[Spring]Method Injection

原創

HeapStackk

2020-02-20 20:03

Spring-framwork 提供了一种基于方法级的注入方式

考虑一种情况，一个singleton A 和一个 prototype B，A中有一个方法每次执行的时候都需要一个B的实例，由于Spring容器在初始A的时候已经初始好一切，那么这个时候如何做到每次执行该方法的时候，提供一个依赖B呢？

解决有两种方法：

1.通过实现 ApplicationContextAware 接口，硬编码实现每次调用该方法的时候注入一个实例B，然而这种方法会使代码和注入过程耦合在一起

2.提供一个abstract方法，Spring使用CGLIB重写抽象方法提供注入（Method Injection）

方法注入，提供了方法级的注入方式，保证每次执行到该方法的时候都会提供一个新的B实例来使用，由Spring容器通过配置完成解耦工作。

Command接口：

package com.interfaces;

public interface Command {
	void setState(String commandState);
	String execute();
}

Command实现：

package com.domain;

import com.interfaces.Command;

public class AttackCommand implements Command {
	private String commandState;
	private static int count = 0;
	private final int id = count++;
	public AttackCommand() {
		System.out.println("command init");
	}

	public String execute() {
		return "Attack Command " + id + ": starting attack " + commandState;
	}


	public void setState(String commandState) {
		this.commandState = commandState;
	}
}

Method 1:

package com.domain;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

import com.interfaces.Command;

public class CoupleCommandManager implements ApplicationContextAware {
	private ApplicationContext applicationContext;

	public String process(String commandState) {
		Command command = createCommand();
		command.setState(commandState);
		return command.execute();
	}

	protected Command createCommand() {
		return applicationContext.getBean("attackCommand", Command.class);
	}

	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
		this.applicationContext = applicationContext;
	}

}

Method 2:

package com.domain;

import com.interfaces.Command;

public abstract class CommandManager {
	public String process(String commandState){
		Command command = createCommand();
		command.setState(commandState);
		return command.execute();
	}
	
	protected abstract Command createCommand();
	
}

xml配置文件

	<bean id="attackCommand" class="com.domain.AttackCommand" scope="prototype"/>
	
	<bean id="coupleCommandManager" class="com.domain.CoupleCommandManager"></bean>
	<bean id="commandManager" class="com.domain.CommandManager">
		<lookup-method name="createCommand" bean="attackCommand"/>
	</bean>

java cfg:

 @Bean
	@Scope("prototype")
	public Command attackCommand() {
		return new AttackCommand();
	}

	@Bean
	public CommandManager commandManager() {
		return new CommandManager() {

			@Override
			protected Command createCommand() {
				return attackCommand();
			}
		};
	}