесть о настоящем человеке']]
...

动作的算法会有所不同。可能有必要在将书插入书架之前进行动态分类。我只是不知道如何做到这一点，而且每个书架上仍然有大约相同数量的书籍。当书的数量不是 5 的倍数时，必须从第一个书架开始添加。也就是说，如果有 7 本书，那么第一层和第二层书架上会有两本书，其他书架上有一本。

任务是从字符串中仅获取唯一元素，必须删除所有重复元素。例子：

Input:
String line = "Однажды в стране и однажды в мире";
Output:
"стране и мире"

首先我得到一个单词数组

String[] words = str.replaceAll("[^\\da-zA-Za-яёА-ЯЁ ]", "").toLowerCase().split(" ");

然后我需要遍历这个数组并将第一个元素与后续元素进行比较，如果发现重复，则获取下一个元素，如果不重复，则将其放入List<String> uniqueWords = new ArrayList<>() 我写的列表中：

for (int i = 0; i < words.length; i++) {
    String temp = words[i];
    for (int j = 0; j < uniqueWords.size(); j++) {
        if (uniqueWords.get(j).equals(temp)){
            break;
        } else {
             uniqueWords.add(temp);
           }
      }
  }

for(String cell : uniqueWords){
    result.append(cell).append(" ");
 }
System.out.println(result);

但它不起作用。我遗漏了一些东西并且做错了，但我无法弄清楚。我想在不使用Map I ask for help in this matter 的情况下做到这一点。

给你一个由n 个数字组成的数组（数字可以是正数也可以是负数）和一个数字t。有必要找到最接近t的数组的三个元素的总和。例如 n = [-1, 2, 1, -4]; t = 1; 总和= -1 + 2 + 1 = 2；

我不知道如何遍历数组以获取所有可能选项的三个元素的总和。帮助我理解

我正在spring mvc使用Oracle. hibernate当我对数据库进行查询并选择所有数据时，得到一个对象列表，然后我获取这个列表的大小，然后一切正常。但是从数据库中提取所有数据是不好的。我需要发出一个请求，该请求将返回满足传递给请求的参数的行数。为此，我正在尝试使用Criteria. 我创建了一个构建器、一个谓词并执行了一个查询，但结果不是我所期望的。查询中的 Hibernate 进行交叉连接，然后将表中的所有行乘以包含所需参数的行。表中只有7条记录，其中只有4条满足参数，查询结果是28条，而不是预期的4条。下面是代码片段。实体类：

@Entity(name = "Relationship")
@Table(name = "RELATIONSHIP")
public class Relationship extends IdEntity{
    private Long id;
    private User userFrom;
    private User userTo;
    private Date acceptedFriends;
    private RelationshipStatusType statusType;
    private Set<User> users = new HashSet<>();

    public Relationship() {
    }

    @Id
    @SequenceGenerator(name = "R_SHIP_SQ", sequenceName = "RELATIONSHIP_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "R_SHIP_SQ")
    @Column(name = "RELATIONSHIP_ID")
    @Override
    public Long getId() {
        return id;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_USER_FROM")
    public User getUserFrom() {
        return userFrom;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_USER_TO")
    public User getUserTo() {
        return userTo;
    }

    @Enumerated(EnumType.STRING)
    @Column(name = "STATUS_TYPE")
    public RelationshipStatusType getStatusType() {
        return statusType;
    }

    @JsonIgnore
    @ManyToMany(mappedBy = "statuses")
    Set<User> getUsers() {
        return users;
    }

枚举类：

public enum RelationshipStatusType {
    REQUESTED("REQUESTED"),
    CANCELED("CANCELED"),
    DECLINED("DECLINED"),
    DELETED("DELETED"),
    ACCEPTED("ACCEPTED");

    private String value;

    RelationshipStatusType(final String value){
        this.value = value;
    }

    public String getValue(){
        return value;
    }

    @Override
    public String toString(){
        return this.getValue();
    }
}

DAO：

@Repository("relationshipDAO")
@Transactional
public class RelationshipDAO extends GeneralDAO<Relationship> {

    private static final String GET_RELATIONSHIP = "SELECT * FROM RELATIONSHIP WHERE ID_USER_FROM = ? AND ID_USER_TO = ?";

    @SuppressWarnings("unchecked")
    public Relationship getRelationship(Long idUserFrom, Long idUserTo)throws InternalServerError {
        Relationship relationship;
        NativeQuery<Relationship> query = (NativeQuery<Relationship>) getEntityManager().createNativeQuery(GET_RELATIONSHIP, Relationship.class);
        try {
            relationship = query.setParameter(1, idUserFrom).setParameter(2, idUserTo).uniqueResult();
        }catch (NoResultException e){
            System.err.println(e.getMessage());
            throw e;
        }
        return relationship;
    }

    @SuppressWarnings("unchecked")
    public long getQuantityFriends(Long idUser, String status) throws InternalServerError{

        CriteriaBuilder criteriaBuilder = getEntityManager().getCriteriaBuilder();
        CriteriaQuery<Long> criteriaQuery = criteriaBuilder.createQuery(Long.class);
        Root<Relationship> relationshipRoot = criteriaQuery.from(Relationship.class);
        Predicate idUserPredicate = criteriaBuilder.equal(relationshipRoot.get("userTo"), idUser);
        Predicate statusPredicate = criteriaBuilder.equal(relationshipRoot.get("statusType"), RelationshipStatusType.valueOf(status));
        criteriaQuery.select(criteriaBuilder.count(criteriaQuery.from(Relationship.class)))
                .where(criteriaBuilder.and(idUserPredicate, statusPredicate));
        TypedQuery<Long> query = getEntityManager().createQuery(criteriaQuery);
        System.out.println("Quantity rows = " + query.getSingleResult());
        return query.getSingleResult();
    }
}

作为请求的结果，我在控制台中看到了这个：

23-May-2019 01:01:22.049 INFO [http-nio-8080-exec-9] org.hibernate.hql.internal.QueryTranslatorFactoryInitiator.initiateService HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select count(relationsh1_.RELATIONSHIP_ID) as col_0_0_ from RELATIONSHIP relationsh0_ cross join RELATIONSHIP relationsh1_ where relationsh0_.ID_USER_TO=90 and relationsh0_.STATUS_TYPE=?
Quantity rows = 28

为什么会弹出以cross join​​及如何解决？

我正在尝试制作一个迷你应用程序，类似于公告板。我似乎无法让它通过过滤器进行搜索。我试过了CriteriaBuilder，它没有弄清楚那里有什么以及为什么。然后我决定通过创建对数据库的动态查询来进行过滤。数据库Oracle。实体Ad- 声明：

