<context:component-scan>

<context:component-scan>：扫描指定包，如果发现有指定注解，那么该类将由Spring进行管理。

举例子：

package com.zhangpn.componentScan;

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

@Component("user")
public class User {

    @Value(value = "1")
    private String id;

    @Value(value = "zhangpn")
    private String name;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + "]";
    }

}

package com.zhangpn.componentScanS;

import javax.annotation.Resource;

import org.springframework.stereotype.Component;

import com.zhangpn.componentScan.User;

@Component("person")
public class Person {
    
    @Resource(name = "user")
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Person [user=" + user + "]";
    }

}

<?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-4.3.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">

</beans>

由componentScan.xml可知，我们忘记了写<context:component-scan>标签，也就是没有开启注解扫描。此时，执行一个测试方法会出现什么结果呢？

package com.zhangpn.componentScanTest;

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

import com.zhangpn.componentScanS.Person;

public class Main {

    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("componentScan.xml");
        Person person = (Person) applicationContext.getBean("person");
        System.out.println(person);
    }

}

测试结果显示：

六月 11, 2018 9:36:46 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@179d3b25: startup date [Mon Jun 11 09:36:46 CST 2018]; root of context hierarchy
六月 11, 2018 9:36:46 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [componentScan.xml]
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'person' available
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:680)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1183)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:284)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1081)
    at com.zhangpn.componentScanTest.Main.main(Main.java:12)

抛出了org.springframework.beans.factory.NoSuchBeanDefinitionException异常，意思就是No bean named 'person' available不能获得一个名字叫'person'的bean，可以得出，componentScan.xml加载后，并没有扫描到我们想得到的类。

---

接下来，我们把<context:component-scan>标签加上

<?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-4.3.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">
    <context:component-scan base-package="com.zhangpn.*"></context:component-scan>
</beans>

base-package="com.zhangpn.*" 意思扫描com.zhangpn包以及子包，再次测试：

六月 11, 2018 9:45:03 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@179d3b25: startup date [Mon Jun 11 09:45:03 CST 2018]; root of context hierarchy
六月 11, 2018 9:45:03 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [componentScan.xml]
Person [user=User [id=1, name=zhangpn]]

由结果可以得到：这样就是我们想要的结果。

---

 

由标签<context:component-scan base-package="com.zhangpn.*"></context:component-scan>可以看出：com.zhangpn.* 其中“ * ”代表匹配com.zhangpn下任意子包。

也可以这样表示：

<context:component-scan base-package="com.zhangpn.componentScan,com.zhangpn.componentScanS"></context:component-scan>

把每一个包都表示出来。

---

 

    <context:component-scan base-package="com.zhangpn.componentScan"></context:component-scan>
    <context:component-scan base-package="com.zhangpn.componentScanS"></context:component-scan>

---

说明： “ * ” 匹配：例如 "com.zhangpn.*"表示，以“com.zhangpn.”开头的包都会被Spring扫描到

<context:component-scan base-package="*"></context:component-scan>

以上标签表示扫描所有的包。