调用 forward() 时出现 IllegalStateException

Question

我正在尝试学习 abt servlet。我在调用 forward() 时收到 IllegalStateException。错误发生在 LoginBean.do if 块中我调用 forward 的地方。

        process(request,response);
}

private void process(HttpServletRequest request, HttpServletResponse response) {
    // TODO Auto-generated method stub
    String uri = request.getRequestURI();
    RequestDispatcher rd = null;
    CAppModel model = new CAppModel();

    System.out.println("Inside process ()");
    try{
    if(uri.contains("/Login"))
    {
        System.out.println("Inside Login.do");
        rd = request.getRequestDispatcher("Login.jsp");
        rd.forward(request,response);
    }

    if(uri.contains("/Register.do"))
    {
        System.out.println("inside Register.do");
    }

    if(uri.contains("/LoginBean.do"))
    {

        System.out.println("Inside LoginBean.do");
        LoginBean lb = (LoginBean)request.getAttribute("login");
        System.out.println("toString(): "+lb.toString());
        String result = model.authenticate(lb);
        System.out.println("CS: result of auth "+result);

        if(result.equals("Success"))
        {
            System.out.println("Inside if Success of loginbean");
            HttpSession session = request.getSession(true);
            session.setAttribute("user", lb.getEmail());
            rd = request.getRequestDispatcher("Menu.jsp");
            rd.forward(request, response);

        }
        else
        {
            System.out.println("failed auth "+result);
            request.setAttribute("errorMsg", result);
            rd = request.getRequestDispatcher("Login.jsp");             
            rd.forward(request,response);
        }


    }
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    process(request,response);
}

}

我收到以下错误

java.lang.IllegalStateException: Cannot forward after response has been committed
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:328)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
at com.aditya.CApp.ControllerServlet.process(ControllerServlet.java:69)
at com.aditya.CApp.ControllerServlet.doGet(ControllerServlet.java:31)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:721)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
at org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:741)
at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:711)
at org.apache.jsp.LoginInt_jsp._jspService(LoginInt_jsp.java:104)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1527)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1484)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

Answer 1

包含 /LoginBean.do 的请求将触发 2 if 块导致 2 次转发被调用，导致第二次转发后出现错误。虽然您可以将 if 语句重新排列为

if (uri.contains("/LoginBean.do")) {
  ...
else if (uri.contains("/LoginBean")) {
  ...

通常，针对每个 if 块功能使用单独的 servlet 更简单。

Answer 2

你必须return;后一个转发。否则下面的代码也会执行......在你的情况下包含 /Login 和 /LoginBean.do

的条件

调用 forward() 时出现 IllegalStateException

Getting an IllegalStateException when i call forward()

java

servlets

illegalstateexception