@Entity
@Table(name = "AD")
public class Ad extends IdEntity{
    private Long id;
    private User user;
    private String name;
    private String description;
    private Integer price;
    private String city;
    private String numberPhone;
    private Date dateFrom;
    private Date dateTo;
    private CurrencyType currencyType;
    private CategoryType categoryType;
    private SubcategoryType subcategoryType;

    public Ad() {
    }

    @Id
    @SequenceGenerator(name = "AD_SQ", sequenceName = "AD_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "AD_SQ")
    @Column(name = "ID_AD")
    @Override
    public Long getId() {
        return id;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_USER")
    public User getUser() {
        return user;
    }

    @Column(name = "AD_NAME", nullable = false)
    public String getName() {
        return name;
    }

    @Column(name = "AD_DESCRIPTION", nullable = false)
    public String getDescription() {
        return description;
    }

    @Column(name = "PRICE", nullable = false)
    public Integer getPrice() {
        return price;
    }

    @Column(name = "CITY", nullable = false)
    public String getCity() {
        return city;
    }

    @Column(name = "NUMBER_PHONE", nullable = false)
    public String getNumberPhone() {
        return numberPhone;
    }

    @Column(name = "DATE_FROM", nullable = false)
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy'T'hh:mm")
    public Date getDateFrom() {
        return dateFrom;
    }

    @Column(name = "DATE_TO", nullable = false)
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy'T'hh:mm")
    public Date getDateTo() {
        return dateTo;
    }

    @Enumerated(EnumType.STRING)
    @Column(name = "CURRENCY_TYPE", nullable = false)
    public CurrencyType getCurrencyType() {
        return currencyType;
    }

    @Enumerated(EnumType.STRING)
    @Column(name = "CATEGORY_TYPE", nullable = false)
    public CategoryType getCategoryType() {
        return categoryType;
    }

    @Enumerated(EnumType.STRING)
    @Column(name = "SUBCATEGORY_TYPE", nullable = false)
    public SubcategoryType getSubcategoryType() {
        return subcategoryType;
    }

    @JsonCreator
    public static Ad createFromJson(String jsonString){
        ObjectMapper objectMapper = new ObjectMapper();
        Ad ad = null;

        try {
            ad = objectMapper.readValue(jsonString, Ad.class);
        }catch (IOException e){
            e.printStackTrace();
        }
        return ad;
    //getters and setters, equals and hash code 
    //I don’t give this data, but they exist
    }

Filter：

public class Filter {
    private CategoryType categoryType;
    private String city;
    private String description;

    public Filter() {
    }

    public CategoryType getCategoryType() {
        return categoryType;
    }

    public void setCategory(CategoryType categoryType) {
        this.categoryType = categoryType;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    @JsonCreator
    public static Filter createFromJson(String jsonString){
        ObjectMapper objectMapper = new ObjectMapper();
        Filter filter = null;

        try {
            filter = objectMapper.readValue(jsonString, Filter.class);
        }catch (IOException e){
            e.printStackTrace();
        }
        return filter;
    }

    @Override
    public String toString() {
        return new StringJoiner(", ", Filter.class.getSimpleName() + "[", "]")
                .add("categoryType=" + categoryType)
                .add("city='" + city + "'")
                .add("description='" + description + "'")
                .toString();
    }
}

类AdDAO：

@Repository("adDAO")
@Transactional
public class AdDAO extends GeneralDAO<Ad> {

    @SuppressWarnings("SqlResolve")
    private static final String SQL_GET_ADS_BY_CURRENT_DATE = "SELECT * FROM AD WHERE ROWNUM < 101 AND DATE_TO > ? ORDER BY DATE_TO DESC";
    private static final String SQL_GET_ADS_BY_FILTER = "SELECT * FROM AD WHERE ROWNUM < 101 AND DATE_TO > ? AND AD_DESCRIPTION LIKE ?";

    //1. получить текущую дату
    //2. сравнить в запросе текущую дату с датой объекта
    //3. если дата объекта меньше текущей даты то взять этот объект из базы данных
    //4. выводить только 100 последних объектов удовлетворяющих условию по дате
    @SuppressWarnings("unchecked")
    public List<Ad> get100Ad(){
        Date currentDate = new Date();

        NativeQuery<Ad> query = (NativeQuery<Ad>) getEntityManager().createNativeQuery(SQL_GET_ADS_BY_CURRENT_DATE, Ad.class);
        return query.setParameter(1, currentDate, TemporalType.TIMESTAMP).getResultList();
    }

    @SuppressWarnings("unchecked")
    public List<Ad> findAds(Filter filter){
        Date currentDate = new Date();
        String findByWord = filter.getDescription();
        System.out.println("FindByWord " + findByWord);

        NativeQuery<Ad> adQuery = (NativeQuery<Ad>) getEntityManager().createNativeQuery(createQuery(filter), Ad.class);
        adQuery.setParameter(2, "%'" + findByWord + "'%");
        adQuery.setParameter(1, currentDate, TemporalType.TIMESTAMP);

        return adQuery.getResultList();
    }

    private String createQuery(Filter filter){
        StringBuilder stringBuilder = new StringBuilder();

        stringBuilder.append(SQL_GET_ADS_BY_FILTER);

        if (filter.getCategoryType() != null){
            stringBuilder.append(" AND CATEGORY_TYPE = '").append(filter.getCategoryType().toString()).append("'");
        }

        if (filter.getCity() != null){
            stringBuilder.append(" AND CITY = '").append(filter.getCity()).append("'");
        }

        return stringBuilder.append(" ORDER BY DATE_TO DESC").toString();
    }
}

获取最后一百个广告的方法get100Ad()，考虑到日期，工作并返回找到的广告。并且该方法findAds(Filter filter)不断返回一个空列表，尽管数据库中有满足请求的对象。告诉我出了什么事？我的错误或错误是什么？

到目前为止，我已经设法只填充i[0] i[1]和j[0] j[1]，即只有两行和两列。这是代码：

    private static final int ROWS = 6;
    private static final int COLUMN = 6;

        public static void main(String[] args) {
            show(deepArray1());

        }

        private static int[][] deepArray1(){
            int[][] arrays = new int[ROWS][COLUMN];
            int x = 1;
            int y = 1;

            for (int i = 0; i < ROWS; i++) {
                for (int j = 0; j < COLUMN; j++) {
                    if (i == 0 || j == 0){
                        arrays[i][j] = 1;
                    }
                    if (i == 1){
                        arrays[i][j] = x++;
                    }
                    if (j == 1){
                        arrays[i][j] = y++;
                    }

