1、手动声明组件

一个正常的 bean.

package com.h3.customer.dao;

public class customerdao 
{
	@override
	public string tostring() {
		return "hello , this is customerdao";
	}	
}

dao 层.

package com.h3.customer.services;

import com.h3.customer.dao.customerdao;

public class customerservice 
{
	customerdao customerdao;

	public void setcustomerdao(customerdao customerdao) {
		this.customerdao = customerdao;
	}

	@override
	public string tostring() {
		return "customerservice [customerdao=" + customerdao + "]";
	}
		
}

<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-2.5.xsd">
	
	<bean id="customerservice" class="com.h3.customer.services.customerservice">
		<property name="customerdao" ref="customerdao" />
	</bean>

	<bean id="customerdao" class="com.h3.customer.dao.customerdao" />

</beans>

执行程序

package com.h3.common;

import org.springframework.context.applicationcontext;
import org.springframework.context.support.classpathxmlapplicationcontext;

import com.h3.customer.services.customerservice;

public class app 
{
    public static void main( string[] args )
    {
    	applicationcontext context = 
    	  new classpathxmlapplicationcontext(new string[] {"spring-customer.xml"});

    	customerservice cust = (customerservice)context.getbean("customerservice");
    	system.out.println(cust);
    	
    }
}

输出结果

customerservice [customerdao=hello , this is customerdao]

2. 自动组件扫描

package com.h3.customer.dao;

import org.springframework.stereotype.component;

@component
public class customerdao 
{
	@override
	public string tostring() {
		return "hello , this is customerdao";
	}	
}

package com.h3.customer.services;

import org.springframework.beans.factory.annotation.autowired;
import org.springframework.stereotype.component;

import com.h3.customer.dao.customerdao;

@component
public class customerservice 
{
	@autowired
	customerdao customerdao;

	@override
	public string tostring() {
		return "customerservice [customerdao=" + customerdao + "]";
	}
} 

将这个“context:component”在bean配置文件，这意味着，在 spring 中启用自动扫描功能。base-package 是指明存储组件，spring将扫描该文件夹，并找出bean(注解为@component)并注册到 spring 容器。

<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:component-scan base-package="com.h3.customer" />

</beans>

执行它

package com.h3.common;

import org.springframework.context.applicationcontext;
import org.springframework.context.support.classpathxmlapplicationcontext;

import com.h3.customer.services.customerservice;

public class app 
{
    public static void main( string[] args )
    {
    	applicationcontext context = 
    	   new classpathxmlapplicationcontext(new string[] {"spring-autoscan.xml"});

    	customerservice cust = (customerservice)context.getbean("customerservice");
    	system.out.println(cust);
    	
    }
}

输出结果

customerservice [customerdao=hello , this is customerdao]

自定义自动扫描组件名称

customerservice cust = (customerservice)context.getbean("customerservice");

要创建组件的自定义名称，你可以这样自定义名称：

@service("aaa")
public class customerservice 
...

customerservice cust = (customerservice)context.getbean("aaa");

自动组件扫描注释类型

• @component – 指示自动扫描组件。
• @repository – 表示在持久层dao组件。
• @service – 表示在业务层服务组件。
• @controller – 表示在表示层控制器组件。

@target({elementtype.type})
@retention(retentionpolicy.runtime)
@documented
@component
public @interface repository {

	string value() default "";

} 

你可能会发现，所有的 @repository, @service 或 @controller 被注解为 @component。因此，我们可以只使用 @component 对所有组件进行自动扫描？是的，spring会自动扫描所有组件的 @component 注解。

dao 层

package com.h3.customer.dao;

import org.springframework.stereotype.repository;

@repository
public class customerdao 
{
	@override
	public string tostring() {
		return "hello , this is customerdao";
	}	
}

service 层

package com.h3.customer.services;

import org.springframework.beans.factory.annotation.autowired;
import org.springframework.stereotype.service;

import com.h3.customer.dao.customerdao;

@service
public class customerservice 
{
	@autowired
	customerdao customerdao;

	@override
	public string tostring() {
		return "customerservice [customerdao=" + customerdao + "]";
	}
		
}