spring boot 源码解析17-mvc自动化配置揭秘

2023年11月19日 358次阅读 来源: Spring Boot

前言

之前的几篇文章,我们介绍到了spring 4 带来的改变–> java 零配置,那么spring boot 是怎么在它的基础上实现自动配置的呢?由于这点设计的范围过大,因此这里我们就只关注mvc方面的自动化配置,涉及如下几个类:

  • EmbeddedServletContainerAutoConfiguration(这个已经在spring boot 源码解析12-servlet容器的建立中分析过了,这里就不分析了)
  • DispatcherServletAutoConfiguration
  • ErrorMvcAutoConfiguration(在spring boot 源码解析14-ImportSelector及默认错误页面中已经有解释过了,这里就不解释了)
  • WebMvcAutoConfiguration(这里的内容比较多,我们下一篇文章进行分析)
  • HttpMessageConvertersAutoConfiguration
  • HttpEncodingAutoConfiguration
  • MultipartAutoConfiguration
  • ServerPropertiesAutoConfiguration
  • WebClientAutoConfiguration

DispatcherServletAutoConfiguration

  1. DispatcherServletAutoConfiguration 在类上声明了如下注解:

    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(EmbeddedServletContainerAutoConfiguration.class)
    1. @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE) 说明了它在自动化配置有高优先级
    2. @Configuration 是一个配置类,会交由ConfigurationClassPostProcessor进行加载
    3. @ConditionalOnWebApplication 必须在web环境下生效
    4. @ConditionalOnClass(DispatcherServlet.class) 必须在类路径下有DispatcherServlet存在
    5. @AutoConfigureAfter(EmbeddedServletContainerAutoConfiguration.class) 在EmbeddedServletContainerAutoConfiguration之后进行加载

  2. 由于DispatcherServletAutoConfiguration有2个内部类,DispatcherServletConfiguration,DispatcherServletRegistrationConfiguration.根据加载规则,会优先加载内部类再加载DispatcherServletAutoConfiguration中的定义.接下来我们分别看下其实现:

    1. DispatcherServletConfiguration有如下注解:

      @Configuration
@Conditional(DefaultDispatcherServletCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
      • @Configuration 表明其是一个配置类

      • @Conditional(DefaultDispatcherServletCondition.class) 引入了一个条件类,其判断逻辑如下:

            public ConditionOutcome getMatchOutcome(ConditionContext context,
    AnnotatedTypeMetadata metadata) {
ConditionMessage.Builder message = ConditionMessage
        .forCondition("Default DispatcherServlet");
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
List<String> dispatchServletBeans = Arrays.asList(beanFactory
        .getBeanNamesForType(DispatcherServlet.class, false, false));
if (dispatchServletBeans.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
    return ConditionOutcome.noMatch(message.found("dispatcher servlet bean")
            .items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
if (beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
    return ConditionOutcome
            .noMatch(message.found("non dispatcher servlet bean")
                    .items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
if (dispatchServletBeans.isEmpty()) {
    return ConditionOutcome
            .match(message.didNotFind("dispatcher servlet beans").atAll());
}
return ConditionOutcome.match(message
        .found("dispatcher servlet bean", "dispatcher servlet beans")
        .items(Style.QUOTE, dispatchServletBeans)
        .append("and none is named " + DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
        1. 如果beanFactory 中存在id 为 dispatcherServlet,类型为DispatcherServlet的bean ,返回不匹配.否则进入第2步
        2. 如果beanFactory中包含id为dispatcherServlet的bean,返回不匹配
        3. 如果beanFactory中不包含类型为DispatcherServlet的bean,返回匹配
        4. 其他情况下,返回匹配
      • @ConditionalOnClass(ServletRegistration.class)–> 当前的类路径下存在ServletRegistration.class.

      • @EnableConfigurationProperties(WebMvcProperties.class)–> 导入了一个属性配置类,其WebMvcProperties.class有如下注解:

        @ConfigurationProperties(prefix = "spring.mvc")

        这也就意味着我们在application.properties 中配置spring.mvc前缀的属性,就会自动配置到WebMvcProperties中.