                }
            }
            return arrays;
        }

private static void show(int[][] arrays){
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLUMN; j++) {
                System.out.print(" " + arrays[i][j] + " ");
            }
            System.out.println();
        }
    }

此外，我了解单元格[2] [2]填充了单元格总和获得的值[2][1] + [1][2]，随后的单元格根据此原理填充。在这种情况下，数组的长度已经等于(COLUMN / 3) * 2，即原始长度的三分之二。但我不知道如何用代码编写它。请帮我完成这部分任务。

我查询String SQL_SUM_FILES_SIZE_IN_STORAGE = "SELECT SUM(SIZE_FILE) FROM FILE_ JOIN STORAGE_ ON FILE_.STORAGE_ID_F = STORAGE_.STORAGE_ID WHERE STORAGE_.STORAGE_ID = :idParam";数据库，使用数据库Oracle，得到列中所有值的总和SIZE_FILE。我正在尝试这样做：

public Integer sumSizeFilesInStorage(Long idStorage){
    Integer amount;

    try (Session session = createSessionFactory().openSession()){
        NativeQuery query = session.createNativeQuery(SQL_SUM_FILES_SIZE_IN_STORAGE);
        query.setParameter("idParam", idStorage);
        amount = (Integer) query.getSingleResult();
    }
    return amount;
}

但我收到一个错误：

Exception in thread "main" java.lang.IllegalArgumentException: Unknown parameter position: 1
    at org.hibernate.query.internal.QueryParameterBindingsImpl.getBinding(QueryParameterBindingsImpl.java:240)
    at org.hibernate.query.internal.AbstractProducedQuery.setParameter(AbstractProducedQuery.java:503)
    at org.hibernate.query.internal.NativeQueryImpl.setParameter(NativeQueryImpl.java:592)
    at org.hibernate.query.internal.NativeQueryImpl.setParameter(NativeQueryImpl.java:56)
    at dz_spring_3.dao.FileDAO.sumSizeFilesInStorage(FileDAO.java:122)
    at dz_spring_3.Demo.main(Demo.java:11)

如果我尝试这样做amount = (Long) query.uniqueResult();，我会收到一个错误：

Exception in thread "main" java.lang.ClassCastException: java.math.BigDecimal cannot be cast to java.lang.Long
    at dz_spring_3.dao.FileDAO.sumSizeFilesInStorage(FileDAO.java:123)
    at dz_spring_3.Demo.main(Demo.java:11)

但我不知道如何将其转换为正确的类型（（

告诉我如何将从请求中收到的金额分配给变量Integer amount？

我需要通过查询file从数据库中获取对象列表。GET有两个类：

File:

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.databind.ObjectMapper;

import javax.persistence.*;
import java.io.IOException;
import java.util.Objects;

@Entity
@Table(name = "FILE_")
public class File {

    private Long id;
    private Long storageId;
    private String name;
    private String format;
    private Long size;
    private Storage storage;

    public File() {
    }

    @Id
    @SequenceGenerator(name = "F_SQ", sequenceName = "FILE_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "F_SQ")
    @Column(name = "FILE_ID")
    public Long getId() {
        return id;
    }

    @JsonIgnore
    //@JoinColumn(name = "STORAGE_ID_F")
    public Long getStorageId() {
        return storageId;
    }

    @Column(name = "NAME_FILE")
    public String getName() {
        return name;
    }

    @Column(name = "FORMAT_FILE")
    public String getFormat() {
        return format;
    }

    @Column(name = "SIZE_FILE")
    public Long getSize() {
        return size;
    }

    @JsonIgnore
    @ManyToOne(targetEntity = Storage.class, fetch = FetchType.LAZY)
    @JoinColumn(name = "STORAGE_ID_F")
    public Storage getStorage() {
        return storage;
    }

    @JsonCreator
    public static File createFromJson(String jsonString){

        ObjectMapper objectMapper = new ObjectMapper();

        File file = null;
        try {
            file = objectMapper.readValue(jsonString, File.class);
        }catch (IOException e){
            e.printStackTrace();
        }

        return file;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setStorageId(Long storageId) {
        this.storageId = storageId;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setFormat(String format) {
        this.format = format;
    }

    public void setSize(Long size) {
        this.size = size;
    }

    public void setStorage(Storage storage) {
        this.storage = storage;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        File file = (File) o;
        return Objects.equals(storageId, file.storageId) &&
                Objects.equals(name, file.name) &&
                Objects.equals(format, file.format) &&
                Objects.equals(size, file.size) &&
                Objects.equals(storage, file.storage);
    }

    @Override
    public int hashCode() {
        return Objects.hash(storageId, name, format, size, storage);
    }

    @Override
    public String toString() {
        return "File{" +
                "id=" + id +
                " name='" + name + '\'' +
                ", format='" + format + '\'' +
                ", size=" + size +
                ", storage=" + storage.getId() +
                '}';
    }
}

Storage：

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.databind.ObjectMapper;

import javax.persistence.*;
import java.io.IOException;
import java.util.List;
import java.util.Objects;

@Entity
@Table(name = "STORAGE_")
public class Storage {

    private Long id;
    private String formatsSupported;
    private String storageCountry;
    private Long storageSize;
    private List<File> files;

    public Storage() {
    }

    @Id
    @SequenceGenerator(name = "ST_SQ", sequenceName = "STORAGE_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "ST_SQ")
    @Column(name = "STORAGE_ID")
    public Long getId() {
        return id;
    }

    @Column(name = "FORMAT_SUPPORTED")
    public String getFormatsSupported() {
        return formatsSupported;
    }

    @Column(name = "COUNTRY_STORAGE")
    public String getStorageCountry() {
        return storageCountry;
    }

    @Column(name = "SIZE_STORAGE")
    public Long getStorageSize() {
        return storageSize;
    }

    @OneToMany(mappedBy = "storage", fetch = FetchType.LAZY, targetEntity = File.class)
    public List<File> getFiles() {
        return files;
    }

    @JsonCreator
    public static Storage createFromJson(String jsonString){

        ObjectMapper objectMapper = new ObjectMapper();

        Storage storage = null;
        try {
            storage = objectMapper.readValue(jsonString, Storage.class);
        }catch (IOException e){
            e.printStackTrace();
        }

        return storage;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setFormatsSupported(String formatsSupported) {
        this.formatsSupported = formatsSupported;
    }

    public void setStorageCountry(String storageCountry) {
        this.storageCountry = storageCountry;
    }

    public void setStorageSize(Long storageSize) {
        this.storageSize = storageSize;
    }

    public void setFiles(List<File> files) {
        this.files = files;
    }
}

在类Controller中，一个方法请求从数据库中获取对象列表，使用数据库Oracle：

import com.fasterxml.jackson.databind.ObjectMapper;
import dz_spring_3.dao.FileDAO;
import dz_spring_3.dao.StorageDAO;
import dz_spring_3.model.File;
import dz_spring_3.model.Storage;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;
import java.io.BufferedReader;
import java.io.IOException;

