java.lang.NullPointerException 问题
用myeclipse10.0 刚开始的时候是可以的~ 之后把.metadata文件夹删掉 重新导入项目之后，可以正常编译，但是运行的时候，页面无法显示，会提示java.lang.NullPointerException 这样的错误：具体错误如下：
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:541)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:375)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:55)
root cause
java.lang.NullPointerException
org.apache.jsp.login_jsp._jspInit(login_jsp.java:27)
org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:159)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:329)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:55)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.
login.jsp 第27行代码如下：
<form action="main.jsp" target="_top" method="POST" name="loginForm" id="loginForm" type="POST">
请各位大神帮帮忙~ 看看问题可能出现在哪里~ 刚开始做JAVA 菜鸟一枚~~ 希望各位能够说的简单点~
谢谢~~~ --------------------编程问答-------------------- 贴全部login.jsp吧。 那个行号是login.jsp被转换成servelt后的java代码的行号。 --------------------编程问答-------------------- java.lang.NullPointerException
org.apache.jsp.login_jsp._jspInit(login_jsp.java:27)
27行不是指JSP，而是指JSP所生成的Servlet的源码。
JSP贴出来看看吧，应该前几行。 --------------------编程问答-------------------- jsp页面：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="ww" uri="webwork"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>welcome</title>
<link rel="stylesheet" type="text/css" href="css/style.css">
<script language="JavaScript" type="text/JavaScript">
function openChgPwd()
{
window.open("changePwd.jsp", "_self");
}
function openWelcome()
{
window.open("main[1].htm", "_top");
}
function submitForm() {
document.all.loginForm.action = "loginAction.action?m_action=login";
document.all.loginForm.target = "_top";
document.all.loginForm.submit();
}
</script>
</head>
<body leftmargin="0" topmargin="0">
<form action="main.jsp" target="_top" method="POST" name="loginForm" id="loginForm" type="POST">
<table width="800" height="600" border="0" align="center">
<tr>
<th valign="top" background="images/bg_denglu.GIF" scope="col"><table width="384" height="555" border="0" align="left" cellpadding="0" cellspacing="0">
<tr>
<td width="100%" height="403"> </td>
</tr>
<tr>
<td width="100%" height="150" valign="top"><table width="70%" height="139" border="0" cellpadding="0" cellspacing="0">
<tr>
<td><table width="63%" border="0" align="center" cellpadding="0" cellspacing="0">
<ww:if test="errorMessage != null">
<tr>
<td align="center" colspan="2" class="loginTitle"><font color="red"><ww:property value="errorMessage"/></font> </td>
</tr>
</ww:if>
<tr>
<td width="62%" valign="middle" class="loginTitle">用户名：</td>
<td width="62%" align="right"><input type="text" name="model.username" size="12" class="loginInput" onMouseOver="this.focus();" value=<ww:property value="username"/>> </td>
</tr>
<tr>
<td class="loginTitle"> </td>
<td valign="top"> </td>
</tr>
<tr>
<td width="62%" valign="middle" class="loginTitle">密 码：</td>
<td width="62%" align="right" valign="top"><input type="password" name="model.password" size="16" class="loginPasswd" onMouseOver="this.focus();" onkeydown="if(event.keyCode==13) submitForm()" value=<ww:property value="password"/>> </td>
</tr>
</table></td>
</tr>
<tr>
<td height="67" align="center"><input name="Submit" type="button" class="loginButton" value="登 录" onClick="submitForm()"> </td>
</tr>
</table></td>
</tr>
</table></th>
</tr>
</table>
</form>
</body>
</html>
--------------------编程问答-------------------- document.all.loginForm.action = "loginAction.action?m_action=login";
<form action="main.jsp" target="_top" method="POST" name="loginForm" id="loginForm" type="POST">
