import java.util.HashMap;import java.util.Map;public class LoginService{    private Map
     
       map;        public LoginService(){        map=new HashMap
      
       ();                map.put("张三", "123");        map.put("李四", "123");        map.put("王五", "123");        map.put("赵六", "1234");        map.put("孙七", "1234");    }            public boolean login(String name,String password) throws NoUserException,ErrorPswdException{                if(map.containsKey(name)){            String pswd=map.get(name);                        if(pswd.equals(password)==false){                throw new ErrorPswdException("用户名"+name+"的密码不是"+password);            }        }else{            throw new NoUserException("DB里没有这个用户名");        }                return true;    }        public static void main(String[] args){        LoginService service=new LoginService();        String name="张三1";        String pswd="1235";                try{            boolean passed=service.login(name,pswd);                        System.out.println("欢迎"+name+"登录系统.");        }catch(NullPointerException e){            System.out.println("数据库未就绪，请通知系统管理员.");        }catch(NoUserException e){            System.out.println("用户名"+name+"不存在,即将前往注册页面");        }catch(ErrorPswdException e){            System.out.println("用户的"+name+"密码"+pswd+"不正确,请明确后再输入");        }catch(Exception e){            e.printStackTrace();        }    }}
      
     

两个异常类：

public class ErrorPswdException extends Exception{    public ErrorPswdException(String msg){        super(msg);    }}

public class NoUserException extends Exception{    public NoUserException(String msg){        super(msg);    }}