本人刚学习java，用angularjs+html+css做的前端，在编写登录系统的时候，发生了这样一个情况，后端我写了一个简单的关于登录验证的java文件，下面贴出源代码

package com.csii.action.login;

import java.sql.*;

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 LoginAction extends HttpServlet{

static  String USERNAME;

static  String PASSWORD;

public static void main(String[] args) {

Connection conn=null;

Statement stmt=null;

String dbURL="jdbc:sqlserver://localhost:1433;DatabaseName=webuser";

String userName="sa";

String userPassword="123456";

try {

Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");

   

conn=DriverManager.getConnection(dbURL,userName,userPassword);

    System.out.println("数据库库连接成功");

    System.out.println("创建数据库中。。。");

    stmt=conn.createStatement();

    

    String sql="select * from User_Info ";

    ResultSet rs = stmt.executeQuery(sql);

    ResultSetMetaData metaData =  rs.getMetaData();  

    while(rs.next()){    //next（）获取里面的内容

       

       USERNAME=rs.getString(1);

        PASSWORD=rs.getString(2);

        

}} catch (Exception e) { 

    e.printStackTrace();// TODO: handle exception

} 

}

public String method1() {

String a=USERNAME;

return a;

}

public String method2() {

String b=PASSWORD;

return b;

}

    public static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException {

        doPost(req, resp);

        

    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException {

   

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

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

        PrintWriter pw = resp.getWriter();

        String A=this.method1();

        String B=this.method2();

        System.out.println(A);

        System.out.println(B);

        if(A.equals(uname) && B.equals(pword))

        {

            pw.write("username and password is right!");

        }else

        {

            pw.write("username or password is wrong!");

        }

    }

}

在这个java文件中一开始定义了一个全局变量USERNAME和PASSWORD，在第一个main方法中将这两个变量进行赋值，USERNAME=abcdefghi，PASSWORD=123456789，在main方法中可以打印出来USERNAME和PASSWORD的值，但是在doget和dopost方法中我是用System.out.println却只能输出空白行并且我在前端无论输入什么都是返回username or password is wrong!，我想请大家帮帮我