两个的action怎么不一样，既然是一个submit --------------------编程问答-------------------- 楼主这个比较麻烦了，全用的标签，并没有直接JSP代码。
楼主要设法去找找所生成Servlet的Java源码看看了：org/apache/jsp/login_jsp.java --------------------编程问答-------------------- .metadata文件夹 记录了eclipse工作环境的一些配置，记录了对eclipse的一些配置。
删掉是可以，不过删掉之后，
对eclipse的配置就还原为默认的了，需重新配置；
eclipse下也没有了原来的工程，需要重新导入。
删掉之后没有什么错误，只是上面这些需要重新配置了。
楼主上面说的空指针的问题，你把工程重新导入进来，并配置好tomcat，编译路径，之后刷新整个工程重新编译就应该好了。不是什么大问题。 --------------------编程问答-------------------- 是不是你的路径出现了问题，一般出现500 400这些就是路径的问题 --------------------编程问答-------------------- --------------------编程问答-------------------- 500一般是代码中的方法问题吧，跟你删除的那个文件没关系的。仔细找到编译后的文件看看。 --------------------编程问答-------------------- 我觉得代码有问题的可能性不大吧~ 之前都可以运行的~ 就是在删除了那个文件夹之后才出现的这个问题~
所以会不会是哪里配置有问题啊？
--------------------编程问答-------------------- 对了~ 我之前用的是myeclipse9.0 重装了10.0之后 用的还是9.0的工作目录 所以配置文件夹什么的 都没有改的~ 之后删除了.metadata文件夹之后 再重新导入目录就有这个问题了
是不是跟添加的一些JAR包有关系？？ --------------------编程问答-------------------- 编译后文件：
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class login_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();
private static java.util.List _jspx_dependants;
private org.apache.jasper.runtime.TagHandlerPool _005fjspx_005ftagPool_005fww_005fif_005ftest;
private org.apache.jasper.runtime.TagHandlerPool _005fjspx_005ftagPool_005fww_005fproperty_005fvalue_005fnobody;
private javax.el.ExpressionFactory _el_expressionfactory;
private org.apache.AnnotationProcessor _jsp_annotationprocessor;
public Object getDependants() {
return _jspx_dependants;
}
public void _jspInit() {
_005fjspx_005ftagPool_005fww_005fif_005ftest = org.apache.jasper.runtime.TagHandlerPool.getTagHandlerPool(getServletConfig());
_005fjspx_005ftagPool_005fww_005fproperty_005fvalue_005fnobody = org.apache.jasper.runtime.TagHandlerPool.getTagHandlerPool(getServletConfig());
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());
}
public void _jspDestroy() {
_005fjspx_005ftagPool_005fww_005fif_005ftest.release();
_005fjspx_005ftagPool_005fww_005fproperty_005fvalue_005fnobody.release();
}
public void _jspService(HttpServletRequest request, HttpServletResponse response)
throws java.io.IOException, ServletException {
PageContext pageContext = null;
HttpSession session = null;
ServletContext application = null;
ServletConfig config = null;
JspWriter out = null;
Object page = this;
JspWriter _jspx_out = null;
PageContext _jspx_page_context = null;
try {
response.setContentType("text/html; charset=UTF-8");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("\r\n");
out.write(" \r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">\r\n");
out.write("<title>welcome</title>\r\n");
out.write("<link rel=\"stylesheet\" type=\"text/css\" href=\"css/style.css\">\r\n");
out.write("<script language=\"JavaScript\" type=\"text/JavaScript\">\r\n");
out.write("\r\n");
out.write("function openChgPwd()\r\n");
out.write("{\r\n");
out.write("\twindow.open(\"changePwd.jsp\", \"_self\");\r\n");
out.write("}\r\n");
out.write("function openWelcome()\r\n");
out.write("{\r\n");
out.write("\twindow.open(\"main[1].htm\", \"_top\");\r\n");
out.write("}\r\n");
out.write("\r\n");
out.write("function submitForm() {\t\r\n");
out.write("\tdocument.all.loginForm.action = \"loginAction.action?m_action=login\";\r\n");
out.write("\tdocument.all.loginForm.target = \"_top\";\r\n");
out.write("\tdocument.all.loginForm.submit();\r\n");
out.write("}\r\n");
out.write("</script>\r\n");
out.write("</head>\r\n");
out.write("<body leftmargin=\"0\" topmargin=\"0\">\r\n");