    2. DispatcherServletConfiguration中有如下被@Bean注解的方法

      1. dispatcherServlet,注册dispatcherServlet,id为dispatcherServlet.代码如下:

        @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet() {
// 实例化DispatcherServlet
DispatcherServlet dispatcherServlet = new DispatcherServlet();
// 设置是否允许分发Option请求,默认为true
dispatcherServlet.setDispatchOptionsRequest(
        this.webMvcProperties.isDispatchOptionsRequest());
// 设置是否允许分发Trace请求,默认为false
dispatcherServlet.setDispatchTraceRequest(
        this.webMvcProperties.isDispatchTraceRequest());
// 设置是否没有handeler处理请求时抛出异常,默认为false
dispatcherServlet.setThrowExceptionIfNoHandlerFound(
        this.webMvcProperties.isThrowExceptionIfNoHandlerFound());
return dispatcherServlet;
}
        1. 实例化DispatcherServlet
        2. 设置是否允许分发Option请求,默认为true
        3. 设置是否允许分发Trace请求,默认为false
        4. 设置是否没有handeler处理请求时抛出异常,默认为false

      2. multipartResolver,代码如下:

        @Bean
@ConditionalOnBean(MultipartResolver.class)
@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
public MultipartResolver multipartResolver(MultipartResolver resolver) {
            return resolver;
}

        在beanFactory中存在MultipartResolver类型的bean时,但是其id不是multipartResolver,那么此时就会重新注册一个id为multipartResolver的bean。

    3. DispatcherServletRegistrationConfiguration,有如下注解:

      @Configuration
@Conditional(DispatcherServletRegistrationCondition.class)// 当beanFactory中有DispatcherServlet,并且id为dispatcherServlet
@ConditionalOnClass(ServletRegistration.class) // ServletRegistration在类路径存在的话
@EnableConfigurationProperties(WebMvcProperties.class)
@Import(DispatcherServletConfiguration.class)
      • @Configuration表明其是一个配置类

      • @Conditional(DispatcherServletRegistrationCondition.class) 引入了DispatcherServletRegistrationCondition条件类,其判断逻辑如下:

        @Override
public ConditionOutcome getMatchOutcome(ConditionContext context,
    AnnotatedTypeMetadata metadata) {
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
ConditionOutcome outcome = checkDefaultDispatcherName(beanFactory);
if (!outcome.isMatch()) {
    return outcome;
}
return checkServletRegistration(beanFactory);
}
        1. 获得beanFactory

        2. 调用checkDefaultDispatcherName,看是否beanFactory中是否包含id 为dispatcherServlet,类型为DispatcherServlet的bean.如果不包含,则直接返回不匹配,否则进行第3步.代码如下:

          private ConditionOutcome checkDefaultDispatcherName(
ConfigurableListableBeanFactory beanFactory) {
List<String> servlets = Arrays.asList(beanFactory
    .getBeanNamesForType(DispatcherServlet.class, false, false));
boolean containsDispatcherBean = beanFactory
    .containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
if (containsDispatcherBean
    && !servlets.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
return ConditionOutcome
        .noMatch(startMessage().found("non dispatcher servlet")
                .items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
return ConditionOutcome.match();
}
          1. 获得DispatcherServlet类型的bean
          2. containsDispatcherBean =beanFactory 中是否包含id为 dispatcherServlet的bean
          3. 如果beanFactory 中包含id 为dispatcherServlet的bean,但是其类型不是DispatcherServlet,则返回不匹配,否则返回匹配

        3. checkServletRegistration 代码如下:

          private ConditionOutcome checkServletRegistration(
ConfigurableListableBeanFactory beanFactory) {
ConditionMessage.Builder message = startMessage();
List<String> registrations = Arrays.asList(beanFactory
    .getBeanNamesForType(ServletRegistrationBean.class, false, false));
boolean containsDispatcherRegistrationBean = beanFactory
    .containsBean(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
if (registrations.isEmpty()) {
if (containsDispatcherRegistrationBean) {
    return ConditionOutcome
            .noMatch(message.found("non servlet registration bean").items(
                    DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
return ConditionOutcome
        .match(message.didNotFind("servlet registration bean").atAll());
}
if (registrations
    .contains(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)) {
return ConditionOutcome.noMatch(message.found("servlet registration bean")
        .items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
if (containsDispatcherRegistrationBean) {
return ConditionOutcome
        .noMatch(message.found("non servlet registration bean").items(
                DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
return ConditionOutcome.match(message.found("servlet registration beans")
    .items(Style.QUOTE, registrations).append("and none is named "
            + DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
          1. 获得beanFactory中类型为ServletRegistrationBean的bean name
          2. containsDispatcherRegistrationBean = beanFactory中是否包含id 为dispatcherServletRegistration的bean

