{推荐} 新人 index.jsp空指针错，求大神解释

Question

exceptionorg.apache.jasper.JasperException: Exception in JSP: /index.jsp:234231:         <table width="100%" border="0" cellspacing="1"
232:  cellpadding="1" class="tableBorder">
233:  <%
234:  Iterator iter = pl.iterator(); 
235: 
236:  while (iter.hasNext()) {
237:  Project pro = (Project) iter.next();Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:451)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
cn.edu.bit.servlet.EncodingFilter.doFilter(EncodingFilter.java:66)
root causejava.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:302)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
cn.edu.bit.servlet.EncodingFilter.doFilter(EncodingFilter.java:66)

Answer 1

JSP代码
<td width="532" valign="top">
<table width="100%" height="100%" border="1" cellpadding="0"
cellspacing="0">
<tr>
<td background="images/front/bg_1.gif">
新闻:
</td>
</tr>
<tr>
<td valign="top"> <control:news />
</td>
</tr>
<tr>
<td>
&nbsp;
</td>
</tr>
<tr>
<td background="images/front/bg_1.gif">
在研项目:
</td>
</tr>
<tr>
<td valign="top">
<%
ArrayList pl = (ArrayList) Project_Manager.getProjectList();
%>
<div align="center">
<table width="100%" border="0" cellspacing="1"
cellpadding="1" class="tableBorder">
<%
Iterator iter = pl.iterator();  while (iter.hasNext()) {
Project pro = (Project) iter.next();
%>
<tr bgcolor="E4EDF9">
<td align="center" class="titleText">
<%=pro.getName()%>
</td>
<td>
&nbsp;
</td>
</tr>
<tr bgcolor="F1F3F5">
<td width="20%" align="center" class="normalText">
起始时间:
</td>
<td width="80%" class="normalText">
<%=pro.getTime()%>
</td>
</tr>
<tr bgcolor="F1F3F5">
<td align="center" class="normalText">
简介:
</td>
<td class="normalText">
<%=pro.getInfo()%>
</td>
</tr>
<tr>
<td colspan="2">
&nbsp;
</td>
</tr>
<%
}
%>
<tr>
<td colspan="2">
&nbsp;
</td>
</tr>
</table>
</td>
</tr>
</table>
</td>

Answer 2

java.sql.SQLException: Access denied for user 'admin'@'localhost' (using password: YES)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:946)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:885)
at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3421)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1247)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2748)
at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at cn.edu.bit.DBQuery.DataProcess.getConnection(DataProcess.java:35)
at cn.edu.bit.business.Project_Manager.getProjectList(Project_Manager.java:132)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:294)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at cn.edu.bit.servlet.EncodingFilter.doFilter(EncodingFilter.java:66)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:875)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Unknown Source)有多了个DB错，可是我的账号密码都是admin 啊
package cn.edu.bit.DBQuery;
import java.sql.*;/**
 * 
 * @author liuyu
 *2007-7-21
 */
public class DataProcess {

DataProcess(){

}

/**
 * 
 * @return
 */

public static Connection getConnection()
{
String CLASSFORNAME="org.gjt.mm.mysql.Driver";    String SERVANDDB = "jdbc:mysql://localhost:3306/Lab?user=admin&password=admin&useUnicode=true&characterEncoding=utf-8";


Connection con;

try
{
Class.forName(CLASSFORNAME);

con = DriverManager.getConnection(SERVANDDB,"admin","admin");

return con;
}
catch(Exception e)
{
e.printStackTrace();

return null;
} }

Answer 3

system.out.println(pl); 估计集合木有东西，未判断空就用来迭代

Answer 4

空指针异常，很有可能是你的pl为nill，用断点查看一下就知道了，输出也试试，

Answer 5

是的，PL是空的，现在问题在于本地的数据库mysql连不上；
2013-11-6 23:32:57 org.apache.catalina.startup.Catalina start
信息: Server startup in 1391 ms
str==null
java.sql.SQLException: Access denied for user 'admin'@'localhost' (using password: YES)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:946)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:885)
at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3421)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1247)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2748)
at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
DB类；package cn.edu.bit.DBQuery;
import java.sql.*;/**
 * 
 * @author liuyu
 *2007-7-21
 */
public class DataProcess {

DataProcess(){

}

/**
 * 
 * @return
 */

public static Connection getConnection()
{
String CLASSFORNAME="org.gjt.mm.mysql.Driver";    String SERVANDDB = "jdbc:mysql://localhost:3306/Lab?user=admin&password=admin&useUnicode=true&characterEncoding=utf-8";


Connection con;

try
{
Class.forName(CLASSFORNAME);

con = DriverManager.getConnection(SERVANDDB,"admin","admin");

return con;
}
catch(Exception e)
{
e.printStackTrace();

return null;
} }


/**
 * 
 * @param SQL
 * @return
 */
public static int nCount(String SQL)
{
Connection myConnection = getConnection();
int count = 0;

try
{
Statement stm = myConnection.createStatement();

ResultSet result = stm.executeQuery(SQL);

if(result.next())
{
count = result.getInt(1);

result.close();
}

stm.close();

myConnection.close();

}
catch(Exception e)
{
e.printStackTrace();
}

return count;
}

/**
 * 
 * @param SQL
 */
public static void ExeQuery(String SQL)
{
Connection con = getConnection();
try
{
Statement stmt = con.createStatement();

stmt.executeUpdate(SQL);

stmt.close();

con.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}


/**
 * 
 * @param SQL
 * @param con
 * @return
 */
public static ResultSet getResult(String SQL,Connection con)
{
ResultSet rs = null;

try{
Statement stmt = con.createStatement();

rs = stmt.executeQuery(SQL);

}catch(SQLException e)
{
e.printStackTrace();
}

return rs;

}

/**
 * 
 * @param con
 */
public static void CloseConnection(Connection con)
{
try
{
con.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}

/**
 * 
 * @param rs
 */

public static void CloseResultSet(ResultSet rs)
{
try
{
rs.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}}

Answer 6

我晕解决了，是root权限问题， 默认的用户名是root    ，安装的时候3个密码框第一个写,root密码其他两个写登陆密码，不要和root重了不然在窗口能进去，但用代码连接的时候就没权限，希望帮助其他人，感谢回答的没个大神！