Bean的自动装配01

自动装配是Spring满足Bean依赖的一种方式；Spring会在上下文自动寻找，并自动给bean装配属性。

在Spring中有三种装配的方式：

1. 在xml中显示的配置；
2. 隐式的自动装配bean【重要】；
3. 在Java中显示配置。

1、搭建环境

1. 编写实体类；

   package com.beyond.pojo;
   
   public class Cat {
       public void shut(){
           System.out.println("喵~");
       }
   }
   

   package com.beyond.pojo;
   
   public class Dog {
       public void shut(){
           System.out.println("汪~");
       }
   }
   

   package com.beyond.pojo;
   
   public class People {
       private String name;
       private Cat cat;
       private Dog dog;
   
       public String getName() {
           return name;
       }
   
       public void setName(String name) {
           this.name = name;
       }
   
       public Cat getCat() {
           return cat;
       }
   
       public void setCat(Cat cat) {
           this.cat = cat;
       }
   
       public Dog getDog() {
           return dog;
       }
   
       public void setDog(Dog dog) {
           this.dog = dog;
       }
   
       @Override
       public String toString() {
           return "People{" +
                   "name='" + name + '\'' +
                   ", cat=" + cat +
                   ", dog=" + dog +
                   '}';
       }
   }
   

2. 编写beans.xml文件；

   <?xml version="1.0" encoding="UTF-8"?>
   <beans xmlns="http://www.springframework.org/schema/beans"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
           https://www.springframework.org/schema/beans/spring-beans.xsd">
   
       <bean id="cat" class="com.beyond.pojo.Cat"/>
       <bean id="dog" class="com.beyond.pojo.Dog"/>
   
       <bean id="people" class="com.beyond.pojo.People">
           <property name="name" value="小明"/>
           <property name="cat" ref="cat"/>
           <property name="dog" ref="dog"/>
       </bean>
   
   </beans>
   

3. 测试。

   import com.beyond.pojo.People;
   import org.junit.Test;
   import org.springframework.context.ApplicationContext;
   import org.springframework.context.support.ClassPathXmlApplicationContext;
   
   public class MyTest {
       @Test
       public void test01(){
           ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
   
           People people = context.getBean("people", People.class);
           people.getCat().shut();
           people.getDog().shut();
       }
   }
   

2、byName自动装配

1. 编写beans.xml文件；

   <?xml version="1.0" encoding="UTF-8"?>
   <beans xmlns="http://www.springframework.org/schema/beans"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
           https://www.springframework.org/schema/beans/spring-beans.xsd">
   
       <bean id="cat" class="com.beyond.pojo.Cat"/>
       <bean id="dogccwd" class="com.beyond.pojo.Dog"/>
   
       <!--
       autowire="byName"表示会自动在容器上下文中查找，和自己对象set方法后面的值对应的 beanid
       -->
       <bean id="people" class="com.beyond.pojo.People" autowire="byName">
           <property name="name" value="小明"/>
       </bean>
   
   </beans>
   

2. 测试。

   import com.beyond.pojo.People;
   import org.junit.Test;
   import org.springframework.context.ApplicationContext;
   import org.springframework.context.support.ClassPathXmlApplicationContext;
   
   public class MyTest {
       @Test
       public void test01(){
           ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
   
           People people = context.getBean("people", People.class);
   
           /*
           喵~
   
           java.lang.NullPointerException              空指针异常
               at MyTest.test01(MyTest.java:13)
            */
           people.getCat().shut();
           people.getDog().shut();
       }
   }