java - 使用列表和复选框的 Spring MVC 数据绑定(bind)

Question

我知道已经有人提出了有关此事的问题，但我找到的答案都没有解决我的问题。

我的数据库上有多对多关系。我正在使用 JPA 和 Hibernate 来创建和更改我的表。这是我的模型类:

Book.java

@Entity
@Table(name="tb_books")
public class Book implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false, insertable = false)
    private Integer id;

    @Column(name = "title", nullable = false, length = 255)
    private String title;

    @Column(name = "author", nullable = false, length = 255)
    private String author;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
    @JoinTable(name = "book_tag",
               joinColumns = { @JoinColumn(name = "fk_book") },
               inverseJoinColumns = { @JoinColumn(name = "fk_tag") })
    private List<Tag> tags;

    //getters, setters, equals and hash methods...

}

标签.java

@Entity
@Table(name="tb_tags")
public class Tag implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Integer id;

    @Column(name = "description", nullable = false, length = 255)
    private String description;

    //getters, setters, equals and hash methods...
}

我正在尝试使用 Spring MVC 使用来自 JSP 的数据在我的 book_tag 表上进行插入和更新。这是我的 Controller 和插入页面:

BookController.java

@Controller
@RequestMapping(value = "/book")
public class BookController {

    @Autowired
    private BookService bookService;

    /*
        Controller method that gets us to the adding book page. 
    */    
    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public ModelAndView addBookPage() {

        List<Tag> tags = tagService.getTags(); //all tags from the database

        ModelAndView modelAndView = new ModelAndView("form-book");
        modelAndView.addObject("book", new Book());
        modelAndView.addObject("tags", tags);

        return modelAndView;
    }

    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public ModelAndView addBookProcess(@ModelAttribute Book book) {

        bookService.addBook(book);
        return new ModelAndView("redirect:/book/add");
    }

    //...

}

form-b​​ook.jsp

<form:form method="POST" modelAttribute="book" action="${pageContext.request.contextPath}/book/add.html">
<table>
    <tbody>
        <tr>
            <td>Title:</td>
            <td><form:input path="title" autocomplete="off" /></td>
        </tr>
        <tr>
            <td>Author:</td>
            <td><form:input path="author" autocomplete="off" /></td>
        </tr>
        <tr>
            <td colspan="2">

                <form:checkboxes path="tags" 
                items="${tags}" 
                itemLabel="description"
                itemValue="id"/>

            </td>
        </tr>
        <tr>
            <td><input type="submit" value="Add" /></td>
            <td><input type="button" onclick="location.href = '${pageContext.request.contextPath}/index'" value="Cancel"/></td>
        </tr>
    </tbody>
</table>

</form:form>

一切工作正常，除了当我尝试更新或插入选中一个或多个复选框的书籍时。当我尝试这样做时，我只是得到一个“错误请求”页面，我想是因为我在数据绑定(bind)方面做了一些错误。

这是我应该处理这种情况的方式吗？有没有更好的办法？我做错了什么？

Answer 1

显然，来自复选框的列表实际上是一个字符串数组，它无法按照模型类的定义转换为标签列表。

我通过创建自定义 PropertyEditor 解决了我的问题，它允许我将复选框与标签列表绑定(bind)。

public class TagPropertyEditor extends PropertyEditorSupport {

    private TagService tagService;

    public TagPropertyEditor(TagService tagService){
        this.tagService = tagService;
    }

    @Override
    public String getAsText() {
        return ((Tag) getValue()).getId().toString();
    }

    @Override
    public void setAsText(String incomingId) throws IllegalArgumentException {
        Tag tag = tagService.getTag(Integer.valueOf(incomingId));
        setValue(tag);
    }
}

然后在我的 BookController 上注册:

//...
@InitBinder
public void initBinder(WebDataBinder binder){
    binder.registerCustomEditor(Tag.class, new TagPropertyEditor(tagService));
}

这是我的 JSP 上的 checkboxes 标记:

 <form:checkboxes path="tags" 
                  items="${tags}"
                  itemLabel="description"
                  itemValue="id"/>