          3. 如果beanFactory中不包含ServletRegistrationBean的bean

            1. 包含id为dispatcherServletRegistration的bean,则返回不匹配
            2. 如果不包含id为dispatcherServletRegistration的bean,则返回匹配
          4. 如果在beanFactory中类型为ServletRegistrationBean的bean name 中包含dispatcherServletRegistration则返回不匹配
          5. 如果在beanFactory中类型为ServletRegistrationBean的bean name 中不包含dispatcherServletRegistration,且 beanFactory中包含id 为dispatcherServletRegistration的bean,则返回不匹配
          6. 其他情况(beanFactory中类型为ServletRegistrationBean的bean name 中不包含dispatcherServletRegistration,其不包含id为dispatcherServletRegistration的bean),返回匹配.
      • @EnableConfigurationProperties(WebMvcProperties.class) 可通过spring.mvc 进行配置
      • @Import(DispatcherServletConfiguration.class) 导入了DispatcherServletConfiguration 的配置.

    4. DispatcherServletRegistrationConfiguration 中没有内部类,只有一个被@bean注解的方法,代码如下:

      @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public ServletRegistrationBean dispatcherServletRegistration(
        DispatcherServlet dispatcherServlet) {
            ServletRegistrationBean registration = new ServletRegistrationBean(
            dispatcherServlet, this.serverProperties.getServletMapping());
    registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
    registration.setLoadOnStartup(
            this.webMvcProperties.getServlet().getLoadOnStartup());
    if (this.multipartConfig != null) {
        registration.setMultipartConfig(this.multipartConfig);
    }
    return registration;
}
      1. 当beanfactory中存在id 为dispatcherServlet,类型为DispatcherServlet则会进行注册(id 为 dispatcherServletRegistration,类型为ServletRegistrationBean),否则不进行注册。
      2. 直接使用DispatcherServlet和server配置中的servletPath路径构造ServletRegistrationBean, ServletRegistrationBean实现了ServletContextInitializer接口，在onStartup方法中对应的Servlet注册到Servlet容器中,所以这里DispatcherServlet会被注册到Servlet容器中，对应的urlMapping为server.servletPath配置.默认为/,加载顺序为-1.

HttpMessageConvertersAutoConfiguration

  1. HttpMessageConvertersAutoConfiguration在类上有如下注解:

    @Configuration
@ConditionalOnClass(HttpMessageConverter.class)
@AutoConfigureAfter({ GsonAutoConfiguration.class, JacksonAutoConfiguration.class })
@Import({ JacksonHttpMessageConvertersConfiguration.class,
    GsonHttpMessageConvertersConfiguration.class })
    • @Configuration–>配置类
    • @ConditionalOnClass(HttpMessageConverter.class)–>当前类路径下存在HttpMessageConverter
    • @AutoConfigureAfter({ GsonAutoConfiguration.class, JacksonAutoConfiguration.class }) –> 在GsonAutoConfiguration,JacksonAutoConfiguration之后进行加载
    • @Import({ JacksonHttpMessageConvertersConfiguration.class,GsonHttpMessageConvertersConfiguration.class })–>导入了JacksonHttpMessageConvertersConfiguration,GsonHttpMessageConvertersConfiguration的配置

  2. HttpMessageConvertersAutoConfiguration中有StringHttpMessageConverterConfiguration内部类,因此为因此对其进行加载.

    1. StringHttpMessageConverterConfiguration有如下注解:

      @Configuration
@ConditionalOnClass(StringHttpMessageConverter.class)
@EnableConfigurationProperties(HttpEncodingProperties.class)
      1. 当前类路径下存在StringHttpMessageConverter
      2. 可以在application.properties中通过spring.http.encoding进行配置

    2. StringHttpMessageConverterConfiguration中声明的bean只有一个,当beanFactory中不存在StringHttpMessageConverter时进行注册,如下:

      @Bean
@ConditionalOnMissingBean
public StringHttpMessageConverter stringHttpMessageConverter() {
    StringHttpMessageConverter converter = new StringHttpMessageConverter(
            this.encodingProperties.getCharset());
    converter.setWriteAcceptCharset(false);
    return converter;
}

      StringHttpMessageConverter 默认编码为:UTF-8

  3. HttpMessageConvertersAutoConfiguration 只注册了一个HttpMessageConverters,当beanFactory中不存在HttpMessageConverters的bean时.代码如下:

    @Bean
@ConditionalOnMissingBean
public HttpMessageConverters messageConverters() {
    return new HttpMessageConverters(this.converters == null
            ? Collections.<HttpMessageConverter<?>>emptyList() : this.converters);
}

