Spring使用Setter完成依赖注入方式

时间：2021-12-20 04:35:08

对依赖注入的理解

依赖：实体间的所有依赖由容器创建

注入：容器负责完成实体间依赖互相注入的任务

 

使用Setter完成不同类型属性的注入

实体类Student

package indi.stitch.pojo;
import java.util.*;
public class Student {
  private String name;
  private Address address;
  private String[] books;
  private List<String> hobbys;
  private Set<String> games;
  private Map<String, String> card;
  private Properties info;
  private String wife;
  public String getName() {
      return name;
  }
  public void setName(String name) {
      this.name = name;
  }
  public Address getAddress() {
      return address;
  }
  public void setAddress(Address address) {
      this.address = address;
  }
  public String[] getBooks() {
      return books;
  }
  public void setBooks(String[] books) {
      this.books = books;
  }
  public List<String> getHobbys() {
      return hobbys;
  }
  public void setHobbys(List<String> hobbys) {
      this.hobbys = hobbys;
  }
  public Set<String> getGames() {
      return games;
  }
  public void setGames(Set<String> games) {
      this.games = games;
  }
  public Map<String, String> getCard() {
      return card;
  }
  public void setCard(Map<String, String> card) {
      this.card = card;
  }
  public String getWife() {
      return wife;
  }
  public void setWife(String wife) {
      this.wife = wife;
  }
  public Properties getInfo() {
      return info;
  }
  public void setInfo(Properties info) {
      this.info = info;
  }
  @Override
  public String toString() {
      return "Student{" +
              "name='" + name + '\'' + "\n" +
              ", address=" + address.toString() + "\n" +
              ", books=" + Arrays.toString(books) + "\n" +
              ", hobbys=" + hobbys + "\n" +
              ", games=" + games + "\n" +
              ", card=" + card + "\n" +
              ", info=" + info + "\n" +
              ", wife='" + wife + '\'' +
              '}';
  }
}

实体类引用的复杂类型Address

package indi.stitch.pojo;
public class Address {
  private String address;
  public String getAddress() {
      return address;
  }
  public void setAddress(String address) {
      this.address = address;
  }
  @Override
  public String toString() {
      return "Address{" +
              "address='" + address + '\'' +
              '}';
  }
}

String字符串类型注入

<property name="name" value = "stitch" />

复杂VO类型注入

配置文件中增加复杂类型bean(Address)的依赖配置

<bean id = "address" class="indi.stitch.pojo.Address">
      <property name="address" value="北京" />
  </bean>
<bean id = "student" class = "indi.stitch.pojo.Student">

实体类Student的bean属性依赖对其进行引用

<property name="address" ref="address"/>

数组类型注入

<property name="books">
          <array>
              <value>西游记</value>
              <value>三国演义</value>
              <value>红楼梦</value>
              <value>水浒传</value>
          </array>
</property>

List集合类型注入

<property name="hobbys">
          <list>
              <value>唱歌</value>
              <value>跳舞</value>
              <value>打篮球</value>
          </list>
</property>

Set集合类型注入

<property name="games">
          <set>
              <value>英雄联盟</value>
              <value>穿越火线</value>
              <value>刺激战场</value>
          </set>
</property>

Map键值对类型注入

<property name="card">
          <map>
              <entry key="学生卡" value="123456"/>
              <entry key="身份证" value="111111222222223333" />
          </map>
</property>

Properties类型注入

<property name="info">
          <props>
              <prop key="sex">男</prop>
              <prop key="age">18</prop>
          </props>
</property>

null类型注入

<property name="wife">
          <null />
      </property>

整体配置文件

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean id = "address" class="indi.stitch.pojo.Address">
      <property name="address" value="北京" />
  </bean>
  <bean id = "student" class = "indi.stitch.pojo.Student">
      <!-- String字符串类型注入-->
      <property name="name" value = "stitch" />
      <!--复杂VO类型注入-->
      <property name="address" ref="address"/>
      <!--数组类型注入-->
      <property name="books">
          <array>
              <value>西游记</value>
              <value>三国演义</value>
              <value>红楼梦</value>
              <value>水浒传</value>
          </array>
      </property>
      <!--List集合类型注入-->
      <property name="hobbys">
          <list>
              <value>唱歌</value>
              <value>跳舞</value>
              <value>打篮球</value>
          </list>
      </property>
      <!--Set集合类型注入-->
      <property name="games">
          <set>
              <value>英雄联盟</value>
              <value>穿越火线</value>
              <value>刺激战场</value>
          </set>
      </property>
      <!--Map键值对类型注入-->
      <property name="card">
          <map>
              <entry key="学生卡" value="123456"/>
              <entry key="身份证" value="111111222222223333" />
          </map>
      </property>
      <!--Properties类型注入-->
      <property name="info">
          <props>
              <prop key="sex">男</prop>
              <prop key="age">18</prop>
          </props>
      </property>
      <!--null类型注入-->
      <property name="wife">
          <null />
      </property>
  </bean>
</beans>

测试类

import indi.stitch.pojo.Student;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
  public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      Student student  = (Student) context.getBean("student");
      System.out.println(student.toString());
  }
}

输出结果：

Spring使用Setter完成依赖注入方式

 

Spring解决setter方式的循环依赖的原理

1.通过构造函数创建A对象 （A对象是半成品，还没有注入属性和调用init方法）

2.将半成品A对象封装成工厂对象存入三级缓存

3.A对象需要注入B对象，发现缓存里还没有B对象，开始创建B对象

4.通过构造函数创建B对象（B对象是半成品，还没有注入属性和调用init方法）同样在三级缓存中创建B工厂对象

5.B对象需要注入A对象；从三级缓存中获取A工厂对象，使用工厂对象获取半成品A对象同时放入

二级缓存中，提前曝光A对象，同时删除A工厂对象

6.B对象继续注入其它属性和初始化，之后将完成品B对象放入完成品缓存一级缓存，同时删除B工厂对象

7.A对象获取单例B的引用完成属性注入

8.B对象继续注入其它属性和初始化，之后将完成品A对象放入完成品缓存一级缓存同时删除二级缓存中的A

以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。

原文链接：https://blog.csdn.net/qq_39209361/article/details/114047114

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