圣诞树动画

Question

Alex

Asked:2020-05-04 21:57:45 +0800 CST2020-05-04 21:57:45 +0800 CST 2020-05-04 21:57:45 +0800 CST

列表到 Json 序列化

772

大家好。并立即问题：如何将 List 转换为 Json

如果我将一个Car 对象转换为 Json-obj，那么一切都很好

Car cars = carSrv.getById(1);
 Gson gson = new GsonBuilder().create();
 String jse = gson.toJson(cars);

尝试使用列表执行此操作时（Json 中的列表）

 List<Car> cars = carSrv.getAll();
 Gson gson = new GsonBuilder().create();
 String jse = gson.toJson(cars);

执行崩溃：

    java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?
    at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:76)
    at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:69)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ArrayTypeAdapter.write(ArrayTypeAdapter.java:93)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at com.google.gson.Gson.toJson(Gson.java:661)
    at com.google.gson.Gson.toJson(Gson.java:640)
    at com.google.gson.Gson.toJson(Gson.java:595)
    at com.google.gson.Gson.toJson(Gson.java:575)
...

我正在使用 Gson 库：

        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.6.2</version>
        </dependency>

在网上的某个地方，我找到了一个带有类型指示的解决方案：

 List<Car> cars = carSrv.getAll();
 Gson gson = new GsonBuilder().create();
 Type listType = new TypeToken<List<Car>>() {}.getType();
String jse = gson.toJson(cars, listType);

没有帮助！相同的ekzepshn

我在这里找到了另一个解决方案和很多重复项:) 不过，我认为这里的问题不在于休眠，而在于序列化

 List<Car> cars = carSrv.getAll();
 Gson gson = new GsonBuilder()
            .registerTypeAdapterFactory(HibernateProxyTypeAdapter.FACTORY)
            .create();
 String jse = gson.toJson(cars);

我从示例中获取了 HibernateProxyTypeAdapter 类。

public class HibernateProxyTypeAdapter extends TypeAdapter<HibernateProxy> {

public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
    @Override
    @SuppressWarnings("unchecked")
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        return (HibernateProxy.class.isAssignableFrom(type.getRawType()) ? (TypeAdapter<T>) new HibernateProxyTypeAdapter(gson) : null);
    }
};
private final Gson context;

private HibernateProxyTypeAdapter(Gson context) {
    this.context = context;
}

@Override
public HibernateProxy read(JsonReader in) throws IOException {
    throw new UnsupportedOperationException("Not supported");
}

@SuppressWarnings({"rawtypes", "unchecked"})
@Override
public void write(JsonWriter out, HibernateProxy value) throws IOException {
    if (value == null) {
        out.nullValue();
        return;
    }
    // Retrieve the original (not proxy) class
    Class<?> baseType = Hibernate.getClass(value);
    // Get the TypeAdapter of the original class, to delegate the serialization
    TypeAdapter delegate = context.getAdapter(TypeToken.get(baseType));
    // Get a filled instance of the original class
    Object unproxiedValue = ((HibernateProxy) value).getHibernateLazyInitializer()
            .getImplementation();
    // Serialize the value
    delegate.write(out, unproxiedValue);
}

}

没有帮助！查看例外：

2018-РјР°СЏ-04 16:33:00.829 ERROR [http-nio-8080-exec-8] o.s.b.w.s.ErrorPageFilter - Forwarding to error page from request [/aes/by/id] due to exception [null]
java.lang.StackOverflowError: null
    at com.google.gson.internal.bind.TypeAdapters$11.write(TypeAdapters.java:317)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:968)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:97)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:61)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at ua.avk.carwash.adapter.HibernateProxyTypeAdapter.write(HibernateProxyTypeAdapter.java:54)
    at ua.avk.carwash.adapter.HibernateProxyTypeAdapter.write(HibernateProxyTypeAdapter.java:19)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:112)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:239)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:968)

这是 Car 类本身，以防万一：

    @JsonInclude(JsonInclude.Include.NON_NULL)
@Entity
@Table(name = "Car")
public class Car implements Serializable, Storable {
    private static final long serialVersionUID = 1000000000000111L;
    public static final String GET_BY_NAME = "select e from Car e where e.name = ?1";
    public static final String GET_BY_TYPE = "select e from Car e where e.carType = ?1";
    public static final String GET_BY_NUMBER = "select e from Car e where e.number = ?1";
    public static final String GET_BY_CLIENT = "select e from Car e where e.client = ?1";

    private Long id;
    private String name;
    private String number;
    private CarType carType;
    private Client client;
    private List<Order> orderList = new ArrayList<>();

