[Spring] 基于注解来配置Bean

于 2017-09-06 12:57:18 发布
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分类专栏： Spring 文章标签： spring 注解 bean
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本文链接：https://blog.youkuaiyun.com/u010216743/article/details/77865081
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本文介绍Spring框架中组件扫描的基本原理及配置方法，包括如何使用注解如@Component、@Service等进行组件标记，并通过<context:component-scan>进行组件扫描。此外还探讨了组件装配的细节，包括@Autowired和@Qualifier的用法。

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Bean的配置方式

  • 基于XML文件的方式
  • 基于注解的方式（基于注解配置Bean，基于注解来装配Bean的属性）

在classpath中扫描组件

  • 组件扫描：Spring能够从classpath下自动扫描、侦测和实例化具有特定注解的组件

  • 特定组件包括：

    • @component：基本注解，标识了一个受Spring管理的组件
    • @Respositoy：标识持久层组件
    • @Service：标识服务层组件
    • @Controller：标识表现层组件

  • 对于扫描到的组件，Spring有默认的命名规则，使用非限定类名，第一个字母小写，也可以在注解中通过value属性标识组件的名称

  • 当在组件类中使用了特定的注解后，还需要在Spring的配置文件中声明<context:component-scan>：

    • TestObject.java
    package com.glemontree.spring.annotation;

import org.springframework.stereotype.Component;

@Component
public class TestObject {

}
    • UserController.java
    package com.glemontree.spring.annotation.controller;

import org.springframework.stereotype.Controller;

@Controller
public class UserController {
    public void execute() {
        System.out.println("UserController execute...");
    }
}
    • UserRepository.java UserRepositoryImpl.java
    package com.glemontree.spring.annotation.repository;

public interface UserRepository {
    void save();
}
    package com.glemontree.spring.annotation.repository;

import org.springframework.stereotype.Repository;

@Repository("userRepository")
public class UserRepositoryImpl implements UserRepository {

    public void save() {
        // TODO Auto-generated method stub
        System.out.println("UserRepository Save...");
    }

}
    • UserService.java
    package com.glemontree.spring.annotation.sevice;

import org.springframework.stereotype.Service;

@Service
public class UserService {
    public void add() {
        System.out.println("UserService add...");
    }
}
    • 配置文件：
    <?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-4.0.xsd">
    <!--扫描com.glemontree.spring.annotation包及其子包-->
    <context:component-scan base-package="com.glemontree.spring.annotation">
    </context:component-scan>
</beans>
    • 测试方法
    package com.glemontree.spring.annotation;

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

import com.glemontree.spring.annotation.controller.UserController;
import com.glemontree.spring.annotation.repository.UserRepository;
import com.glemontree.spring.annotation.sevice.UserService;

public class Main {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-annotation.xml");
        TestObject to = (TestObject) ctx.getBean("testObject");
        System.out.println(to);

        UserController uc = (UserController) ctx.getBean("userController");
        System.out.println(uc);

        UserService us = (UserService) ctx.getBean("userService");
        System.out.println(us);

        UserRepository ur = (UserRepository) ctx.getBean("userRepository");
        System.out.println(ur);
    }
}

    • 解析：

    • base-package：指定一个需要扫描的基类包，Spring将会扫描这个基类包里极其子包里的所有类

    • 当需要扫描多个包时，可以使用逗号分隔

    • 如果仅希望扫描特定的类而非基包下的所有类，可使用resource-pattern属性过滤特定的类：

      <!--可以通过resource-pattern指定扫描的资源-->
<context:component-scan
                      base-package="com.glemontree.spring.beans"
                      resource-pattern:"autowire/*.class"/>

    • <context:include-filter>子结点表示包含哪些指定表达式的组件，该子结点需要use-default-filter配合使用，即设置<context:component-scan>的use-default-filter属性为false；

      <?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-4.0.xsd">
<context:component-scan 
    base-package="com.glemontree.spring.annotation"
    use-default-filters="false">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
</context:component-scan>
</beans>

    • <context:exclude-filter>子结点表示排除哪些指定表达式的组件；

      <?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-4.0.xsd">
<context:component-scan 
    base-package="com.glemontree.spring.annotation">
        <!--不包含标注了@Repository的类-->
    <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
</context:component-scan>
</beans>

    • <context:component-scan>下可以包含多个<context:include-filter>和<context:exclude-filter>子结点

