Spring注解驱动开发——自动装配 @Autowired @Qualifier @Primary

Posted 2021-08-05 mangoubiubiu

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自动装配;
Spring利用依赖注入（DI）,完成对IOC容器中各个组件的依赖关系赋值；
1)丶@Autowired: 自动注入
1 默认优先按照类型去容器中找队应的组件：applica.getBean(UserDao.class);找到就赋值
2 如果找到多个相同类型的组件，再将属性的名称作为组件的id去容器中查找
applica.getBean("userDao");
3 @Qualifier("bookDao");使用@Qualifier指定需要装配的组件的id,而不是使用属性名
4 自动装配默认一定要将属性赋值好，没有就会报错；
可以使用@Autowired(required=false);作为非必需的
5 @Primary,让Spring进行自动装配的时候，默认使用首选的bean
也可以继续使用@Qualifier指定需要装配的bean的名字
UserService{
@Autowired
UserDao userDao;
}

@Autowired

1 默认优先按照类型去容器中找队应的组件：applica.getBean(UserServiceImpl.class);找到就赋值

配置类

package com.mongoubiubiu.conf;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;

import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.serviceImpl.UserServiceImpl;


@Configuration
@ComponentScan({"com.mongoubiubiu.service","com.mongoubiubiu.dao","com.mongoubiubiu.controller"})
public class MainConfigOfAutowired {


    
}

组件类

package com.mongoubiubiu.service.serviceImpl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Service;

import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.UserService;

@Service
public class UserServiceImpl implements UserService {
 
    
    @Autowired
    private UserDao userDao;
    
    public void print(){
        System.out.println("userDao:"+userDao);
    }

    @Override
    public String toString() {
        return "UserServiceImpl [userDao2=" + userDao + "]";
    }
    
}

package com.mongoubiubiu.dao;

import org.springframework.stereotype.Repository;

//名字默认是类名小写
@Repository
public class UserDao {
    
    
    
    

}

测试类

package com.mongougbiubiu.test;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Scope;

import com.mongoubiubiu.conf.MainConfigOfAutowired;
import com.mongoubiubiu.conf.MainConfigOfLifeCycle;
import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.UserService;
import com.mongoubiubiu.service.serviceImpl.UserServiceImpl;

public class IOCTest_Autowired {
    
    
    @Test
    public void Test01(){
        //创建ioc 容器
        AnnotationConfigApplicationContext applica=    new AnnotationConfigApplicationContext(MainConfigOfAutowired.class);
        UserService userService=applica.getBean(UserServiceImpl.class);

         userService.print();

        System.out.println(userService);
    } 

}

结果

因为userDao上有@Repository 加载配置类的时候又用@ComponentScan 扫描过该包所以userDao 被注册到了容器中， bean id 为类名首字母小写。

此时再获取bean 发现和 @Autowired自动装配的bean 为同一对象

2 如果找到多个相同类型的组件，再将属性的名称作为组件的id去容器中查找applica.getBean("userDao");

配置类

配置类里注册一个UserDao 此时bean id 为 userDao2

package com.mongoubiubiu.conf;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;

import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.serviceImpl.UserServiceImpl;

@Configuration
@ComponentScan({"com.mongoubiubiu.service","com.mongoubiubiu.dao","com.mongoubiubiu.controller"})
public class MainConfigOfAutowired {

    @Bean("userDao2")
    public UserDao userDao(){
        
        UserDao user=new UserDao();
        user.setLable("2");
        return user;
    }
    
}

组件类

package com.mongoubiubiu.dao;

import org.springframework.stereotype.Repository;

//名字默认是类名小写
@Repository
public class UserDao {
    
    public String lable="1";

    public String getLable() {
        return lable;
    }

    public void setLable(String lable) {
        this.lable = lable;
    }

    @Override
    public String toString() {
        return "UserDao [lable=" + lable + "]";
    }
    
    
    
    
    

}

package com.mongoubiubiu.service.serviceImpl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Service;

import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.UserService;

@Service
public class UserServiceImpl implements UserService {
 
    
    //@Qualifier("userDao")
    @Autowired
    private UserDao userDao;
    
    public void print(){
        System.out.println("userDao:"+userDao);
    }

    @Override
    public String toString() {
        return "UserServiceImpl [userDao2=" + userDao + "]";
    }
    
}

测试类

package com.mongougbiubiu.test;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Scope;

import com.mongoubiubiu.conf.MainConfigOfAutowired;
import com.mongoubiubiu.conf.MainConfigOfLifeCycle;
import com.mongoubiubiu.dao.UserDao;
import com.mongoubiubiu.service.UserService;
import com.mongoubiubiu.service.serviceImpl.UserServiceImpl;

public class IOCTest_Autowired {
    
    
    @Test
    public void Test01(){
        //创建ioc 容器
        AnnotationConfigApplicationContext applica=    new AnnotationConfigApplicationContext(MainConfigOfAutowired.class);
        UserService userService=applica.getBean(UserServiceImpl.class);

        System.out.println(userService);
    } 

}