JSP：getOutputStream() has already been called for this response

JSP頁面，用小腳本顯示一張圖片

<%@page import="java.io.OutputStream"%>
<%@page import="java.io.FileInputStream"%>
<%@page import="java.io.InputStream"%>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<% String path=request.getRealPath("/"); response.setContentType("image/png"); InputStream is=new FileInputStream(path+"img/2.png"); byte[] content=new byte[is.available()]; is.read(content); OutputStream os=response.getOutputStream(); os.write(content,0,content.length); %>

 

瀏覽器正常顯示了圖片，可是控制檯報錯:

一月 12, 2018 11:45:53 上午 org.apache.catalina.core.StandardWrapperValve invoke 嚴重: Servlet.service() for servlet [jsp] in context with path [/jsp2] 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:624) at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:211) at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:118) at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:111) at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:184) at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:120) at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75) at org.apache.jsp.從新定向_jsp._jspService(從新定向_jsp.java:143) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)

 

錯誤提示：

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

getOutputStream 被重複調用的。可是我本身之調用了一次，到底在什麼地方被調用了呢？

查找緣由：

查找兩處，瀏覽器代碼，以及jsp翻譯後的java文件

  1 /*
  2  * Generated by the Jasper component of Apache Tomcat
  3  * Version: Apache Tomcat/8.5.24
  4  * Generated at: 2018-01-12 04:05:33 UTC
  5  * Note: The last modified time of this file was set to
  6  *       the last modified time of the source file after
  7  *       generation to assist with modification tracking.
  8  */
  9 package org.apache.jsp;
 10 
 11 import javax.servlet.*;
 12 import javax.servlet.http.*;
 13 import javax.servlet.jsp.*;
 14 import java.io.OutputStream;
 15 import java.io.FileInputStream;
 16 import java.io.InputStream;
 17 
 18 public final class 從新定向_jsp extends org.apache.jasper.runtime.HttpJspBase
 19     implements org.apache.jasper.runtime.JspSourceDependent,
 20                  org.apache.jasper.runtime.JspSourceImports {
 21 
 22   private static final javax.servlet.jsp.JspFactory _jspxFactory =
 23           javax.servlet.jsp.JspFactory.getDefaultFactory();
 24 
 25   private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;
 26 
 27   private static final java.util.Set<java.lang.String> _jspx_imports_packages;
 28 
 29   private static final java.util.Set<java.lang.String> _jspx_imports_classes;
 30 
 31   static {
 32     _jspx_imports_packages = new java.util.HashSet<>();
 33     _jspx_imports_packages.add("javax.servlet");
 34     _jspx_imports_packages.add("javax.servlet.http");
 35     _jspx_imports_packages.add("javax.servlet.jsp");
 36     _jspx_imports_classes = new java.util.HashSet<>();
 37     _jspx_imports_classes.add("java.io.OutputStream");
 38     _jspx_imports_classes.add("java.io.FileInputStream");
 39     _jspx_imports_classes.add("java.io.InputStream");
 40   }
 41 
 42   private volatile javax.el.ExpressionFactory _el_expressionfactory;
 43   private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;
 44 
 45   public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
 46     return _jspx_dependants;
 47   }
 48 
 49   public java.util.Set<java.lang.String> getPackageImports() {
 50     return _jspx_imports_packages;
 51   }
 52 
 53   public java.util.Set<java.lang.String> getClassImports() {
 54     return _jspx_imports_classes;
 55   }
 56 
 57   public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
 58     if (_el_expressionfactory == null) {
 59       synchronized (this) {
 60         if (_el_expressionfactory == null) {
 61           _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
 62         }
 63       }
 64     }
 65     return _el_expressionfactory;
 66   }
 67 
 68   public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
 69     if (_jsp_instancemanager == null) {
 70       synchronized (this) {
 71         if (_jsp_instancemanager == null) {
 72           _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
 73         }
 74       }
 75     }
 76     return _jsp_instancemanager;
 77   }
 78 
 79   public void _jspInit() {
 80   }
 81 
 82   public void _jspDestroy() {
 83   }
 84 
 85   public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
 86       throws java.io.IOException, javax.servlet.ServletException {
 87 
 88     final java.lang.String _jspx_method = request.getMethod();
 89     if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
 90       response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD");
 91       return;
 92     }
 93 
 94     final javax.servlet.jsp.PageContext pageContext;
 95     javax.servlet.http.HttpSession session = null;
 96     final javax.servlet.ServletContext application;
 97     final javax.servlet.ServletConfig config;
 98     javax.servlet.jsp.JspWriter out = null;
 99     final java.lang.Object page = this;
100     javax.servlet.jsp.JspWriter _jspx_out = null;
101     javax.servlet.jsp.PageContext _jspx_page_context = null;
102 
103 
104     try {
105       response.setContentType("text/html; charset=UTF-8");
106       pageContext = _jspxFactory.getPageContext(this, request, response,
107                   null, true, 8192, true);
108       _jspx_page_context = pageContext;
109       application = pageContext.getServletContext();
110       config = pageContext.getServletConfig();
111       session = pageContext.getSession();
112       out = pageContext.getOut();
113       _jspx_out = out;
114 
115       out.write("\r\n");//注意此處out被調用 116       out.write("\r\n");
117       out.write("\r\n");
118       out.write("\r\n");
119 
120 String path=request.getRealPath("/");
121 response.setContentType("image/png");
122 InputStream is=new FileInputStream(path+"img/2.png");
123 byte[] content=new byte[is.available()];
124 is.read(content);
125 OutputStream os=response.getOutputStream();
126 os.write(content,0,content.length);
127 
128     } catch (java.lang.Throwable t) {
129       if (!(t instanceof javax.servlet.jsp.SkipPageException)){
130         out = _jspx_out;
131         if (out != null && out.getBufferSize() != 0)
132           try {
133             if (response.isCommitted()) {
134               out.flush();
135             } else {
136               out.clearBuffer();
137             }
138           } catch (java.io.IOException e) {}
139         if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
140         else throw new ServletException(t);
141       }
142     } finally {
143       _jspxFactory.releasePageContext(_jspx_page_context);
144     }
145   }
146 }

 

爲何會被調用輸入換行呢？ 查找 jsp：

 

標出紅線的四個地方有換行，正好4個，和翻譯後的java文件中符合。

縮進掉這幾個回車，就沒有問題了，圖片正常顯示，控制檯沒有報錯。