struts2做下载功能时，不管正常点下载还是点取消。在tomcat的日志文做中都会出错异常。
不管正常点下载还是点取消。在tomcat的log日志文件中都会出错异常"localhost.2012-05-24.log"
但在tomcat的服务端后面（CMD窗口）中，并没有出异常。网上找了一下，都没有找到解决方法。

2012-5-24 8:55:03 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [default] in context with path [/OTD] 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:851)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:533)
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.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
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:999)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)
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)


------解决方案--------------------
/**
* 下载文件
* @param filePath 文件路径(物理路径)
* @param fileName 源文件名称
* @param response
*/
public void downLoadFile(String filePath, String fileName, HttpServletResponse response) {
File file = new File(filePath);
if (!file.exists() || file.isDirectory()) {
return;
}
InputStream input =null;
OutputStream output = null;
try {
input = new FileInputStream(file);
output = response.getOutputStream();
response.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
byte[] buffer = new byte[1024];
int i = 0;
while ((i = input.read(buffer)) != -1) {
output.write(buffer, 0, i);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if(null !=output) {
output.flush();
output.close();
}
if(null !=input) {
input.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}


用这个方法试试看
------解决方案--------------------

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/**
* 下载文件
* @param filePath 文件路径(物理路径)
* @param fileName 源文件名称
* @param response
*/
public void downLoadFile(String filePa