一：今天在使用struts2做文件上传时出现了该异常：

警告: Unable to parse request
org.apache.commons.fileupload.FileUploadBase$SizeLimitExceededException: the request was rejected because its size (5897994) exceeds the configured maximum (2097152)at org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.<init>(FileUploadBase.java:937)at org.apache.commons.fileupload.FileUploadBase.getItemIterator(FileUploadBase.java:331)at org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:351)at org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest.parseRequest(JakartaMultiPartRequest.java:151)at org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest.processUpload(JakartaMultiPartRequest.java:90)at org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest.parse(JakartaMultiPartRequest.java:80)at org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper.<init>(MultiPartRequestWrapper.java:75)at org.apache.struts2.dispatcher.Dispatcher.wrapRequest(Dispatcher.java:753)at org.apache.struts2.dispatcher.ng.PrepareOperations.wrapRequest(PrepareOperations.java:140)at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:83)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)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:103)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:861)at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)at java.lang.Thread.run(Unknown Source)
2014-7-31 22:53:04 com.opensymphony.xwork2.util.logging.commons.CommonsLogger warn
警告: the request was rejected because its size (5897994) exceeds the configured maximum (2097152)

为什么会出现这个错误？

查看struts.properties中有这么一句struts.multipart.parser=Jakarta，实际上这一句也可以不写因为这是struts2为了支持文件上传默认的。那么这个Jakarta到底是什么东西呢？实际上Jakarta实际上就是org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest类。打开JakartaMultiPartRequest.java的源代码你会发现这个类实现了MultiPartRequest接口，在这个类封装了对底层ServletFileUpload的操作，由于common-fileupload组件默认最大支持上传文件的大小为2M,当我们上传大于2M的文件时，就会出现上面的异常。是这个异常的发生导致了fileUpload拦截器没有机会执行，所以看到的是页面没有任何变化，也没有任何提示信息，只是在控制台打印出了上面的异常。解决的办法在struts.properties文件中把struts.multipart.maxSize设置成一个比较大的值，也是就说maxSize远远要大于可能上传文件的大小和fileUpload拦截器中maxinumSize的值。 如可以配置：struts.multipart.maxSize=10000000 即可。

默认的在struts中的default.properties中有这句话：struts.multipart.maxSize=2097152 将上传文件限制为2MB

我的配置是:在struts.xml中加入<constant name="struts.multipart.maxSize" value="524288000" />将默认的上传文件最大值变成500MB

Web容器启动的时候加载文件的时候先加载default.properties，然后再加载struts.xml配置文件。