    • <context:include-filter>和<context:exclude-filter>子结点支持多种类型的过滤表达式，常用的有：

      • annotation：所有标注了xxxAnnotation的类
      <?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-4.0.xsd">
    <context:component-scan 
        base-package="com.glemontree.spring.annotation">
        <!--不包含标注了@Repository的类-->
        <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
    </context:component-scan>
</beans>
      • assinable：所有继承或扩展xxxService的类
      <?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-4.0.xsd">
    <!-- <context:component-scan 
        base-package="com.glemontree.spring.annotation"
        use-default-filters="false">
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
    </context:component-scan> -->
    <context:component-scan 
        base-package="com.glemontree.spring.annotation"
        use-default-filters="true">
        <!--排除所有UserRepository和继承自UserRepository的类-->
        <context:exclude-filter type="assignable" expression="com.glemontree.spring.annotation.repository.UserRepository"/>
    </context:component-scan>
</beans>
      <?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-4.0.xsd">
    <!-- <context:component-scan 
        base-package="com.glemontree.spring.annotation"
        use-default-filters="false">
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
    </context:component-scan> -->
    <context:component-scan 
        base-package="com.glemontree.spring.annotation"
        use-default-filters="false">
        <context:include-filter type="assignable" expression="com.glemontree.spring.annotation.repository.UserRepository"/>
    </context:component-scan>
</beans>

组件装配

<context:component-scan>元素还会自动注册AutowiredAnnotationBeanPostProcessor实例，该实例可以自动装配具有@Autowired和@Resource、@Inject注解的属性。

  • Autowired：可以自动装配具有兼容类型的单个Bean属性

    • 构造器、普通字段（即使是非public）以及一切具有参数的方法都可以应用@Autowired注解

    • 默认情况下，所有使用@Autowired注解的属性都要被设置，当Spring找不到匹配的Bean装配属性时，会抛出异常，若某一属性允许不被设置，可以设置@Autowired注解的required属性为false

    • 默认情况下，当IOC容器里存在多个类型兼容Bean时，通过类型的自动装配将无法工作，此时可以在@Qualifier注解里提供Bean的名称，Spring允许对方法的入参标注@Qualifier以指定注入Bean的名称：

    package com.glemontree.spring.annotation.sevice;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

import com.glemontree.spring.annotation.repository.UserRepository;

@Service
public class UserService {

    private UserRepository userRepository;

    @Autowired
    @Qualifier("userRepositoryImpl") // 通过@Qualifier指定Bean的名称，注意是bean的名称而不是类的名称
    public void setUserRepository(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    public void add() {
        System.out.println("UserService add...");
        userRepository.save();
    }
}

    另外一种写法如下：

    package com.glemontree.spring.annotation.sevice;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

import com.glemontree.spring.annotation.repository.UserRepository;

@Service
public class UserService {

    private UserRepository userRepository;

    // 将@Qualifier写在入参的前面
    @Autowired
    public void setUserRepository(@Qualifier("userRepositoryImpl")UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    public void add() {
        System.out.println("UserService add...");
        userRepository.save();
    }
}

泛型依赖注入

  • BaseRepository.java

    package com.glemontree.spring.generic.di;

public class BaseRepository<T> {

}

  • BaseService.java

    package com.glemontree.spring.generic.di;

import org.springframework.beans.factory.annotation.Autowired;

public class BaseService<T> {
    // BaseService依赖于BaseRepository，通过@Autowired建立关系
@Autowired
protected BaseRepository<T> repository;
public void add() {
    System.out.println("add...");
    System.out.println(repository);
}
}

  • User.java

    package com.glemontree.spring.generic.di;

public class User {

}

  • UserRepositpry.java

    package com.glemontree.spring.generic.di;

import org.springframework.stereotype.Repository;

// 通过@Repository注解注册bean
@Repository
public class UserRepository extends BaseRepository<User>{

}

  • UserService.java

    package com.glemontree.spring.generic.di;

import org.springframework.stereotype.Service;

// 通过@Service注解注册bean
@Service
public class UserService extends BaseService<User>{

}

  • beans-generic-di.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-4.0.xsd">

// 通过下面这段话UserRepository和UserService两个bean会被注册
<context:component-scan base-package="com.glemontree.spring.generic.di"></context:component-scan>
</beans>

虽然UserService和UserRepository之间并没有建立直接的联系，但是两个泛型类BaseService<T>和BaseRepository<T>之间通过@Autowired建立了联系，因此它们的两个子类UserService和UserRepository也建立了联系。

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