    @JsonView(Views.User.class)
    @JsonProperty("id")
    @Id
    @GeneratedValue(generator = "increment")
    @GenericGenerator(name = "increment", strategy = "increment")
    @Column(name = "car_id", nullable = false)
    @Override
    public Long getId() {
        return id;
    }

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

    @JsonProperty("name")
    @JsonView(Views.User.class)
    @Size(max = 50, message = "{size.field}")
    @Column(name = "name", nullable = true, insertable = true, updatable = true, length = 50)
    public String getName() {
        return name;
    }

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

    @JsonProperty("number")
    @JsonView(Views.User.class)
    @Size(max = 8, message = "The car number must be {min} to {max} characters in length.")
    @Column(name = "number", nullable = true, insertable = true, updatable = true, length = 8)
    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @JsonProperty("cartype")
    @JsonView(Views.User.class)
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "type_id", nullable = true, insertable = true, updatable = true)
    public CarType getCarType() {
        return carType;
    }

    public void setCarType(CarType carType) {
        this.carType = carType;
    }

    @JsonProperty("client")
    @JsonView(Views.User.class)
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "client_id", nullable = true, insertable = true, updatable = true)
    public Client getClient() {
        return client;
    }

    public void setClient(Client client) {
        this.client = client;
    }

    //@Transient
    @JsonProperty("orders")
    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonView(Views.Admin.class)
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
    //@Column(name = "order_id")
    public List<Order> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }

    @Override
    public String toString() {
        return String.format("%d, %s, %s, %s, %s;", id, name, number, carType, client);
    }

    /**
     * The method Copy the object of the car
     *
     * @param u - the object of the car
     */
    public void copy(Car u) {
        this.setClient(u.getClient());
        this.setOrderList(u.getOrderList());
        this.setName(u.getName());
        this.setNumber(u.getNumber());
        this.setCarType(u.getCarType());
    }

    /**
     * Override hashCode for correct work equals
     *
     * @return hashCode
     */
    @Override
    public int hashCode() {
        return new HashCodeBuilder()
                .append(this.client)
                .append(this.name)
                .append(this.number)
                .append(this.carType)
                .toHashCode();
    }

    /**
     * Compares of the car
     *
     * @param obj for compare
     * @return true if equals
     */
    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Car))
            return false;
        if (obj == this)
            return true;

        Car u = (Car) obj;
        return new EqualsBuilder()
                .append(this.client, u.client)
                .append(this.name, u.name)
                .append(this.number, u.number)
                .append(this.carType, u.carType)
                .isEquals();
    }

}

问题：在这种情况下如何将 List 转换为 Json

1 个回答

Voted

Alex · Answer 1 · 2020-05-05T15:30:55+08:00

据我了解，图书馆Gson也不喜欢实体中的双向关系。在对抗实体或这些实例中的双向关系时：

java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?

并且可能：

Infinity Exception

顺便说一句，这更清楚地表达了问题的本质！

帮助过我：

用替换库Gson，Jackson即：

<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-core-asl</artifactId>
    <version>1.9.13</version>
</dependency>

使用注释@JsonIgnore或一对@JsonBackReferenceand ，您可以在这里@JsonManagedReference阅读它们，这里
- @JsonManagedReference常规序列化：
- @JsonIgnore，@JsonBackReference序列化异常；

我是这样申请的：

车类

@Entity
@Table(name = "Car")
public class Car implements Serializable, Storable {
    private static final long serialVersionUID = 1000000000000111L;
    public static final String GET_BY_NAME = "select e from Car e where e.name = ?1";
    public static final String GET_BY_TYPE = "select e from Car e where e.carType = ?1";
    public static final String GET_BY_NUMBER = "select e from Car e where e.number = ?1";
    public static final String GET_BY_CLIENT = "select e from Car e where e.client = ?1";

    private Long id;
    private String name="";
    private String number="";
    private CarType carType = new CarType();
    private Client client = new Client();
    private List<Order> orderList = new ArrayList<>();

    @JsonProperty("id")
    @Id
    @GeneratedValue(generator = "increment")
    @GenericGenerator(name = "increment", strategy = "increment")
    @Column(name = "car_id", nullable = false)
    @Override
    public Long getId() {
        return id;
    }

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

    @JsonProperty("name")
    @Size(max = 50, message = "{size.field}")
    @Column(name = "name", nullable = true, insertable = true, updatable = true, length = 50)
    public String getName() {
        return name;
    }

