这种错误怎么解决呢？

ijse 2009-08-06 01:34:34

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
Regist.doPost(Regist.java:26)
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.

--------------------------------------------------------------------------------

Apache Tomcat/6.0.13

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ijse 2009-08-06

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我明白了!!!
把它换成:

ConnSql ConMySql = new ConnSql();

这样就好使了!!

谢谢各位了!!马上结贴!!

ijse 2009-08-06

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[Quote=引用 4 楼 aywrenyue 的回复:]
在定义了这个变量
Java code ConnSql ConMySql=null;
之后就没有实例化，而你紧接着就是用了
Java codeConMySql.Update("insert into users values(null,'"+ username+"','"+ password+"','"+ gentle+"','"+ email+"');");
所以null错
[/Quote]
ConnSql ConMySql = null;
这是MyEclipse提示的,我也不太清楚.那这问题要怎么解决? 我怎么实例化呢?对不起我是初学者,请讲得稍微详细点儿..谢谢啦.

紫炎圣骑 2009-08-06

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楼上正解！

java.lang.NullPointerException 空指针异常了！

aywrenyue 2009-08-06

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在定义了这个变量

 ConnSql ConMySql = null;

之后就没有实例化，而你紧接着就是用了

ConMySql.Update("insert into users values(null,'" + username + "','"

                + password + "','" + gentle + "','" + email + "');");

所以null错

ijse 2009-08-06

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[Quote=引用 2 楼 haoziheyezi 的回复:]
空指针异常嘛

有东东为空你就拿来用了
[/Quote]
我不想贴代码的，也许大家不太喜欢看，但我还是要贴代码。。、

import java.io.IOException;

import java.io.PrintWriter;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



public class Regist extends HttpServlet {

	private static final long serialVersionUID = 1L;

	



	protected void doPost(HttpServletRequest req, HttpServletResponse resp)

			throws ServletException, IOException {

		ConnSql ConMySql = null;

		req.setCharacterEncoding("utf-8");

		resp.setContentType("text/html;charset=utf-8");

		

		PrintWriter out = resp.getWriter();



		String username = req.getParameter("userName");

		String password = req.getParameter("passWord");

		String gentle = req.getParameter("gentle");

		String email = req.getParameter("email");



		ConMySql.Update("insert into users values(null,'" + username + "','"

				+ password + "','" + gentle + "','" + email + "');");

		out.println("<html><head><title>注册成功</title><body>");

		out.println("<table><tr><td colspan='2'>恭喜注册成功!您的注册信息是:</td></tr>");

		out.println("<tr><td>用户名:</td><td>" + username + "</td></tr>");

		out.println("<tr><td>密码:</td><td>" + password + "</td></tr>");

		out.println("<tr><td>性别:</td><td>" + gentle + "</td></tr>");

		out.println("<tr><td>email:</td><td>" + email + "</td></tr>");

	}

}

这是那个页面调用的Servlet代码，然后下面还有那个类的代码：

import java.io.IOException;

import java.io.PrintWriter;

import java.sql.*;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



public class ConnSql extends HttpServlet {



	private static final long serialVersionUID = 1L;

	public String DataBase = "jdbc:mysql://localhost/ijseblog?user=root&password=clslist";

	ConnSql()

	{

		

	}

	public void Connection() {

		try {

			Class.forName("com.mysql.jdbc.Driver");

		} catch (ClassNotFoundException e) {

			e.printStackTrace();

		}

	}



	public ResultSet Execute(String sql) {

		ResultSet rs = null;

		Connection conn = null;

		Statement stm = null;

		Connection();

		try {

			conn = DriverManager.getConnection(DataBase);

			stm = conn.createStatement();

			rs = stm.executeQuery(sql);

		} catch (SQLException e) {

			System.out.println("SQLException:" + e.getMessage());

			System.out.println("SQLState:" + e.getSQLState());

			System.out.println("VendorError:" + e.getErrorCode());

		}

		return rs;

	}



	public int Update(String sql) {

		int rt = 0;

		Connection conn = null;

		Statement stm = null;

		Connection();

		try {

			conn = DriverManager.getConnection(DataBase);

			stm = conn.createStatement();

			rt = stm.executeUpdate(sql);

		} catch (SQLException e) {

			System.out.println("SQLException:" + e.getMessage());

			System.out.println("SQLState:" + e.getSQLState());

			System.out.println("VendorError:" + e.getErrorCode());

		}

		return rt;

	}



	public static void main(String args) {

		System.out.println("ok!");

	}



	protected void doPost(HttpServletRequest req, HttpServletResponse resp)

			throws ServletException, IOException {

		doGet(req, resp);

	}



	protected void doGet(HttpServletRequest req, HttpServletResponse resp)

			throws ServletException, IOException {



		req.setCharacterEncoding("utf-8");

		resp.setContentType("text/html;charset=utf-8");

		String username = req.getParameter("UserName");



		PrintWriter out = resp.getWriter();



		Connection();

		ResultSet rs = Execute("Select * from users where dbusername='"

				+ username + "'");

		try {

			while (rs.next()) {

				out.println("<html><head><title>查询结果</title></head><body>"

						+ rs.getString("dbusername") + "的密码是:"

						+ rs.getString("dbpassword") + "</body></html>");

			}

		} catch (SQLException e) {

			System.out.println("SQLException:" + e.getMessage());

			System.out.println("SQLState:" + e.getSQLState());

			System.out.println("VendorError:" + e.getErrorCode());

		}

	}



}