主要是解决JSON因Hibernate映射生成的集合的转化出现的死循环问题。

这个方法很重要

     public String ajaxJsonByObjectDirecdt(Object obj, String[] filterNames){
         JsonConfig jsonConfig = new JsonConfig();
         jsonConfig.setIgnoreDefaultExcludes(false);
         jsonConfig.setCycleDetectionStrategy(CycleDetectionStrategy.LENIENT);    //防止自包含

         if(filterNames != null){
             //这里是核心，过滤掉不想使用的属性
             jsonConfig .setExcludes(filterNames) ;
         }
         JSONObject jsonObj = JSONObject.fromObject(obj, jsonConfig);
         //ajax()方法主要功能是将数据通过输出流输出到Client
         return ajax(jsonObj.toString(), "text/html");

     }
对于参数，String[] filterNames，这个字符串数组中存放的是变量的名字(句柄)，而不是变量的类型。

     public String getUserLoginInfo(){
         User user = (User)getSession().getAttribute(USER);
                 //要过滤的属性集合
         String[] filterNames =
                 new String[]{"role", "operatingHistories", "helpInfoBoards", "replyInfos",
                 "helpInfos", "credits", "users", "user",
                 "helpInfoBoard"};

         return ajaxJsonByObjectDirecdt(user, filterNames);
     }

其中User类含有以下属性：

 public class User implements java.io.Serializable {

     // Fields

     private String id;
     private Role role;
     private String username;
     private String studentNum;
     private String address;
     private Integer age;
     private String nickname;
     private String sex;
     private String qq;
     private String phonenumber;
     private String fixedTelephone;
     private String password;
     private Timestamp registerDate;
     private String imgUrl;
     private String email;
     private String question;
     private String answer;
     private Timestamp totalOnlineDate;
     private Set<OperatingHistory> operatingHistories = new HashSet<OperatingHistory>(
             0);
     private Set<HelpInfoBoard> helpInfoBoards = new HashSet<HelpInfoBoard>(0);
     private Set<ReplyInfo> replyInfos = new HashSet<ReplyInfo>(0);
     private Set<HelpInfo> helpInfos = new HashSet<HelpInfo>(0);
     private Set<Credit> credits = new HashSet<Credit>(0);

