Question

在JSP页面中，当用户注销时，我将使用以下代码删除其登录cookie：

Cookie killMyCookie = new Cookie("cookie1", null);
killMyCookie.setMaxAge(0);
killMyCookie.setPath("/JSPLearn");
response.addCookie(killMyCookie);
killMyCookie = new Cookie("cookie2", null);
killMyCookie.setMaxAge(0);
killMyCookie.setPath("/JSPLearn");
response.addCookie(killMyCookie);

在此之后，我正在打电话

response.sendRedirect("index.jsp");

它正在抛出NullPointerException。

为什么响应为空？

堆栈跟踪：

java.lang.NullPointerException
at java.net.URLEncoder.encode(URLEncoder.java:205)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:175)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1542)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at  com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:849)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:746)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1045)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:228)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:722)

Answer 1

检查你的index.jsp文件我认为你有一个request.getParameter（“”）;对于变量，当您使用重定向时，您应该为该变量发送一个值。

Answer 2

答案在于

org.apache.jsp.index_jsp._jspService(index_jsp.java:175)

我认为你正在尝试像URLEncoder.encode这样的第一个参数，即要编码的字符串是Null并且它正在抛出java.lang.NullPointerException

应该是

URLEncoder.encode("Hello World", "UTF-8");

尝试在JSP中访问“响应”时获取NullPointerException

2 个答案: