java.util.ConcurrentModificationException异常

java.util.ConcurrentModificationException异常


java.util.SubList.checkForComodification(AbstractList.java:752)
    java.util.SubList.listIterator(AbstractList.java:682)
    java.util.AbstractList.listIterator(AbstractList.java:284)
    java.util.SubList.iterator(AbstractList.java:678)
    java.util.AbstractCollection.toString(AbstractCollection.java:414)
    java.lang.String.valueOf(String.java:2827)
    java.lang.StringBuilder.append(StringBuilder.java:115)
    com.qieast.platform.admincp.action.StudentAction.toString(StudentAction.java:28)
    java.lang.String.valueOf(String.java:2827)
    java.lang.StringBuilder.append(StringBuilder.java:115)
    com.opensymphony.xwork2.validator.ValidationInterceptor.doBeforeInvocation(ValidationInterceptor.java:232)
    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:261)
    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:142)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:166)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485)
    org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    org.apache.struts2.dispatcher.ActionContextCleanUp.doFilter(ActionContextCleanUp.java:102)
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    com.qieast.platform.servlet.filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:114)
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
    org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    java.lang.Thread.run(Thread.java:619)






以下为转的内容
今天又见诡异的ConcurrentModificationException异常，异常以下：
java.util.ConcurrentModificationException
    at java.util.SubList.checkForComodification(AbstractList.java:855)
    at java.util.SubList.size(AbstractList.java:728)

看文档知道是正对这个list迭代的时候另外一个线程增加或者删除了list中一个元素，那么迭代函数就会抛出这个异常，而改变其中某个元素的属性值之类的，对迭代过程不影响。

不过今天诡异的是，我这个List肯定不会有add，remove的， List subList = list.subList(limit,offset). 而这个subList我是不会去更新它的。
但是问题还是出现了。 调试查看subList 发现这个家伙拥有的元素内容好像还是list的内容，只不过size是limit，这样的话也就是说 list.subList返回的一个封装的subList，实际的内容还是list的内容。

解决方法：修改list.subList， 使得返回复制拷贝后的list，先new ArrayList，然后把符合条件的从list里面一个个copy过去。



Java List Deep copy
2009年06月03日 14:42
       Java中函数调用参数默认都是以引用传递的方式，这样的话传入一个ArrayList,在函数里面修改这个list的值，比如说加一下Object到list中，函数调用结束之后，该ArrayList的值也就随之改变了，但如果在函数里面生成另外一个List,如通过Hibernate查询数据库返回一个list，并直接把这个list赋值给传入的ArrayList，则函数执行完之后里面的内容不会有变化。究其原因，也就是在对象的浅拷贝跟深拷贝这里，直接赋值，只是浅拷贝，只是将对象的指针指向同一个对象，当函数执行完之后，后续的操作还是基于原先的对象所指向的位置，所以改动没有起效。
      解决的方法当然就是在函数里把List深度拷贝到参数中，最容易理解的方式就是遍历一下整个list,逐个添加到参数ArrayList中，但这样代码比较笨拙。代码更简洁的方式是调用List的addAll方法，将整个list直接加到参数ArrayList中。