@org.springframework.stereotype.Controller
public class Controller {

    @Autowired
    Service service;

    @Autowired
    StorageDAO storageDAO;

    @Autowired
    FileDAO fileDAO;

    @RequestMapping(method = RequestMethod.POST, value = "/saveFile", produces = "text/plain")
    @ResponseBody
    public String saveFile(HttpServletRequest req)throws IOException {

        File file = mappingFile(req);

        if (file.getId() != null)
            return "Storage with id - " + file.getId() + " can`t be saved in DB.";

        file.setStorageId(storageDAO.findById(3L).getId());

        service.saveFile(file);

        return "File with id - " + file.getId() + " saved success.";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/file", produces = "text/plain")
    @ResponseBody
    public String getAllFile(){

        return service.getAllFile().toString();
    }

    private File mappingFile(HttpServletRequest req)throws IOException {

        StringBuilder stringBuilder = new StringBuilder();

        try(BufferedReader reader = req.getReader()) {
            String line;

            while ((line = reader.readLine()) != null){
                System.out.println("Line in wile (mapping) - " + line);
                stringBuilder.append(line);
            }
        }

        ObjectMapper objectMapper = new ObjectMapper();

        String input = objectMapper.writeValueAsString(stringBuilder.toString());

        File file = objectMapper.convertValue(input, File.class);

        return file;
    }

类FileDAO：

import dz_spring_3.model.File;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.NativeQuery;

import javax.persistence.TypedQuery;
import java.util.List;

public class FileDAO extends GeneralDAO<File> {

    private static final String SQL_GET_ALL_FILES = "SELECT * FROM FILE_";
    private static final String SQL_GET_BY_ID_FILE = "SELECT * FROM FILE_ WHERE FILE_ID = ?";

    @SuppressWarnings("unchecked")
    public List<File> getAllFile(){
        List<File> files;

        try(Session session = createSessionFactory().openSession()) {

            NativeQuery query = session.createNativeQuery(SQL_GET_ALL_FILES);
            files = query.addEntity(File.class).list();

        }catch (HibernateException e){
            System.err.println(e.getMessage());
            throw new HibernateException("Operation failed");
        }
        return files;
    }

    public File saveFile(File file) {

        Transaction tr = null;
        try(Session session = createSessionFactory().openSession()) {
            tr = session.getTransaction();
            tr.begin();

            session.save(file);

            tr.commit();
        }catch (HibernateException e){
            System.err.println("Save is failed.");
            System.err.println(e.getMessage());
            if (tr != null)
                tr.rollback();
        }

        return file;
    }

    public void updateFile(File file){

        Transaction transaction = null;
        try(Session session = createSessionFactory().openSession()) {
            transaction = session.getTransaction();
            transaction.begin();

            session.update(file);

            transaction.commit();
        }
        catch (HibernateException e){

            if (transaction != null)
                transaction.rollback();

            System.err.println(e.getMessage());
            throw new HibernateException("Operation failed.");
        }
    }

    public void deleteFile(Long id){

        Transaction transaction = null;
        try(Session session = createSessionFactory().openSession()) {
            transaction = session.getTransaction();
            transaction.begin();

            session.delete(findById(id));

            transaction.commit();
        }
        catch (HibernateException e){

            if (transaction != null)
                transaction.rollback();

            System.err.println(e.getMessage());
            throw new HibernateException("Operation failed.");
        }
    }

    @SuppressWarnings("unchecked")
    public File findById(Long id){

        File file;

        try(Session session = createSessionFactory().openSession()) {

            NativeQuery query = session.createNativeQuery(SQL_GET_BY_ID_FILE);
            if (getSingleResult(query, id) == null){
                file = null;
            }
            else
                file = (File) query.addEntity(File.class).setParameter(1, id).getSingleResult();

        }catch (HibernateException e){
            System.err.println(e.getMessage());
            throw new HibernateException("Operation failed.");
        }
        return file;
    }

    private <T> T getSingleResult(TypedQuery<T> query, Long id){
        query.setMaxResults(1);

        List<T> list = query.setParameter(1, id).getResultList();

        if (list == null || list.isEmpty()){

            return null;
        }
        return list.get(0);
    }
}

在我启动服务器Tomcat并发出请求 http://localhost:8080/file后，出现了几个错误，这是堆栈跟踪：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not execute query
        org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
        org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    Root Cause

    javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not execute query
        org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:149)
        org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157)
        org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1423)
        dz_spring_3.dao.FileDAO.getAllFile(FileDAO.java:24)
        dz_spring_3.Service.getAllFile(Service.java:56)
        dz_spring_3.Controller.getAllFile(Controller.java:111)
        sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        java.lang.reflect.Method.invoke(Method.java:498)
        org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
        org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
        org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
        org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
        org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    Root Cause

    org.hibernate.exception.GenericJDBCException: could not execute query
        org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:47)
        org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
        org.hibernate.loader.Loader.doList(Loader.java:2695)
        org.hibernate.loader.Loader.doList(Loader.java:2675)
        org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2507)
        org.hibernate.loader.Loader.list(Loader.java:2502)
        org.hibernate.loader.custom.CustomLoader.list(CustomLoader.java:335)
        org.hibernate.internal.SessionImpl.listCustomQuery(SessionImpl.java:2161)
        org.hibernate.internal.AbstractSharedSessionContract.list(AbstractSharedSessionContract.java:1016)
        org.hibernate.query.internal.NativeQueryImpl.doList(NativeQueryImpl.java:152)
        org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1414)
        dz_spring_3.dao.FileDAO.getAllFile(FileDAO.java:24)
        dz_spring_3.Service.getAllFile(Service.java:56)
        dz_spring_3.Controller.getAllFile(Controller.java:111)
        sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        java.lang.reflect.Method.invoke(Method.java:498)
        org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
        org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
        org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
        org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
        org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    Root Cause

