Question

尝试以编程方式运行Web应用程序。编写了一个自动部署Web应用程序的代码。部署Web应用程序后，我使用URL类通过一些输入调用servlet并打印响应，如下所示。

    //code to start Tomcat server and deploy the web app
    String myUrl = "http://localhost:8080/CrossSiteScripting?user=shri&passwd=firstPassword";
    URL url = new URL(myUrl); 
    HttpURLConnection con = (HttpURLConnection)url.openConnection();
    con.setRequestMethod("GET");
    BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
    String inputLine;
    StringBuffer response = new StringBuffer();
    String httpMethod = con.getRequestMethod();
    while((inputLine=in.readLine()) != null){
        response.append(inputLine);
    }
    in.close();
    System.out.println("\n----------------------\nHTTP Method : "+ httpMethod +"\nOutput: "+response.toString());

我正在调用servlet的doGet()方法。 doGet方法中的代码如下所示。

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      String user = request.getParameter("user");
      String pwd = request.getParameter("passwd");
      request.setAttribute("user", user);
      request.setAttribute("passwd", pwd);
      PrintWriter pw = response.getWriter();
      pw.write("Inside doGet method of Servlet\nuser name: "+user+"password= "+pwd);
      RequestDispatcher view = request.getRequestDispatcher("homePage.jsp");
      view.forward(request, response);
}

如果我在doget方法view.forward(request, response);中注释掉最后一行，那么我就可以获得预期的响应。但如果没有注释，那么我得到NullPointerException，服务器返回HTTP响应代码500。
这是我在使用URL类运行应用程序时遇到的错误。

    asAug 07, 2015 11:53:47 AM org.apache.catalina.core.StandardContext setPath
    WARNING: A context path must either be an empty string or start with a '/' and do not end with a '/'. The path [/] does not meet these criteria and has been changed to []
    C:\Users\IBM_ADMIN\workspace\Initiate Tomcat\.
    Host: StandardEngine[Tomcat].StandardHost[localhost]

    starting server...
    Aug 07, 2015 11:53:47 AM org.apache.coyote.AbstractProtocol init
    INFO: Initializing ProtocolHandler ["http-nio-8080"]

    Aug 07, 2015 11:53:47 AM org.apache.tomcat.util.net.NioSelectorPool getSharedSelector

    INFO: Using a shared selector for servlet write/read

    Aug 07, 2015 11:53:47 AM org.apache.catalina.core.StandardService startInternal

    INFO: Starting service Tomcat

    Aug 07, 2015 11:53:47 AM org.apache.catalina.core.StandardEngine startInternal

    INFO: Starting Servlet Engine: Apache Tomcat/8.0.23

    Aug 07, 2015 11:53:48 AM org.apache.catalina.util.SessionIdGeneratorBase createSecureRandom
    INFO: Creation of SecureRandom instance for session ID generation using [SHA1PRNG] took [173] milliseconds.
    Aug 07, 2015 11:53:48 AM org.apache.coyote.AbstractProtocol start
    INFO: Starting ProtocolHandler ["http-nio-8080"]

    started.
    Initiating URL: http://localhost:8080/CrossSiteScripting?user=shri&user=manoj&user=shrikant&passwd=firstPassword&passwd=admino
    Aug 07, 2015 11:53:48 AM org.apache.catalina.core.StandardWrapperValve invoke
    SEVERE: Servlet.service() for servlet [CrossSiteScripting] in context with path [/] threw exception
    java.lang.NullPointerException
        at penetration.testing.CrossSiteScripting.doGet(CrossSiteScripting.java:41)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:575)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
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.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:1521)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1177)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:857)

    Exception in thread "main" java.io.IOException: Server returned HTTP response code: 500 for URL: http://localhost:8080/CrossSiteScripting?user=shri&user=manoj&user=shrikant&passwd=firstPassword&passwd=admino
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1638)
at main.java.launch.Main.main(Main.java:92)

由于view.forward()方法，最后一行可能会抛出异常。哪个将控件转发到JSP.还有其他方法吗？我希望JSP页面能够像在浏览器中打开时那样执行。

这是目录结构：

    +InitiateTomcat
    |-- +src
    |---|- +main.java.launch
    |---|--- main.java //the main class from where I start Tomcat server and deploy a web application
    |---|- +penetration.testing
    |---|--- CrossSitrScripting.java // the servlet which am calling
    |-- +WebContent
          +WEB-INF
             homePage.jsp  // the homepage

Answer 1

500 http状态代码意味着服务器无法满足请求并且意外＆＃34;意外＆＃34;错误发生了，我猜那个页面＆＃34; homePage.jsp＆＃34;无法通过此URL访问，请尝试直接通过浏览器访问它以进行验证。

Answer 2

您在CrossSiteScripting.java:41

获得空指针

你说的是：

view.forward(request, response);

因此，由此生成的视图为null，因为它无法找到homePage.jsp

RequestDispatcher view = request.getRequestDispatcher("homePage.jsp");

如果您的homePage.jsp位于与当前页面相同的相对位置，那么您需要使用＆＃34; homePage.jsp＆＃34;如果homePage.jsp在根目录中，那么你应该使用正斜杠＆＃34; /＆＃34;因此指向根＆＃34; /homePage.jsp＆＃34;

我假设您应该在转发前使用正斜杠，同时转发如下：

RequestDispatcher view = request.getRequestDispatcher("/homePage.jsp");

Answer 3

我猜错误或异常就在这里

 RequestDispatcher view = request.getRequestDispatcher("homePage.jsp");

如果您直接编写homePage.jsp，则访问homePage.jsp之类的页面应为空字符串或以'/'开头，路径为：

C:\Users\IBM_ADMIN\workspace\Initiate Tomcat\homePage.jsp

所以你应该这样做

RequestDispatcher view = request.getRequestDispatcher("/homePage.jsp");

Answer 4

无法通过URL直接访问WEB-INF目录中的任何内容。请将homePage.jsp文件移到WEB-INF目录之外，然后尝试访问它。我希望它能奏效。

问候和Sandeep

空指针异常：HTTP响应代码500

4 个答案: