Spring_002 依赖注入方式实现

一、Spring的依赖注入（DI）

在Spring框架下，当Bean实例A运行过程中需要引用另外一个Bean实例B时，Spring框架会创建Bean的实例B，并将实例B通过实例A的构造函数、set方法、自动装配和注解方式注入到实例A，这种注入实例Bean到另外一个实例Bean的过程叫做依赖注入。

依赖注入的好处就是尽可能隔离Bean之间的代码耦合，提高Bean重用的可能性，并尽量降低程序代码的维护难度，Spring框架通过依赖注入技术将不同的Bean融合起来，完成复杂业务操作，但又确保了每个Bean相对的独立性。

Spring框架提供构造函数注入、设置方法注入、自动装配注入和注解注入四种注入方式。

1、基于构造函数的依赖注入

BybService.java

public class BybService {
    public String name;

    public String getName() {
        return name;
    }

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

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

    public String sayByb(){
        System.out.println("Byb"+name);
        return "Byb"+name;
    }
}

HelloWorld.java

public class HelloWorld {
    private String message;

    private BybService bybService;

    public HelloWorld(BybService bybService) {
        this.bybService=bybService;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public void getMessage() {
        System.out.println("message : " + message);
    }

    public void sayHello(){
        System.out.println(bybService.sayByb());
    }

}

Bean.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="helloWorld" class="HelloWorld">
        <constructor-arg ref="BybService"></constructor-arg>
    </bean>
    <bean id="BybService" class="BybService">
        <property name="name" value="Hello World!" />
    </bean>

</beans>

Main.App

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args){
        ApplicationContext context = new ClassPathXmlApplicationContext("Bean.xml");

        HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
        BybService bybService=(BybService) context.getBean("BybService");
        obj.sayHello();
    }
}

　运行MainApp.java

2、基于set方法注入（属性注入）

  HelloWorld.java

public class HelloWorld {
    private String message;

    private BybService bybService;

    public void setMessage(String message) {
        this.message = message;
    }

    public void getMessage() {
        System.out.println("message : " + message);
    }

    public void sayHello(){
        System.out.println(bybService.sayByb());
    }

    public BybService getBybService() {
        return bybService;
    }

    public void setBybService(BybService bybService) {
        this.bybService = bybService;
    }
}

BybService.java

public class BybService {
    public String name;

    public String getName() {
        return name;
    }

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

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

    public String sayByb(){
        System.out.println("Byb"+name);
        return "Byb"+name;
    }
}

　Bean.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="helloWorld" class="HelloWorld">
        <property name="message" value="Hello World!" />
        <property name="BybService" ref="BybService"></property>
    </bean>
    <bean id="BybService" class="BybService">
        <property name="name" value="Hello World!" />
    </bean>

</beans>

　MainApp.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args){
        ApplicationContext context = new ClassPathXmlApplicationContext("Bean.xml");

        HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
        BybService bybService=(BybService) context.getBean("BybService");
        obj.sayHello();
    }

}

　运行MainApp.java

3、注解注入

Bean.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:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
	http://www.springframework.org/schema/context
	http://www.springframework.org/schema/context/spring-context-2.5.xsd">

    <context:annotation-config />
    <bean id="helloWorld" class="HelloWorld">
        <property name="message" value="aaa!" />
    </bean>
    <bean id="BybService" class="BybService">
        <property name="name" value="Hello World!" />
    </bean>

</beans>

BybService.java

public class BybService {
    public String name;

    public String getName() {
        return name;
    }

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

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

    public String sayByb(){
        System.out.println("Byb"+name);
        return "Byb"+name;
    }
}

HelloWorld.java

import org.springframework.beans.factory.annotation.Autowired;

public class HelloWorld {
    private String message;

    @Autowired
    private BybService bybService;

    public void setMessage(String message) {
        this.message = message;
    }

    public void getMessage() {
        System.out.println("message : " + message);
    }

    public void sayHello(){
        System.out.println(bybService.sayByb());
    }
}

　MainApp.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args){
        ApplicationContext context = new ClassPathXmlApplicationContext("Bean.xml");

        HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
        BybService bybService=(BybService) context.getBean("BybService");
        obj.sayHello();
        //bybService.sayByb();
    }

}

　运行结果如下：

 二、Spring注入依赖的时间

Spring在创建beanFactory实例化类的时候，先加载类，然后调用类的构造器进行初始化，在完成初始化进行依赖注入（常见的就是set注入，通过执行set方法）。

三、使用eclipse创建注入Bean实例

继续写我们的第一个Spring程序，这次我们使用依赖注入的方式实现程序

第一步，建立我们的Spring_002程序，并在程序中添加BookDao.java、BookDaoImpl.java、BookService.java、BookServiceImpl.java、

