身份验证时,我们常常要返回一个User对象,然而又要知道到底是什么地方错误。我们可以用Exception进行控制!下面是我写的一个例子,你可以加上数据库连接! public class Login{ public User validate(String userName,String password) throws InvalidNameException,WrongPasswordException{ if(userName.equals("java")){ if(password.equals("java")){ return new User(userName). }else{ throw new WrongPasswordException(). } }else{ throw new InvalidNameException(). } //return null. }
public static void main(String[] args){ Login l=new Login(). User user=null. try{ user=l.validate("javac","java"). }catch(InvalidNameException invalidName){ System.out.println("The username is invalid!"). }catch(WrongPasswordException wrongPassword){ System.out.println("The password is wrong"). } if(!(user==null)){ System.out.println(user.getUserName()). } } } class User{ private String userName. public User(String userName){ this.userName=userName. } public void setUserName(String userName){ this.userName=userName. } public String getUserName(){ return userName. } } class InvalidNameException extends Exception{ public InvalidNameException(){ } } class WrongPasswordException extends Exception{ public WrongPasswordException(){ } }