如何实现自定义SpringBoot的Starter组件
作者:令狐前生
一、前言
想要自定义starter组件,首先要了解springboot是如何加载starter的,也就是springboot的自动装配机制原理。
1.1、starter加载原理
springboot通过一个@SpringBootApplication注解启动项目,springboot在项目启动的时候,会将项目中所有声明为Bean对象(注解、xml)的实例信息全部加载到ioc容器当中。 除此之外也会将所有依赖到的starter里的bean信息加载到ioc容器中,从而做到所谓的零配置,开箱即用。
1.1.1、加载starter
首先通过通过注解@SpringBootApplication找到@EnableAutoConfiguration注解进行加载starter。
再通过注解@EnableAutoConfiguration下注解@import找到AutoConfigurationImportSelector类加载器实现。
这个AutoConfigurationImportSelector类会去其引用的依赖jar包下,找到一个”spring.factories”文件,一般spring.factories文件里都会声明该依赖所提供的核心功能bean配置信息。文件一般在依赖jar包的META-INF文件夹下面。
以spring-boot版本2.7.7为例,加载spring.factories的代码在:
AutoConfigurationImportSelector.java->selectImports(AnnotationMetadata annotationMetadata)->getAutoConfigurationEntry(annotationMetadata)->getCandidateConfigurations(annotationMetadata, attributes)->SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader())->loadSpringFactories(classLoaderToUse):
private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) { Map<String, List<String>> result = (Map)cache.get(classLoader); if (result != null) { return result; } else { HashMap result = new HashMap(); try { Enumeration urls = classLoader.getResources("META-INF/spring.factories"); while(urls.hasMoreElements()) { URL url = (URL)urls.nextElement(); UrlResource resource = new UrlResource(url); Properties properties = PropertiesLoaderUtils.loadProperties(resource); Iterator var6 = properties.entrySet().iterator(); while(var6.hasNext()) { Entry<?, ?> entry = (Entry)var6.next(); String factoryTypeName = ((String)entry.getKey()).trim(); String[] factoryImplementationNames = StringUtils.commaDelimitedListToStringArray((String)entry.getValue()); String[] var10 = factoryImplementationNames; int var11 = factoryImplementationNames.length; for(int var12 = 0; var12 < var11; ++var12) { String factoryImplementationName = var10[var12]; ((List)result.computeIfAbsent(factoryTypeName, (key) -> { return new ArrayList(); })).add(factoryImplementationName.trim()); } } } result.replaceAll((factoryType, implementations) -> { return (List)implementations.stream().distinct().collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)); }); cache.put(classLoader, result); return result; } catch (IOException var14) { throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var14); } } }
举例如:spring-boot-autoconfig的spring.factories.
二、自定义starter
上面了解了springboot加载starter原理,其实就是加载依赖jar包下的spring.factories文件。所以我们要自定义starter,就需要在项目中建立一个META-INF的文件夹,然后在该文件夹下面建一个spring.factories文件,文件里将你需要提供出去的bean实例信息配置好就行。
2.1、代码
2.1.1、新建springboot项目。
简单演示所以需求配置任务依赖。如springboot构建很慢,或者打包的时候下载依赖很慢,可在pom文件中添加如下仓库配置,可以加快构建速度。
<repositories> <repository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </repository> </repositories> <pluginRepositories> <pluginRepository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </pluginRepository> </pluginRepositories>
注意:spring官方规定自定义组件的命名:
SpringBoot官方命名方式
格式:spring-boot-starter-{模块名}
举例:spring-boot-starter-web
自定义命名方式
格式:{模块名}-spring-boot-starter
举例:mystarter-spring-boot-starter
2.1.2、项目构建完成后,在resources文件夹下面新建META-INF文件夹,并新建spring.factories文件。
2.1.3、因为我们是作为插件来使用,所以我们不需要启动类,删除启动类。并新建几个类:
一个接口AnimalService:
package com.example.demospringbootstarter.service; /** * @Project: demo-spring-boot-starter * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 15:12 */ public interface AnimalService { String say(); }
两个接口实现类CatService和DogService:
package com.example.demospringbootstarter.service; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import org.springframework.stereotype.Service; /** * @Project: demo-spring-boot-starter * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 14:49 */ @Service public class CatService implements AnimalService{ public static String name = "cat"; @Override public String say() { return "喵喵"; } }