    java.sql.SQLException: Недопустимое имя столбца
        oracle.jdbc.driver.OracleStatement.getColumnIndex(OracleStatement.java:3965)
        oracle.jdbc.driver.InsensitiveScrollableResultSet.findColumn(InsensitiveScrollableResultSet.java:299)
        oracle.jdbc.driver.GeneratedResultSet.getLong(GeneratedResultSet.java:1361)
        org.hibernate.type.descriptor.sql.BigIntTypeDescriptor$2.doExtract(BigIntTypeDescriptor.java:63)
        org.hibernate.type.descriptor.sql.BasicExtractor.extract(BasicExtractor.java:47)
        org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:261)
        org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:257)
        org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:247)
        org.hibernate.type.AbstractStandardBasicType.hydrate(AbstractStandardBasicType.java:333)
        org.hibernate.persister.entity.AbstractEntityPersister.hydrate(AbstractEntityPersister.java:2854)
        org.hibernate.loader.Loader.loadFromResultSet(Loader.java:1747)
        org.hibernate.loader.Loader.instanceNotYetLoaded(Loader.java:1673)
        org.hibernate.loader.Loader.getRow(Loader.java:1562)
        org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:732)
        org.hibernate.loader.Loader.processResultSet(Loader.java:991)
        org.hibernate.loader.Loader.doQuery(Loader.java:949)
        org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:341)
        org.hibernate.loader.Loader.doList(Loader.java:2692)
        org.hibernate.loader.Loader.doList(Loader.java:2675)
        org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2507)
        org.hibernate.loader.Loader.list(Loader.java:2502)
        org.hibernate.loader.custom.CustomLoader.list(CustomLoader.java:335)
        org.hibernate.internal.SessionImpl.listCustomQuery(SessionImpl.java:2161)
        org.hibernate.internal.AbstractSharedSessionContract.list(AbstractSharedSessionContract.java:1016)
        org.hibernate.query.internal.NativeQueryImpl.doList(NativeQueryImpl.java:152)
        org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1414)
        dz_spring_3.dao.FileDAO.getAllFile(FileDAO.java:24)
        dz_spring_3.Service.getAllFile(Service.java:56)
        dz_spring_3.Controller.getAllFile(Controller.java:111)
        sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        java.lang.reflect.Method.invoke(Method.java:498)
        org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
        org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
        org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
        org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
        org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    Note The full stack trace of the root cause is available in the server logs.

据我了解，这个问题是由于字段storageId，当我完全删除它时，会读取数据库中的数据。但是我需要这个字段，以便将对象存储在数据库中以file访问该文件所在id的存储空间。storage好吧，当您尝试file通过请求保存到数据库时Post，也会出现错误：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Unable to release JDBC Connection
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
</pre><p><b>Root Cause</b></p><pre>javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Unable to release JDBC Connection
org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:149)
    org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157)
    org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1423)
    org.hibernate.query.Query.getResultList(Query.java:146)
    dz_spring_3.dao.StorageDAO.getSingleResult(StorageDAO.java:119)
    dz_spring_3.dao.StorageDAO.findById(StorageDAO.java:103)
    dz_spring_3.Controller.saveFile(Controller.java:98)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
</pre><p><b>Root Cause</b></p><pre>org.hibernate.exception.JDBCConnectionException: Unable to release JDBC Connection
    org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:115)
    org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
    org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
    org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.releaseConnection(LogicalConnectionManagedImpl.java:199)
    org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.afterTransaction(LogicalConnectionManagedImpl.java:162)
    org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.afterTransaction(JdbcCoordinatorImpl.java:288)
    org.hibernate.internal.SessionImpl.afterOperation(SessionImpl.java:557)
    org.hibernate.internal.SessionImpl.listCustomQuery(SessionImpl.java:2168)
    org.hibernate.internal.AbstractSharedSessionContract.list(AbstractSharedSessionContract.java:1016)
    org.hibernate.query.internal.NativeQueryImpl.doList(NativeQueryImpl.java:152)
    org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1414)
    org.hibernate.query.Query.getResultList(Query.java:146)
    dz_spring_3.dao.StorageDAO.getSingleResult(StorageDAO.java:119)
    dz_spring_3.dao.StorageDAO.findById(StorageDAO.java:103)
    dz_spring_3.Controller.saveFile(Controller.java:98)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
</pre><p><b>Root Cause</b></p><pre>java.sql.SQLRecoverableException: Закрытое соединение

文件hibernate.cfg.xml：

Что-то делаю не правильно, а вот что именно не могу понять. Прошу подсказать или объяснить, как мне получить список объектов и сохранять объекты file в базу данных.

我的任务是创建post запрос一个对象，从中获取一个对象Item并将其保存到数据库Oracle中。为了模拟一个请求，我在其中使用Postmen并创建了一个这样的请求：

我使用该库来处理jackson：

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.6.3</version>
    </dependency>

实体类：

import javax.persistence.*;
import java.util.Date;

@Entity
@Table(name = "ITEM")
public class Item {
    private Long id;
    private String name;
    private Date dateCreated;
    private Date lastUpdateDate;
    private String description;

    public Item() {
    }

    public Item(String name, Date dateCreated, Date lastUpdateDate, String description) {
        this.name = name;
        this.dateCreated = dateCreated;
        this.lastUpdateDate = lastUpdateDate;
        this.description = description;
    }

    @Id
    @SequenceGenerator(name = "IT_SQ", sequenceName = "ITEM_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "IT_SQ")
    public Long getId() {
        return id;
    }

    @Column(name = "NAME")
    public String getName() {
        return name;
    }

    @Column(name = "DATE_CREATED")
    public Date getDateCreated() {
        return dateCreated;
    }

    @Column(name = "LAST_UPDATE_DATE")
    public Date getLastUpdateDate() {
        return lastUpdateDate;
    }

    @Column(name = "DESCRIPTION")
    public String getDescription() {
        return description;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setDateCreated(Date dateCreated) {
        this.dateCreated = dateCreated;
    }

    public void setLastUpdateDate(Date lastUpdateDate) {
        this.lastUpdateDate = lastUpdateDate;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    @Override
    public String toString() {
        return "Item{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", dateCreated=" + dateCreated +
                ", lastUpdateDate=" + lastUpdateDate +
                ", description='" + description + '\'' +
                '}';
    }
}

方法doPost：

import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;

@WebServlet(urlPatterns = "/test")
public class MyServlet extends HttpServlet {

    private ItemDAO itemDAO = new ItemDAO();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)throws IOException {
        //передать параметр из строки браузера в метод
        //найти по параметру объект в базе
        //вернуть объект в строковом представлении в браузер

        //String id = req.getParameter("param");

        //long idItem = Long.parseLong(id);

        //ItemDAO itemDAO = new ItemDAO();

        //itemDAO.findById(Long.parseLong(req.getParameter("param")));

        resp.getWriter().println(itemDAO.findById(Long.parseLong(req.getParameter("param"))).toString());