ApplicationContext.xml

第二步 在BookDao接口中配置一个addBook方法

package com.zk.myspring;

public interface BookDao {
	public void addBook();
}

在BookDaoImpl中实现addBook方法

package com.zk.myspring;

public class BookDaoImpl implements BookDao{
	@Override
	public void addBook() {
		// TODO Auto-generated method stub
		System.out.println("addBook");
	}
}

在BookService接口中配置addBook方法

package com.zk.myspring;

public interface BookService {
	public abstract void addBook();
}

在BookServiceImpl方法中实现addBook方法

package com.zk.myspring;

public class BookServiceImpl implements BookService{

	//方式一：接口等于实现类
	//private BookDao bookDao=new BookDaoImpl();
	//方式二：接口+set方法
	private BookDao bookdao;
	
	public void setBookdao(BookDao bookdao) {//依赖注入
		this.bookdao = bookdao;
	}

	@Override
	public void addBook() {
		// TODO Auto-generated method stub
		//this.bookdao.addBook();
		System.out.println("add book");
	}
}

注意在BookServiceImpl文件中，我们使用接口+set方法实现，并在setBookdao方法中实现依赖注入，使得BookService依赖于BookDao

第三步 配置我们的ApplicationContext.xml，使用property属性将BookDao注入进BookService

<property name="bookdao" ref="bookDaoId"></property> 

<property> 用于属性注入   

name:bean的属性名，通过setter方法获得

ref:另一个bean的id值的引用

<?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:util="http://www.springframework.org/schema/util"
       xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">
<!-- 创建Dao -->
<!-- 模拟spring执行过程
创建Service实例:BookService bookservice=new BookServiceImpl();  IOC <bean>
创建Dao实例:BookDao bookDao=new BookDaoImpl();   IOC
将dao设置给service:bookservice.setBookDao(bookDao);    DI  <property>

<property> 用于属性注入
name:bean的属性名，通过setter方法获得
ref:另一个bean的id值的引用
 -->
<!--创建Dao  -->
<bean id="bookDaoId" class="com.zk.myspring.BookDaoImpl"></bean>
<!-- 创建service -->
<bean id="bookServiceId" class="com.zk.myspring.BookServiceImpl">
<property name="bookdao" ref="bookDaoId"></property>
</bean>
</beans>

第四步 创建一个test方法，对配置文件进行测试

package com.zk.myspring;

import org.junit.Test;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;

public class TestBook {
	public static void main(String[]args)
	{
		//从spring容器中获得
		String path="ApplicationContext.xml";
		ApplicationContext ac=new ClassPathXmlApplicationContext(path);
		BookService bs=(BookService) ac.getBean("bookServiceId");
		bs.addBook();
	}
	@Test
	public void test1(){
		//使用BeanFactory实例化
		String path="ApplicationContext.xml";
		BeanFactory bf=new XmlBeanFactory(new ClassPathResource(path));
		BookService bs=(BookService) bf.getBean("bookServiceId");
		bs.addBook();
	}
}

得出输出

依赖注入方式配置spring成功

三、使用ideal创建Spring依赖注入实例

首先创建一个Spring项目

创建BybService.java、HelloWorld.java、MainApp.java和资源文件Bean.xml

BybService.java

public class BybService {
    public String name;

    public String getName() {
        return name;
    }

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

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

    public void sayByb(){
        System.out.println("Byb"+name);
    }
}

 HelloWorld.java

public class HelloWorld {
    private String message;

    private BybService bybService;

    public void setMessage(String message) {
        this.message = message;
    }

    public void getMessage() {
        System.out.println("message : " + message);
        bybService.sayByb();
    }

    public BybService getBybService() {
        return bybService;
    }

    public void setBybService(BybService bybService) {
        this.bybService = bybService;
    }
}

　MainApp.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args){
        ApplicationContext context = new ClassPathXmlApplicationContext("Bean.xml");

        HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
        BybService bybService=(BybService) context.getBean("BybService");
        obj.getMessage();
        bybService.sayByb();
    }

}

　Bean.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="helloWorld" class="HelloWorld">
        <property name="message" value="Hello World!" />
        <property name="bybService" ref="BybService"></property>
    </bean>
    <bean id="BybService" class="BybService">
        <property name="name" value="Hello World!" />
    </bean>

</beans>

Spring容器可以配置Bean，注入属性，而且可以维护Bean与Bean之间的关系。　

<bean>标签的作用是当spring框架加载的时候，spring会自动创建一个bean，并放入内存。当ApplicationContext context = new ClassPathXmlApplicationContext("Bean.xml");执行的时候，Spring容器就会被创建，同时applicationContext.xml中配置，Bean就会被创建放入（内存[HashMap/HashTable]）中。