Spring-02-依赖注入DI

五、依赖注入——DI

5.1 Setter注入（最常用）

• 实体类

  public class Address {
      private String province;
      private String city;
      private String district;
  }
  

  public class People {
      private String name;
      private Address address;
      private String[] cars;
      private List<String> phones;
      private Map<String, String> relationship;
      private Set<String> vips;
      private String wife;
      private Properties info;
  }
  

• beans.xml配置

  <bean id="address" class="com.pbx.pojo.Address">
    <property name="province" value="浙江省"/>
    <property name="city" value="杭州市"/>
    <property name="district" value="西湖区"/>
  </bean>
  
  <bean id="bruce" class="com.pbx.pojo.People">
    <!--常规注入-->
    <property name="name" value="BruceXu" />
      
    <!--引用Bean进行注入-->
    <property name="address" ref="address"/>
      
    <!--注入数组-->
    <property name="cars">
        <array>
            <value>奔驰</value>
            <value>奥迪</value>
            <value>宝马</value>
        </array>
    </property>
      
    <!--注入List-->
    <property name="phones">
        <list>
            <value>iphone</value>
            <value>华为</value>
            <value>小米</value>
        </list>
    </property>
      
    <!--注入Map-->
    <property name="relationship">
        <map>
            <entry key="老板" value="马云"/>
            <entry key="二次元老婆" value="蕾姆"/>
        </map>
    </property>
      
    <!--注入Set-->
    <property name="vips">
        <set>
            <value>爱奇艺</value>
            <value>腾讯视频</value>
            <value>芒果tv</value>
        </set>
    </property>
      
    <!--注入空指针-->
    <property name="wife">
        <null/>
    </property>
      
    <!--注入Properties-->
    <property name="info">
        <props>
            <prop key="手机号">11122223333</prop>
            <prop key="身份证号">111111222222223333</prop>
        </props>
    </property>
      
  </bean>
  

• 测试

  package com.pbx;
  
  import com.pbx.pojo.People;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.support.ClassPathXmlApplicationContext;
  
  /**
   * @author BruceXu
   * @date 2020/11/17
   */
  public class Test {
      public static void main(String[] args) {
          ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
          People people = (People) context.getBean("bruce");
          System.out.println(people);
      }
  }
  

  

5.2 构造器注入

• 实体类

  public class Student {
      private int id;
      private String name;
      private String garde;
      
      public Student(int id, String name, String garde) {
          this.id = id;
          this.name = name;
          this.garde = garde;
      }
  }
  

• beans.xml

  <!--通过构造器参数下标注入-->
  <bean id="student1" class="com.pbx.pojo.Student">
      <constructor-arg index="0" value="1"/>
      <constructor-arg index="1" value="张三"/>
      <constructor-arg index="2" value="一年级"/>
  </bean>
  
  <!--通过构造器形参名称注入-->
  <bean id="student2" class="com.pbx.pojo.Student">
      <constructor-arg name="id" value="2"/>
      <constructor-arg name="name" value="李四"/>
      <constructor-arg name="garde" value="二年级"/>
  </bean>
  
  <!--通过参数类型注入-->
  <bean id="student3" class="com.pbx.pojo.Student">
      <constructor-arg type="int" value="3"/>
      <constructor-arg type="java.lang.String" value="王五"/>
      <constructor-arg type="java.lang.String" value="三年级"/>
  </bean>
  
  <bean id="student4" class="com.pbx.pojo.Student">
      <constructor-arg type="int" value="3"/>
      <constructor-arg type="java.lang.String" value="四年级"/>
      <constructor-arg type="java.lang.String" value="赵六"/>
  </bean>
  

• 测试

  @Test
  public void test() {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      Student student = (Student) context.getBean("student1");
      System.out.println(student);
      System.out.println("==============");
      student = (Student) context.getBean("student2");
      System.out.println(student);
      System.out.println("==============");
      student = (Student) context.getBean("student3");
      System.out.println(student);
      System.out.println("==============");
      student = (Student) context.getBean("student4");
      System.out.println(student);
  }
  

  

5.3 命名空间注入

• 命名空间注入的方式可以简化Spring配置文件的编写，适用于简单类型属性的注入

• 实体类

  public class User {
      private int id;
      private String name;
      private Address address;
  }
  

• user.xml

  <?xml version="1.0" encoding="UTF-8"?>
  <beans xmlns="http://www.springframework.org/schema/beans"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:p="http://www.springframework.org/schema/p"
         xmlns:c="http://www.springframework.org/schema/c"
         xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  
      <bean id="user1" class="com.pbx.pojo.User" p:id="1" p:name="张三"/>
      <bean id="user2" class="com.pbx.pojo.User" c:id="2" c:name="李四"/>
      
  </beans>
  

• 测试

  @Test
  public void test2() {
      ApplicationContext context = new ClassPathXmlApplicationContext("user.xml");
      User user1 = context.getBean("user1", User.class);
      System.out.println(user1);
      User user2 = context.getBean("user2", User.class);
      System.out.println(user2);
  }
  

• 注意

  • 要使用命名空间注入，需要导入命名空间的约束文件

    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:c="http://www.springframework.org/schema/c"
    

  • p命名空间和c命名空间实际上是代表标签 <property> 和 <constructor-arg>

5.4 自动装配

• Spring可以不用显式的配置bean的property属性，通过自动装配也可以完成Bean的注入

• Spring‘的自动装配机制主要依赖两个操作

  • 组件扫描：Spring会扫描被容器中的bean
  • 自动装配：Spring会根据某些条件来自动装配那些设置了自动装配的Bean

• 常见的自动装配方式

  • byName
    • Spring会自动寻找和bean中属性名同名的bean进行装配
  • byType
    • Spring会自动寻找和bean中属性类型相同的bean进行装配。如果有多个类型相同的bean，那么要报错

• 环境搭建

  • 实体类

    public class People {
        private String name;
        private Dog dog;
        private Cat cat;
    }
    

    public class Cat implements Pet {
        @Override
        public void shout() {
            System.out.println("Cat::shout()");
        }
    }
    

    public class Dog implements Pet {
        @Override
        public void shout() {
            System.out.println("Dog::shout()");
        }
    }
    

  • beans.xml

    <bean id="cat" class="com.pbx.pojo.Cat"/>
    <bean id="dog" class="com.pbx.pojo.Dog"/>
    
    <bean id="p1" class="com.pbx.pojo.People" autowire="byName">
    </bean>
    
    <bean id="p2" class="com.pbx.pojo.People" autowire="byType">
    </bean>
    

• 测试

  @Test
  public void test01() {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      People p1 = context.getBean("p1", People.class);
      People p2 = context.getBean("p2", People.class);
  
      p1.show();
      System.out.println("================");
      p2.show();
  
  }