在做图形验证码的时候随便从网上找了段代码，结果出现了这个异常，详细内容如下：
( 4361578 ms) [http - 8080 - Processor25] ERROR: org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[ / xixibar].[jsp]#invoke : Servlet.service() for servlet jsp threw exceptionjava.lang.IllegalStateException: getOutputStream() has already been called for this response at org.apache.catalina.connector.Response.getWriter(Response.java: 599 ) at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java: 195 ) at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java: 124 ) at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java: 117 ) at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java: 182 ) at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java: 115 ) at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java: 75 ) at org.apache.jsp.image_jsp._jspService(image_jsp.java: 105 ) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java: 97 ) at javax.servlet.http.HttpServlet.service(HttpServlet.java: 802 ) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java: 334 ) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java: 314 ) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java: 264 ) at javax.servlet.http.HttpServlet.service(HttpServlet.java: 802 ) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java: 252 ) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java: 173 ) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java: 213 ) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java: 178 ) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java: 126 ) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java: 105 ) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java: 107 ) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java: 148 ) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java: 869 ) at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java: 664 ) at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java: 527 ) at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java: 80 ) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java: 684 ) at java.lang.Thread.run(Thread.java: 595 )
刚开始都没看明白怎么回事，后来找Google帮忙，找到如下解释：
在tomcat5下jsp中出现此错误一般都是在jsp中使用了输出流（如输出图片验证码，文件下载等），没有妥善处理好的原因。具体的原因就是在tomcat中jsp编译成servlet之后在函数_jspService(HttpServletRequest request, HttpServletResponse response)的最后有一段这样的代码 finally ... { if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context); } 这里是在释放在jsp中使用的对象，会调用response.getWriter(),因为这个方法是和response.getOutputStream()相冲突的！所以会出现以上这个异常。然后当然是要提出解决的办法，其实挺简单的（并不是和某些朋友说的那样 -- 将jsp内的所有空格和回车符号所有都删除掉），在使用完输出流以后调用以下两行代码即可：out.clear();out = pageContext.pushBody();
照这个方法添加了两行代码，果然OK了！
