tomcat HTTP Status 500 - 的错误,救命啊！！！！

目前我的电脑里装有jdk1.6 ，tomcat6，http://localhost:8080/能打开，但是打开http://localhost:8080/myapp/index.jsp，就显示：
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:522)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpSe

java.lang.NullPointerException
是空指针~~这个应该了解吧
打个比方session提交至本页 首次访问index.jsp出现什么？必然NullPointerException
还有你也有可能是数据库连接问题
MySql连接方法
public class BaseDao {

private static final String DRIVER="com.mysql.jdbc.Driver";
private static final String URL="jdbc:mysql://127.0.0.1:3306/mysql? ?=?";
private static final String USER="user";
private static final String PASS="password";

public static Connection getCon()
{
Connection con =null;
Class.forName(DRIVER);
con=DriverMangaer.getConnection(URL,USER,PASS);
return con;
}
public static void closeAll(ResultSet rs,PreparedStatement ps,Connection con
{
if(rs!=null)
{
rs.close();
rs=null;
}
if(ps!=null)
{
ps.close();
ps=null
}
if(con!=null&&con.isClosed())
{
con.close();