java中MySQL与驱动jdbc连接不上，想请教高手：jdbc驱动：mysql-connector-java-5.1.29-bin.jar怎么用啊？

package net.chat;
import java.sql.*;
import java.lang.ClassNotFoundException;
public class BaseConn {
private Connection conn = null;
private Statement stmt = null;
private PreparedStatement ps = null;
private ResultSet rs = null;
public BaseConn() throws SQLException,ClassNotFoundException{
try
{
String driverName ="com.mysql.jdbc.Driver";
String userName = "root";
String passWord = "123";
String url="jdbc:mysql://localhost:3306/ChatRoom";
Class.forName(driverName);
Connection conn = DriverManager.getConnection(url,userName,passWord);
return ;
}
catch(SQLException e)
{
System.out.println("Error occured when Connect DataBase:"+e);
throw e;
}
catch(ClassNotFoundException e)
{
System.out.println("Error occured when Connect DataBase:"+e);
throw e;
}
}
public PreparedStatement preparedStatement(String sql) throws SQLException
{
try
{
ps = conn.prepareStatement(sql);
return ps;
}catch(SQLException e)
{
System.out.println("Error occured when create preparedStatement:"+e);
throw e;
}
}
public ResultSet executeQuery(String sql) throws SQLException
{
rs = null;
try {
rs = stmt.executeQuery(sql);
}
catch (SQLException ex) {
System.out.println("Error occured when query database：" + ex);
throw ex;
}
return rs;
}
public int executeUpdate(String sql) throws SQLException
{
try {
conn.setAutoCommit(false);
int re = stmt.executeUpdate(sql);
conn.commit();
return re;
}
catch (SQLException e) {
conn.rollback();
System.out.println("Error occured when update database：" + e);
throw e;
}
}
public ResultSet executeQuery() throws SQLException
{
try {
return ps.executeQuery();
}
catch (SQLException e) {
System.out.println("Error occured when query database：" + e);
throw e;
}
}
public int executeUpdate() throws SQLException
{
try {
conn.setAutoCommit(false);
int r = ps.executeUpdate();
conn.commit();
return r;
}
catch (SQLException e) {
conn.rollback();
System.out.println("Error occured when update database：" + e);
throw e;
}
}
public boolean closeDB() throws SQLException
{
try {
if (this.rs != null)
rs.close();
if (this.stmt != null)
this.stmt.close();
if (this.ps != null)
this.ps.close();
if (this.conn != null)
conn.close();
return true;
}
catch (SQLException e) {
System.out.println("Error occured when close database：" + e);
throw e;
}
}
}
求解，真的不懂，谢谢！
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:5
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

java.lang.NullPointerException
net.chat.BaseConn.preparedStatement(BaseConn.java:43)
net.chat.CheckLogin.checklogin(CheckLogin.java:33)
org.apache.jsp.chklogin_jsp._jspService(chklogin_jsp.java:100)

已经放了，但是数据库接不上。原来这个程序是接SqlServer2005的，我的是MySQL，想改成MYSQL,但是不会改。。一直接不上数据库

已经放了，但是数据库接不上。原来这个程序是接SqlServer2005的，我的是MySQL，想改成MYSQL,但是不会改。。一直接不上数据库

先确认MySQL数据库能在命令行下连接查询，然后确保程序里面的sql语句正确。

"先确认MySQL数据库能在命令行下连接查询"这个是什么意思？SqlServer2005的语句与MySQL的语句不同吗？

”MySQL数据库能在命令行下连接查询“是什么意思？sql语句SqlServer2005与MySQL的不一样吗？

晚上了我试试具体连接方法。