自定义Starters(自动配置Bean)

1,创建Spring Startes Project的项目

2,修改pom.xml文件如下：

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>gjx.comMVC_demo2</groupId>
    <artifactId>spring_boot_mystarters</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>spring_boot_mystarters</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>11</java.version>
    </properties>
    <dependencies>
        
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- 增加自身的自动配置 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
            
        </dependency>
        <!-- 增加自身的自动配置 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

3，创建属性配置类

作用：用来自动配置bean所需要的参数

package gjx.comIOC_demo2.spring_boot_mystarters;

import org.springframework.boot.context.properties.ConfigurationProperties;
//读取对应的配置文件中的属性到配置类中
@ConfigurationProperties(prefix = "my")
public class MyProperties {
    private static String msg="天师默认值";
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg=msg;
    }
}

4，创建将要自动配置（注入的类）

package gjx.comIOC_demo2.spring_boot_mystarters;

public class MyService {
    private String msg;
    public String sayMsg() {
        return "my"+msg;
    }
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg=msg;
    }
}

5，创建自动配置的类

@Configuration
//开启属性配置类提供的参数来配置MyService类
@EnableConfigurationProperties(MyProperties.class)
//类加载器（类路径中）是否存在MyService.class指定的类
@ConditionalOnClass(MyService.class)
//应用环境中属性是否存在指定的值
@ConditionalOnProperty(prefix = "my",value = "enabled",matchIfMissing = true)

public class MyAutoConfiguration {
    @Autowired
    private MyProperties myProperties;
    @Bean
    //当容器中不存在MyService的Bean时自动配置这个Bean
    @ConditionalOnMissingBean(MyService.class)
    public MyService myService() {
        MyService myService=new MyService();
        //用属性配置类中的属性进行配置
        myService.setMsg(myProperties.getMsg());
        return myService;
    }
}

6，注册配置

作用：告诉Spring Boot这个是可以自动配置的

在resource/META-INF/spring.factories文件

org.springframework.boot.autoconfigure.EnableAutoConfiguration=
gjx.comIOC_demo2.spring_boot_mystarters.MyAutoConfiguration

注意： 的作用是换行后依然可以读取，有多个自动配置用  ，(逗号)分离