SpringBoot2.0源码阅读理解
2022年 SpringBoot2.0源码阅读理解
1. 静态资源配置原理
- SpringBoot启动默认加载 xxxAutoConfiguration类（自动配置类）
- SpringMVC功能的自动配置类，webMvcAutoConfiguration，生效
//MVC的自动配置
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)//spring没有这个类型的组件的时候这个自动配置才生效
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
-
给容器配置了什么？
@Configuration(proxyBeanMethods = false) @Import(EnableWebMvcConfiguration.class) @EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class }) @Order(0) public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {}配置文件的相关属性和xxx进行了绑定。WebMvcProperties == spring.mvc、ResourceProperties == spring.resources
拓展知识：配置类只有一个有参构造器
@Configuration(proxyBeanMethods = false)
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, WebProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ServletContextAware {
private static final Log logger = LogFactory.getLog(WebMvcConfigurer.class);
private final Resources resourceProperties;
private final WebMvcProperties mvcProperties;
private final ListableBeanFactory beanFactory;
private final ObjectProvider<HttpMessageConverters> messageConvertersProvider;
private final ObjectProvider<DispatcherServletPath> dispatcherServletPath;
private final ObjectProvider<ServletRegistrationBean<?>> servletRegistrations;
private final ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer;
private ServletContext servletContext;
//===========================================================================================
//只有一个有参构造器
//有参构造器所有的参数都会从容器中确认
//resourceProperties 获取和Spring.resource绑定的所有的值的对象
//mvcProperties 获取和spring.mvc绑定的所有的值对象
//beanFactory spring的beanFactory
//messageConvertersProvider 找到所有的messageConverters
//resourceHandlerRegistrationCustomizer 找到 资源处理器的自定义器。======静态资源重点学习=========
//dispatcherServletPath
//servletRegistrations 给应用注册Servlet、Filter....
public WebMvcAutoConfigurationAdapter(WebProperties webProperties, WebMvcProperties mvcProperties,
ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
ObjectProvider<DispatcherServletPath> dispatcherServletPath,
ObjectProvider<ServletRegistrationBean<?>> servletRegistrations) {
this.resourceProperties = webProperties.getResources();
this.mvcProperties = mvcProperties;
this.beanFactory = beanFactory;
this.messageConvertersProvider = messageConvertersProvider;
this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
this.dispatcherServletPath = dispatcherServletPath;
this.servletRegistrations = servletRegistrations;
this.mvcProperties.checkConfiguration();
}
加载静态资源方法：
即：
spring:
# mvc:
# static-path-pattern: /res/**
resources:
add-mappings: false 禁用所有静态资源规则
欢迎页的访问配置：
HandlerMapping，处理器映射。保存了每一个Handler能处理哪些请求
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
this.mvcProperties.getStaticPathPattern());
welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
return welcomePageHandlerMapping;
//WelcomePageHandlerMapping
//里面对静态资源的重定向做了限制
WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
ApplicationContext applicationContext, Resource welcomePage, String staticPathPattern) {
if (welcomePage != null && "/**".equals(staticPathPattern)) {
//要使用欢迎页功能，必须是/**
logger.info("Adding welcome page: " + welcomePage);
setRootViewName("forward:index.html");
}
else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
//调用Controller index
logger.info("Adding welcome page template: index");
setRootViewName("index");
}
}
参数处理原理【HandlerAdapter：spring处理设计思想：装饰者模式】
- HandlerMapping中找到能处理请求的Handler(Controller.method)
- 为当前Handler找一个适配器HandlerAdapter;RequestMappingHandlerAdapter
理解：我们在Controller层写的所有请求，在spring底层都会走到我们的WebMvcAutoConfigurationAdapter,这里的话就会调用我们所有请求都要使用到的DispatcherServlet，其中doDispatch方法就是真正的请求处理逻辑
在处理中最重要的一步是:
1、 HandlerAdapter
2、执行目标方法
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
继续往下看：
再往里：
//ServletInvocableHandlerMethod【调用我们在Controller自己写的代码了】
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
3、参数解析器-HandlerMethodArgumentResolver
确定将要执行的目标方法的每一个参数的值是什么;
SpringMVC目标方法能写多少种参数类型。取决于参数解析器。
- 当前解析器是否支持解析这种参数
- 支持就调用 resolveArgument
4、返回值处理器
5、如何确定目标方法每一个参数的值
============InvocableHandlerMethod==========================
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
MethodParameter[] parameters = getMethodParameters();
if (ObjectUtils.isEmpty(parameters)) {
return EMPTY_ARGS;
}
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
args[i] = findProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
if (!this.resolvers.supportsParameter(parameter)) {
throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
}
try {
args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
}
catch (Exception ex) {
// Leave stack trace for later, exception may actually be resolved and handled...
