Sprint注入和bean的自动装配以及Autowired的用法

1、Spring注入

Spring注入常用的有两种方式，第一种是设值注入，第二种是构造注入。

1、设值注入

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="book" class="com.wry.bean.Book"></bean>  
       <bean id="reader" class="com.wry.bean.Reader">
       	   <property name="book" ref="book" />
       </bean>  
</beans>

Book.java

package com.wry.bean;

public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

Reader.java

package com.wry.bean;

public class Reader {
	private Book book;

	public void setBook(Book book) {
		this.book = book;
	}
	
	public void readBook(){
		book.read();
	}
}

测试

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

2、构造器注入

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="book" class="com.wry.bean.Book"></bean>  
       <bean id="reader" class="com.wry.bean.Reader">
       	   <constructor-arg name="book" ref="book" />
       </bean>  
</beans>

Book.java

package com.wry.bean;

public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

Reader.java

package com.wry.bean;

public class Reader {
	private Book book;

	public Reader(Book book){
		this.book = book;
	}
	
	public void readBook(){
		book.read();
	}
}

测试

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

2、bean的自动装配

bean的自动装配有三种方式，第一种通过byName，第二种通过byType，第三种通过constructor。

1、通过byName

在Spring的配置文件头部加入default-autowire = “byName”，在xml中定义的bean不要property参数(或者constructor-arg)。

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"
           default-autowire = "byName">  
             
       <bean id="book" class="com.wry.bean.Book"></bean>  
       <bean id="reader" class="com.wry.bean.Reader"></bean>  
</beans> 

Book.java

package com.wry.bean;

public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

Reader.java

package com.wry.bean;

public class Reader {
	private Book book;

	public void setBook(Book book) {
		this.book = book;
	}

	public void readBook(){
		book.read();
	}
}

测试

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

2、通过byType

在Spring的配置文件头部加入default-autowire = “byType”，因为是通过类型注入的，所以bean中的id可以改名称，当然也可以bean的id删除。

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"
           default-autowire = "byType">  
             
       <bean class="com.wry.bean.Book"></bean>  
       <bean id="reader" class="com.wry.bean.Reader"></bean>  
</beans> 

Book.java

package com.wry.bean;

public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

Reader.java

package com.wry.bean;

public class Reader {
	private Book book;

	public void setBook(Book book) {
		this.book = book;
	}

	public void readBook(){
		book.read();
	}
}

测试

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

3、通过constructor

在Spring的配置文件头部加入default-autowire = “constructor”，因为是通过构造器注入的，所以bean中的id可以改名称，当然也可以bean的id删除。

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"
           default-autowire = "constructor">
       <bean class="com.wry.bean.Book"></bean>  
       <bean id="reader" class="com.wry.bean.Reader"></bean>  
</beans>

Book.java

package com.wry.bean;

public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

Reader.java

package com.wry.bean;

public class Reader {
	private Book book;

	public Reader(Book book){
		this.book = book;
	}

	public void readBook(){
		book.read();
	}
}

测试

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

3、Autowired的用法

配置文件统一配置如下：

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans" 
	   xmlns:context="http://www.springframework.org/schema/context"
       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
           http://www.springframework.org/schema/context 
           http://www.springframework.org/schema/context/spring-context-3.0.xsd">
       <context:component-scan base-package="com.wry.bean"></context:component-scan>
</beans>

Book.java代码统一如下：

package com.wry.bean;

import org.springframework.stereotype.Component;

@Component
public class Book {
	public void read(){
		System.out.println("readding book");
	}
}

测试代码统一如下：

public class Demo {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
		Reader reader = (Reader)context.getBean("reader");
		reader.readBook();
	}
}

1、成员变量方式

Reader.java
package com.wry.bean;

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

@Component
public class Reader {
	
	@Autowired
	private Book book;

	public void readBook(){
		book.read();
	}
}

2、set方法方式

package com.wry.bean;

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

@Component
public class Reader {

	private Book book;

	@Autowired
	public void setBook(Book book) {
		this.book = book;
	}

	public void readBook(){
		book.read();
	}
}

3、构造器方式

package com.wry.bean;

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

@Component
public class Reader {

	private Book book;

	@Autowired
	public Reader(Book book){
		this.book = book;
	}

	public void readBook(){
		book.read();
	}
}

Autowired的使用说明
1、默认情况下，如果因找不到合适的bean将会导致autowiring失败抛出异常，可以通过下面的方式避免：

@Component
public class Reader {

	@Autowired(required = false)
	private Book book;

	public void readBook(){
		book.read();
	}
}

2、每个类只能有一个构造器被标记为required = true

3、可以注解那些众所周知的解析依赖性接口，比如：BeanFactory、ApplicationContext、Environment、ResourceLoader、ApplicationEventPublisher、MessageSource等。