jsp - 为 JSP 设置 404 错误页面

Question

我正在尝试在 JSP 中设置自定义错误页面。我收到一个错误，我不知道为什么。我研究了很多帖子，但似乎找不到答案。当我访问应该向我抛出 404 的页面时，它会将我发送到 native Tomcat 错误页面而不是我自己的错误页面并抛出此错误。

Apr 30, 2015 11:33:35 AM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at org.apache.jsp.PageNotFound_jsp._jspService(PageNotFound_jsp.java:104)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:489)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:467)
    at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:338)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:203)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Apr 30, 2015 11:33:35 AM org.apache.catalina.core.StandardHostValve custom
SEVERE: Exception Processing ErrorPage[errorCode=404, location=/PageNotFound.jsp]
org.apache.jasper.JasperException: An exception occurred processing JSP page /PageNotFound.jsp at line 38

35:         </div>
36:         
37:         Message:
38:         <div><%=exception.getMessage() %></div>
39:         StackTrace:
40:         <div><%
41:         StringWriter stringWriter = new StringWriter();


Stacktrace:
    at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:489)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:467)
    at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:338)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:203)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at org.apache.jsp.PageNotFound_jsp._jspService(PageNotFound_jsp.java:104)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    ... 22 more

这是 web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>MyProject</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
    <error-page>
        <error-code>500</error-code>
        <location>/PageNotFound.jsp</location>
    </error-page>

    <error-page>
        <error-code>404</error-code>
        <location>/PageNotFound.jsp</location>
    </error-page>

    <error-page>
        <exception-type>java.lang.Exception</exception-type>
        <location>/PageNotFound.jsp</location>
    </error-page>

</web-app>

还有我的 PageNotFound.jsp

<%@ page isErrorPage="true" import="java.io.*" language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<link rel="icon" href="img/favicon.ico" type="image/x-icon">
<link rel="shortcut icon" href="img/favicon.ico" type="image/x-icon" />

<title>Sample Page</title>

</head>
<body>
<!--content-->
 <div class="container">
        <div class="row">
            <article class="span6 error">
                <img src="img/error.png" alt="">
            </article>
            <article class="span6">
                <div class="row">
                    <div class="span6">
                        <h5>Sorry!</h5>
                        <h6>page not found</h6>
                        <div class="row">
                            <article class="span4">
                                <p class="margBot1">The page you are looking for might have been removed, had its name changed, or is temporarily unavailable.</p>
                                <p class="margBot1">Please try using our search box below to look for information on the website</p>

                            </article>
                        </div>
                    </div>
                </div>
            </article>
        </div>

        Message:
        <div><%=exception.getMessage() %></div>
        StackTrace:
        <div><%
        StringWriter stringWriter = new StringWriter();
        PrintWriter printWriter = new PrintWriter(stringWriter);
        exception.printStackTrace(printWriter);
        out.println(stringWriter);
        printWriter.close();
        stringWriter.close();
        %></div>

 </div>


</body>
</html>

Answer 1

正在尝试呈现您的 PageNotFound.jsp。查看最后的堆栈跟踪。

但是，在尝试呈现该页面时出现异常。此行中的“异常”变量为空:

<div><%=exception.getMessage() %></div>

我认为只要在 java 层中有异常，那么这个 will 变量就不会为 null。所以在错误页面中包含它是有意义的。

但是在404条件下，Java层没有异常，所以为null。所以，我认为这段代码和它下面的代码块不属于用于 404 条件的页面。