net.sf.json.JSONException:Struts 2中的层次结构中存在一个循环 [英] net.sf.json.JSONException: There is a cycle in the hierarchy in Struts 2

问题描述

我正在使用实现ModelDriven的Struts类.我能够从jQuery传递数据并将数据保存在数据库中.

I am using Struts class which implements ModelDriven. I am able to pass the data from jQuery and save the data on the database.

当我尝试取回数据并将其传递回jQuery时，我不确定为什么它在jQuery中不可用.我确定我的基本流程中缺少一些东西.

When I try to retrieve the data back and pass it back to jQuery, I am not sure why it's not available in jQuery. I am sure I am missing something with the basic flow..

这是我的动作课.

public HttpHeaders index() {
    model = projectService.getProjectDetails(project.getUserID());
    return new DefaultHttpHeaders("success").setLocationId("");
} 

@Override
public Object getModel() {
    return project;
}

public Project getProject() {
    return project;
}

public void setProject(Project project) {
    this.project = project;
}

这是我的jQuery

Here is my jQuery

function getProjectDetails() {
    var userID = localStorage.getItem('userID');
    var request = $.ajax({
        url : '/SUH/project.json',
        data : {
            userID : userID
        },
        dataType : 'json',
        type : 'GET',
        async : true
    });

    request.done(function(data) {
        console.log(JSON.stringify(data));
        $.each(data, function(index, element) {
            console.log('element project--->' + index + ":" + element);

        });
    });

    request.fail(function(jqXHR, textStatus) {
        console.log('faik');
    });
}

Action类中的模型对象具有所有可用数据，但我尝试返回模型或项目对象，但两者均无效.

The model object in the Action class has all the data available but I tried to return model or project objects but both didn't work.

推荐答案

默认情况下，Struts2 REST插件正在使用 json- lib 用于序列化您的bean.如果您使用的是ModelDriven，则它在处理结果时将直接访问您的模型.由于您在请求URL中使用扩展名.json，因此将按扩展名选择内容类型处理程序.应该是JsonLibHandler.

By default Struts2 REST plugin is using json-lib for serialization your beans. If you are using ModelDriven then it accesses your model directly when it processes a result. Since you are using the extension .json in the request URL the content type handler is selected by extension. It should be JsonLibHandler.

如果obj是数组或列表，则此处理程序正在使用JSONArray.fromObject(obj)；否则，将使用JSONObject.fromObject(obj)来获取可以序列化并写入响应的JSONObejct.

This handler is using JSONArray.fromObject(obj) if obj is an array or list or JSONObject.fromObject(obj) otherwise to get JSONObejct that could be serialized and written to the response.

obj是getModel()返回的值，在您的情况下为project.

The obj is the value returned by getModel(), in your case it will be project.

因为JsonLibHandler使用默认的JsonConfig，所以除非它们是public字段，否则不能从要序列化的Bean中排除属性.

Because JsonLibHandler is using default JsonConfig you can't exclude properties from the bean to be serialized unless they are public fields.

JsonConfig可以支持json-lib的以下功能:

The following features of json-lib could be powered with JsonConfig:

• 循环检测，有两种默认策略(默认抛出 一个例外)，您可以注册自己的
• 何时跳过瞬态字段 序列化为JSON(默认为不跳过)跳过JAP @Transient注释 序列化为JSON时的方法(默认=不跳过)
• 排除豆 序列化为JSON时的属性和/或映射键 (默认= ['class'，'metaClass'，'declaringClass'])
• 过滤器提供了 序列化为时排除/包含属性的更详细的信息 JSON或转换回Java

• Cycle detection, there are two default strategies (default throws an exception), you can register your own
• Skip transient fields when serailizing to JSON (default=don't skip) Skip JAP @Transient annotated methods when serailizing to JSON (default=don't skip)
• Exclude bean properties and/or map keys when serailizing to JSON (default=['class','metaClass','declaringClass'])
• Filters provide a finer detail for excluding/including properties when serializing to JSON or transforming back to Java

---

您可以找到此代码段，该代码段可以排除某些属性.

---

You can find this code snippets that allows you to exclude some properties.

排除属性

String str = "{'string':'JSON', 'integer': 1, 'double': 2.0, 'boolean': true}";  
JsonConfig jsonConfig = new JsonConfig();  
jsonConfig.setExcludes( new String[]{ "double", "boolean" } );  
JSONObject jsonObject = (JSONObject) JSONSerializer.toJSON( str, jsonConfig );  
assertEquals( "JSON", jsonObject.getString("string") );        
assertEquals( 1, jsonObject.getInt("integer") );        
assertFalse( jsonObject.has("double") );     
assertFalse( jsonObject.has("boolean") );     

排除属性(带有过滤器)

String str = "{'string':'JSON', 'integer': 1, 'double': 2.0, 'boolean': true}";  
JsonConfig jsonConfig = new JsonConfig();  
jsonConfig.setJsonPropertyFilter( new PropertyFilter(){    
   public boolean apply( Object source, String name, Object value ) {    
      if( "double".equals(value) || "boolean".equals(value) ){    
         return true;    
      }    
      return false;    
   }    
});    
JSONObject jsonObject = (JSONObject) JSONSerializer.toJSON( str, jsonConfig );  
assertEquals( "JSON", jsonObject.getString("string") );        
assertEquals( 1, jsonObject.getInt("integer") );        
assertFalse( jsonObject.has("double") );     
assertFalse( jsonObject.has("boolean") );

但是您可以选择使用自己的ContentTypeHandler覆盖默认值.

But you have an option to use your own ContentTypeHandler to override defaults.

替代方法是使用Jackson库来处理请求.如文档页面中所述:使用Jackson框架作为JSON ContentTypeHandler .

The alternative is to use Jackson library to handle request. As described in the docs page: Use Jackson framework as JSON ContentTypeHandler.

默认JSON内容处理程序构建在JSON-lib之上.如果 您更喜欢使用Jackson框架进行JSON序列化， 可以将JacksonLibHandler配置为json的内容处理程序 要求.

The default JSON Content Handler is build on top of the JSON-lib. If you prefer to use the Jackson framework for JSON serialisation, you can configure the JacksonLibHandler as Content Handler for your json requests.

首先，您需要将jackson依赖项添加到您的Web应用程序中 通过下载jar文件并将其放在WEB-INF/lib下或通过添加 在pom.xml中的依赖项部分中跟随以下xml代码段 您正在使用maven作为构建系统.

First you need to add the jackson dependency to your web application by downloading the jar file and put it under WEB-INF/lib or by adding following xml snippet to your dependencies section in the pom.xml when you are using maven as build system.

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

现在您可以用Jackson内容覆盖Content Handler. struts.xml中的处理程序:

Now you can overwrite the Content Handler with the Jackson Content Handler in the struts.xml:

<bean type="org.apache.struts2.rest.handler.ContentTypeHandler" name="jackson" class="org.apache.struts2.rest.handler.JacksonLibHandler"/>
<constant name="struts.rest.handlerOverride.json" value="jackson"/>

<!-- Set to false if the json content can be returned for any kind of http method -->
<constant name="struts.rest.content.restrictToGET" value="false"/> 

<!-- Set encoding to UTF-8, default is ISO-8859-1 -->
<constant name="struts.i18n.encoding" value="UTF-8"/>

---

之后，您可以使用@JsonIgnore注释.

---

After that you can use @JsonIgnore annotation.

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