簡單解決getOutputStream() has already been called for

out.clear(); 
out = pageContext.pushBody(); 

// 輸出圖象到頁面 
ImageIO.write(image, "JPEG", response.getOutputStream()); 

錯誤類型

java.lang.IllegalStateException: getOutputStream() has already been called for this response

三月 19, 2014 2:59:26 下午 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/webofficeDemo] threw exception [java.lang.IllegalStateException: getOutputStream() has already been called for this response] with root cause
java.lang.IllegalStateException: getOutputStream() has already been called for this response
	at org.apache.catalina.connector.Response.getWriter(Response.java:639)
	at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:214)
	at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
	at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)
	at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:190)
	at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:126)
	at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:80)
	at org.apache.jsp.web.getfile_jsp._jspService(getfile_jsp.java:109)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
	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:1004)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1852)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:722)

產生這樣的異常緣由:是web容器生成的servlet代碼中有out.write(""),這個和JSP中調用的 response.getOutputStream()產生衝突.即Servlet規範說明，不能既調用 response.getOutputStream()，又調用response.getWriter(),不管先調用哪個，在調用第二個時候應會拋出 IllegalStateException，由於在jsp中，out變量其實是經過response.getWriter獲得的，你的程序中既用了 response.getOutputStream，又用了out變量，故出現以上錯誤。