Spring(2)：依赖注入DI

 依赖注入DI

• 当某个角色(可能是一个Java实例，调用者)需要另一个角色(另一个Java实例，被调用者)的协助时，在 传统的程序设计过程中，通常由调用者来创建被调用者的实例。但在Spring里，创建被调用者的工作不再由调用者来完成，因此称为控制反转;创建被调用者 实例的工作通常由Spring容器来完成，然后注入调用者，因此也称为依赖注入

• 所谓依赖注入，是指程序运行过程中，如果需要调用另一个对象协助时，无须在代码中创建被调用者，而是依赖于外部的注入。Spring的依赖注入对调用者和被调用者几乎没有任何要求，完全支持对POJO之间依赖关系的管理

 

例题

1，建实体类Address和Student

Student

public class Student {
    private String name;
    private Address address;
    private String[] books;
    private List<String> hobbys;
    private Map<String,String> card;
    private Set<String> games;
    private String girlFriend;
    private Properties info;

    public Student() {
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public void setBooks(String[] books) {
        this.books = books;
    }

    public void setHobbys(List<String> hobbys) {
        this.hobbys = hobbys;
    }

    public void setCard(Map<String, String> card) {
        this.card = card;
    }

    public void setGames(Set<String> games) {
        this.games = games;
    }

    public void setGirlFriend(String girlFriend) {
        this.girlFriend = girlFriend;
    }

    public void setInfo(Properties info) {
        this.info = info;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", address=" + address.toString() +
                ", books=" + Arrays.toString(books) +
                ", hobbys=" + hobbys +
                ", card=" + card +
                ", games=" + games +
                ", girlFriend='" + girlFriend + '\'' +
                ", info=" + info +
                '}';
    }
}

 

Address

public class Address {
    private String address;

    public Address() {
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Address{" +
                "address='" + address + '\'' +
                '}';
    }
}

2，建配置文件 beans.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!--Address-->
    <bean id="addr" class="pojo.Address">
        <property name="address" value="西安"/>
    </bean>

    <!--Student-->
    <bean id="Student" class="pojo.Student">

        <!--常量注入 普通字段-->
        <property name="name" value="闪电侠"/>

        <!--Bean注入 引用其他bean使用ref-->
        <property name="address" ref="addr"/>

        <!--数组注入-->
        <property name="books">
            <array>
                <value>西游记</value>
                <value>水浒传</value>
                <value>红楼梦</value>
                <value>三国演义</value>
            </array>
        </property>

        <!--List注入-->
        <property name="hobbys">
            <list>
                <value>代码</value>
                <value>电影</value>
                <value>音乐</value>
            </list>
        </property>

        <!--Map注入-->
        <property name="card">
            <map>
                <entry key="IdCard" value="666666888888884444"/>
                <entry key="银行卡" value="111122223333444"/>
            </map>
        </property>

        <!--Set注入-->
        <property name="games">
            <set>
                <value>王者荣耀</value>
                <value>绝地求生</value>
            </set>
        </property>

        <!--Null空值注入-->
        <property name="girlFriend">
            <null/>
        </property>

        <!--Properties注入-->
        <property name="info">
            <props>
                <prop key="学号">2019032324</prop>
                <prop key="性别">男</prop>
                <prop key="姓名">闪电侠</prop>
            </props>
        </property>

    </bean>
    
</beans>

3，编写测试类

import org.junit.Test;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class StudentTest {
    @Test
    public void Test(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Student student = (Student) context.getBean("Student");
        System.out.println(student.toString());
    }
}

 

4，运行结果