我写了一个servlet接受和处理用户输入的信息，但总是返回null，不知道那点错了，请高手看看，访问的时候不报任何错误，就是打印出来总是null
Conn.java文件如下
package classes.conn;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class Conn
{
    private static Connection conn;
    private Conn()
    {
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/news","root","123123");
        }catch(Exception e)
        {
        }
    }
    public static Connection getConnection()
    {
        if(conn==null)
        {
            new Conn();
        }
        return conn;
    }

}


LoginBean.java文件如下
package classes.login;

import java.sql.*;
import classes.conn.Conn;

public class LoginBean
{
    public LoginBean()
    {
    }
    public String loginYanZheng(String name,String pwd)
    {
        String result = null;
        Connection conn = Conn.getConnection();
        Statement statement = null;
        ResultSet rs = null;
        try{
            statement = conn.createStatement();
            rs = statement.executeQuery("select userpwd from user where username='"+name+"'");

            if (rs.next())
            {
                if(pwd.equals(rs.getString(1)))
                {
                    result="ok";
                }else
                {
                    result="pwd is wrong";
                }
            }else
            {
                result="nouser";
            }
            try
            {
                if(rs!=null)rs.close();
                if(statement!=null)statement.close();
                if(conn!=null)conn.close();
            }catch(Exception e)
            {
            }
        }catch(Exception e)
        {
            try
            {
                if(rs!=null) rs.close();
                if(statement!=null) statement.close();
                if(conn!=null) conn.close();
            }catch(Exception ee)
            {
            }
        }
        return result;
    }
}

LoginServlet.java文件如下
package servlet.login;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
import classes.login.LoginBean;

public class LoginServlet extends HttpServlet
{
    public void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException
    {
        PrintWriter out=response.getWriter();
        response.setContentType("text/html");
        String name=request.getParameter("user");
        String pwd=request.getParameter("pwd");
        LoginBean lb=new LoginBean();
        String result=lb.loginYanZheng(name,pwd);
        out.println("name="+name);
        out.println("pwd="+pwd);
        out.println("result="+result);
        /*
        if(result=="ok")
        {
            out.println("ok");
        }else if(result=="nouser")
        {
            out.println("no user");
        }else if(result=="pwd is wrong")
        {
            out.println("pwd wrong");
        }
        */
        
    }
    public void doGet(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException
    {
        doPost(request,response);
    }
}
在浏览器访问时没有任何错误，但result的值总是打印出null,而name和pwd没有任何问题
文件组织是这样的在classes目录下面有classes目录和servlet目录
有下面的Test.java测试没有任何问题
import java.util.*;
import classes.login.LoginBean;
public class Test
{
    public static void main(String[] args)
    {
        LoginBean lb=new LoginBean();
        String result=lb.loginYanZheng("hushan","12");
        System.out.println(result);
    }
}
Web.xml文件里是这样的
    <servlet>
        <servlet-name>loginservlet</servlet-name>
        <servlet-class>servlet.login.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>loginservlet</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>