Springboot源码

Springboot 源码阅读

springboot 最大的特点就是自动配置，我们引入对应的 jar 包，springboot 帮助我们进行自动配置，可以省去很多繁琐的配置步骤。

启动类

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/**
 * @author kyle
 */
@SpringBootApplication
public class SpringbootRestDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootRestDemoApplication.class, args);
    }
}

@SpringBootApplication

该注解由 SpringBootConfiguration, EnableAutoConfiguration,ComponentScan 三个注解组成

@SpringBootConfiguration

标明这是 springboot application 配置类, 以下几种方法排除自动配置类。

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// 排除自动配置的类
1. @SpringBootConfiguration (exclude = {DataSourceAutoConfiguration.class})
2. @SpringBootApplication(excludeName = {"org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration"})
3. @EnableAutoConfiguration
(exclude = {DataSourceAutoConfiguration.class})
4. @EnableAutoConfiguration
(excludeName = {"org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration"})
5. 配置文件
spring:     
  autoconfigure:
    exclude:
      - org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
      - org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration

@ComponentScan

扫描该路径下的类，注入的容器中，默认扫描 SpringbootRestDemoApplication 该包路径下的所有类

@EnableAutoConfiguration

启动自动配置

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@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration

@AutoConfigurationPackage

表明包含该注解的类包应该注册

@Import(AutoConfigurationImportSelector.class)

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META-INF/spring-autoconfigure-metadata.properties
AutoConfigurationImportSelector.class

	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;
	}

	protected Class<?> getSpringFactoriesLoaderFactoryClass() {
		return EnableAutoConfiguration.class;
	}

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

	// 
	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
		MultiValueMap<String, String> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}

		try {
            // public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"
			Enumeration<URL> urls = (classLoader != null ?
					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			result = new LinkedMultiValueMap<>();
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) {
					String factoryTypeName = ((String) entry.getKey()).trim();
					for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
						result.add(factoryTypeName, factoryImplementationName.trim());
					}
				}
			}
			cache.put(classLoader, result);
			return result;
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
	}

META-INF/spring.factories
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\