JavaBean转json错误

Question

Document类：
public class DocBean {
private String docId;
private String docName;
private String typeId;
private String typeName;
private String content;
private String docTime;
private String views;
private String cover;
}

page类
public class Page {
private int pageNo;
private int totalItem;
private int pageSize;
private String typeId;
private List<DocBean> doc=new ArrayList<DocBean>();
}

转化代码：
JSONObject page_json=JSONObject.fromObject(page);

error：
net.sf.json.JSONException: There is a cycle in the hierarchy!

at net.sf.json.util.CycleDetectionStrategy$StrictCycleDetectionStrategy.handleRepeatedReferenceAsObject(CycleDetectionStrategy.java:97)
at net.sf.json.JSONObject._fromBean(JSONObject.java:833)
at net.sf.json.JSONObject.fromObject(JSONObject.java:168)
at net.sf.json.AbstractJSON._processValue(AbstractJSON.java:265)
at net.sf.json.JSONObject._processValue(JSONObject.java:2808)
at net.sf.json.JSONObject.processValue(JSONObject.java:2874)
at net.sf.json.JSONObject.setInternal(JSONObject.java:2889)
at net.sf.json.JSONObject.setValue(JSONObject.java:1577)
at net.sf.json.JSONObject._fromBean(JSONObject.java:934)
at net.sf.json.JSONObject.fromObject(JSONObject.java:168)
at net.sf.json.JSONObject.fromObject(JSONObject.java:130)
at hyit.dataBind.DocBind.initDocList(DocBind.java:124)
at hyit.dataBind.DocBind.test01(DocBind.java:132)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Answer 1

fastjson有相当简便的方式

/**
 * 把Java对象转换成json字符串
 *
 * @param object 待转化为JSON字符串的Java对象
 * @return json 串 or null
 */
public static <T> String parseObjToJson(T object) {
    String string = null;
    try {
        //string = JSON.toJSONString(object);
        string = JSONObject.toJSONString(object);
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
    return string;
}

Answer 2

net.sf.json
从maven中央仓库可以看出这个json库最后一次更新是2010年,基本上是废弃了.这么多JSON解析库,随便一个一搜一大把,fastjson,Jackson,gson,随便找个用吧,个人推荐fastjson

Answer 3

这个问题，我之前也遇到过：对象嵌套对象的情况，不能直接用 JSONObject.fromObject(page) 这方法。
我当时处理的办法很low。代码仅供参考：

public static void fromJson(String jsonStr) throws Exception{
        JSONArray jsonArray = JSONArray.fromObject(jsonStr);
        Object[] objs = jsonArray.toArray();
        for (Object object : objs) {
             JSONObject jsonObject = JSONObject.fromObject(object);
             if(jsonObject.has("images")){ // 嵌套的对象
                  String imgString = jsonObject.getString("images");
                  JSONArray imgArray = JSONArray.fromObject(imgString);
                  Object[] imgObjs = imgArray.toArray();
                  for (Object object2 : imgObjs) {
                    JSONObject jsonObject2 = JSONObject.fromObject(object2);
                    System.out.println(jsonObject2.getString("height")+"\t"+jsonObject2.getString("url"));
                }
             }
             if(jsonObject.has("countrys")){ // 嵌套的对象
                String countrysString = jsonObject.getString("countrys");
                List<String> stringList = binder.getMapper().readValue(countrysString, List.class);
                System.out.println("String List:");
                for (String element : stringList) {
                    System.out.print(element+"\t");
                }
             }
             System.out.println(jsonObject.getString("offerId")+"\t"+jsonObject.getString("name"));
        }
    }

你也可以选择百度：java 对象嵌套 转json

Answer 4

你可以考虑给每个变量生成默认的get和set方法。

Answer 5

谢邀。net.sf.json印象中是比较老的一个包，建议使用jackson和gson。关键字可以搜索google:

• jackson object to json

• gson object to json

Answer 6

net.sf.json.JSONObject jsonObject = net.sf.json.JSONObject.fromObject(JsonStr);
Map<String, Class> classMap = new HashMap<String, Class>();
classMap.put("selectInfo", SelectPropsDto.class);
classMap.put("checkBoxInfo", CheckPropsDto.class);
classMap.put("radioInfo", RadioPropsDto.class);
GoodsDto goods = (GoodsDto) net.sf.json.JSONObject.toBean(jsonObject, GoodsDto .class,classMap);

多看看文档！希望能帮到你