嵌套异常是 java.lang.IllegalStateException：无法将类型 [java.lang.String] 的值转换为所需类型

nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type

提问by dlinx90

I am getting the following validation error when I try to submit my form. The dropdown box populated with values from Document.java gives this error:

当我尝试提交表单时出现以下验证错误。用来自 Document.java 的值填充的下拉框给出了这个错误：

Failed to convert property value of type java.lang.String to required type 
testapp.domain.Document for property document_number; nested exception is 
java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] 
to required type [testapp.domain.Document] for property document_number: no matching 
editors or conversion strategy found

Is there something wrong with my mapping?

我的映射有问题吗？

Document.java mapping

Document.java 映射

    @OneToMany(mappedBy="document_number", cascade = CascadeType.ALL)
private Set<DocumentRevision> documentRevisions;

public void setDocumentRevisions(Set<DocumentRevision> documentRevisions){
    this.documentRevisions = documentRevisions;
}

DocumentRevision.java mapping

DocumentRevision.java 映射

    @ManyToOne(cascade = CascadeType.ALL)
@JoinColumn(name="DOCUMENT_NUMBER")
private Document document_number; 

public void setDocument_number(Document document_number){
    this.document_number = document_number;
}

public Document getDocument_number(){
    return document_number;
}

The relationship between the two tables is that several DocumentRevisionscan have the same DocumentNumberbut a single DocumentRevisioncan only have one DocumentNumber

两个表的关系是多个DocumentRevisions可以有相同的DocumentNumber，而单个DocumentRevision只能有一个DocumentNumber

Thank you for your help

谢谢您的帮助

/D

/D

Edit

编辑

I am using spring 3.0 and hibernate 3. Hereis a recent thread by me which includes the controller and jsp page.

我正在使用 spring 3.0 和 hibernate 3。这是我最近的一个线程，其中包括控制器和 jsp 页面。

Edit 2

编辑 2

Here is the DAO Implementation method that is supposed to save the document_number into DocumentRevision

这是应该将 document_number 保存到 DocumentRevision 中的 DAO 实现方法

    public void saveDocumentRevision(DocumentRevision documentRevision) {
    this.sessionFactory.getCurrentSession().save(documentRevision); 
}

Edit 3

编辑 3

I believe this is the part of the code where document_number should be recorded. Do I have to use "documentNumberList" somewhere in the .POST method? How would I do that in that case?

我相信这是应该记录 document_number 的代码部分。我是否必须在 .POST 方法中的某处使用“documentNumberList”？在那种情况下我该怎么做？

part of controller:

控制器的一部分：

@RequestMapping(value="/add", method=RequestMethod.GET)
public String getDocumentRevision(Model model) {
DocumentRevision documentRevision = new DocumentRevision();
model.addAttribute("documentRevisionAttribute", documentRevision);
model.addAttribute("documentNumberList", documentService.retrieveAllDocumentNumbers());

return "new-documnent-revision";
}


@RequestMapping(value="/add", method=RequestMethod.POST)
public String postDocumentRevision(@ModelAttribute("documentRevisionAttribute") @Valid DocumentRevision documentRevision, BindingResult result) {

if(result.hasErrors()){
    return "new-document-revision";
}

documentRevisionService.createDocumentRevision(documentRevision);
return "redirect:/testapp/document-revision/list";  
}

Update

更新

I have added the following to my controller:

我已将以下内容添加到我的控制器中：

    /**
 * Property editor to map Documents from documents IDs.
 */

 class DocumentPropertyEditor extends PropertyEditorSupport {

    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        Document value =  documentService.retrieveDocumentNumber(text);
        setValue(value);
    }

    @Override
    public String getAsText() {
        Document d = (Document) getValue();
        return d != null ? String.valueOf(d.getDocumentNumber()) : "";
    }

}


@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(Document.class, new DocumentPropertyEditor());
}

I am now getting a NullPointerException:

我现在收到一个 NullPointerException：

java.lang.NullPointerException
testapp.controller.DocumentRevisionController$DocumentPropertyEditor.getAsText(DocumentRevisionController.java:59)

Why isn't the getter in th PropertyEditor getting a value?

为什么 PropertyEditor 中的 getter 没有获得值？

Edit 4

编辑 4

the retrieveDocumentNumber(text) method:

retrieveDocumentNumber(text) 方法：

    public Document retrieveDocumentNumber(String text){
    return (Document) this.sessionFactory.getCurrentSession().get(Document.class, text);
}

采纳答案by Jose Luis Martin

Spring WebDataBinder fail to convert the String document_numberto a Document instance when populating the documentRevision model attribute. You have two posibilities:

String document_number填充 documentRevision 模型属性时，Spring WebDataBinder 无法将 转换为 Document 实例。你有两种可能：

• Initialize the WebDataBinderwith a PropertyEditorthat can handle the conversion. Most direct, but work only for this controller.

• Register a Converter<String, Document>

• WebDataBinder用PropertyEditor可以处理转换的a初始化。最直接，但仅适用于该控制器。

• 注册一个 Converter<String, Document>

if choose the first, annotate a controller method with @InitBinderannotation and register the property editor. Seems like you only need to fetch the document from database by document_number. See Customizing WebDataBinder initatizationon reference documentation.

如果选择第一个，用注解注解控制器方法@InitBinder并注册属性编辑器。似乎您只需要通过 document_number 从数据库中获取文档。请参阅参考文档中的自定义 WebDataBinder 初始化。

Edit

编辑

Property editor example to map Documents to/from Ids Strings.

将文档映射到/从 Id 字符串映射的属性编辑器示例。

/**
 * Property editor to map Documents from documents IDs.
 */
 class DocumentPropertyEditor extends PropertyEditorSupport {

    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        Long id = Long.parseLong(text);
        Document value = id == 0 ? null : documentService.get(id);
        setValue(value);
    }

    @Override
    public String getAsText() {
        Document d = (Document) getValue();
        return d != null ? String.valueOf(d.getId()) : "";
    }
}

For the second approach, look at Validation, Data Binding, and Type Conversionto see how to create and register a Converterin the Spring ConversionService.

对于第二种方法，查看验证、数据绑定和类型转换以了解如何Converter在 Spring 中创建和注册 a ConversionService。