getWriter() 和Response.getOutputStream冲突

java.lang.IllegalStateException异常:简单分析和简单解决方案

今天写java验证码程序，完成后使用一切正常，但是总抛出java.lang.IllegalStateException异常，虽然并不影响正常使用，但看了总让人觉得很不舒服，检查代码并没有错，最后上网查了不少资料，终于发现原因之所在。 我们在做文件上传或者下载，或者过滤等操作时，可能要用到页面的输出流. 例如在JSP使用： 　　　　response.reset(); 　　　　response.setContentType(”application/vnd.ms-excel”); 　　　　OutputStream os = response.getOutputStream();　　 抛出异常： ERROR [Engine] StandardWrapperValve[jsp]: Servlet.service() for servlet jsp threw exception java.lang.IllegalStateException: getOutputStream() has already been called for this response 从网上找了下资料，综合一下原因分析： 这是web容器生成的servlet代码中有out.write(””)，这个和JSP中调用的response.getOutputStream()产生冲突. 即Servlet规范说明，不能既调用 response.getOutputStream()，又调用response.getWriter()，无论先调用哪一个，在调用第二个时候应会抛出 IllegalStateException，因为在jsp中，out变量是通过response.getWriter得到的，在程序中既用了response.getOutputStream，又用了out变量，故出现以上错误。 解决方案： 1.在程序中添加： out.clear(); out = pageContext.pushBody(); 就可以了； 2，不要在%］［%之间写内容包括空格和换行符 3，在页面写入图片的时候，需要flush（） 　OutputStream output=response.getOutputStream(); 　output.flush(); 4，在页面确定写入 有人说可能是tomcat的bug，我给她回了封信: :我看了看这里，http://www.javathinker.org /main.jsp？bc=showessay.jsp＋filename=tomcat/tomcat_question_chapter13.htm 这里是你回复别人的一个帖子，里面的观点基本上和我理解的一样，但是你最后写到可能是tomcat的bug，我想解释一下:在jsp中，out是内嵌对象，即已经设置了PrintWriter out=response.getWriter();这样在再次getOutputStream()得到输出流时(比如转发过滤、下载文件时)就出错了 (写排斥锁)，我不止一次看到有人的文件下载页面在后台不断打印这个异常。而在servlet中没有默认out内置对象，所以没有出错.你可以在 servlet中添加out对象试试，应该会报异常的.所以正确的处理方式就应该是:在servlet中做控制层，在业务处理以前不要获得out对象，当业务操作失败或出现异常时再生成out对象回显操作结果。 实际案例： 一次在做项目，做一个地图搜索，返回json数据流，由于没有使用flush，造成界面无法显示。 package com.segsec.gisap.servlet; import java.io.IOException; import java.io.InputStream; import java.net.MalformedURLException; import java.net.URL; import java.net.URLEncoder; import java.util.Enumeration; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class ServletUtil { @SuppressWarnings("unchecked") public static void forward(String url, HttpServletRequest request, HttpServletResponse response) throws IOException{ forward(url, request, response, "utf-8"); } @SuppressWarnings("unchecked") public static void forward(String url, HttpServletRequest request, HttpServletResponse response, String encode) throws IOException{ StringBuilder surl = new StringBuilder(url); Enumeration er = request.getParameterNames(); if(er.hasMoreElements()){ String name = (String) er.nextElement(); surl.append("?").append(name).append("=").append(URLEncoder.encode(request.getParameter(name), encode)); } while(er.hasMoreElements()){ String name = (String) er.nextElement(); surl.append("&").append(name).append("=").append(URLEncoder.encode(request.getParameter(name), encode)); } // System.out.println("surl:" + surl); InputStream is = null; ServletOutputStream os = null; try { os = response.getOutputStream(); URL u = new URL(surl.toString()); is = u.openStream(); byte[] buff = new byte[1024]; int len; while((len = is.read(buff)) != -1){ os.write(buff, 0, len); } os.flush(); } catch (MalformedURLException e) { e.printStackTrace(); throw new IOException(e); }finally{ try{ if(is != null){ is.close(); } }catch (IOException e) { e.printStackTrace(); } try{ if(os != null){ os.close(); } }catch (IOException e) { e.printStackTrace(); } } } } package com.segsec.gisap.servlet; import java.io.IOException; import java.io.PrintWriter; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Properties; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import mapbar.MapbarInterface; import mapbar.bean.Poi; import com.general.FormatUtil; import com.googlecode.jsonplugin.JSONUtil; import com.segsec.gisap.dao.MenuDAO; import com.segsec.gisap.util.Config; /** * 通过省份名称和查询条件查找地名 * @author Administrator * 电召的按地址搜索和 