Question

我正在制作一个带有用户个人资料的Java网络应用程序我有一个profileServlet，负责呈现两个页面：profile.jsp和editProfile.jsp
调用profileServlet的第一个源是页面顶部的菜单链接，如下所示：
<a href="profileServlet?param=profile">Profile</a>

第二个来源是profile.jsp中的“编辑”按钮：
<form name="editProfile" method="GET" action="profileServlet?param=editProf"><input type="submit" value="Edit"></form>

现在在profileServlet中，根据我想要重定向到profile.jsp或editProfile.jsp的param值。这是代码：
if(request.getParameter("param").equals("profile")) { response.sendRedirect("profile.jsp"); } else if (request.getParameter("param").equals("editProf")) { response.sendRedirect("editProfile.jsp"); }

但我一直得到java.lang.NullPointerException 你能帮忙吗？

Stacktrace：

24.04.2014 11:44:30 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [profilePage.profileServlet] in context with path [/LinkedIn] threw exception
java.lang.NullPointerException
    at profilePage.profileServlet.doGet(profileServlet.java:126)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Answer 1

您的请求参数param可能为null，您可以像下面这样执行，也可以在使用变量之前进行适当的空检查

if ("profile".equals(request.getParameter("param")) {
    response.sendRedirect("profile.jsp");
} else if ("editProf".equals(request.getParameter("param")) {
    response.sendRedirect("editProfile.jsp");
}

此外，请确保将代码放在各自的doGet / doPost处理程序中，或者为两者都设置一个处理程序。

示例：

@Override protected void doGet(HttpServletRequest request, HttpServletResponse response) { handleGetAndPost(request, response); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) { handleGetAndPost(request, response); } private void handleGetAndPost(HttpServletRequest request, HttpServletResponse response) { if ("profile".equals(request.getParameter("param")) { response.sendRedirect("profile.jsp"); } else if ("editProf".equals(request.getParameter("param")) { response.sendRedirect("editProfile.jsp"); } }

Answer 2

您应该在提交表单时使用帖子请求，并且有两种不同的处理程序方法。 GET返回空表单，POST处理提交的表单。

Answer 3

最好添加空检查。看起来你无法获得param

    if (request.getParameter("param") != null && request.getParameter("param").equals("profile")) {
        response.sendRedirect("profile.jsp");
    } else if (request.getParameter("param") != null && request.getParameter("param").equals("editProf")) {
        response.sendRedirect("editProfile.jsp");
    }

Java从两个源调用一个servlet

3 个答案: