Spring SPI机制实现自动装配 实现自定义Starter组件

一. springboot的自动装配

1. @SpringBootApplication ---> @EnableAutoConfinguration ---> @Import(AutoConfigurationImportSelector.class)

2. AutoConfigurationImportSelector类实现了DeferredImportSelector接口

public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
		ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {

重写了其selectImports方法得到相关的注解配置类的全名称:

@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
				.loadMetadata(this.beanClassLoader);
		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
				annotationMetadata);
		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}

selectImprts内调用了getAutoConfigurationEntry方法,

protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
			AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return EMPTY_ENTRY;
		}
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
		configurations = removeDuplicates(configurations);
		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, exclusions);
		configurations.removeAll(exclusions);
		configurations = filter(configurations, autoConfigurationMetadata);
		fireAutoConfigurationImportEvents(configurations, exclusions);
		return new AutoConfigurationEntry(configurations, exclusions);
	}

再进入getCandidateConfiguration方法,

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
				getBeanClassLoader());
		Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "
				+ "are using a custom packaging, make sure that file is correct.");
		return configurations;
	}

最后:SpringFactoriesLoader的loadFactoryNames方法,能得到所有的spring.factories内的配置内容,告知spring相关的配置类,加载对应的bean;

public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
		String factoryClassName = factoryClass.getName();
		return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
	}

二. 根据SPI机制实现自己的自动装配类

类似于redis的使用,项目启动,可以自动注入redisTemplate,开箱即用;

注意: 这个是个普通的maven项目,完成后intall到仓库中,其他项目直接依赖使用

其中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.zsw.example</groupId>
  <artifactId>order-api</artifactId>
  <version>1.1-SNAPSHOT</version>

  <name>order-api</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>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.18.12</version>
    </dependency>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.1.7.RELEASE</version>
      <optional>true</optional><!--optional 为true , 不传递此依赖-->
    </dependency>

  </dependencies>

</project>

1. 自定义相关参数类

@Data
@ConfigurationProperties(prefix = "zsw")
public class MyRedisProperty {

    private String  host = "127.0.0.1";

    private Integer port = 6666;

    private Integer timeOut;

    private Boolean ssl;
}

2. 自定义服务端,类似于redisTemplate

@Data
public class MyRedisClient {

    private String address;

    public MyRedisClient(MyRedisProperty myRedisProperty) {
        this.address = myRedisProperty.getHost() + ":" + myRedisProperty.getPort();
    }
}

3. 自定义相关配置类,用于加载client,类似于RedisAutoConfiguration

@EnableConfigurationProperties(MyRedisProperty.class) // 属性注入,自动装载MyRedisProperty
@Configuration
@ConditionalOnProperty(prefix = "zsw", value = "enable") // 满足条件才加载此配置类
public class MyRedisAutoConfiguration {

    @Bean
    public MyRedisClient myRedisClient(MyRedisProperty myRedisProperty) {
        System.out.println("myRedisProperty: " + myRedisProperty.getHost() + "  " + myRedisProperty.getPort());
        return new MyRedisClient(myRedisProperty);
    }
}

3.2 测试配置类是否完善,能否装载client,要将@ConditionalOnProperty注释掉,否则不加载的,测试类:

/**
 * 测试configuration
 *
 * @author zhangshiwei
 * @since 2020年9月21日 11:15:34
 */
public class ConfigurationTest {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(
                MyRedisAutoConfiguration.class);
        System.out.println("从spring容器中获取对象 MyRedisClient: " + applicationContext.getBean(MyRedisClient.class));
    }
}

3.3 测试ConfigurationTest 结果:

4. 新建resources.MET-INF文件夹,在MET-INF内新建文件: spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.zsw.example.spring.factories.MyRedisAutoConfiguration

5. 待使用MyRedisClient的项目,添加依赖

		<!-- spring.factories 自动装配测试-->
		<dependency>
			<groupId>com.zsw.example</groupId>
			<artifactId>order-api</artifactId>
			<version>1.1-SNAPSHOT</version>
		</dependency>

6. 待使用MyRedisClient的项目,yml配置新增

zsw:
  enable: true
  host: 127.0.0.1
  port: 1234

7. 添加测试类

/**
 * SpringFactories 测试控制类
 *
 * @author zhangshiwei
 * @since 2020年9月21日 11:01:26
 */
@RequestMapping("/springFactories")
@RestController
public class SpringFactoriesTestController {

    @Autowired
    private MyRedisClient myRedisClient;

    @RequestMapping("/address")
    public String test() {
        return myRedisClient.getAddress();
    }
}

8. 测试结果:

转载:springboot中SPI机制_johnhuster的专栏-优快云博客一、从java类加载机制说起java中的类加载器负载加载来自文件系统、网络或者其他来源的类文件。jvm的类加载器默认使用的是双亲委派模式。三种默认的类加载器Bootstrap ClassLoader、Extension ClassLoader和System ClassLoader（Application ClassLoader）每一个中类加载器都确定了从哪一些位置加载文件。于此同时我们也可以通...https://blog.youkuaiyun.com/john1337/article/details/92803089