HttpEncodingAutoConfiguration

  1. HttpEncodingAutoConfiguration类上有如下注解:

    @Configuration
@EnableConfigurationProperties(HttpEncodingProperties.class)
@ConditionalOnWebApplication
@ConditionalOnClass(CharacterEncodingFilter.class)
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
    • @Configuration –> 配置类
    • @EnableConfigurationProperties(HttpEncodingProperties.class) –> 可通过spring.http.encoding.xxx 进行配置
    • @ConditionalOnWebApplication–>web 环境
    • @ConditionalOnClass(CharacterEncodingFilter.class) –> 当前类路径下存在CharacterEncodingFilter
    • @ConditionalOnProperty(prefix = “spring.http.encoding”, value = “enabled”, matchIfMissing = true) –> spring.http.encoding的值为true时,方可进行配置,默认为true

  2. HttpEncodingAutoConfiguration中不存在内部类,其注册了2个bean,分别如下:

    1. 注册CharacterEncodingFilter,当beanFactory中不存在CharacterEncodingFilter类型的bean时.代码如下；

      @Bean
@ConditionalOnMissingBean(CharacterEncodingFilter.class)
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;
}

      声明了CharacterEncodingFilter,默认编码为UTF-8,对请求进行强制编码(默认),对响应编码为utf-8为false(默认,可通过spring.http.encoding.forceResponse = true 进行配置)

    2. 注册LocaleCharsetMappingsCustomizer.无条件.代码如下:

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

MultipartAutoConfiguration

  1. MultipartAutoConfiguration类上有如下注解:

    @Configuration
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class,
    MultipartConfigElement.class })
@ConditionalOnProperty(prefix = "spring.http.multipart", name = "enabled", matchIfMissing = true)
@EnableConfigurationProperties(MultipartProperties.class)
    • @Configuration –> 配置类
    • @ConditionalOnClass({ Servlet.class,StandardServletMultipartResolver.class,MultipartConfigElement.class }) –> 当前类路径下存在Servlet,StandardServletMultipartResolver,MultipartConfigElement
    • @ConditionalOnProperty(prefix = “spring.http.multipart”, name = “enabled”, matchIfMissing = true)–> spring.http.multipart.enabled 等于true,进行配置,默认为true
    • @EnableConfigurationProperties(MultipartProperties.class) 可通过spring.http.multipart.xxx 进行配置

  2. MultipartAutoConfiguration中没有配置类,其注册了2个bean,代码如下:

    1. 注册MultipartConfigElement,当beanFactory中不存在MultipartConfigElement时注册.代码如下:

      @Bean
@ConditionalOnMissingBean
public MultipartConfigElement multipartConfigElement() {
return this.multipartProperties.createMultipartConfig();
}

      调用:

      public MultipartConfigElement createMultipartConfig() {
MultipartConfigFactory factory = new MultipartConfigFactory();
if (StringUtils.hasText(this.fileSizeThreshold)) {
    factory.setFileSizeThreshold(this.fileSizeThreshold);
}
if (StringUtils.hasText(this.location)) {
    factory.setLocation(this.location);
}
if (StringUtils.hasText(this.maxRequestSize)) {
    factory.setMaxRequestSize(this.maxRequestSize);
}
if (StringUtils.hasText(this.maxFileSize)) {
    factory.setMaxFileSize(this.maxFileSize);
}
return factory.createMultipartConfig();
}
      1. 文件大小默认为0,也就是不限制
      2. 默认请求大小为 10MB
      3. 最大文件大小为 1MB

    2. 注册 StandardServletMultipartResolver.当beanFactory不存在MultipartResolver时.代码如下:

      @Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
@ConditionalOnMissingBean(MultipartResolver.class)
public StandardServletMultipartResolver multipartResolver() {
StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
return multipartResolver;
}

ServerPropertiesAutoConfiguration

  1. ServerPropertiesAutoConfiguration 有如下注解:

    @Configuration
@EnableConfigurationProperties
@ConditionalOnWebApplication
    • @Configuration–> 注解类

    • @EnableConfigurationProperties –> 当beanFactory中不存在org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor时,注册如下2个bean:

      1. id 为org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor,class为ConfigurationPropertiesBindingPostProcessor
      2. id为org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.store,class为ConfigurationPropertiesBindingPostProcessor
    • @ConditionalOnWebApplication–>web环境

