Spring自动扫描组件

作者: 攻城狮susht | 来源:发表于2020-04-27 11:52 被阅读0次

Spring将所有的bean都纳入到IoC中创建、管理和维护，一个系统往往有成千上万的组件，如果需要手动将所有组件都放入spring容器中去管理，这样spring配置文件将变得非常冗余且庞大，管理也将十分不方便。

从Spring2.5开始引入了组件自动扫描机制，你可以不用在xml文件中配置繁琐的bean，Spring会自动扫描、检查你指定包的bean或component。

Spring容器提供了@Component和@Bean注解来标记如何向IoC容器添加Bean。在@Component基础上又派生出

@Controller， @Service和@Repository这三个注解（在其他的Spring工程或包中还有更多的派生）。

@Controller、@Service和@Repository注释是在@Component基础上添加了角色的组件，它们分别用于表示层、服务层和数据访问层。

下面是一个简单的Spring项目，包括自定义的service和dao层。我们研究一下在Spring中手动声明组件和自动扫描组件之间的区别。

1、手动声明组件

创建EmployeeServicebean ，如下所示。

EmployeeService.java

package com.wxbsht.spring.componentscan.example.service;

import com.wxbsht.spring.componentscan.example.dao.EmployeeDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * @author HP-susht
 * @create 2020/4/27 11:31
 */

public class EmployeeService {

    private EmployeeDao employeeDao;
    
    public void setEmployeeDao(EmployeeDao employeeDao) {
        this.employeeDao = employeeDao;
    }

    public void doSomething(){
        System.out.println("Inside EmployeeService's doSomething() method.");
        employeeDao.doSomething();
    }
}

创建EmployeeDaobean ，如下所示。

EmployeeDao.java

package com.wxbsht.spring.componentscan.example.dao;

import org.springframework.stereotype.Repository;

/**
 * @author HP-susht
 * @create 2020/4/27 11:32
 */
public class EmployeeDao {

    public void doSomething() {
        System.out.println("Inside EmployeeDao's doSomething() method.");
    }
}

Bean配置文件(beans.xml)， Spring中的普通Bean配置。

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

    <bean id="employeeDao" class="com.wxbsht.spring.componentscan.example.dao.EmployeeDao"/>
    <bean id="employeeService" class="com.wxbsht.spring.componentscan.example.service.EmployeeService">
        <property name="employeeDao" ref="employeeDao"/>
    </bean>
</beans>

运行主程序MainApplication.java

package com.wxbsht.spring.componentscan.example;

import com.wxbsht.spring.componentscan.example.config.AppConfig;
import com.wxbsht.spring.componentscan.example.service.EmployeeService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author HP-susht
 * @create 2020/4/27 11:35
 */
public class MainApplication {
    public static void main(String[] args) {
        ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
        EmployeeService service = context.getBean(EmployeeService.class);
        service.doSomething();
    }
}

输出

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

2、自动扫描组件

在Spring框架中，我们可以使用以下命令来启用组件自动扫描

<context:component-scan/>基于XML的配置中的元素
@ComponentScan 基于Java的配置中的注释
AnnotationConfigApplicationContext#scan()方法

2.1、创建Spring组件

创建EmployeeServicebean ，如下所示。

EmployeeService.java

package com.wxbsht.spring.componentscan.example.service;

import com.wxbsht.spring.componentscan.example.dao.EmployeeDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * @author HP-susht
 * @create 2020/4/27 11:31
 */

@Service
public class EmployeeService {

    @Autowired
    private EmployeeDao employeeDao;

    public void doSomething(){
        System.out.println("Inside EmployeeService's doSomething() method.");
        employeeDao.doSomething();
    }
}

创建EmployeeDaobean ，如下所示。

EmployeeDao.java

package com.wxbsht.spring.componentscan.example.dao;

import org.springframework.stereotype.Repository;

/**
 * @author HP-susht
 * @create 2020/4/27 11:32
 */

@Repository
public class EmployeeDao {

    public void doSomething() {
        System.out.println("Inside EmployeeDao's doSomething() method.");
    }
}