package com.example.demospringbootstarter.service; import org.springframework.stereotype.Service; /** * @Project: demo-spring-boot-starter * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 14:49 */ @Service public class DogService implements AnimalService{ public static String name = "dog"; @Override public String say() { return "汪汪"; } }
再建一个配置AnimalProperties类,方便注入属性值:
package com.example.demospringbootstarter.config; import lombok.Data; import org.springframework.boot.context.properties.ConfigurationProperties; /** * @Project: demo-spring-boot-starter * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 15:37 */ @Data @ConfigurationProperties(prefix = "animal") public class AnimalProperties { private String name; }
最后新建一个核心自动装备配置类:
package com.example.demospringbootstarter.config; import com.example.demospringbootstarter.service.AnimalService; import com.example.demospringbootstarter.service.CatService; import com.example.demospringbootstarter.service.DogService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.context.properties.EnableConfigurationProperties; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; /** * @Project: demo-spring-boot-starter * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 14:48 */ @Configuration @EnableConfigurationProperties(AnimalProperties.class) public class AnimalAutoConfig { @Autowired private AnimalProperties animalProperties; @Bean public AnimalService demoService(){ switch (animalProperties.getName()){ case "cat": return new CatService(); case "dog": return new DogService(); default: return null; } } }
META-INF/spring.factories的内容为:
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.example.demospringbootstarter.config.AnimalAutoConfig
以上步骤都好后,使用maven命令打包:
mvn clean install -Dmaven.test.skip=true
或者使用idea的LIfecycle点击对应操作(注意不是plugin下的命令操作)。
pom.xml内容为:
<?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>2.3.4.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.example</groupId> <artifactId>demo-spring-boot-starter</artifactId> <version>0.0.4-SNAPSHOT</version> <name>demo-spring-boot-starter</name> <description>Demo project for Spring Boot</description> <properties> <java.version>8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> </dependencies> <repositories> <repository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </repository> </repositories> <pluginRepositories> <pluginRepository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </pluginRepository> </pluginRepositories> </project>
三、组件集成依赖测试
3.1、新启另一个项目中,引入刚刚打包的pom依赖
<dependency> <groupId>com.example</groupId> <artifactId>demo-spring-boot-starter</artifactId> <version>0.0.4-SNAPSHOT</version> </dependency>
3.2、新建一个controller,里面注入上面提供的AnimalService类并调用其方法
package com.cjb.mavendemo.controllers; import com.example.demospringbootstarter.service.AnimalService; import com.example.inputoutputlogspringbootstarter.config.PrintResponseTime; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; /** * @Project: maven-demo * @Description: * @Author: chengjiangbo * @Date: 2023/2/7 10:26 */ @RestController @RequestMapping(value = "/test") public class TestController { @Autowired private AnimalService animalService; @PrintResponseTime @GetMapping("/call") public String call(){ return animalService.say(); } }
3.3、application.properties内容配置参数"animal.name"值
3.4、最后通过项目启动类启动项目(项目启动类就一个@SpringBootApplicaiton注解)
package com.cjb.mavendemo; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class MavenDemoApplication { public static void main(String[] args) { SpringApplication.run(MavenDemoApplication.class, args); } }
3.5、接口测试
调用http接口测试:
修改"animal.name"值为"cat",再次调用http接口访问:
四、源码地址,参考资料
组件代码:https://download.csdn.net/download/u010132847/87426046
集成自定义组件代码:https://download.csdn.net/download/u010132847/87426048
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