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException{
        //считать данные из запроса
        //по ключам промапить объект
        //сделать валидацию, проверить есть ли объект с таким айди в базе
        //сохранить объект в базу
        StringBuilder stringBuilder = new StringBuilder();
        String line = null;

        BufferedReader reader = req.getReader();
        while ((line = reader.readLine()) != null){
            stringBuilder.append(line);
        }

        String json = stringBuilder.toString();

        System.out.println("Input string - " + json);

        ObjectMapper objectMapper = new ObjectMapper();
        Item item = objectMapper.convertValue(json, Item.class);

        System.out.println("Object after mapping: " + item);


    }

我运行它来检查对象是如何映射的，我得到一个错误：

06-Jul-2018 11:35:38.841 SEVERE [http-nio-8080-exec-5] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [MyServlet] in context with path [] threw exception
 java.lang.IllegalArgumentException: Can not instantiate value of type [simple type, class Item] from String value ('{    "name":"Item1",    "dateCreated":"04.07.2018",    "lastUpdateDate":"05.07.2018",    "description":"description1"}'); no single-String constructor/factory method
 at [Source: N/A; line: -1, column: -1]
    at com.fasterxml.jackson.databind.ObjectMapper._convert(ObjectMapper.java:3459)
    at com.fasterxml.jackson.databind.ObjectMapper.convertValue(ObjectMapper.java:3378)
    at MyServlet.doPost(MyServlet.java:53)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:494)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:412)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1385)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class Item] from String value ('{    "name":"Item1",    "dateCreated":"04.07.2018",    "lastUpdateDate":"05.07.2018",    "description":"description1"}'); no single-String constructor/factory method
 at [Source: N/A; line: -1, column: -1]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:878)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:281)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:284)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1176)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:145)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
    at com.fasterxml.jackson.databind.ObjectMapper._convert(ObjectMapper.java:3454)
    ... 26 more

告诉我我做错了什么以及如何修复我的错误以便创建一个对象Item。

我无法弄清楚为什么Exception in thread "main" java.lang.IllegalArgumentException: Unknown entity: java.lang.Long在运行 delete 方法时会发生错误(Long id)。这些方法save(Item item), update(Item item) and findById(Long id可以正常工作。请告诉我可能出了什么问题。类Item：

import javax.persistence.*;
import java.util.Date;

@Entity
@Table(name = "ITEM")
public class Item {
    private Long id;
    private String name;
    private Date dateCreated;
    private Date lastUpdateDate;
    private String description;

    public Item() {
    }

    public Item(String name, Date dateCreated, Date lastUpdateDate, String description) {
        this.name = name;
        this.dateCreated = dateCreated;
        this.lastUpdateDate = lastUpdateDate;
        this.description = description;
    }

    @Id
    @SequenceGenerator(name = "IT_SQ", sequenceName = "ITEM_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "IT_SQ")
    public Long getId() {
        return id;
    }

    @Column(name = "NAME")
    public String getName() {
        return name;
    }

    @Column(name = "DATE_CREATED")
    public Date getDateCreated() {
        return dateCreated;
    }

    @Column(name = "LAST_UPDATE_DATE")
    public Date getLastUpdateDate() {
        return lastUpdateDate;
    }

    @Column(name = "DESCRIPTION")
    public String getDescription() {
        return description;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setDateCreated(Date dateCreated) {
        this.dateCreated = dateCreated;
    }

    public void setLastUpdateDate(Date lastUpdateDate) {
        this.lastUpdateDate = lastUpdateDate;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    @Override
    public String toString() {
        return "Item{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", dateCreated=" + dateCreated +
                ", lastUpdateDate=" + lastUpdateDate +
                ", description='" + description + '\'' +
                '}';
    }
}

类ItemDAO：

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.NativeQuery;

public class ItemDAO {

    private static SessionFactory sessionFactory;

    private static final String SQL_GET_ITEM_BY_ID = "SELECT * FROM ITEM WHERE ID = ?";

    public Item save(Item item){

        Transaction transaction = null;
        try(Session session = createSessionFactory().openSession()) {
            transaction = session.getTransaction();
            transaction.begin();

            session.save(item);

            transaction.commit();
            System.out.println("Saved successfully");
        }catch (HibernateException e){
            System.err.println("Saved is failed");
            System.err.println(e.getMessage());
            if (transaction != null)
                transaction.rollback();
        }
        return item;
    }

    public void update(Item item){

        Transaction transaction = null;
        try (Session session = createSessionFactory().openSession()){
            transaction = session.getTransaction();
            transaction.begin();

            session.update(item);

            System.out.println("Update was successful");

            transaction.commit();
        }catch (HibernateException e){
            System.err.println("Save is failed");
            System.err.println(e.getMessage());
            if (transaction != null)
                transaction.rollback();
        }
    }

    public void delete(Long id){

        Transaction transaction = null;
        try (Session session = createSessionFactory().openSession()){
            transaction = session.getTransaction();
            transaction.begin();

            session.delete(id);

            System.out.println("Recording deleted successfully");

            transaction.commit();
        }catch (HibernateException e){
            System.err.println("Save is failed");
            System.err.println(e.getMessage());
            if (transaction != null)
                transaction.rollback();
        }
    }

    @SuppressWarnings("unchecked")
    public Item findById(Long id){

        Item item;

        try (Session session = createSessionFactory().openSession()){

            NativeQuery query = session.createNativeQuery(SQL_GET_ITEM_BY_ID);
            item = (Item) query.addEntity(Item.class).setParameter(1, id).getSingleResult();

        }catch (HibernateException e){
            System.err.println("Save is failed");
            System.err.println(e.getMessage());
            throw e;
        }
        System.out.println("Save is done");

        return item;
    }

    private static SessionFactory createSessionFactory(){
        if (sessionFactory == null){
            sessionFactory = new Configuration().configure().buildSessionFactory();
        }
        return sessionFactory;
    }
}

Pom file：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>crud-servlet</groupId>
    <artifactId>crud-servlet</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.0-b07</version>
            <!--<scope>provided</scope>-->
        </dependency>

        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc7</artifactId>
            <version>12.1.0</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.16.Final</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.6.3</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

文件hibernate.cfg.xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="hibernate.connection.url">jdbc:oracle:thin:@gromcode-lesson.cjqbbseqr63c.eu-central-1.rds.amazonaws.com:1521:ORCL</property>
        <property name="hibernate.connection.username">main</property>
        <property name="hibernate.connection.password">ifgjrkzr</property>

        <property name="show_sql">true</property>
        <mapping class="Item"></mapping>
    </session-factory>

