Spring点滴七：Spring中依赖注入(Dependency Injection:DI)

时间：2023-03-09 05:28:27
Spring点滴七：Spring中依赖注入(Dependency Injection:DI)

Spring机制中主要有两种依赖注入：Constructor-based Dependency Injection(基于构造方法依赖注入) 和 Setter-based Dependency Injection(基于Setter方法依赖注入)

一、Contructor-based Dependency Injection(基于构造方法注入)

在bean标签中通过使用<constructor-arg />标签来实现

spring.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">

    <bean id="a" class="com.test.spring.A">
       <!-- 引用其它bean两种不同实现-->

       <constructor-arg>

          <ref bean="b"/>

       </constructor-arg>

       <constructor-arg ref="c"/>

       <constructor-arg name="name" value="张三"/>

    </bean>

    <bean id="b" class="com.test.spring.B">

    </bean>

    <bean id="c" class="com.test.spring.C">

    </bean>

</beans>

Java 类：

package com.test.spring;

public class A {

    private B b;

    private C c;

    private String name;

    public A(B b, C c, String name) {

        this.b = b;

        this.c = c;

        this.name = name;

    }

    public B getB() {

        return b;

    }

    public void setB(B b) {

        this.b = b;

    }

    public C getC() {

        return c;

    }

    public void setC(C c) {

        this.c = c;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "A [b=" + b + ", c=" + c + ", name=" + name + "]";

    }

}

-------------------------------------------------------------------------------------------------------------------------------------------------

package com.test.spring;

public class B {

}

-------------------------------------------------------------------------------------------------------------------------------------------------

package com.test.spring;

public class C {

}

测试：

package com.test.spring;

import org.junit.Before;

import org.junit.Test;

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T {

    AbstractApplicationContext applicationcontext=null;

    @Before

    public void before() {

        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");

        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});

        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");

    }

    @Test

    public void  test() {

        A a=applicationcontext.getBean(A.class);

        System.out.println(a);

    }

}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 14:02:53  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 14:02:53 CST 2017]; root of context hierarchy
2017-03-19 14:02:53  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》Spring ApplicationContext容器初始化完毕了......
A [b=com.test.spring.B@4899c2aa, c=com.test.spring.C@66bb4c22, name=张三]

Spring 官网API提供够了使用静态工厂方法来实现上述功能：

Spring.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">    

   <bean id="a" class="com.test.spring.A" factory-method="getInstence">

       <constructor-arg>

          <ref bean="b"/>

       </constructor-arg>

       <constructor-arg ref="c"/>

       <constructor-arg name="name" value="张三"/>

    </bean>

    <bean id="b" class="com.test.spring.B">

    </bean>

    <bean id="c" class="com.test.spring.C">

    </bean>

</beans>

Java类：

package com.test.spring;

public class A {

    private B b;

    private C c;

    private String name;

    /**

     * 创建一个私有的构造方法

     * @param b

     * @param c

     * @param name

     */

    private A(B b, C c, String name) {

        this.b = b;

        this.c = c;

        this.name = name;

    }

    public static A getInstence(B b,C c,String name){

        System.out.println("调用了静态的工厂方法");

        A a = new A(b,c,name);

        return a;

    }

    public B getB() {

        return b;

    }

    public void setB(B b) {

        this.b = b;

    }

    public C getC() {

        return c;

    }

    public void setC(C c) {

        this.c = c;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "A [b=" + b + ", c=" + c + ", name=" + name + "]";

    }

}

--------------------------------------------------------------------------------
B.java C.java（略）

测试：

package com.test.spring;

import org.junit.Before;

import org.junit.Test;

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T {

    AbstractApplicationContext applicationcontext=null;

    @Before

    public void before() {

        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");

        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});

        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");

    }

    @Test

    public void  test() {

        A a=applicationcontext.getBean(A.class);

        A a2=applicationcontext.getBean(A.class);

        System.out.println(a==a2);//发现A的实例对象是单例的

        System.out.println(a);

        System.out.println(a2);

    }

}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 14:22:31  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@17ad352e: startup date [Sun Mar 19 14:22:31 CST 2017]; root of context hierarchy
2017-03-19 14:22:31  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
调用了静态的工厂方法
》》》Spring ApplicationContext容器初始化完毕了......
true
A [b=com.test.spring.B@176730bb, c=com.test.spring.C@77b050fd, name=张三]
A [b=com.test.spring.B@176730bb, c=com.test.spring.C@77b050fd, name=张三]

2.Setter-based Dependency Injection（基于Setter方式依赖注入）:该注入方式是经常使用的

spring.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">

   <bean id="a" class="com.test.spring.A">

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

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

       <property name="name" value="张三"/>

    </bean>

    <bean id="b" class="com.test.spring.B">

    </bean>

    <bean id="c" class="com.test.spring.C">

    </bean>

</beans>

Java类：

package com.test.spring;

public class A {

    private B b;

    private C c;

    private String name;

    public B getB() {

        return b;

    }

    public void setB(B b) {

        this.b = b;

    }

    public C getC() {

        return c;

    }

    public void setC(C c) {

        this.c = c;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "A [b=" + b + ", c=" + c + ", name=" + name + "]";

    }

}

测试：

package com.test.spring;

import org.junit.Before;

import org.junit.Test;

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T {

    AbstractApplicationContext applicationcontext=null;

    @Before

    public void before() {

        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");

        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});

        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");

    }

    @Test

    public void  test() {

        //BeanLifecycle beanLifecycle =applicationcontext.getBean("beanLifecycle",BeanLifecycle.class);

        //applicationcontext.close();

        //applicationcontext.registerShutdownHook();

        A a=applicationcontext.getBean(A.class);

        System.out.println(a);

    }

}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 14:34:20  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@17ad352e: startup date [Sun Mar 19 14:34:20 CST 2017]; root of context hierarchy
2017-03-19 14:34:20  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》Spring ApplicationContext容器初始化完毕了......
A [b=com.test.spring.B@49daafb9, c=com.test.spring.C@3446c090, name=张三]

这两种注入方式在Spring配置文件中可以一起使用

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