       //more methods.
 }
两端代码参照下，就知道怎么使用了。

后台异常信息：

 INFO  com.opensymphony.xwork2.config.ConfigurationManager
 Detected container provider org.apache.struts2.convention.ClasspathConfigurationProvider@67b0eb2c needs to be reloaded.  Reloading all providers.
 INFO  com.opensymphony.xwork2.config.ConfigurationManager
 Detected package provider org.apache.struts2.convention.ClasspathConfigurationProvider@67b0eb2c needs to be reloaded.  Reloading all providers.
 INFO  com.opensymphony.xwork2.config.ConfigurationManager
 Detected package provider org.apache.struts2.convention.ClasspathConfigurationProvider@31af5c3 needs to be reloaded.  Reloading all providers.
 INFO  com.opensymphony.xwork2.config.ConfigurationManager
 Detected package provider org.apache.struts2.convention.ClasspathPackageProvider@5efcd6cc needs to be reloaded.  Reloading all providers.
 INFO  com.opensymphony.xwork2.config.providers.XmlConfigurationProvider
 Parsing configuration file [struts-default.xml]
 INFO  com.opensymphony.xwork2.config.providers.XmlConfigurationProvider
 Parsing configuration file [struts-plugin.xml]
 INFO  com.opensymphony.xwork2.config.providers.XmlConfigurationProvider
 Parsing configuration file [struts.xml]
 INFO  com.opensymphony.xwork2.config.impl.DefaultConfiguration
 Overriding property struts.i18n.reload - old value: false new value: true
 INFO  com.opensymphony.xwork2.config.impl.DefaultConfiguration
 Overriding property struts.configuration.xml.reload - old value: false new value: true
 INFO  org.apache.struts2.config.BeanSelectionProvider
 Loading global messages from i18n
 INFO  org.apache.struts2.spring.StrutsSpringObjectFactory
 Initializing Struts-Spring integration...
 INFO  com.opensymphony.xwork2.spring.SpringObjectFactory
 Setting autowire strategy to name
 INFO  org.apache.struts2.spring.StrutsSpringObjectFactory
 ... initialized Struts-Spring integration successfully
 2014-06-03 01:07:12 Test: Reloading class 'student.life.support.platform.action.BaseAction'.
 hql:from student.life.support.platform.model.User as model where model.username = ?
 Hibernate:
     select
         user0_.id as id62_,
         user0_.address as address62_,
         user0_.age as age62_,
         user0_.answer as answer62_,
         user0_.email as email62_,
         user0_.fixed_telephone as fixed6_62_,
         user0_.img_url as img7_62_,
         user0_.nickname as nickname62_,
         user0_.password as password62_,
         user0_.phonenumber as phonenu10_62_,
         user0_.qq as qq62_,
         user0_.question as question62_,
         user0_.register_date as register13_62_,
         user0_.role_id as role18_62_,
         user0_.sex as sex62_,
         user0_.student_num as student15_62_,
         user0_.total_online_date as total16_62_,
         user0_.username as username62_
     from
         studentlifesupportplatform.user user0_
     where
         user0_.username=?
 WARN  net.sf.json.JSONObject
 Property 'handler' has no read method. SKIPPED
 Hibernate:
     select
         role0_.id as id61_0_,
         role0_.role_permissions as role2_61_0_,
         role0_.role_type as role3_61_0_
     from
         studentlifesupportplatform.role role0_
     where
         role0_.id=?
 Hibernate:
     select
         users0_.role_id as role18_1_,
         users0_.id as id1_,
         users0_.id as id62_0_,
         users0_.address as address62_0_,
         users0_.age as age62_0_,
         users0_.answer as answer62_0_,
         users0_.email as email62_0_,
         users0_.fixed_telephone as fixed6_62_0_,
         users0_.img_url as img7_62_0_,
         users0_.nickname as nickname62_0_,
         users0_.password as password62_0_,
         users0_.phonenumber as phonenu10_62_0_,
         users0_.qq as qq62_0_,
         users0_.question as question62_0_,
         users0_.register_date as register13_62_0_,
         users0_.role_id as role18_62_0_,
         users0_.sex as sex62_0_,
         users0_.student_num as student15_62_0_,
         users0_.total_online_date as total16_62_0_,
         users0_.username as username62_0_
     from
         studentlifesupportplatform.user users0_
     where
         users0_.role_id=?
 WARN  net.sf.json.JSONObject
 Property 'transactionTimeout' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'URL' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'array' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'asciiStream' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'bigDecimal' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'binaryStream' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'blob' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'boolean' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'byte' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'bytes' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'characterStream' has no read method. SKIPPED
 WARN  net.sf.json.JSONObject
 Property 'clob' has no read method. SKIPPED
 ERROR  freemarker.runtime
 Method public java.lang.String org.apache.commons.lang.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on net.sf.json.JSONException: java.lang.reflect.InvocationTargetException
 Method public java.lang.String org.apache.commons.lang.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on net.sf.json.JSONException: java.lang.reflect.InvocationTargetException
 The problematic instruction:
 ----------
 ==> ${msg[0]} [on line 68, column 29 in org/apache/struts2/dispatcher/error.ftl]
 ----------

 Java backtrace for programmers:
 ----------
 freemarker.template.TemplateModelException: Method public java.lang.String org.apache.commons.lang.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on net.sf.json.JSONException: java.lang.reflect.InvocationTargetException
     at freemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:130)
     at freemarker.ext.beans.SimpleMethodModel.get(SimpleMethodModel.java:138)
     at freemarker.core.DynamicKeyName.dealWithNumericalKey(DynamicKeyName.java:111)
     at freemarker.core.DynamicKeyName._getAsTemplateModel(DynamicKeyName.java:90)
     at freemarker.core.Expression.getAsTemplateModel(Expression.java:89)
     at freemarker.core.Expression.getStringValue(Expression.java:93)
     at freemarker.core.DollarVariable.accept(DollarVariable.java:76)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.MixedContent.accept(MixedContent.java:92)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.IfBlock.accept(IfBlock.java:82)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.IteratorBlock$Context.runLoop(IteratorBlock.java:179)
     at freemarker.core.Environment.visit(Environment.java:417)
     at freemarker.core.IteratorBlock.accept(IteratorBlock.java:102)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.MixedContent.accept(MixedContent.java:92)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.IfBlock.accept(IfBlock.java:82)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.MixedContent.accept(MixedContent.java:92)
     at freemarker.core.Environment.visit(Environment.java:210)
     at freemarker.core.Environment.process(Environment.java:190)
     at freemarker.template.Template.process(Template.java:237)
     at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:797)
     at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:519)
     at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
     at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
     at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
     at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:123)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
     at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
     at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:171)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
     at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
     at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
     at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
     at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     at java.lang.Thread.run(Thread.java:662)
 Caused by: java.lang.NullPointerException
     at freemarker.ext.beans.SimpleMemberModel.unwrapArguments(SimpleMemberModel.java:85)
     at freemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:106)
     ... 49 more
 2014-6-3 1:07:12 org.apache.catalina.core.StandardWrapperValve invoke
 严重: Servlet.service() for servlet [default] in context with path [/StudentLifeSupportPlatformSystem] threw exception
 java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
     at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:451)
     at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:801)
     at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:519)
     at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
     at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
     at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
     at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:123)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
     at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
     at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:171)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
     at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
     at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
     at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
     at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     at java.lang.Thread.run(Thread.java:662)

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