本人剛學習java，用angularjs+html+css做的前端，在編寫登錄系統的時候，發生了這樣一個情況，后端我寫了一個簡單的關于登錄驗證的java文件，下面貼出源代碼

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("數據庫庫連接成功");

    System.out.println("創建數據庫中。。。");

    stmt=conn.createStatement();

    

    String sql="select * from User_Info ";

    ResultSet rs = stmt.executeQuery(sql);

    ResultSetMetaData metaData =  rs.getMetaData();  

    while(rs.next()){    //next（）獲取里面的內容

       

       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!");

        }

    }

}

在這個java文件中一開始定義了一個全局變量USERNAME和PASSWORD，在第一個main方法中將這兩個變量進行賦值，USERNAME=abcdefghi，PASSWORD=123456789，在main方法中可以打印出來USERNAME和PASSWORD的值，但是在doget和dopost方法中我是用System.out.println卻只能輸出空白行并且我在前端無論輸入什么都是返回username or password is wrong!，我想請大家幫幫我