getOutputStream() has already been called for this response的解决方法
《轻量级J2EE企业应用实战》一书的第2章有一个使用SerlvetResponse输出图像的例子，代码如下：
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<%
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BufferedImage image
= new BufferedImage(400, 400
, BufferedImage.TYPE_INT_RGB);
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Graphics g =
image.getGraphics();
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g.fillRect(0,0,400,400
);
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g.setColor(new Color(255,0,0
));
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g.fillArc(20,20,100,100,30,120
);
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g.setColor(new Color(0,255,0
));
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g.fillArc(20,20,100,100,150,20
);
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g.setColor(new Color(0,0,255
));
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g.fillArc(20,20,100,100,270,120
);
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g.setColor(new Color(0,0,0
));
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g.drawString("red:climb" , 300, 80
);
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g.drawString("green:swim", 300, 120
);
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g.drawString("blue:jump", 300, 160
);
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ImageIO.write(image, "bmp"
, response.getOutputStream());
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//
out.clear();
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//out = pageContext.pushBody();
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%>
在Tomcat下运行时抛出如下异常：
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at org.apache.catalina.connector.Response.getWriter(Response.java:601)
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at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:196
)
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at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125
)
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at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118
)
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at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:185
)
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at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:116
)
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at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:76
)
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at org.apache.jsp.pages.drawImage_jsp._jspService(drawImage_jsp.java:84)
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at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98
)
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at javax.servlet.http.HttpServlet.service(HttpServlet.java:803
)
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at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328
)
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at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315
)
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at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265
)
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at javax.servlet.http.HttpServlet.service(HttpServlet.java:803
)
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at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269
)
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at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188
)
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at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210
)
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at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174
)
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at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127
)
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at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117
)
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at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108
)
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at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151
)
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at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870
)
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at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665
)
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at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528
)
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at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81
)
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at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685
)
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at java.lang.Thread.run(Thread.java:595)
查看转换后的JSP代码，发现第84行如下(绿色高亮处)：
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public void
_jspService(HttpServletRequest request, HttpServletResponse response)
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throws java.io.IOException, ServletException 
{
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JspFactory _jspxFactory = null;
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PageContext pageContext = null;
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HttpSession session = null;
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ServletContext application = null;
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ServletConfig config = null;
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JspWriter out = null;
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Object page = this;
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JspWriter _jspx_out = null;
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PageContext _jspx_page_context = null;
![]()
![]()
![]()
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try {
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_jspxFactory = JspFactory.getDefaultFactory();
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response.setContentType("text/html; charset=UTF-8");
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pageContext = _jspxFactory.getPageContext(this, request, response,
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null, true, 8192, true);
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_jspx_page_context = pageContext;
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application = pageContext.getServletContext();
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config = pageContext.getServletConfig();
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session = pageContext.getSession();
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out = pageContext.getOut();
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_jspx_out = out;
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out.write("\r\n");
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out.write("\n");
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out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\n");
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out.write("<html>\n");
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out.write("<head>\n");
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out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">\n");
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out.write("<title>Draw Image</title>\n");
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out.write("</head>\n");
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out.write("<body>\n");
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out.write("\r\n");
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BufferedImage image = new BufferedImage(400, 400, BufferedImage.TYPE_INT_RGB);
![]()
Graphics g = image.getGraphics();
![]()
g.fillRect(0,0,400,400);
![]()
g.setColor(new Color(255,0,0));
![]()
g.fillArc(20,20,100,100,30,120);
![]()
g.setColor(new Color(0,255,0));
![]()
g.fillArc(20,20,100,100,150,20);
![]()
g.setColor(new Color(0,0,255));
![]()
g.fillArc(20,20,100,100,270,120);
![]()
g.setColor(new Color(0,0,0));
![]()
g.drawString("red:climb" , 300, 80);
![]()
g.drawString("green:swim", 300, 120);
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g.drawString("blue:jump", 300, 160);
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ImageIO.write(image, "bmp", response.getOutputStream());
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//out.clear();
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//out = pageContext.pushBody();
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out.write("\r\n");
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out.write("</body>\n");
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out.write("</html>");
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} catch (Throwable t) {
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if (!(t instanceof SkipPageException)){
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out = _jspx_out;
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if (out != null && out.getBufferSize() != 0)
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out.clearBuffer();
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if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
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}
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} finally {
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if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context);
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}
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}
我们看到在JSP页面释放资源的时候，调用了ServetResponse.getWriter()方法，之后程序即抛出异常了，查看Servlet的API发现问题：
解决方法如下：
将JSP页面的最后两行代码的注释去掉，这两行代码的作用如下：
out.clear()：清空缓存的内容。
pageContext.pushBody()：参考API
public BodyContent pushBody()
在Tomcat下运行时抛出如下异常：
查看转换后的JSP代码，发现第84行如下(绿色高亮处)：
{{{{{我们看到在JSP页面释放资源的时候，调用了ServetResponse.getWriter()方法，之后程序即抛出异常了，查看Servlet的API发现问题：
public java.io.PrintWriter getWriter() throws java.io.IOException
-
Returns a
PrintWriterobject that can send character text to the client. ThePrintWriteruses the character encoding returned bygetCharacterEncoding(). If the response's character encoding has not been specified as described ingetCharacterEncoding(i.e., the method just returns the default valueISO-8859-1),getWriterupdates it toISO-8859-1.Calling flush() on the
PrintWritercommits the response.Either this method or
getOutputStream()may be called to write the body, not both. -
- Returns:
-
a
PrintWriterobject that can return character data to the client - Throws:
-
UnsupportedEncodingException- if the character encoding returned bygetCharacterEncodingcannot be used -
java.lang.IllegalStateException- if thegetOutputStreammethod has already been called for this response object -
java.io.IOException- if an input or output exception occurred - See Also:
-
getOutputStream(),setCharacterEncoding(java.lang.String)
解决方法如下：
将JSP页面的最后两行代码的注释去掉，这两行代码的作用如下：
out.clear()：清空缓存的内容。
pageContext.pushBody()：参考API
public BodyContent pushBody()
-
Return a new BodyContent object, save the current "out" JspWriter, and update the value of the "out" attribute in the page scope attribute namespace of the PageContext.
- Returns:
- the new BodyContent
·返回一个新的BodyContent(代表一个HTML页面的BODY部分内容）
·保存JspWriter实例的对象out
·更新PageContext的out属性的内容
转自：http://www.blogjava.net/pengpenglin/archive/2008/01/19/176532.html