创建一个springboot starter页面

环境
java1.8
springboot 2.7.1
pom.xml文件
项目目录

<?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>2.7.1</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.yestea</groupId><artifactId>digest-spring-boot-starter</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>digest-spring-boot-starter</name><description>digest-spring-boot-starter</description><url/><licenses><license/></licenses><developers><developer/></developers><scm><connection/><developerConnection/><tag/><url/></scm><properties><java.version>1.8</java.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-tomcat</artifactId><scope>provided</scope></dependency><dependency><groupId>commons-codec</groupId><artifactId>commons-codec</artifactId><version>1.17.1</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><!--    <build>-->
<!--        <plugins>-->
<!--            <plugin>-->
<!--                <groupId>org.springframework.boot</groupId>-->
<!--                <artifactId>spring-boot-maven-plugin</artifactId>-->
<!--            </plugin>-->
<!--        </plugins>-->
<!--    </build>--></project>

application.properties

spring.application.name=digest-spring-boot-starter
digest.type=md5

service目录
Digest.java 接口

package com.yestea.service;public interface Digest {String digest(String raw);
}

impl目录接口实现类
Md5Digest.java

package com.yestea.service.impl;import com.yestea.service.Digest;
import org.apache.commons.codec.digest.DigestUtils;public class Md5Digest implements Digest {public String digest(String raw) {System.out.println("使用MD5加密");return DigestUtils.md5Hex(raw);}
}

ShaDigest.java实现接口

package com.yestea.service.impl;import com.yestea.service.Digest;
import org.apache.commons.codec.digest.DigestUtils;public class ShaDigest implements Digest {public String digest(String raw) {System.out.println("使用SHA1加密");return DigestUtils.sha1Hex(raw);}
}

config目录setting.java 读取application.properties配置信息加载到类

package com.yestea.config;import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.stereotype.Component;//@Component
@ConfigurationProperties(prefix = "digest")
public class setting {private String type;public String getType() {return type;}public void setType(String type) {this.type = type;}
}

config.java

package com.yestea.config;import com.yestea.service.Digest;
import com.yestea.service.impl.Md5Digest;
import com.yestea.service.impl.ShaDigest;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
@EnableConfigurationProperties(setting.class)
public class config {@Bean@ConditionalOnProperty(prefix = "digest", name = "type", havingValue = "md5")public Digest Md5Digest(){return new Md5Digest();}@Bean@ConditionalOnProperty(prefix = "digest", name = "type", havingValue = "sh")public Digest ShaDigest(){return new ShaDigest();}
}

EnableConfigurationProperties

@EnableConfigurationProperties 是 Spring Boot 提供的一个注解，主要作用如下：
启用配置属性功能
用于启用 @ConfigurationProperties 注解的类，使其能够从配置文件中自动绑定属性值
只有在添加了 @EnableConfigurationProperties 后，@ConfigurationProperties 注解的类才会被 Spring 容器管理
自动注册配置属性类
将指定的 @ConfigurationProperties 类注册为 Spring Bean
无需手动使用 @Component 或 @Configuration 

DigestSpringBootStarterApplication.java

package com.yestea;import com.yestea.config.setting;
import com.yestea.service.Digest;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;import javax.annotation.Resource;//@SpringBootApplication
public class DigestSpringBootStarterApplication {public static void main(String[] args) {ConfigurableApplicationContext run = SpringApplication.run(DigestSpringBootStarterApplication.class, args);setting bean = run.getBean(setting.class);System.out.println(bean);
//        Digest bean1 = run.getBean(Digest.class);
//        System.out.println(bean1);}}

注意打包成jar包时候@SpringBootApplication必须删除不然会提示有两个无法执行
下面是重头戏，引用时候必须知道从什么地方读取
resources目录下创建META-INF创建spring.factories文件

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.yestea.config.config

为什么是这个目录这个需要看源码
点开SpringBootApplication注解可以看到

public @interface SpringBootApplication {@AliasFor(annotation = EnableAutoConfiguration.class)Class<?>[] exclude() default {};@AliasFor(annotation = EnableAutoConfiguration.class)String[] excludeName() default {};@AliasFor(annotation = ComponentScan.class,attribute = "basePackages")String[] scanBasePackages() default {};@AliasFor(annotation = ComponentScan.class,attribute = "basePackageClasses")Class<?>[] scanBasePackageClasses() default {};@AliasFor(annotation = ComponentScan.class,attribute = "nameGenerator")Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;@AliasFor(annotation = Configuration.class)boolean proxyBeanMethods() default true;
}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({AutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";Class<?>[] exclude() default {};String[] excludeName() default {};
}

AutoConfigurationImportSelector.class注解
摘抄一部分内容可以看到

    protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {List<String> configurations = new ArrayList(SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader()));ImportCandidates.load(AutoConfiguration.class, this.getBeanClassLoader()).forEach(configurations::add);Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you are using a custom packaging, make sure that file is correct.");return configurations;}

接下来进行maven clean install 本地仓库打包之后另外项目引入pom.xml文件
测试代码

package com.yestea;import com.yestea.service.Digest;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
@SpringBootTest
public class MybatisPlus01test3 {@Autowiredprivate Digest digest;@Testpublic void test01(){System.out.println(digest.digest("123456"));}
}

执行结果

使用SHA1加密
7c4a8d09ca3762af61e59520943dc26494f8941b