    <!--<open_tag params>value</open_tag>-->
</hibernate-configuration>

实际的堆栈跟踪有错误：

    июн 26, 2018 7:35:33 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {5.2.16.Final}
июн 26, 2018 7:35:33 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
июн 26, 2018 7:35:33 PM org.hibernate.boot.jaxb.internal.stax.LocalXmlResourceResolver resolveEntity
WARN: HHH90000012: Recognized obsolete hibernate namespace http://hibernate.sourceforge.net/hibernate-configuration. Use namespace http://www.hibernate.org/dtd/hibernate-configuration instead.  Support for obsolete DTD/XSD namespaces may be removed at any time.
июн 26, 2018 7:35:34 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.0.1.Final}
июн 26, 2018 7:35:34 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
июн 26, 2018 7:35:34 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [oracle.jdbc.driver.OracleDriver] at URL [jdbc:oracle:thin:@gromcode-lesson.cjqbbseqr63c.eu-central-1.rds.amazonaws.com:1521:ORCL]
июн 26, 2018 7:35:34 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {user=main, password=****}
июн 26, 2018 7:35:34 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
июн 26, 2018 7:35:34 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
июн 26, 2018 7:35:35 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.Oracle10gDialect
Exception in thread "main" java.lang.IllegalArgumentException: Unknown entity: java.lang.Long
    at org.hibernate.internal.SessionImpl.fireDelete(SessionImpl.java:1000)
    at org.hibernate.internal.SessionImpl.delete(SessionImpl.java:929)
    at ItemDAO.delete(ItemDAO.java:61)
    at Demo.main(Demo.java:23)
Caused by: org.hibernate.MappingException: Unknown entity: java.lang.Long
    at org.hibernate.metamodel.internal.MetamodelImpl.entityPersister(MetamodelImpl.java:620)
    at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1635)
    at org.hibernate.event.internal.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:82)
    at org.hibernate.event.internal.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:56)
    at org.hibernate.internal.SessionImpl.fireDelete(SessionImpl.java:993)
    ... 3 more

Process finished with exit code -1

一切似乎都是正确的，但某处缺少某些东西......

请帮助我理解这个艰难的时刻。我有两个实体类User，Hotel它们有字段long id和吸气剂。一对UserDAO继承HotelDAO自其中一个通用GeneralDAO<T>方法的类public T save(T t)。该方法的逻辑如下，如果id等于则保存对象0，即if(t.getId() == 0)我将对象保存到数据库中。您能否解释一下如何访问类字段User并Hotel在其中使用它们GeneralDAO<T>？

我有两个数组，其中包含格式作为字符串。例如：

formatsStorage [png, txt, doc]
formatsFile [jpg, txt, doc]

数组元素可以按任何顺序排列。例子：

formatsStorage [doc, png, txt]
formatsFile [txt, jpg, doc]

我需要创建一个方法来检查 , 中formatsFile的所有格式是否与formatsStorage. true如果数组中的每种格式formatsFile都在数组中formatsStorage，则该方法应返回，false如果数组formatsFile包含不在数组中的格式，则返回formatsStorage。

这是我到目前为止所做的，但它不能正常工作：

public boolean checkFormatAll(List<File> filesFrom, Storage storageTo) throws Exception {
    if (filesFrom == null || storageTo == null)
        throw new Exception("Incoming data contains an error");

    String[] formatsStorage = storageTo.getFormatSupported().split(",");

    Set<String> strings = new HashSet<>();

    for (File file : filesFrom) {
        strings.add(file.getFormat());
    }

    String[] formatsFile = strings.toArray(new String[strings.size()]);

    System.out.println("Formats in Storage " + Arrays.toString(formatsStorage));
    System.out.println("Formats in file " + Arrays.toString(formatsFile));

    boolean format = true;
    int countStorage = 0;
    int countFile = 0;

    /*if (formatsFile.length == 1){
        for (String fileFormat : formatsFile){
            for (String storageFormat : formatsStorage){
                if (fileFormat != null && storageFormat != null && fileFormat.equals(storageFormat.trim())){
                    return true;
                }
                else format = false;
            }
        }
    }*/  //Не знаю, оставлять это в отдельном ифе или всё делать в одном ?

    for (String fileFormat : formatsFile) {
        if (fileFormat != null) {
            for (String storageFormat : formatsStorage) {
                if (storageFormat != null && fileFormat.equals(storageFormat.trim()) && formatsFile.length == 1) {
                    return true;
                } else format = false;

                if (storageFormat != null && !fileFormat.equals(storageFormat.trim()) && formatsFile.length != 1) {
                    continue;
                } else format = false;

                if (storageFormat != null && !fileFormat.equals(storageFormat.trim()) && formatsFile.length - 1 != countFile) {
                    continue;
                }

                if (storageFormat != null && fileFormat.equals(storageFormat.trim())) {
                    format = true;
                    break;
                }

                System.out.println("Format in box storage - " + storageFormat + "; Line array Storage - " + countStorage);
                System.out.println("Format in box file - " + fileFormat + "; Line array File - " + countFile);

                countStorage++;
            }
            countFile++;
        }
    }
    return format;
}

我知道您需要将数组的每个元素与数组formatsFile的元素进行比较formatsStorage。为此，我通过 elements 进行双循环formatsStorage，但显然我在比较条件中犯了错误。请帮助修复错误。

有一堂课

public class File {

            private String format;
        }
//создаю список и помещаю в него объекты
List<File> filesFrom = new ArrayList<>();
        filesFrom.add(file1);
        filesFrom.add(file2);
        filesFrom.add(file3);
        filesFrom.add(file4);
        filesFrom.add(file5);

format某些对象的字段值是相同的。例如：file1 - "txt", file2 - "txt", file3 - "doc", file4 - "jpg",file5 - "txt" 我需要删除具有重复字段值的对象，以便最终只保留具有不同格式的对象。也就是说，对象file1, file3,file4

我正在尝试执行以下操作

for (int i = filesFrom.size() - 1; i > -1 ; i--) {
        if (filesFrom.get(0).getFormat().equals(filesFrom.get(i).getFormat())){
            filesFrom.remove(i);
        }
    }

事实证明，列表开头和结尾的所有文件都被删除，只有格式doc和jpg. 请告诉我如何达到预期的结果。

并且可能通过iterator它会更正确吗？但我不明白如何

数据库甲骨文。有三个数据表。我需要显示经理的姓名和他的最大交易量，在某个时间段内，如果这些最大值有几个，则全部显示。到目前为止，只显示了为每个名称汇总的名称和交易金额。这是我的要求