  2. ServerPropertiesAutoConfiguration中没有配置内部类,只有2个被@bean注解的方法,如下:

    1. 注册ServerProperties,当beanFactory中不存在ServerProperties时.代码如下:

          @Bean
@ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
public ServerProperties serverProperties() {
return new ServerProperties();
}

    2. 注册DuplicateServerPropertiesDetector,代码如下:

          @Bean
public DuplicateServerPropertiesDetector duplicateServerPropertiesDetector() {
return new DuplicateServerPropertiesDetector();
}

      在内置容器配置时会用到,该bean的作用是为了确保只存在一个ServerProperties bean的定义。代码如下:

          @Override
public void customize(ConfigurableEmbeddedServletContainer container) {
    // ServerProperties handles customization, this just checks we only have
    // a single bean
    String[] serverPropertiesBeans = this.applicationContext
            .getBeanNamesForType(ServerProperties.class);
    Assert.state(serverPropertiesBeans.length == 1,
            "Multiple ServerProperties beans registered " + StringUtils
                    .arrayToCommaDelimitedString(serverPropertiesBeans));
}

WebClientAutoConfiguration

  1. WebClientAutoConfiguration 有如下注解:

    @Configuration
@AutoConfigureAfter(HttpMessageConvertersAutoConfiguration.class)
    • @Configuration–> 配置类
    • @AutoConfigureAfter(HttpMessageConvertersAutoConfiguration.class) –> HttpMessageConvertersAutoConfiguration 之后进行加载

  2. WebClientAutoConfiguration中只有一个内部类,RestTemplateConfiguration

    1. RestTemplateConfiguration 注解如下:

      @Configuration
@ConditionalOnClass(RestTemplate.class)
      • @Configuration –> 配置类
      • @ConditionalOnClass(RestTemplate.class)–> 当前类路径下存在RestTemplate

    2. RestTemplateConfiguration只注册了一个RestTemplateBuilder.当beanFactory中不存在RestTemplateBuilder时.代码如下:

      @Bean
@ConditionalOnMissingBean
public RestTemplateBuilder restTemplateBuilder() {
    RestTemplateBuilder builder = new RestTemplateBuilder();
    HttpMessageConverters converters = this.messageConverters.getIfUnique();
    if (converters != null) {
        builder = builder.messageConverters(converters.getConverters());
    }
    List<RestTemplateCustomizer> customizers = this.restTemplateCustomizers
            .getIfAvailable();
    if (!CollectionUtils.isEmpty(customizers)) {
        customizers = new ArrayList<RestTemplateCustomizer>(customizers);
        AnnotationAwareOrderComparator.sort(customizers);
        builder = builder.customizers(customizers);
    }
    return builder;
}
      1. 实例化RestTemplateBuilder
      2. 如果存在HttpMessageConverters,则进行配置
      3. 如果存在RestTemplateCustomizer,则排序后,进行配置

自动化配置加载流程解析

spring boot 声明了这么多的自动化配置类,那么它的加载流程是怎么的,我们就拿DispatcherServletConfiguration来分析,其它的配置类,加载流程都是一样的.

  1. DispatcherServletAutoConfiguration加载顺序:

    @SpringBootApplication有@EnableAutoConfiguration注解,又因为@Import(EnableAutoConfigurationImportSelector.class),因此在ConfigurationClassParser#doProcessConfigurationClass中会调用processImports 进行处理,最终调用EnableAutoConfigurationImportSelector#selectImports进行处理获得org.springframework.boot.autoconfigure.EnableAutoConfiguration 的配置,因为EnableAutoConfigurationImportSelector是DeferredImportSelector的子类,因此会添加到deferredImportSelectors中,最终在ConfigurationClassParser#processDeferredImportSelectors进行处理.最终调用processImports 进行对org.springframework.boot.autoconfigure.EnableAutoConfiguration配置的类依次进行加载,此时就会对DispatcherServletAutoConfiguration进行加载。

    DispatcherServletAutoConfiguration 不是ImportSelector，ImportBeanDefinitionRegistrar 的子类,因此会当做一个配置类调用processConfigurationClass进行加载.(注意此时DispatcherServletAutoConfiguration是由该应用所导入的) 由于其有内部类,因此会首先加载DispatcherServletConfiguration和DispatcherServletRegistrationConfiguration.

  2. DispatcherServletConfiguration因为有@EnableConfigurationProperties 注解,在@EnableConfigurationProperties注解上有@Import,因此会调用ConfigurationClassParser#processImports.

