haogui

@SpringBootApplication

​ 这个注解中

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
    .....
}

我们可以进入@EnableAutoConfiguration，中这 个注解里面是和配置相关，自动注入相关，开启自动注入

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    ....
}

@import表示需要将里面的class进行导入，于是我们进入AutoConfigurationImportSelector类中，在这个类中能看到很多其中有几个类加载器，我们可以看其中的selectImports方法

@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
				.loadMetadata(this.beanClassLoader);
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
        //获得默认配置
		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 StringUtils.toStringArray(configurations);
	}

我们随后可以进入这个获取默认配置的方法

	/**
	 * Return the auto-configuration class names that should be considered. By default
	 * this method will load candidates using {@link SpringFactoriesLoader} with
	 * {@link #getSpringFactoriesLoaderFactoryClass()}.
	 * @param metadata the source metadata
	 * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation
	 * attributes}
	 * @return a list of candidate configurations
	 */
	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;
	}

META-INF/spring.factories,中的就是默认配置，我们可以点开这个类所在的位置

查看其中的spring.factories，你会发现里面全部都是默认的配置。

或者从springApplication类出发

	/**
	 * Create a new {@link SpringApplication} instance. The application context will load
	 * beans from the specified primary sources (see {@link SpringApplication class-level}
	 * documentation for details. The instance can be customized before calling
	 * {@link #run(String...)}.
	 * @param resourceLoader the resource loader to use
	 * @param primarySources the primary bean sources
	 * @see #run(Class, String[])
	 * @see #setSources(Set)
	 */
	@SuppressWarnings({ "unchecked", "rawtypes" })
	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
		this.webApplicationType = WebApplicationType.deduceFromClasspath();
        
		setInitializers((Collection) getSpringFactoriesInstances(
				ApplicationContextInitializer.class));
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		this.mainApplicationClass = deduceMainApplicationClass();
	}

你能够找到着个方法，随后查看getSpringFactoriesInstance()方法，追溯下去你能看到loadSpringFactories()

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

		try {
            //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()) {
					List<String> factoryClassNames = Arrays.asList(
							StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
					result.addAll((String) entry.getKey(), factoryClassNames);
				}
			}
			cache.put(classLoader, result);
			return result;
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
	}

在这里你也可以看到他将META-INF/spring.factories中的配置全部加载进来了，随后setInitializers()

springboot 内置tomcat的加载

在spring.factories搜索WebServer相关的配置

我们可以点击查看其中ServletWebServerFactoryAutoConfiguration类，摘抄些许代码如下

	@Bean
	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new ServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
	}



/**
 * {@link Conditional} that only matches when the specified classes are on the classpath.
 *
 * @author Phillip Webb
 */
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnClassCondition.class)
public @interface ConditionalOnClass {

	/**
	 * The classes that must be present. Since this annotation is parsed by loading class
	 * bytecode, it is safe to specify classes here that may ultimately not be on the
	 * classpath, only if this annotation is directly on the affected component and
	 * <b>not</b> if this annotation is used as a composed, meta-annotation. In order to
	 * use this annotation as a meta-annotation, only use the {@link #name} attribute.
	 * @return the classes that must be present
	 */
	Class<?>[] value() default {};

	/**
	 * The classes names that must be present.
	 * @return the class names that must be present.
	 */
	String[] name() default {};

}

ConditionalOnClass注解，从注解的注释中读到，在加载类之前，注解中的class必须存在。@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")，于是可以了解到"org.apache.catalina.startup.Tomcat必须存在。点进去了你就会发现Tomcat类，他就是apache的tomcat，可总上看到他了

 * <p>
 * There are a variety of 'add' methods to configure servlets and webapps. These
 * methods, by default, create a simple in-memory security realm and apply it.
 * If you need more complex security processing, you can define a subclass of
 * this class.
 *
 * <p>
 * This class provides a set of convenience methods for configuring webapp
 * contexts, all overloads of the method <code>addWebapp</code>. These methods
 * create a webapp context, configure it, and then add it to a {@link Host}.
 * They do not use a global default web.xml; rather, they add a lifecycle
 * listener that adds the standard DefaultServlet, JSP processing, and welcome
 * files.
 *
 * <p>

add方法将其加入webapps。

aop加载

同样在spring.factories中搜索aop,你就会看到如下代码

/*
 * Copyright 2012-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.autoconfigure.aop;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.Advice;
import org.aspectj.weaver.AnnotatedElement;

import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

/**
 * {@link org.springframework.boot.autoconfigure.EnableAutoConfiguration
 * Auto-configuration} for Spring's AOP support. Equivalent to enabling
 * {@link org.springframework.context.annotation.EnableAspectJAutoProxy} in your
 * configuration.
 * <p>
 * The configuration will not be activated if {@literal spring.aop.auto=false}. The
 * {@literal proxyTargetClass} attribute will be {@literal true}, by default, but can be
 * overridden by specifying {@literal spring.aop.proxy-target-class=false}.
 *
 * @author Dave Syer
 * @author Josh Long
 * @see EnableAspectJAutoProxy
 */
@Configuration
@ConditionalOnClass({ EnableAspectJAutoProxy.class, Aspect.class, Advice.class,
		AnnotatedElement.class })
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)
public class AopAutoConfiguration {

	@Configuration
	@EnableAspectJAutoProxy(proxyTargetClass = false)
	@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false", matchIfMissing = false)
	public static class JdkDynamicAutoProxyConfiguration {

	}

	@Configuration
	@EnableAspectJAutoProxy(proxyTargetClass = true)
	@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true", matchIfMissing = true)
	public static class CglibAutoProxyConfiguration {

	}

}

是不是突然感觉到，EnableAspectJAutoProxy.class, Aspect.class, Advice.class,在你使用apo的时候都是那么的熟悉。

接着看他内部的方法，你会看到JdkDynamic与Cglib，这就是aop动态生成的2种，一种利用jdk的Dynamic动态代理，通过接口生成一个新的类，而Cglib在可以在父类的基础上直接生成代理类。

顺便说一下他们的区别吧

proxy by subclassing. Spring uses CGLIB for proxy if class is not implementing interface.

其他的配置也于此类似