servlet程序中抛出的java.lang.nullpointer异常

Question

我正在为一个只有5个问题的在线考试创建一个3层Web应用程序.我使用html并设计了一个servlet来将数据发布到mysql数据库,我将其命名为'test',表格为'st1'.我使用MyEclipse Blue 8.6.1,它有一个内置的MyEclipse Tomcat 6.0.13.doPost()方法中servlet的编码如下:

try
{
    String url="jdbc:mysql://localhost:3306/test";
    Class.forName("com.mysql.jdbc.Driver");
    connect=DriverManager.getConnection(url,"root","root");
    message="Connection Sucessfull";
}
catch(ClassNotFoundException cnfex){
    cnfex.printStackTrace();
}
catch(SQLException sqlex){
    sqlex.printStackTrace();
}
catch(Exception excp){
    excp.printStackTrace();
}
seat_no=request.getParameter("Seat_No");
name=request.getParameter("Name");
ans1=request.getParameter("group1");
ans2=request.getParameter("group2");
ans3=request.getParameter("group3");
ans4=request.getParameter("group4");
ans5=request.getParameter("group5");
if(ans1.equals("True"))
    Total+=2;
if(ans2.equals("False"))
    Total+=2;
if(ans3.equals("True"))
    Total+=2;
if(ans4.equals("False"))
    Total+=2;
if(ans5.equals("False"))
    Total+=2;
try
{
    Statement stmt=connect.createStatement();
    String query="INSERT INTO st1("+"seat_no,name,marks"+")VALUES('"+seat_no+"','"+name+"','"+Total+"')";
    stmt.executeUpdate(query);
    stmt.close();
}

当我编译应用程序时,我不断收到异常:

HTTP Status 500 - 

type Exception report
message: 
description The server encountered an internal error () that prevented it from fulfilling this request.
exception :
java.lang.NullPointerException
    s3.doPost(s3.java:52)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note :The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs

---

但我找不到任何可用于MyEclipse Tomcat 6.0.13的日志.任何人都可以帮我克服这个例外吗？这是我的学术项目!提前致谢 !!

Answer 1

看看文件s3.java,第52行.