自動依賴注入大大簡化了我們的工作量，但是也有缺陷，如果一個介面有多個實現類，我們該注入哪一個呢？一種方法是設定其中一個bean不參與自動注入。

package shangbo.spring.example38;

public interface MessageService {
	String getMessage();
}

package shangbo.spring.example38;

public class MessageServiceDBImpl implements MessageService {

	public String getMessage() {
		return "This message from database";
	}

}

 

package shangbo.spring.example38;

public class MessageServiceFileImpl implements MessageService {

	public String getMessage() {
		return "This message from file";
	}

}

package shangbo.spring.example38;

public class MessagePrinter {

    private MessageService service;

    public void setService(MessageService service) {
		this.service = service;
	}

	public void printMessage() {
        System.out.println(service.getMessage());
    }
}

 

<?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">

	<!-- 
		全域性設定自動注入方式
	-->
	
	<!-- 
		兩個物件繼承自同一介面
		autowire-candidate="false" 表示該物件不參與自動注入
	 -->
	<bean class="shangbo.spring.example38.MessageServiceDBImpl" autowire-candidate="false" />
	<bean class="shangbo.spring.example38.MessageServiceFileImpl"/>
	<bean class="shangbo.spring.example38.MessagePrinter"/>
	
</beans>
 

package shangbo.spring.example38;

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

public class App {

	public static void main(String[] args) {
		// 例項化 Spring IoC 容器
		ApplicationContext context = new ClassPathXmlApplicationContext("example.xml", MessagePrinter.class);
		
		// 從容器中獲得 MessagePrinter 的例項
		MessagePrinter printer = context.getBean(MessagePrinter.class);
		
		// 使用物件
		printer.printMessage();
	}
}

我們也可以設定全域性設定哪些物件不引數自動注入。

<?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"
        default-autowire-candidates="messageServiceDBImpl">

	<!-- 
		全域性設定名為 messageServiceDBImpl 不參與自動注入
		可以指定多個值，逗號分隔
	-->
	
	<!-- 
		兩個物件繼承自同一介面
	 -->
	<bean id = "messageServiceDBImpl" class="shangbo.spring.example39.MessageServiceDBImpl"/>
	<bean class="shangbo.spring.example39.MessageServiceFileImpl"/>
	<bean class="shangbo.spring.example39.MessagePrinter"/>
	
</beans>

–
– 聲 明：轉載請註明出處
– Last Updated on 2017-05-25
– Written by ShangBo on 2017-05-25
– End