    1. 在该方法中会调用EnableConfigurationPropertiesImportSelector#selectImports方法,最终返回的是org.springframework.boot.context.properties.EnableConfigurationPropertiesImportSelector.ConfigurationPropertiesBeanRegistrar,org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessorRegistrar.代码如下:

      return new String[] { ConfigurationPropertiesBeanRegistrar.class.getName(),
    ConfigurationPropertiesBindingPostProcessorRegistrar.class.getName() };

    2. ConfigurationPropertiesBeanRegistrar,ConfigurationPropertiesBindingPostProcessorRegistrar 是ImportBeanDefinitionRegistrar的子类,因此会实例化加入到DispatcherServletConfiguration中的ImportBeanDefinitionRegistrar.代码如下:

      configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());

      处理完@Import后,依次处理被@bean注解的方法(dispatcherServlet,multipartResolver),此时向configClass加入了BeanMethod.代码如下:

      Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
    configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}

    3. DispatcherServletConfiguration因为有@Import(DispatcherServletConfiguration.class)注解,因此也就间接导入了DispatcherServletConfiguration,EnableConfigurationPropertiesImportSelector.

      因此加载时会先调用ConfigurationClassParser#processImports.在该方法中会依次遍历DispatcherServletConfiguration,EnableConfigurationPropertiesImportSelector,对于EnableConfigurationPropertiesImportSelector的处理,和DispatcherServletConfiguration一样,这里就不在赘述了.

      对于DispatcherServletConfiguration的处理,会调用processConfigurationClass(candidate.asConfigClass(configClass)),注意此时candidate指的是DispatcherServletConfiguration, configClass指的是DispatcherServletRegistrationConfiguration。

      asConfigClass代码如下:

      public ConfigurationClass asConfigClass(ConfigurationClass importedBy) throws IOException {
    if (this.source instanceof Class) {
        return new ConfigurationClass((Class<?>) this.source, importedBy);
    }
    return new ConfigurationClass((MetadataReader) this.source, importedBy);
}

      调用

      public ConfigurationClass(MetadataReader metadataReader, ConfigurationClass importedBy) {
this.metadata = metadataReader.getAnnotationMetadata();
this.resource = metadataReader.getResource();
this.importedBy.add(importedBy);
}

      经过这步处理,意味着DispatcherServletConfiguration所对应的ConfigurationClass是被DispatcherServletRegistrationConfiguration导入的.

      在ConfigurationClassParser#processConfigurationClass中,首先从configurationClasses中查看DispatcherServletConfiguration是否解析过,这里由于DispatcherServletConfiguration已经解析过了,同时DispatcherServletConfiguration是被DispatcherServletRegistrationConfiguration导入的,因此会调用ConfigurationClass#mergeImportedBy.这里的代码如下:

      ConfigurationClass existingClass = this.configurationClasses.get(configClass);
if (existingClass != null) {
    if (configClass.isImported()) {
        if (existingClass.isImported()) {
            existingClass.mergeImportedBy(configClass);
        }
        // Otherwise ignore new imported config class; existing non-imported class overrides it.
        return;
    }
    else {
        // Explicit bean definition found, probably replacing an import.
        // Let's remove the old one and go with the new one.
        this.configurationClasses.remove(configClass);
        for (Iterator<ConfigurationClass> it = this.knownSuperclasses.values().iterator(); it.hasNext();) {
            if (configClass.equals(it.next())) {
                it.remove();
            }
        }
    }
}

      ConfigurationClass#mergeImportedBy 代码如下:

          public void mergeImportedBy(ConfigurationClass otherConfigClass) {
this.importedBy.addAll(otherConfigClass.importedBy);
}

      注意,这里加入的是DispatcherServletRegistrationConfiguration

      处理完@Import后,处理被@bean注解的方法–>dispatcherServletRegistration。和DispatcherServletConfiguration一样.

    4. 由于DispatcherServletAutoConfiguration没有被@bean注解的方法,因此DispatcherServletAutoConfiguration的解析到此结束

      因此DispatcherServletAutoConfiguration共解析了3个配置类:

      1. DispatcherServletConfiguration
      2. DispatcherServletRegistrationConfiguration
      3. DispatcherServletAutoConfiguration

      接下来会调用ConfigurationClassBeanDefinitionReader#loadBeanDefinitions进行处理

    5. ConfigurationClassBeanDefinitionReader#loadBeanDefinitions.在该方法中会依次遍历之前解析的ConfigurationClass,调用loadBeanDefinitionsForConfigurationClass.代码如下:

      private void loadBeanDefinitionsForConfigurationClass(ConfigurationClass configClass,
    TrackedConditionEvaluator trackedConditionEvaluator) {

if (trackedConditionEvaluator.shouldSkip(configClass)) {
    String beanName = configClass.getBeanName();
    if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
        this.registry.removeBeanDefinition(beanName);
    }
    this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
    return;
}

if (configClass.isImported()) {
    registerBeanDefinitionForImportedConfigurationClass(configClass);
}
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
    loadBeanDefinitionsForBeanMethod(beanMethod);
}
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

      该方法的逻辑如下:

      1. 判断是否需要跳过.

