java.lang.IllegalStateException: Cannot forward after response has been committed

错误信息：

严重: Servlet.service() for servlet ShowBaby threw exception

java.lang.IllegalStateException: Cannot forward after response has been committed

at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:312)

at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)

at com.shyy.jb.epet.servlet.ShowBabyServlet.doGet(ShowBabyServlet.java:37)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at com.shyy.jb.epet.Filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:32)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)

at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)

at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)

at java.lang.Thread.run(Unknown Source)

源代码：

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String id=request.getParameter("id");

if (null==id||id.equals("")) {

request.setAttribute("error", "没有指定宠物编号!");

// response.sendRedirect("/WEB-INF/jsp/error.jsp");//重定向,在浏览器端改变地址栏地址

request.getRequestDispatcher("/WEB-INF/jsp/error.jsp").forward(request, response);//转发，在服务器端跳转，地址不变

}

Integer petId=Integer.valueOf(id);

PetInfoBiz biz=new PetInfoBizImpl();

PetInfo petInfo=biz.load(petId);//根据ID加载宠物信息

if (null==petInfo) {

request.setAttribute("error", "没有指定编号的宠物记录!");//没有这个ID的宠物则跳转到错误页面

request.getRequestDispatcher("/WEB-INF/jsp/error.jsp").forward(request, response);

}

request.setAttribute("item", petInfo);

request.getRequestDispatcher("/WEB-INF/jsp/pet/petInfo.jsp").forward(request, response);

}

这是一个简单的Servlet，我在地址栏敲入的是：

http://localhost:8080/epet/ShowBaby.do?id=4

数据库里没有4这个ID，理论上来说应该跳转到错误页面的，可是没有。

错误原因：

if{……}else{……}这是逻辑判断语句，只有if{}而没有else{}有时候它还会继续执行外面的语句，所以导致错误

解决办法：

if (null==petInfo) {

request.setAttribute("error", "没有指定编号的宠物记录!");//没有这个ID的宠物则跳转到错误页面

request.getRequestDispatcher("/WEB-INF/jsp/error.jsp").forward(request, response);

}else{

request.setAttribute("item", petInfo);

request.getRequestDispatcher("/WEB-INF/jsp/pet/petInfo.jsp").forward(request, response);

}

}

加else{}

if (null==petInfo) {

request.setAttribute("error", "没有指定编号的宠物记录!");//没有这个ID的宠物则跳转到错误页面

request.getRequestDispatcher("/WEB-INF/jsp/error.jsp").forward(request, response);

return ;

}

request.setAttribute("item", petInfo);

request.getRequestDispatcher("/WEB-INF/jsp/pet/petInfo.jsp").forward(request, response);

}

在if后加个return,这样就不会执行if外面的语句了。OK，问题解决。