if (logger.isDebugEnabled()) {
String exMsg = ex.getMessage();
if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
logger.debug(formatArgumentError(parameter, exMsg));
}
}
throw ex;
}
}
return args;
}
5.1、挨个判断所有参数解析器那个支持解析这个参数
@Nullable
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
if (resolver.supportsParameter(parameter)) {
result = resolver;
//第一次初始执行的时候因为每个元素都要编历判断所以会相对较慢，但后面做了Cache之后就会更快了
this.argumentResolverCache.put(parameter, result);
break;
}
}
}
return result;
}
总结参数解析器底层解析类【requestMapping】请求流程例一：support\InvocableHandlerMethod.class【getMethodArgumentValues】➡️HandlerMethodArgumentResolverComposite【resolveArgument】➡️AbstractNamedValueMethodArgumentResolver【resolveArgument】
5.2、解析这个参数的值
调用各自 HandlerMethodArgumentResolver 的 resolveArgument 方法即可
5.3、自定义类型参数 封装POJO
ServletModelAttributeMethodProcessor 这个参数处理器支持
是否为简单类型。
public static boolean isSimpleValueType(Class<?> type) {
return (Void.class != type && void.class != type &&
(ClassUtils.isPrimitiveOrWrapper(type) ||
Enum.class.isAssignableFrom(type) ||
CharSequence.class.isAssignableFrom(type) ||
Number.class.isAssignableFrom(type) ||
Date.class.isAssignableFrom(type) ||
Temporal.class.isAssignableFrom(type) ||
URI.class == type ||
URL.class == type ||
Locale.class == type ||
Class.class == type));
}
@Override
@Nullable
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
Assert.state(mavContainer != null, "ModelAttributeMethodProcessor requires ModelAndViewContainer");
Assert.state(binderFactory != null, "ModelAttributeMethodProcessor requires WebDataBinderFactory");
String name = ModelFactory.getNameForParameter(parameter);
ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);
if (ann != null) {
mavContainer.setBinding(name, ann.binding());
}
Object attribute = null;
BindingResult bindingResult = null;
if (mavContainer.containsAttribute(name)) {
attribute = mavContainer.getModel().get(name);
}
else {
// Create attribute instance
try {
attribute = createAttribute(name, parameter, binderFactory, webRequest);
}
catch (BindException ex) {
if (isBindExceptionRequired(parameter)) {
// No BindingResult parameter -> fail with BindException
throw ex;
}
// Otherwise, expose null/empty value and associated BindingResult
if (parameter.getParameterType() == Optional.class) {
attribute = Optional.empty();
}
bindingResult = ex.getBindingResult();
}
}
if (bindingResult == null) {
// Bean property binding and validation;
// skipped in case of binding failure on construction.
WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
if (binder.getTarget() != null) {
if (!mavContainer.isBindingDisabled(name)) {
bindRequestParameters(binder, webRequest);
}
validateIfApplicable(binder, parameter);
if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
throw new BindException(binder.getBindingResult());
}
}
// Value type adaptation, also covering java.util.Optional
if (!parameter.getParameterType().isInstance(attribute)) {
attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
}
bindingResult = binder.getBindingResult();
}
// Add resolved attribute and BindingResult at the end of the model
Map<String, Object> bindingResultModel = bindingResult.getModel();
mavContainer.removeAttributes(bindingResultModel);
mavContainer.addAllAttributes(bindingResultModel);
return attribute;
}