TomCat异常之一

十一月 02, 2017 10:30:11 下午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [CheckCodeServlet] in context with path [/day09EE] threw exception
java.lang.IllegalStateException: Cannot create a session after the response has been committed
at org.apache.catalina.connector.Request.doGetSession(Request.java:2995)
at org.apache.catalina.connector.Request.getSession(Request.java:2409)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:896)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:908)
at cn.itcast.web.session.CheckCodeServlet.doGet(CheckCodeServlet.java:35)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
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:478)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
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:799)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

at java.lang.Thread.run(Thread.java:744)

package cn.itcast.web.session;import java.awt.Graphics;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.imageio.ImageIO;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class CheckCodeServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String token=Token.getNum();//bind checkcode to domain objectBufferedImage image=new BufferedImage(50,25,BufferedImage.TYPE_INT_RGB);Graphics g=image.getGraphics();g.drawString(token,15,15);//add interfering linefor(int i=0;i<10;i++){Random r=new Random();int x1=r.nextInt(50);int y1=r.nextInt(25);g.drawLine(x1, y1, x1+4, y1+4);}ImageIO.write(image, "jpg", response.getOutputStream());response.setHeader("expires", "-1");response.setHeader("cache-control", "no-cache");response.setHeader("pragma", "no-cache");HttpSession session=request.getSession();session.setAttribute("checkCodeServer",token);}}class Token{public static String getNum(){Random r=new Random();int num=r.nextInt(10000);return num+"";}}

错误代码

ImageIO.write(image, "jpg", response.getOutputStream());response.setHeader("expires", "-1");response.setHeader("cache-control", "no-cache");response.setHeader("pragma", "no-cache");HttpSession session=request.getSession();session.setAttribute("checkCodeServer",token);

有时候在操作Session时，系统会抛出如下异常

java.lang.IllegalStateException: Cannot create a session after the response has been committed

之所以会出现此类问题是因为我们在Response输出响应后才创建Session的。

(因为那时候服务器已经将数据发送到客户端了，即：就无法发送Session ID 了)

解决办法：

你只需要在你的程序中将创建访问Session的语句【request.getSession()】提前至Response输出数据之前就好了。

例如改成下面的写法OK：

ServletOutputStream out = response.getOutputStream();
// 最好这样紧挨着 response.getOutputStream()
HttpSession seesion = request.getSession();
seesion.setAttribute("xxx", rand);

// 输出数据
out.print("<h1>hello</h1>");
out.close();

转自:http://apps.hi.baidu.com/share/detail/14557440