out.write("<form action=\"main.jsp\" target=\"_top\" method=\"POST\" name=\"loginForm\" id=\"loginForm\" type=\"POST\">\r\n");
out.write("<table width=\"800\" height=\"600\" border=\"0\" align=\"center\">\r\n");
out.write(" <tr>\r\n");
out.write(" <th valign=\"top\" background=\"images/bg_denglu.GIF\" scope=\"col\"><table width=\"384\" height=\"555\" border=\"0\" align=\"left\" cellpadding=\"0\" cellspacing=\"0\">\r\n");
out.write(" \r\n");
out.write(" <tr>\r\n");
out.write(" <td width=\"100%\" height=\"403\"> </td>\r\n");
out.write(" </tr>\r\n");
out.write(" <tr>\r\n");
out.write(" <td width=\"100%\" height=\"150\" valign=\"top\"><table width=\"70%\" height=\"139\" border=\"0\" cellpadding=\"0\" cellspacing=\"0\">\r\n");
out.write(" <tr>\r\n");
out.write(" <td><table width=\"63%\" border=\"0\" align=\"center\" cellpadding=\"0\" cellspacing=\"0\">\r\n");
out.write(" ");
if (_jspx_meth_ww_005fif_005f0(_jspx_page_context))
return;
out.write("\r\n");
out.write("\r\n");
out.write(" \t\r\n");
out.write(" <tr> \t\r\n");
out.write(" <td width=\"62%\" valign=\"middle\" class=\"loginTitle\">用户名：</td>\r\n");
out.write(" <td width=\"62%\" align=\"right\"><input type=\"text\" name=\"model.username\" size=\"12\" class=\"loginInput\" onMouseOver=\"this.focus();\" value=");
if (_jspx_meth_ww_005fproperty_005f1(_jspx_page_context))
return;
out.write("> </td>\r\n");
out.write(" </tr>\r\n");
out.write(" <tr>\r\n");
out.write(" <td class=\"loginTitle\"> </td>\r\n");
out.write(" <td valign=\"top\"> </td>\r\n");
out.write(" </tr>\r\n");
out.write(" <tr>\r\n");
out.write(" <td width=\"62%\" valign=\"middle\" class=\"loginTitle\">密 码：</td>\r\n");
out.write(" <td width=\"62%\" align=\"right\" valign=\"top\"><input type=\"password\" name=\"model.password\" size=\"16\" class=\"loginPasswd\" onMouseOver=\"this.focus();\" onkeydown=\"if(event.keyCode==13) submitForm()\" value=");
if (_jspx_meth_ww_005fproperty_005f2(_jspx_page_context))
return;
out.write("> </td>\r\n");
out.write(" </tr>\r\n");
out.write(" </table></td>\r\n");
out.write(" </tr>\r\n");
out.write(" <tr>\r\n");
out.write(" <td height=\"67\" align=\"center\"><input name=\"Submit\" type=\"button\" class=\"loginButton\" value=\"登 录\" onClick=\"submitForm()\"> </td>\r\n");
out.write(" </tr>\r\n");
out.write(" </table></td>\r\n");
out.write(" </tr>\r\n");
out.write(" \r\n");
out.write(" </table></th>\r\n");
out.write(" </tr>\r\n");
out.write("</table>\r\n");
out.write("</form>\r\n");
out.write("</body>\r\n");
out.write("\r\n");
out.write("</html>\r\n");
} catch (Throwable t) {
if (!(t instanceof SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
try { out.clearBuffer(); } catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
只贴了上面的一部分 看不太懂这个~ --------------------编程问答-------------------- Project clean下，重新编译，重新发布吧，服务器重启再试试看。
（确认是重新发布了。 看生成文件的时间。）
我猜应该不是程序的错误。 --------------------编程问答-------------------- 可以新建个workspace，把原来的项目导入，重新部署试试看，就可以排除是不是删除产生的问题了 --------------------编程问答-------------------- 重建了 还是跟之前一样的问题
%>_<%
--------------------编程问答-------------------- 是重新发布的~~
clean了 还是不行~
--------------------编程问答-------------------- 有种最笨的方法是 新建一个项目，然后把所有的代码都拷贝到新项目里。
就是新建一个JSP，然后把以前的jsp内容复制到新建的里面。
哈哈。 --------------------编程问答--------------------
检查ww:property等类似标签，传给他们的值有null吗？ --------------------编程问答-------------------- loginAction 这个错误是在后台的把 ,看看loginAction断点下 --------------------编程问答-------------------- 空指针异常怎么解决？ --------------------编程问答-------------------- 恩 源码是：rs=st.executeQuery(sql); --------------------编程问答-------------------- 在tomcat的配置文件context.xml文件的<Context>下加上这个代码
<Loader delegate="true" /> 试试看
补充：Java , Eclipse