SELECT SALESMAN.NAME, SUM(DEAL.AMOUNTE)
FROM CUSTOMER
JOIN DEAL ON DEAL.CUSTOMER_ID = CUSTOMER.CUSTOMER_ID AND DEAL.DATE_ BETWEEN '01/08/17' AND '31/08/17'
JOIN SALESMAN ON SALESMAN.SALESMAN_ID = CUSTOMER.SALESMAN_ID
GROUP BY SALESMAN.NAME;

表输出

James Hoog  3000
Mc Lion 4500

告诉我如何更改查询以使其仅返回数字列中的最大值？我试图按需执行，使用它HAVING，但没有任何反应。语法有错误，或者缺少某些东西……某些东西无法达到预期的结果（（

该表有四列id、name和。我需要创建一个 void changeDescription() 方法，该方法从描述超过 100 的所有产品的描述中删除最后一句。我制作了该方法，直到最后一句被删除。 descriptionprice

private static void changeDescription(){
        try(Connection connection = DriverManager.getConnection(DB_URL, USER, PASS); Statement statement = connection.createStatement()) {

            String descriptionNew = "";
            try(ResultSet resultSet = statement.executeQuery("SELECT * FROM PRODUCT")){
                while (resultSet.next()){
                    String description = resultSet.getString(3);
                    if (description.length() > 100){
                        String[] arraySentences = description.split("[.]");
                        arraySentences[arraySentences.length - 1] = "";
                        for (String sentence : arraySentences){
                            if (sentence != null && !sentence.isEmpty()){
                                descriptionNew += sentence + ".";
                            }
                        }
                    }
                }
            }

            System.out.println(descriptionNew);
        }catch (SQLException e){
            System.err.println("Something went wrong");
            e.printStackTrace();
        }
    }

但是后来我不知道如何更新表中的数据，在描述列中。如何在更新请求中替换descriptionNew？

如何确保在输入某个命令后将输入到控制台的数据写入文件？在我的例子中，我们在控制台中输入了一些数据，在输入“end”之后，之前输入的所有内容都应该写入一个文件。对我来说，只有命令本身会被记录下来，而我在控制台中输入的所有内容都不会被记录下来。这是我的代码：

public static void writeToFileFromConsole(String path){

        InputStreamReader reader = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(reader);

        FileWriter writer = null;
        BufferedWriter bufferedWriter = null;

        System.out.println("Enter file content to write in the file:");

        try {
            String line;
            do {
                line = br.readLine();
                writer = new FileWriter(path, true);
                bufferedWriter = new BufferedWriter(writer);

                bufferedWriter.append("\n");
                bufferedWriter.append(line);
            }
            while (!line.equals("wr"));
        }catch (IOException e){
            System.err.println("Can't write to file with path " + path);
        }
        finally {
            try {
                br.close();
                reader.close();
                if (bufferedWriter != null){
                    bufferedWriter.close();
                }
                if (writer != null){
                    writer.close();
                }
            }catch (IOException e){
                System.err.println("File with path " + path + " not found" );
            }
        }
    }

我需要创建一个方法，将用户从控制台输入的所有内容写入给定路径的文件，而不覆盖文件的内容。写入文件必须在单独一行输入 wr 命令后完成。我做了这个方法，但由于它的工作，第一个导管立即起作用。调试程序时显示-该进程无法访问该文件，因为该文件已被另一个进程占用。

public static void writeToFileFromConsole(String path){

        InputStreamReader reader = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(reader);

        FileWriter writer = null;
        BufferedWriter bufferedWriter = null;

        System.out.println("Enter file content to write in the file:");

        try {
            String command = "wr";
            String line;
            line = br.readLine();
            if ((line = br.readLine()).equals(command)) {
                writer = new FileWriter(path, true);
                bufferedWriter = new BufferedWriter(writer);

                bufferedWriter.append("\n");
                bufferedWriter.append(line);
            }
        }catch (IOException e){
            System.err.println("Can't write to file with path " + path);
        }
        finally {
            try {
                reader.close();
                br.close();
                if (writer != null){
                    writer.close();
                }
                if (bufferedWriter != null){
                    bufferedWriter.close();
                }
            }catch (IOException e){
                System.err.println("File with path " + path + " not found" );
            }
        }
    }

告诉我我的错误是什么？以及如何修复它，以便将控制台中输入的数据写入文件。

有一个由空格分隔的数字组成的字符串，一个数字不能超过100。我需要检查输入的数字是否只用一个空格分隔。如果只有一个空格，我返回真，如果有多个，那么我返回假。我检查了字符串中只有数字和空格，但它不适用于空格数。这是我能写的：

private static boolean checkDigital(String word)throws Exception{
        if (word == null)
            throw new Exception("Not text");

        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if (!Character.isDigit(c) && c != ' '){
                return false;
            }
        }
        return true;
    }

告诉我如何正确验证数字之间的空格数。

任务如下：我需要编写一个将一些文本作为输入并返回的方法Map，该方法存储该文本中每个文字字符的重复次数。我把字符串拆分成一个字符数组，存入ArrayList，排序，然后计算每个字符重复了多少次，现在我需要把它Map放入 这是我到目前为止所做的：

public static Map<Character, Integer> countSymbolsNew(String text)throws Exception{
        //сделать отсортированный список
        //посчитать количество повторений каждого символа и занести в переменную
        //результат добавить в мапу
        if (text == null)
            throw new Exception("No text");

    Map<Character, Integer> map = new HashMap<>();
    ArrayList<Character> chars = new ArrayList<>();
    for (int i = 0; i < text.length(); i++) {
        char c = text.toLowerCase().charAt(i);
        if (Character.isLetter(c)){
            chars.add(c);
        }
    }
    Collections.sort(chars);
    System.out.println(chars);
    //надо взять первый элемент массива, пройти им по всему списку и если повторяется то плюсовать счетчик
    //если не повторился то счетчик равен 1
    int maxCount = 0;
    for (Character aChar : chars) {
        int count = 0;
        for (Character ch : chars) {
            if (aChar.equals(ch)){
                count++;
            }
        }
        if (count > maxCount){
            maxCount = count;
        }
        System.out.print(count + " ,");

    }


    return map;
}

理论上，我有点想象元素是如何添加到地图中的，但实际上，我无法做任何进一步的事情。请帮忙解释一下。

例如，有这样一行： String text = "然后骨灰盒被抬到火化现场几圈，作为游行的最后一站。"

我需要将其分解为单词，删除所有标点符号和特殊字符，并将单词放入列表中。

ArrayList words = new ArrayList<>(); Stringword = text.replaceAll(",", " "); - 这里，据我了解，有必要做正则表达式吗？或者你能去掉标点符号和特殊字符吗？