      2. 如果该配置是被导入的,则调用registerBeanDefinitionForImportedConfigurationClass.判断逻辑如下:

        public boolean isImported() {
return !this.importedBy.isEmpty();
}

        registerBeanDefinitionForImportedConfigurationClass代码如下:

        private void registerBeanDefinitionForImportedConfigurationClass(ConfigurationClass configClass) {
AnnotationMetadata metadata = configClass.getMetadata();
AnnotatedGenericBeanDefinition configBeanDef = new AnnotatedGenericBeanDefinition(metadata);
ScopeMetadata scopeMetadata = scopeMetadataResolver.resolveScopeMetadata(configBeanDef);
configBeanDef.setScope(scopeMetadata.getScopeName());
String configBeanName = this.importBeanNameGenerator.generateBeanName(configBeanDef, this.registry);
AnnotationConfigUtils.processCommonDefinitionAnnotations(configBeanDef, metadata);
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(configBeanDef, configBeanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
this.registry.registerBeanDefinition(definitionHolder.getBeanName(), definitionHolder.getBeanDefinition());
configClass.setBeanName(configBeanName);
if (logger.isDebugEnabled()) {
logger.debug("Registered bean definition for imported class '" + configBeanName + "'");
}
}
        1. 根据configClass中配置的AnnotationMetadata 实例化AnnotatedGenericBeanDefinition

        2. 进行属性的设置

          1. 解析该configClass的Scope,一般是singleton
          2. 生成bean的id
          3. 设置bean的一些属性,如LazyInit,Primary等
        3. 生成BeanDefinitionHolder,并对其尝试进行代理,最后向registry进行注册

      3. 遍历该配置类声明的BeanMethods,调用loadBeanDefinitionsForBeanMethod.

      4. 调用loadBeanDefinitionsFromImportedResources 处理该类导入的配置文件
      5. 调用loadBeanDefinitionsFromRegistrars处理该类配置的importBeanDefinitionRegistrars

      关于这部分的详解,可以看spring boot 源码解析11-ConfigurationClassPostProcessor类加载解析

      1. 对于DispatcherServletConfiguration来说,由于该类是被DispatcherServletAutoConfiguration和DispatcherServletRegistrationConfiguration到入的,因此会调用registerBeanDefinitionForImportedConfigurationClass.因为DispatcherServletConfiguration有ConfigurationPropertiesBeanRegistrar,ConfigurationPropertiesBindingPostProcessorRegistrar,因此会调用loadBeanDefinitionsFromRegistrars.代码如下:

        private void loadBeanDefinitionsFromRegistrars(Map<ImportBeanDefinitionRegistrar, AnnotationMetadata> registrars) {
for (Map.Entry<ImportBeanDefinitionRegistrar, AnnotationMetadata> entry : registrars.entrySet()) {
    entry.getKey().registerBeanDefinitions(entry.getValue(), this.registry);
}
}

        因此会依次调用ConfigurationPropertiesBeanRegistrar,ConfigurationPropertiesBindingPostProcessorRegistrar的registerBeanDefinitions.

        1. ConfigurationPropertiesBeanRegistrar#registerBeanDefinitions,代码如下：

              public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
MultiValueMap<String, Object> attributes = metadata
    .getAllAnnotationAttributes(
            EnableConfigurationProperties.class.getName(), false);
List<Class<?>> types = collectClasses(attributes.get("value"));
for (Class<?> type : types) {
String prefix = extractPrefix(type);
String name = (StringUtils.hasText(prefix) ? prefix + "-" + type.getName()
        : type.getName());
if (!registry.containsBeanDefinition(name)) {
    registerBeanDefinition(registry, type, name);
}
}
}

          最终注册了一个id为spring.mvc.org.springframework.boot.autoconfigure.web.WebMvcProperties,类型为org.springframework.boot.autoconfigure.web.WebMvcProperties的bean.