2.2、使用<context：component-scan />元素启用组件扫描

要在基于XML的配置中启用自动组件扫描，使用以下<context:component-scan base-package=""/>元素。

beans.xml

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

     <!--<context:component-scan base-package="com.wxbsht.spring.componentscan.example"/>-->
    
    <context:component-scan base-package="com.wxbsht.spring.componentscan.example.service,
                                         com.wxbsht.spring.componentscan.example.dao"/>
</beans>

运行应用程序MainApplication.java

package com.wxbsht.spring.componentscan.example;

import com.wxbsht.spring.componentscan.example.config.AppConfig;
import com.wxbsht.spring.componentscan.example.service.EmployeeService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author HP-susht
 * @create 2020/4/27 11:35
 */
public class MainApplication {
    public static void main(String[] args) {
        ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
        EmployeeService service = context.getBean(EmployeeService.class);
        service.doSomething();
    }
}

输出

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

2.3、使用@ComponentScan注解启用组件扫描

要在基于Java的配置中启用自动组件扫描。

AppConfig.java

package com.wxbsht.spring.componentscan.example.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @author HP-susht
 * @create 2020/4/27 11:37
 */
@Configuration
@ComponentScan(basePackages = { "com.wxbsht.spring.componentscan.example.dao",
        "com.wxbsht.spring.componentscan.example.service"})
public class AppConfig {
}

运行应用程序。

MainApplication.java

package com.wxbsht.spring.componentscan.example;

import com.wxbsht.spring.componentscan.example.config.AppConfig;
import com.wxbsht.spring.componentscan.example.service.EmployeeService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author HP-susht
 * @create 2020/4/27 11:35
 */
public class MainApplication {
    public static void main(String[] args) {
//        ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
//        EmployeeService service = context.getBean(EmployeeService.class);
//        service.doSomething();

        ApplicationContext context1=new AnnotationConfigApplicationContext(AppConfig.class);
        EmployeeService service1 = context1.getBean(EmployeeService.class);
        service1.doSomething();

    }
}

输出

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

2.4、使用上下文的scan（）方法启用组件扫描

不使用XML或基于java的配置，我们可以使用以下注释configapplicationcontext #scan()方法启用组件扫描。

MainApplication.java

package com.wxbsht.spring.componentscan.example;

import com.wxbsht.spring.componentscan.example.config.AppConfig;
import com.wxbsht.spring.componentscan.example.service.EmployeeService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author HP-susht
 * @create 2020/4/27 11:35
 */
public class MainApplication {
    public static void main(String[] args) {
//        ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
//        EmployeeService service = context.getBean(EmployeeService.class);
//        service.doSomething();

//        ApplicationContext context1=new AnnotationConfigApplicationContext(AppConfig.class);
//        EmployeeService service1 = context1.getBean(EmployeeService.class);
//        service1.doSomething();


        AnnotationConfigApplicationContext context3 =
                new AnnotationConfigApplicationContext();

        context3.scan("com.wxbsht.spring.componentscan.example.service");
        context3.scan("com.wxbsht.spring.componentscan.example.dao");
        context3.refresh();

        EmployeeService service3 = context3.getBean(EmployeeService.class);
        service3.doSomething();
        context3.close();

    }
}

输出

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

2.5、自定义自动扫描组件名称

默认情况下，Spring将组件类名首字母小写后作为组件在容器中的id(employeeService)。您可以使用此名称“employeeService”获取此组件。

    EmployeeService service = (EmployeeService)context.getBean("employeeService");

要为组件创建一个自定义名称，您可以按如下代码自定义名称：

@Service("AAA")
public class EmployeeService 
...

现在，您可以使用“ AAA”这个名称来获取它

    EmployeeService cust = (EmployeeService)context.getBean("AAA");

Spring自动扫描组件

1、手动声明组件

2、自动扫描组件

2.1、创建Spring组件

2.2、使用<context：component-scan />元素启用组件扫描

2.3、使用@ComponentScan注解启用组件扫描

2.4、使用上下文的scan（）方法启用组件扫描

2.5、自定义自动扫描组件名称

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