response.setContentType("text/html");

response.setCharacterEncoding("utf-8");

request.setCharacterEncoding("utf-8");

PrintWriter out = response.getWriter();

List<User> users=new ArrayList<User>();

User u1=new User("张三", 12);

User u2=new User("小美", 15);

users.add(u1);

users.add(u2);

JSONArray json=JSONArray.fromObject(users);

out.write(json.toString());

out.close();

net.sf.json.JSONException: java.lang.SecurityException: class "org.apache.commons.collections.FastHashMap"'s signer information does not match signer information of other classes in the same package

at net.sf.json.JSONObject._fromBean(JSONObject.java:953)

at net.sf.json.JSONObject.fromObject(JSONObject.java:192)

at net.sf.json.JSONArray._processValue(JSONArray.java:2557)

at net.sf.json.JSONArray.processValue(JSONArray.java:2588)

at net.sf.json.JSONArray.addValue(JSONArray.java:2575)

at net.sf.json.JSONArray._fromCollection(JSONArray.java:1082)

at net.sf.json.JSONArray.fromObject(JSONArray.java:145)

at net.sf.json.JSONArray.fromObject(JSONArray.java:127)

at servlet.JsonAjax.doGet(JsonAjax.java:38)

at servlet.JsonAjax.doPost(JsonAjax.java:55)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)

at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)

at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)

at java.lang.Thread.run(Thread.java:619)

Caused by: java.lang.SecurityException: class "org.apache.commons.collections.FastHashMap"'s signer information does not match signer information of other classes in the same package

at java.lang.ClassLoader.checkCerts(ClassLoader.java:776)

at java.lang.ClassLoader.preDefineClass(ClassLoader.java:488)

at java.lang.ClassLoader.defineClass(ClassLoader.java:615)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)