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Accepted
Timur Musharapov
Asked:2020-03-31 19:01:28 +0000 UTC2020-03-31 19:01:28 +0000 UTC

二元运算符'||'的Java错误操作数类型

  • 772

在控制器中有代码（Spring MVC）

@RequestMapping(value = "/books", method = RequestMethod.GET)
public String books(final HttpServletRequest request, final Model model) {
    if (request.getParameter("name") || request.getParameter("publishing_house") || request.getParameter("the_year_of_publishing")) {
        final List<Book> books = bookService.booksBySearch();
    } else {
        final List<Book> books = bookService.getAll();
    }
    model.addAttribute("books", books);
    logger.debug("running in BookController.java -> books()");
    logger.info(JSON.toJSON(request.getRequestURI()));
    logger.info(JSON.toJSON(books));
    return "/book/list.jsp";
}

结果，在编译时，我得到一个错误：

[错误] /C:/Users/Tim/eclipse-workspace/springMVC-mybatis-postgresql-fbcda0e11b1addcac43be8813e16b8b703022591/src/main/java/com/core/newbie/controller/BookController.java:[53,42] 错误的操作数类型二元运算符'||' 第一种类型：java.lang.String 第二种类型：java.lang.String

为什么以及如何解决？

java

1 个回答

  1. Best Answer

    您对此有何期待request.getParameter("name") || request.getParameter("publishing_house")？

    getParameter返回一个字符串。也许你想null检查一下？

    if (request.getParameter("name") != null || request.getParameter("publishing_house") != null || request.getParameter("the_year_of_publishing") != null )

    但即便如此，你的代码也不会编译，因为 您books没有在您的范围之外进行定义if，编译器将在该行抛出错误model.addAttribute("books", books);。

    整个代码将是这样的：

    @RequestMapping(value = "/books", method = RequestMethod.GET)
public String books(final HttpServletRequest request, final Model model) {
    List<Book> books;
    if (request.getParameter("name") != null || request.getParameter("publishing_house") != null || request.getParameter("the_year_of_publishing") != null) {
        books = bookService.booksBySearch();
    } else {
        books = bookService.getAll();
    }
    model.addAttribute("books", books);
    logger.debug("running in BookController.java -> books()");
    logger.info(JSON.toJSON(request.getRequestURI()));
    logger.info(JSON.toJSON(books));
    return "/book/list.jsp";
}
    • 3

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