实体集合转JSON遇到的问题

最近在给IOS的写接口，发现跟ITOO写的接口不一样，ITOO是写好方法，然后把dll文件给他们就行了。而这个是他们需要JSON串，写完以后转成JSON串直接给他们，其实对JSON串也不陌生但是也不是很熟悉，没怎么很深的用过。但是其实挺简单的，只要明白JSON串的结构就好。
但是最近在用的时候就遇到了问题，转的过程中老是失败！！后来经过查找原来是因为我用了hibernate来操作数据库，而json-lib在处理这类结果对象时存在了异常。如下图这个异常。。

Struts Problem Report
Struts has detectedan unhandled exception:
Messages:
FreeMarker template error!

Methodpublic java.lang.Stringorg.apache.commons.lang.exception.NestableRuntimeException.getMessage(int)threw an exception when invoked on net.sf.json.JSONException:java.lang.reflect.InvocationTargetException

The problematic instruction:

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==> ${msgs[0][0]} [on line 76, column 25 inorg/apache/struts2/dispatcher/error.ftl]

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Javabacktrace forprogrammers:

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freemarker.template.TemplateModelException: Method public java.lang.Stringorg.apache.commons.lang.exception.NestableRuntimeException.getMessage(int)threw an exception when invoked on net.sf.json.JSONException:java.lang.reflect.InvocationTargetException

atfreemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:130)

at freemarker.ext.beans.SimpleMethodModel.get(SimpleMethodModel.java:138)

atfreemarker.core.DynamicKeyName.dealWithNumericalKey(DynamicKeyName.java:111)

at freemarker.core.DynamicKeyName._getAsTemplateModel(DynamicKeyName.java:90)

atfreemarker.core.Expression.getAsTemplateModel(Expression.java:89)

at freemarker.core.Expression.getStringValue(Expression.java:93)

atfreemarker.core.DollarVariable.accept(DollarVariable.java:76)

at freemarker.core.Environment.visit(Environment.java:209)

atfreemarker.core.MixedContent.accept(MixedContent.java:92)

atfreemarker.core.Environment.visit(Environment.java:209)

atfreemarker.core.IfBlock.accept(IfBlock.java:82)

atfreemarker.core.Environment.visit(Environment.java:209)

atfreemarker.core.IfBlock.accept(IfBlock.java:82)

atfreemarker.core.Environment.visit(Environment.java:209)

at freemarker.core.MixedContent.accept(MixedContent.java:92)

atfreemarker.core.Environment.visit(Environment.java:209)

atfreemarker.core.Environment.process(Environment.java:189)

atfreemarker.template.Template.process(Template.java:237)

atorg.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:748)

atorg.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:505)

atorg.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)

atorg.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)

atorg.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

atorg.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

atorg.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)

atorg.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)

atorg.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

atorg.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

atorg.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)

atorg.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)

atorg.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)

atorg.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

atorg.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

atorg.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)

atorg.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)

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

atjava.lang.Thread.run(Thread.java:662)

Caused by: java.lang.NullPointerException

atfreemarker.ext.beans.SimpleMemberModel.unwrapArguments(SimpleMemberModel.java:85)

atfreemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:106)

... 37 more

一大串真心的看不懂啊，不过找到关键字一搜就可以明白错误在哪儿呢。但是我却查找了半天。。。
解决方案：
原先转json串只是这样就可以了。

JSONArray arvert = JSONArray.fromObject(实体集合);
json =arvert.toString();

现在需要再加上两句话。

JsonConfigjsonConfig=new JsonConfig();  
jsonConfig.setExcludes(newString[]{"handler","hibernateLazyInitializer"});  
JSONArrayarvert = JSONArray.fromObject实体集合,jsonConfig);
 json = arvert.toString();

实体转json也可以用这种办法解决。
还依稀记得，从刚开始接触这个项目的时候，因为Java没有怎么接触过，遇到问题都是摸不着头脑，后来遇到的问题渐渐的多了，发现越来越不恐惧了，因为知道总有解决办法，而且解决的越来越快，越来越熟练，这就像是一个成长的过程吧。