Spring实现对象注入的三种方法详解

package com.java.demo.dao;
import org.springframework.stereotype.Repository;
@Repository
public class UserRepository {
    public int add() {
        System.out.println("Do UserRepository add method.");
        return 1;
    }
}

package com.java.demo.service;
import com.java.demo.dao.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Service;
@Service
public class UserService {
    // 1. 属性注入
    @Autowired // DI(依赖注入)
    private UserRepository userRepository;
    public int add() {
        System.out.println("Do UserService add method.");
        // 传统写法
//        UserRepository userRepository = new UserRepository();
//        return userRepository.add();
        // Spring V1.0
//        ApplicationContext context =
//                new ClassPathXmlApplicationContext("spring-config.xml");
//        UserRepository userRepository = context.getBean("userRepository",UserRepository.class);
//
//        return userRepository.add();
        // Spring V2.0
        return userRepository.add();
    }
}

package com.java.demo.service;
import com.java.demo.dao.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserService3 {
    private UserRepository userRepository;
    @Autowired
    public void setUserRepository(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    public void sayHi() {
        System.out.println("Do UserService3 sayHi.");
        userRepository.add();
    }
}

package com.java.demo.service;
import com.java.demo.dao.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserService4 {
    private UserRepository userRepository;
    @Autowired
    public UserService4(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    public void sayHi() {
        System.out.println("Do UserService4 sayHi.");
        userRepository.add();
    }
}