        2. ConfigurationPropertiesBindingPostProcessorRegistrar#registerBeanDefinitions,代码如下:

          @Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (!registry.containsBeanDefinition(BINDER_BEAN_NAME)) {
BeanDefinitionBuilder meta = BeanDefinitionBuilder
    .genericBeanDefinition(ConfigurationBeanFactoryMetaData.class);
BeanDefinitionBuilder bean = BeanDefinitionBuilder.genericBeanDefinition(
    ConfigurationPropertiesBindingPostProcessor.class);
bean.addPropertyReference("beanMetaDataStore", METADATA_BEAN_NAME);
registry.registerBeanDefinition(BINDER_BEAN_NAME, bean.getBeanDefinition());
registry.registerBeanDefinition(METADATA_BEAN_NAME, meta.getBeanDefinition());
}
}

          当beanFactory中不存在org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor时,注册如下2个bean:

          1. id 为org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor,class为ConfigurationPropertiesBindingPostProcessor
          2. id为org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.store,class为ConfigurationPropertiesBindingPostProcessor

      2. 对于DispatcherServletRegistrationConfiguration来说,由于该类是被DispatcherServletAutoConfiguration导入的,因此会调用registerBeanDefinitionForImportedConfigurationClass.同样,也会调用loadBeanDefinitionsFromRegistrars.在 ConfigurationPropertiesBeanRegistrar#registerBeanDefinitions中,由于之前已经注册了id为spring.mvc.org.springframework.boot.autoconfigure.web.WebMvcProperties,类型为org.springframework.boot.autoconfigure.web.WebMvcProperties的bean.因此可以任何loadBeanDefinitionsFromRegistrars没有产生任何副作用.

      3. 对于 DispatcherServletAutoConfiguration来说,由于是被spring boot的启动类导入的,因此会调用registerBeanDefinitionForImportedConfigurationClass.又因为该类没有被@bean 注解的方法,没有导入其他的配置,因此后续不再处理.

自动配置总结

配置的bean声明的类条件
DispatcherServlet(id为DispatcherServlet)DispatcherServletConfiguration1.web环境 2.beanFactory不存在dispatcherServlet
MultipartResolver(id为multipartResolver)DispatcherServletConfiguration1.web环境,2.beanFactory不存在dispatcherServlet,3 不存在id为multipartResolver,类型为MultipartResolver的bean
dispatcherServletRegistrationDispatcherServletRegistrationConfiguration1.web环境,2.beanFactory中有DispatcherServlet类型,并且id为dispatcherServlet的bean
StringHttpMessageConverter(id为stringHttpMessageConverter)StringHttpMessageConverterConfiguration1.当前类路径下存在StringHttpMessageConverter,2.beanFactory中不存在StringHttpMessageConverter
HttpMessageConverters(id为messageConverters)HttpMessageConvertersAutoConfiguration1.当前类路径下存在StringHttpMessageConverter,2.beanFactory中不存在HttpMessageConverters
CharacterEncodingFilter(id为characterEncodingFilter)HttpEncodingAutoConfiguration1.web 环境,2.当前类路径下存在CharacterEncodingFilter, 3. beanFactory中不存在CharacterEncodingFilter类型的bean
LocaleCharsetMappingsCustomizer(id为localeCharsetMappingsCustomizer)HttpEncodingAutoConfiguration无
MultipartConfigElement(id为multipartConfigElement)MultipartAutoConfiguration1.当前类路径下存在Servlet,StandardServletMultipartResolver,MultipartConfigElement,2.spring.http.multipart.enabled 等于true,3.beanFactory中不存在MultipartConfigElement
StandardServletMultipartResolver(id为multipartResolver)MultipartAutoConfiguration1.当前类路径下存在Servlet,StandardServletMultipartResolver,MultipartConfigElement,2.spring.http.multipart.enabled 等于true,3.beanFactory中不存在MultipartResolver
ServerProperties(id为serverProperties)ServerPropertiesAutoConfiguration1.web环境,2.beanFactory中不存在ServerProperties
DuplicateServerPropertiesDetector(id为duplicateServerPropertiesDetector)ServerPropertiesAutoConfiguration1.web环境
RestTemplateBuilder(id为restTemplateBuilder)RestTemplateConfiguration1.当前类路径下存在RestTemplate,2.beanFactory中不存在RestTemplateBuilder
    原文作者：Spring Boot
    原文地址: https://blog.csdn.net/qq_26000415/article/details/78996719
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
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