springboot学习笔记之自动配置原理

   自动配置原理

      配置文件参考：https://docs.spring.io/spring-boot/docs/1.5.9.RELEASE/reference/htmlsingle/#common-application-properties

   一）springboot启动的时候会加载主配置类

  

@SpringBootApplication
public class Springbootday01Application {

	public static void main(String[] args) {
		
		SpringApplication.run(Springbootday01Application.class, args);
	}
}

    对于@SpringBootApplication 其实是一个组合注解，点击进去看到如下代码：

   

@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 {

1、 @SpringBootConfiguration 这个注解表示这个代码是springboot的配置类

2、@EnableAutoConfiguration 开启了自动配置功能

         点击@EnableAutoConfiguration进入其代码如下：

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

	String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

	/**
	 * Exclude specific auto-configuration classes such that they will never be applied.
	 * @return the classes to exclude
	 */
	Class[] exclude() default {};

	/**
	 * Exclude specific auto-configuration class names such that they will never be
	 * applied.
	 * @return the class names to exclude
	 * @since 1.3.0
	 */
	String[] excludeName() default {};

}

         1、 利用EnableAutoConfigurationImportSelector给容器中导入一些组件、可以查看selectImports()方法的内容；

               

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

	private static final String[] NO_IMPORTS = {};

	private static final Log logger = LogFactory
			.getLog(AutoConfigurationImportSelector.class);

	private static final String PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE = "spring.autoconfigure.exclude";

	private ConfigurableListableBeanFactory beanFactory;

	private Environment environment;

	private ClassLoader beanClassLoader;

	private ResourceLoader resourceLoader;

	@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
				.loadMetadata(this.beanClassLoader);
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
		List configurations = getCandidateConfigurations(annotationMetadata,
				attributes);
		configurations = removeDuplicates(configurations);
		Set exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, exclusions);
		configurations.removeAll(exclusions);
		configurations = filter(configurations, autoConfigurationMetadata);
		fireAutoConfigurationImportEvents(configurations, exclusions);
		return StringUtils.toStringArray(configurations);
	}

                 List configurations = getCandidateConfigurations(annotationMetadata, attributes);获取候选的配置

                

             将 类路径下 META-INF/spring.factories 里面配置的所有EnableAutoConfiguration的值加入到了容器中；

            每一个这样的 xxxAutoConfiguration类都是容器中的一个组件，都加入到容器中；用他们来做自动配置；

   

2）、每一个自动配置类进行自动配置功能；

3）、以HttpEncodingAutoConfiguration（Http编码自动配置）为例解释自动配置原理；

 

/*
 * 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 com.nari.springbootday01.controller;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.boot.autoconfigure.http.HttpEncodingProperties;
import org.springframework.boot.autoconfigure.http.HttpEncodingProperties.Type;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.filter.OrderedCharacterEncodingFilter;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.web.filter.CharacterEncodingFilter;

/**
 * {@link EnableAutoConfiguration Auto-configuration} for configuring the encoding to use
 * in web applications.
 *
 * @author Stephane Nicoll
 * @author Brian Clozel
 * @since 1.2.0
 */
@Configuration//表示这是一个配置类,以前编写的配置文件一样，也可以给容器中添加组件
/**
 * @EnableConfigurationProperties(HttpEncodingProperties.class)//
 * 启动指定类的
 ConfigurationProperties功能；将配置文件中对应的值和HttpEncodingProperties绑定起来；并把
 HttpEncodingProperties加入到ioc容器中
 */
@EnableConfigurationProperties(HttpEncodingProperties.class)//
/**
 * @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
 * Spring底层@Conditional注解，根据不同的条件，如果
    满足指定的条件，整个配置类里面的配置就会生效； 判断当前应用是否是web应用，如果是，当前配置类生效
 */
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@ConditionalOnClass(CharacterEncodingFilter.class)// //判断当前项目有没有这个类
//CharacterEncodingFilter；SpringMVC中进行乱码解决的过滤器；
/**
 * //判断配置文件中是否存在某个配置 spring.http.encoding.enabled；如果不存在，判断也是成立的
    matchIfMissing = true这个属性 即使我们配置文件中不配置pring.http.encoding.enabled=true，也是默认生效的；
 */
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {
	//他已经和SpringBoot的配置文件映射了
	private final HttpEncodingProperties properties;
	//只有一个有参构造器的情况下，参数的值就会从容器中拿
	public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
		this.properties = properties;
	}

	@Bean //给容器中添加一个组件，这个组件的某些值需要从properties中获取
	@ConditionalOnMissingBean   //判断容器没有这个组件
	public CharacterEncodingFilter characterEncodingFilter() {
		CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
		filter.setEncoding(this.properties.getCharset().name());
		filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
		filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
		return filter;
	}

	@Bean
	public LocaleCharsetMappingsCustomizer localeCharsetMappingsCustomizer() {
		return new LocaleCharsetMappingsCustomizer(this.properties);
	}

	private static class LocaleCharsetMappingsCustomizer implements
			WebServerFactoryCustomizer, Ordered {

		private final HttpEncodingProperties properties;

		LocaleCharsetMappingsCustomizer(HttpEncodingProperties properties) {
			this.properties = properties;
		}

		@Override
		public void customize(ConfigurableServletWebServerFactory factory) {
			if (this.properties.getMapping() != null) {
				factory.setLocaleCharsetMappings(this.properties.getMapping());
			}
		}

		@Override
		public int getOrder() {
			return 0;
		}

	}

}

根据当前不同的条件判断，决定这个配置类是否生效？

   一但这个配置类生效；这个配置类就会给容器中添加各种组件；这些组件的属性是从对应的properties类中获取 的，这些类里面的每一个属性又是和配置文件绑定的；

4  所有在配置文件中能配置的属性都是在xxxxProperties类中封装者‘；配置文件能配置什么就可以参照某个功 能对应的这个属性类

    

@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)// 从配置文件中获取指定的值和bean的属性进行绑定

public class HttpEncodingAutoConfiguration {

	private final HttpEncodingProperties properties;

      精髓： 1）、SpringBoot启动会加载大量的自动配置类

                 2）、我们看我们需要的功能有没有SpringBoot默认写好的自动配置类；

                 3）、我们再来看这个自动配置类中到底配置了哪些组件；（只要我们要用的组件有，我们就不需要再来配置了） 

                  4）、给容器中自动配置类添加组件的时候，会从properties类中获取某些属性。我们就可以在配置文件中指定这 些属性的值；

            xxxxAutoConfigurartion：自动配置类； 给容器中添加组件

           xxxxProperties:封装配置文件中相关属性；

 

@Conditional派生注解

  作用：必须是@Conditional指定的条件成立，才给容器中添加组件，配置配里面的所有内容才生效；

   自动配置类必须在一定的条件下才能生效；