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

    @JsonProperty("number")
    @Size(max = 8, message = "The car number must be {min} to {max} characters in length.")
    @Column(name = "number", nullable = true, insertable = true, updatable = true, length = 8)
    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @JsonProperty("cartype")
    @JsonBackReference
    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "type_id", nullable = true, insertable = true, updatable = true)
    public CarType getCarType() {
        return carType;
    }

    public void setCarType(CarType carType) {
        this.carType = carType;
    }

    @JsonProperty("client")
    @JsonBackReference
    @ManyToOne(fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "client_id", nullable = true, insertable = true, updatable = true)
    public Client getClient() {
        return client;
    }

    public void setClient(Client client) {
        this.client = client;
    }

    @JsonProperty("orders")
    @JsonManagedReference
    //@Transient
    @OneToMany(fetch = FetchType.EAGER, mappedBy = "car")
    public List<Order> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }

    @Override
    public String toString() {
        return String.format("%d, %s, %s, %d, %d, %s", id, name, number, carType.getId(), client.getId(), orderList);
    }

    /**
     * The method Copy the object of the car
     *
     * @param u - the object of the car
     */
    public void copy(Car u) {
        this.setClient(u.getClient());
        this.setOrderList(u.getOrderList());
        this.setName(u.getName());
        this.setNumber(u.getNumber());
        this.setCarType(u.getCarType());
    }

    /**
     * Override hashCode for correct work equals
     *
     * @return hashCode
     */
    @Override
    public int hashCode() {
        return new HashCodeBuilder()
                .append(this.client)
                .append(this.name)
                .append(this.number)
                .append(this.carType)
                .toHashCode();
    }

    /**
     * Compares of the car
     *
     * @param obj for compare
     * @return true if equals
     */
    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Car))
            return false;
        if (obj == this)
            return true;

        Car u = (Car) obj;
        return new EqualsBuilder()
                .append(this.client, u.client)
                .append(this.name, u.name)
                .append(this.number, u.number)
                .append(this.carType, u.carType)
                .isEquals();
    }

}

CarType 类

@Entity
@Table(name = "CarType")
public class CarType implements Serializable, Storable {
    private static final long serialVersionUID = 1000000000000112L;
    public static final String GET_BY_TYPE = "select e from CarType e where e.type = ?1";

    private Long id;
    private String type;
    private List<Car> carList = new ArrayList<>();
    private List<Price> prices = new ArrayList<>();

    @Id
    @GeneratedValue(generator = "increment")
    @GenericGenerator(name = "increment", strategy = "increment")
    @Column(name = "car_type_id", nullable = false)
    @Override
    public Long getId() {
        return id;
    }

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

    @JsonProperty("type")
    @Size(max = 15, message = "{size.field}")
    @Column(name = "type", nullable = true, insertable = true, updatable = true, length = 15)
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }


    @JsonProperty("cars")
    @JsonManagedReference
    //@Transient
    @OneToMany(mappedBy = "carType")
    public List<Car> getCarList() {
        return carList;
    }

    public void setCarList(List<Car> carList) {
        this.carList = carList;
    }



    @JsonProperty("prices")
    @JsonManagedReference
    //@Transient
    @OneToMany(mappedBy = "type")
    public List<Price> getPrices() {
        return prices;
    }

    public void setPrices(List<Price> prices) {
        this.prices = prices;
    }

    @Override
    public String toString() {
        return String.format("%d, %s, %s, %s", id, type, carList, prices);
    }

    /**
     * The method Copy the object of the carList type
     *
     * @param u - the object of the carList type
     */
    public void copy(CarType u) {
        this.setCarList(u.getCarList());
        this.setPrices(u.getPrices());
        this.setType(u.getType());
    }

    /**
     * Override hashCode for correct work equals
     *
     * @return hashCode
     */
    @Override
    public int hashCode() {
        return new HashCodeBuilder()
                .append(this.carList)
                .append(this.prices)
                .append(this.type)
                .toHashCode();
    }

    /**
     * Compares of the carList type
     *
     * @param obj for compare
     * @return true if equals
     */
    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof CarType))
            return false;
        if (obj == this)
            return true;

        CarType u = (CarType) obj;
        return new EqualsBuilder()
                .append(this.carList, u.carList)
                .append(this.prices, u.prices)
                .append(this.type, u.type)
                .isEquals();
    }

}

它帮助了我——我希望它也能帮助你。

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