严重: Servlet.service() for servlet [centralServlet] in context with path [/UserTest] threw exception [Request processing Failed; nested exception is net.sf.json.JSONException: java.lang.reflect.InvocationTargetException] with root cause
java.lang.NullPointerException
    at org.hibernate.tuple.entity.EntityMetamodel.isNaturalIdentifierInsertGenerated(EntityMetamodel.java:1127)

上面的异常是在执行下面的语句出现的：
JSONArrayarray=JSONArray.fromObject(this.users);

出现这bug
出现了两种情况：
1.日期格式
2.hibernate延时加载

解决:日期格式

JsonConfig jsonConfig = new JsonConfig();
jsonConfig.setCycleDetectionStrategy(CycleDetectionStrategy.LENIENT);
jsonConfig.registerJsonBeanProcessor(java.sql.Date.class,new JsDateJsonBeanProcessor());

private java.util.Date createTime; 

JsonConfig cfg = new JsonConfig();   
   
cfg.setExcludes(new String[]{"handler","hibernateLazyInitializer"});