Spring Boot 自动配置 : DispatcherServletAutoConfiguration
概述
自动配置类DispatcherServletAutoConfiguration服务于基于Spring MVC的Spring Boot Web应用，其主要作用是在缺省情况下提供bean :
DispatcherServlet dispatcherServlet通过嵌套配置类
DispatcherServletConfiguration完成。
该bean是Spring MVC核心的前置控制器Servlet。DispatcherServletRegistrationBean dispatcherServletRegistration通过嵌套配置类
DispatcherServletRegistrationConfiguration完成。
该bean的主要目的是将Servlet bean dispatcherServlet注册到Servlet容器。
在定义以上bean的过程中，它使用到了如下前缀配置参数 :
spring.http的配置参数被加载到bean HttpPropertiesspring.mvc的配置参数被加载到bean WebMvcProperties
源代码
源代码版本 : spring-boot-autoconfigure-2.1.3.RELEASE
package org.springframework.boot.autoconfigure.web.servlet;
// 省略 imports
/**
* EnableAutoConfiguration Auto-configuration for the Spring
* DispatcherServlet. Should work for a standalone application where an embedded
* web server is already present and also for a deployable application using
* SpringBootServletInitializer.
*
* @author Phillip Webb
* @author Dave Syer
* @author Stephane Nicoll
* @author Brian Clozel
*/
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
// 仅在当前应用是一个 Servlet Web 应用时才生效
@ConditionalOnWebApplication(type = Type.SERVLET)
// 仅在类 DispatcherServlet 存在于 classpath 上时才生效
@ConditionalOnClass(DispatcherServlet.class)
// 在自动配置类 ServletWebServerFactoryAutoConfiguration 应用之后再应用
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
/*
* The bean name for a DispatcherServlet that will be mapped to the root URL "/"
*/
public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
/*
* The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
*/
public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME =
"dispatcherServletRegistration";
// 嵌套配置类
// 1. 定义 bean DispatcherServlet dispatcherServlet
// 2. 如果类型为 MultipartResolver 的 bean 存在，为其创建一个别名 multipartResolver
@Configuration
// 仅在条件 DefaultDispatcherServletCondition 被满足时才生效 :
// DefaultDispatcherServletCondition 在类型为 DispatcherServlet 或者名称为 dispatcherServlet
// 的 bean 不存在时才被满足
@Conditional(DefaultDispatcherServletCondition.class)
// 仅在类 ServletRegistration 存在于 classpath 上时才生效
@ConditionalOnClass(ServletRegistration.class)
// 确保前缀为 spring.http 的配置参数被加载到 bean HttpProperties
// 确保前缀为 spring.mvc 的配置参数被加载到 bean WebMvcProperties
@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })
protected static class DispatcherServletConfiguration {
private final HttpProperties httpProperties;
private final WebMvcProperties webMvcProperties;
public DispatcherServletConfiguration(HttpProperties httpProperties,
WebMvcProperties webMvcProperties) {
this.httpProperties = httpProperties;
this.webMvcProperties = webMvcProperties;
}
// 定义 bean DispatcherServlet, 使用名称 dispatcherServlet， 这是 Spring MVC 核心的
// 前置控制器Servlet，Spring MVC 定义的所有的控制器方法都最终经由该 DispatcherServlet 派发
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet() {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDispatchOptionsRequest(
this.webMvcProperties.isDispatchOptionsRequest());
dispatcherServlet.setDispatchTraceRequest(
this.webMvcProperties.isDispatchTraceRequest());
dispatcherServlet.setThrowExceptionIfNoHandlerFound(
this.webMvcProperties.isThrowExceptionIfNoHandlerFound());
dispatcherServlet.setEnableLoggingRequestDetails(
this.httpProperties.isLogRequestDetails());
return dispatcherServlet;
}
// 定义 bean MultipartResolver，使用名称 multipartResolver,
// 该 bean 定义的主要任务不是生成一个新的 MultipartResolver bean 实例，而是在该类型的
// bean 存在时，给它起一个别名 multipartResolver，因为 DispatcherServlet 内部会固定使用该名字
@Bean
// 仅在类型为 MultipartResolver 的 bean 存在时才生效
@ConditionalOnBean(MultipartResolver.class)
// 仅在名称为 multipartResolver 的 bean 不存在时才生效
@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
public MultipartResolver multipartResolver(MultipartResolver resolver) {
// Detect if the user has created a MultipartResolver but named it incorrectly
return resolver;
}
}
// 嵌套配置类
@Configuration
// 仅在条件 DispatcherServletRegistrationCondition 满足时才生效
@Conditional(DispatcherServletRegistrationCondition.class)
// 仅在类 ServletRegistration 存在于 classpath 上时才生效
@ConditionalOnClass(ServletRegistration.class)
// 确保前缀为 spring.mvc 的配置参数被加载到 bean WebMvcProperties
@EnableConfigurationProperties(WebMvcProperties.class)
// 导入配置类 DispatcherServletConfiguration
@Import(DispatcherServletConfiguration.class)
protected static class DispatcherServletRegistrationConfiguration {
private final WebMvcProperties webMvcProperties;
private final MultipartConfigElement multipartConfig;
// MultipartConfigElement 的配置可以参考 MultipartAutoConfiguration
public DispatcherServletRegistrationConfiguration(WebMvcProperties webMvcProperties,
ObjectProvider<MultipartConfigElement> multipartConfigProvider) {
this.webMvcProperties = webMvcProperties;
this.multipartConfig = multipartConfigProvider.getIfAvailable();
}
// 定义 bean DispatcherServletRegistrationBean，名称为 dispatcherServletRegistration
// DispatcherServletRegistrationBean 继承自 ServletRegistrationBean,
// 该 bean dispatcherServletRegistration 的目的是将 DispatcherServletConfiguration 配置类中
// 所定义的 bean DispatcherServlet dispatcherServlet 注册到 Servlet 容器
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
// 仅在类型为 DispatcherServlet，名称为 dispatcherServlet 的 bean 存在时才生效
@ConditionalOnBean(value = DispatcherServlet.class, name =
DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServletRegistrationBean dispatcherServletRegistration(
DispatcherServlet dispatcherServlet) {
DispatcherServletRegistrationBean registration =
new DispatcherServletRegistrationBean(dispatcherServlet,
this.webMvcProperties.getServlet().getPath());
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(this.webMvcProperties.getServlet().getLoadOnStartup());
if (this.multipartConfig != null) {
registration.setMultipartConfig(this.multipartConfig);
}
return registration;
}
}
@Order(Ordered.LOWEST_PRECEDENCE - 10)
private static class DefaultDispatcherServletCondition extends SpringBootCondition {
@Override
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));
}
}
@Order(Ordered.LOWEST_PRECEDENCE - 10)
private static class DispatcherServletRegistrationCondition extends SpringBootCondition {
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context,
AnnotatedTypeMetadata metadata) {
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
ConditionOutcome outcome = checkDefaultDispatcherName(beanFactory);
if (!outcome.isMatch()) {
return outcome;
}
return checkServletRegistration(beanFactory);
}
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();
}
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));
}
private ConditionMessage.Builder startMessage() {
return ConditionMessage.forCondition("DispatcherServlet Registration");
}
}
}
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