地图搜索; * */ public class SearchAddress extends HttpServlet { private static final long serialVersionUID = 1L; private boolean searchAddress_use_agent = false; private String searchAddress_agent_url = "http://113.106.90.236/searchAddress"; @Override public void init() throws ServletException { String configPath = Config.getConfigPath(); String systemConfigFile = configPath + "config/system.properties"; try { Properties properties = com.segsec.gisap.util.Util.loadProperties(systemConfigFile); searchAddress_use_agent = Boolean.valueOf(properties.getProperty("searchAddress_use_agent")); searchAddress_agent_url = properties.getProperty("searchAddress_agent_url"); System.out.println("searchAddress_use_agent:" + searchAddress_use_agent); System.out.println("searchAddress_agent_url:" + searchAddress_agent_url); } catch (IOException e) { e.printStackTrace(); } } /** * The doGet method of the servlet. * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } /** * The doPost method of the servlet. * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ @SuppressWarnings("unchecked") public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if(searchAddress_use_agent){ ServletUtil.forward(searchAddress_agent_url, request, response); return; } /* * 从客户端取得 城市名称，对应省份子表的名称,查询条件 */ request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); response.setContentType("application/x-json;charset=UTF-8"); PrintWriter pw=response.getWriter(); String tablename = request.getParameter("tablename"); String restrict= FormatUtil.isoconversionutf8(request.getParameter("restrict")); String iscity=request.getParameter("iscity"); String cityname=request.getParameter("cityname"); int start=Integer.parseInt(request.getParameter("start")); int end=Integer.parseInt(request.getParameter("limit")); String str = request.getParameter("isMapbar"); int isMapbar = 0; if(str != null) { try { isMapbar = Integer.parseInt(str); }catch(Exception e) {} } //如果是Mapbar if(isMapbar == 1) { int limit = end; List ps = MapbarInterface.getPoiByKeyword(cityname, restrict, 1, limit); int size = ps.size(); Map map = new HashMap(); map.put("pagenumbercount", size); Map obj = null; String tmp = null; String[] lonlat = null; List list = new ArrayList(); for(Poi p : ps) { obj = new HashMap(); obj.put("name", p.getName()); tmp = p.getStrlatlon(); if(tmp != null) { lonlat = tmp.split(","); } if(lonlat != null && lonlat.length > 1) { obj.put("lon", lonlat[0]); obj.put("lat", lonlat[1]); } obj.put("addname", p.getAddress()); obj.put("telephone", p.getPhone()); list.add(obj); } map.put("list", list); try{ String resp = JSONUtil.serialize(map); pw.println(resp); pw.flush(); }catch(Exception ex){ System.out.println("Query SearchAddress to Error"+ex); }finally{ pw.close(); } }else { MenuDAO dao = new MenuDAO(); HashMap hm; if(iscity!=null&&cityname!=null){ if(cityname.equals("全国")){ hm = dao.queryPOINTALL(tablename, restrict,start,start+end); }else if(iscity.equals("true")){ hm = dao.queryPOINTCity(tablename, cityname,restrict,start,start+end); }else{ hm = dao.queryPOINTPro(tablename, restrict,start,start+end); } }else{ hm = dao.queryPOINT(tablename, restrict,start,start+end); } try{ /*AJAX 对象序列化一个Object 对象输出到客户端*/ String obj=JSONUtil.serialize(hm); pw.println(obj); pw.flush(); }catch(Exception ex){ System.out.println("Query SearchAddress to Error"+ex); }finally{ pw.close(); } } } } win.findAddressStore .load({ method : 'post', params : { start : 0, limit : 20, 'tablename' : tablename, 'restrict' : restrict, cityname : cityname, isMapbar : 1 // isMapbar || 0 }, callback : function(r,opt,success) { btn.enable(); if (!success) { alert("查找失败!:" + tablename + "\n restrict:" + restrict); } } });