（009）Spring Boot之EnableAutoConfiguration注解详解以及装配其它项目中的bean示例

　　EnableAutoConfiguration注解功能是启动自动配置，SpringBootApplication注解包含EnableAutoConfiguration，所以在启动类上添加SpringBootApplication可以启动自动配置。如图：

 　　该注解可以设置两个属性，exclude和excludeName根据类型或者类的名字排除bean，如下：

　　第83行spring.boot.enableautoconfiguration是指在application.properties中其值要为true（默认true），否则不会自动配置。该注解的导入类

　　AutoConfigurationImportSelector的selectImports方法如下：

　　首先判断application.properties中spring.boot.enableautoconfiguration是否为true，后面调用getCandidateConfigurations方法，如下：

 　　红框标记出在META-INF/spring.factories文件中的配置要加载。请看下面示例：

　　1、新建项目core-bean

　　pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.edu.core</groupId>
    <artifactId>core-bean</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <name>springboot</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>
    
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.3.2.RELEASE</version>
        </dependency>
    </dependencies>

</project>

　　Role.java

package com.edu.core.bean;

public class Role {

}

　　User.java

package com.edu.core.bean;

public class User {

}

　　RunnableConfiguration.java

package com.edu.core.bean;

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

@Configuration
public class RunnableConfiguration {

    @Bean
    public Runnable createRunnable(){
        return () -> {};
    }
}

　　UserConfiguration.java

package com.edu.core.bean;

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

@Configuration
public class UserConfiguration {

    @Bean
    public User createUser(){
        return new User();
    }
}

　　resources/META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.edu.core.bean.RunnableConfiguration,com.edu.core.bean.UserConfiguration,com.edu.core.bean.Role

　　2、新建项目test

　　pom.xml，要把上面项目的依赖加进来

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.edu.spring</groupId>
    <artifactId>springboot</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <name>springboot</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>
    
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.1.6.RELEASE</version>
                <scope>import</scope>
                <type>pom</type>
            </dependency>
        </dependencies>
    </dependencyManagement>
    
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>com.edu.core</groupId>
            <artifactId>core-bean</artifactId>
            <version>1.0.0</version>
        </dependency>
    </dependencies>

</project>

　　App.java

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import com.edu.core.bean.Role;
import com.edu.core.bean.User;

@EnableAutoConfiguration
@ComponentScan
public class App 
{
    public static void main( String[] args )
    {
        ConfigurableApplicationContext context=SpringApplication.run(App.class,args);
        System.out.println(context.getBean(Runnable.class));
        System.out.println(context.getBean(User.class));
        System.out.println(context.getBean(Role.class));
        context.close();
    }
}

　　运行结果如下：

 　　可以看到，通过在项目core-bean的resources/META-INF/spring.factories中设置相关属性，其他项目便可装配bean。

　　在test项目的application.properties中设置spring.boot.enableautoconfiguration=false，运行无法获取bean，如下：

 　　根据类名排除装配bean：

　　App.java

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import com.edu.core.bean.User;

@EnableAutoConfiguration(excludeName= {"excludeName","com.edu.core.bean.RunnableConfiguration"})
@ComponentScan
public class App 
{
    public static void main( String[] args )
    {
        ConfigurableApplicationContext context=SpringApplication.run(App.class,args);
        //System.out.println(context.getBean(Runnable.class));
        System.out.println(context.getBean(User.class));
        //System.out.println(context.getBean(Role.class));
        context.close();
    }
}

　　根据类排除装配bean：

　　App.java

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import com.edu.core.bean.Role;
import com.edu.core.bean.RunnableConfiguration;
import com.edu.core.bean.User;

@EnableAutoConfiguration(exclude= {Role.class,RunnableConfiguration.class})
@ComponentScan
public class App 
{
    public static void main( String[] args )
    {
        ConfigurableApplicationContext context=SpringApplication.run(App.class,args);
        //System.out.println(context.getBean(Runnable.class));
        System.out.println(context.getBean(User.class));
        //System.out.println(context.getBean(Role.class));
        context.close();
    }
}

　　以上两种配置都可以排除bean，需要注释掉获取相关bean的代码，否则程序报错。

　　总结： （1）EnableAutoConfiguration 从classpath搜索所有META-INF/spring.factories配置文件，将其中的配置项装配成bean，加载到spring容器

                   （2）application.properties中，spring.boot.enableautoconfiguration=true 时才生效，默认true

                   （3）可以使用exclude或者excludeName根据类型或者类名排除不需要的bean