2_Spring常用注入方式

1.注入方式：字段（第一天所演示），构造函数，方法注入

2.构造函数注入

package com.jie.ssm.service.impl;
import com.jie.ssm.dao.UserDao;
import com.jie.ssm.entity.User;
import com.jie.ssm.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class UserServiceImpl implements UserService {
    private UserDao userDao;
    @Autowired
    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }
    @Override
    public List<User> getAll() {
        return userDao.selectUsers();
    }
    @Autowired
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}

3.方法注入

package com.jie.ssm.service.impl;
import com.jie.ssm.dao.UserDao;
import com.jie.ssm.entity.User;
import com.jie.ssm.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class UserServiceImpl implements UserService {
    private UserDao userDao;
    //构造函数注入
    /*@Autowired
    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }*/
    @Override
    public List<User> getAll() {
        return userDao.selectUsers();
    }
    @Autowired
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}

4.通过@Repository(“UserDao”)解决不唯一问题（不需要@Primary）

package com.jie.ssm.dao.impl;
import com.jie.ssm.dao.UserDao;
import com.jie.ssm.entity.User;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Repository;
import java.util.List;
//@Primary
@Repository("UserDao2")
public class UserDaoImpl implements UserDao {
    @Override
    public List<User> selectUsers() {
        System.out.println("UserDaoImpl");
        return null;
    }
    @Override
    public User selectByUsername(String username) {
        return null;
    }
    @Override
    public int insert(User user) {
        return 0;
    }
    @Override
    public void update(User user) {
    }
    @Override
    public int delete(int id) {
        return 0;
    }
}

• 不声明默认是类名，命名要和service实现类中要求注入的参数名相同

  @Autowired
  private UserDao userDao2;

• 规则：开始通过名称去在容器中找，如果名称找不到就靠类型去找。
  • @Qualifier指定名称去找，不依靠变量名称，靠@Qualifier的值去找容器中相同名称的

    @Autowired
    @Qualifier("UserDao2")
    private UserDao userDao;

5.java本身也提供一个注解@Resource

package com.jie.ssm.service.impl;
import com.jie.ssm.dao.UserDao;
import com.jie.ssm.entity.User;
import com.jie.ssm.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
import java.util.List;
@Service
public class UserServiceImpl implements UserService {
//    @Autowired
//    @Qualifier("UserDao2")
   @Resource(name = "UserDao2")
    private UserDao userDao;
    //构造函数注入
    /*@Autowired
    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }*/
    @Override
    public List<User> getAll() {
        return userDao.selectUsers();
    }
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}