SpringBoot2注解：@Configuration

@configuration

@Configuration这个注解作用就是告诉 springboot 这是一个配置类。配置类以及类里的方法都可以作为bean。用@Bean标记

@Configuration 包含 proxyBeanMethods字段，默认值是true。返回前检测是否存在实例，保证为单例模式。若proxyBeanMethods=”false”则直接返回实例

注意是先指定代理Bean，再通过Bean调用方法

实例1：

写两个Bean，user和pet

package com.itheima.bean;
 
public class Pet {
    String name;
 
    public Pet() {
    }
 
    public Pet(String name) {
        this.name = name;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    @Override
    public String toString() {
        return "Pet{" +
                "name='" + name + '\'' +
                '}';
    }
}
 
 
package com.itheima.bean;
 
public class User {
    String name;
    int age;
    Pet pet;
 
    public User() {
    }
 
    public User(String name,int age) {
        this.name = name;
        this.age = age;
    }
 
    public User(String name, int age, Pet pet) {
        this.name = name;
        this.age = age;
        this.pet = pet;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public Pet getPet() {
        return pet;
    }
 
    public void setPet(Pet pet) {
        this.pet = pet;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", pet=" + pet +
                '}';
    }
}

Bean的配置类：MyConfig.java，通过@Configuration和@Bean指定装配Bean

@Configuration(proxyBeanMethods = false)
public class MyConfig {
    @Bean
        public User user01(){

        User zhangsan = new User("zhangsan", 18);
//        zhangsan.setPet(pet01());
        return zhangsan;
    }
    @Bean("tom")
    public Pet pet01(){
        return new Pet("tom");
    }
}

　　测试代码：将MyConfig.java作为Bean，将@Configuration（proxyBeanMethod=false)，多次调用Bean的方法，比较返回对象是否相等。

@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run =
                SpringApplication.run(MainApplication.class, args);
//        String[] names = run.getBeanDefinitionNames();
//        for (String name : names) {
//            System.out.println(name);
//        }

        //这个ProxyBeanMethod居然是先代理MyConfig这个bean，
        // 再用bean调用其方法，测试bean的方法返回是否相等，我的天！

        MyConfig bean = run.getBean(MyConfig.class);
        System.out.println(bean);
        User user1 = bean.user01();
        User user2 = bean.user01();
        System.out.println(user1==user2);

//        哥直接用run获取对应的 user01 bean，难怪反复测试都返回true
//        User user01 = run.getBean("user01", User.class);
//        User user02 = run.getBean("user01", User.class);
//        System.out.println(user02==user01);
    }
}