spring1-小结

标签：demospring1 OrderService orderService UserService spring1 小结 public 构造函数

package com.example.demospring1;

import com.example.demospring1.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import java.lang.reflect.Field;





/**
 * @description:
 * @author: 范子祺
 **/
public class Test {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        UserService userService = (UserService)context.getBean("userService");
//测试2  依赖注入
        userService.test();
//结果2 orderService seecom.example.demospring1.service.OrderService@1e67a849




//测试1 默认都是单例bean
//        UserService userService1 = (UserService)context.getBean("userService");
//        UserService userService2 = (UserService)context.getBean("userService");


//        System.out.println(userService);
//        System.out.println(userService1);
//        System.out.println(userService2);
        //结果1
//        com.example.demospring1.service.UserService@1e67a849
//        com.example.demospring1.service.UserService@1e67a849
//        com.example.demospring1.service.UserService@1e67a849

//        UserService userService3 = new UserService();
//        context.getBeanFactory().registerSingleton("xxx",userService3);

//        UserService userService1 = new UserService();
//
//        for (Field field: userService1.getClass().getDeclaredFields()){
//            if (field.isAnnotationPresent(Autowired.class)){
//                field.set(userService1,??);
//            }
//        }

    }
}

@ComponentScan("com.example.demospring1")
public class AppConfig {
}


@Component
public class UserService {

    @Autowired
    private OrderService orderService;

    public void test(){
        System.out.println("orderService see"+orderService);
    }
}


@Component
public class OrderService {
}

1 依赖注入，2 单例bean，

userservice类->无参构造函数->对象->依赖注入->初始化->放入Map单例池->bean对象

希望使用类的时候，它里面的某个属性，已经从数据库中取到值了

userservice中增加

@PostConstruct
    public void a(){
        System.out.println("初始化前");
    }
结果

14:24:27.525 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userService'
初始化前
orderService seecom.example.demospring1.service.OrderService@75f9eccc

继续增加

public class UserService implements InitializingBean {



@PostConstruct
    public void a(){
        System.out.println("初始化前-PostConstruct");
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("初始化前-afterPropertiesSet");
    }


结果
14:28:19.050 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userService'
初始化前-PostConstruct
初始化前-afterPropertiesSet
orderService see：com.example.demospring1.service.OrderService@5d47c63f

　构造函数的证明

类UserService 增加

public UserService() {
        System.out.println("空参构造函数："+orderService);
    }

    public UserService(OrderService orderService) {
        this.orderService = orderService;
        System.out.println("1个入参orderService构造函数："+orderService);
    }
结果
空参构造函数：null
初始化前-PostConstruct
初始化前-afterPropertiesSet
orderService see：com.example.demospring1.service.OrderService@5d47c63f

　自动选择了无参构造函数

OrderService 增加

 public OrderService() {
        System.out.println("空参OrderService"+this);
    }

UserService  修改

//    public UserService() {
//        System.out.println("空参构造函数："+orderService);
//    }

    public UserService(OrderService orderService) {
        this.orderService = orderService;
        System.out.println("1个入参的UserService构造函数："+orderService);
    }


结果

17:49:18.193 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'orderService'
空参OrderServicecom.example.demospring1.service.OrderService@1445d7f
17:49:18.198 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userService'
17:49:18.365 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Autowiring by type from bean name 'userService' via 
constructor to bean named 'orderService'
1个入参的UserService构造函数：com.example.demospring1.service.OrderService@1445d7f
初始化前-PostConstruct
初始化前-afterPropertiesSet
orderService see：com.example.demospring1.service.OrderService@1445d7f

1 依赖注入， 2 单例bean

UserService增加

public UserService(OrderService orderService1,OrderService orderService2) {
        this.orderService = orderService;
        System.out.println("2个入参的UserService构造函数："+orderService);
        System.out.println("2个入参的UserService构造函数h2："+orderService1+"="+orderService2);
    }

结果
17:53:44.235 [main] WARN org.springframework.context.annotation.AnnotationConfigApplicationContext - 
Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.
BeanCreationException: Error creating bean with name 'userService' defined in file [/Users/shenshaonian/Desktop/selfPro/spr
ing/demoSpring1/target/classes/com/example/demospring1/service/UserService.class]: Instantiation of bean failed; nested exc
eption is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.demospring1.service.U
serService]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.example.demospring1.service.UserService.<init>()

多个有参的构造函数，无法判断使用哪个构造函数创建对象

UserService  修改

//    public UserService(OrderService orderService) {
//        this.orderService = orderService;
//        System.out.println("1个入参的UserService构造函数："+orderService);
//    }

public UserService(OrderService orderService1,OrderService orderService2) {
        this.orderService = orderService;
        System.out.println("2个入参的UserService构造函数："+orderService);
        System.out.println("2个入参的UserService构造函数h2："+orderService1+"="+orderService2);
    }

public void test(){
        orderService.orderServicePrint();
        System.out.println("userservice look orderService see："+orderService+"==");
    }


OrderService 增加
public void orderServicePrint(){
        System.out.println("orderServicePrint look");
    }


结果空参
OrderServicecom.example.demospring1.service.OrderService@1445d7f
18:01:15.133 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userService'
18:01:15.236 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Autowiring by type from bean name 'userService' via constructor to bean named 'orderService'
2个入参的UserService构造函数：null
2个入参的UserService构造函数h2：com.example.demospring1.service.OrderService@1445d7f=com.example.demospring1.service.OrderService@1445d7f
初始化前-PostConstruct
初始化前-afterPropertiesSet
orderServicePrint look
userservice look orderService see：com.example.demospring1.service.OrderService@1445d7f==

1 autowire注释的bean一般会在对象使用的时候才会实例化，2 对象放到构造函数的参数中也是一种提前的实例化，最终orderservice的地址都是

1445d7f，这里面是通过cglib代理实现的， cglib是啥， asm是啥，这里我有点搞不清了。可能有错误的地方。

标签：demospring1,OrderService,orderService,UserService,spring1,小结,public,构造函数
From： https://www.cnblogs.com/woainixxx/p/16983701.html

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