自动配置原理
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<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);
}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<ConfigurableServletWebServerFactory>, 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；