fastjson序列化出现StackOverflowError-CFANZ编程社区

今天在一个web项目里开发功能，记录日志用到了fastjson的序列化，把类型为RetreatRecord的数据对象序列化后打印出来。结果出现StackOverflowError。先贴出来异常堆栈：

Exception in thread "main" java.lang.StackOverflowError
  at com.alibaba.fastjson.serializer.JSONSerializer.getContext(JSONSerializer.java:109)
  at com.alibaba.fastjson.serializer.JavaBeanSerializer.writeReference(JavaBeanSerializer.java:251)
  at Serializer_1.write1(Unknown Source)
  at Serializer_1.write(Unknown Source)
  at com.alibaba.fastjson.serializer.JSONSerializer.writeWithFieldName(JSONSerializer.java:390)
  //下面3行堆栈重复300多次
  at Serializer_1.write1(Unknown Source)
  at Serializer_1.write(Unknown Source)
  at com.alibaba.fastjson.serializer.JSONSerializer.writeWithFieldName(JSONSerializer.java:390)

经排查原因，发现派生类RetreatRecord继承自DataEntity，DataEntity里有一个User currentUser字段。User也派生自DataEntity。currentUser的get方法如下：

public User getCurrentUser() {
        if(null==currentUser){
            currentUser=new User();
        }
        return currentUser;
    }

问题就出现在了currentUser为null时给其初始化的这句上。

debug程序可见，fastjson包里JSONSerializer.java的如下方法被死循环执行，直到堆栈溢出。

// D:\workspace\m3\com\alibaba\fastjson\1.2.6\fastjson-1.2.6-sources.jar!\com\alibaba\fastjson\serializer\JSONSerializer.java

public final void writeWithFieldName(Object object, Object fieldName, Type fieldType, int fieldFeatures) {
    try {
        if (object == null) {
            out.writeNull();
            return;
        }

        Class<?> clazz = object.getClass();

        ObjectSerializer writer = getObjectWriter(clazz);

        writer.write(this, object, fieldName, fieldType, fieldFeatures);
    } catch (IOException e) {
        throw new JSONException(e.getMessage(), e);
    }
}

分析：我们知道fastjson是基于流写入的。不难看出，在调用getCurrentUser时，因为currentUser是null，所以要给currentUser初始化，这时fastjson又要调用其getCurrentUser方法，然后又因为currentUser是null而不得不再给currentUser初始化，如此反复。。。，必然导致StackOverflow。

简化我遇到的情况，大家可以运行下面的代码来复现这个bug：

package fastjsonstackoverflow;
import java.io.Serializable;
public class MyEntity implements Serializable {

    String id;
    MyEntity currentUser;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    /**
     * 即使没有定义length字段，fastjson序列化不会出现异常
     * @return
     */
    public int getLength(){
        return 0;
    }

    public MyEntity getCurrentUser() {
        if(null==currentUser){
            currentUser=new MyEntity();
        }
        return currentUser;
    }

    public void setCurrentUser(MyEntity currentUser) {
        this.currentUser = currentUser;
    }
}

package fastjsonstackoverflow;
import com.alibaba.fastjson.JSONObject;
public class MainTest {
    public static void main(String[] args) {
        MyEntity entity = new MyEntity();
//        System.out.println("mydata:"+entity.getCurrentUser());
        System.out.println("mydata:" + JSONObject.toJSONString(entity));
    }
}