springMVC源码探索之RequestMappingHandlerMapping

旧城等待， 2022-12-23 11:20 172阅读 0赞

### RequestMappingHandlerMapping ###

*  简介
 *  方法
 *   *  detectHandlerMethods
     *  afterPropertiesSet
     *  isHandler
     *  getMappingForMethod
     *  createRequestMappingInfo

# 简介 #

RequestMappingHandlerMapping是AbstractHandlerMethodMapping 抽象类的唯一实现类，它的作用 是根据在Controller中的@RequestMapping注解生成RequestMappingInfo。

# 方法 #

上一篇在记录[AbstractHandlerMethodMapping][]源码是有出现过一些方法，AbstractHandlerMethodMapping是抽象类这些方法的具体实现都在子类RequestMappingHandlerMapping 中。

## detectHandlerMethods ##

AbstractHandlerMethodMapping\#detectHandlerMethods() 这个方法的作用是从handler中获取handler method并注册。detectHandlerMethods 有些方法是需要RequestMappingHandlerMapping 实现的，相关方法会在下面介绍。

/** * Look for handler methods in a handler. * @param handler the bean name of a handler or a handler instance */
    	protected void detectHandlerMethods(final Object handler) { 
    		Class<?> handlerType = (handler instanceof String ?
    				obtainApplicationContext().getType((String) handler) : handler.getClass());
    
    		if (handlerType != null) { 
    			//为给定的类返回用户定义的类:通常只是给定的类，如果是cglib生成的子类，则返回原始的类。
    			final Class<?> userType = ClassUtils.getUserClass(handlerType);
    			Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
    					(MethodIntrospector.MetadataLookup<T>) method -> { 
    						try { 
    							// 为处理程序方法提供映射
    							return getMappingForMethod(method, userType);
    						}
    						catch (Throwable ex) { 
    							throw new IllegalStateException("Invalid mapping on handler class [" +
    									userType.getName() + "]: " + method, ex);
    						}
    					});
    			if (logger.isDebugEnabled()) { 
    				logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
    			}
    
    			// 为查找到的handler method 进行注册
    			methods.forEach((method, mapping) -> { 
    				Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
    				registerHandlerMethod(handler, invocableMethod, mapping);
    			});
    		}
    	}

## afterPropertiesSet ##

初始化bean是调用的方法，各种配置设置并调用父类afterPropertiesSet 方法。

@Override
    	public void afterPropertiesSet() { 
    	// 各种配置设置
    		this.config = new RequestMappingInfo.BuilderConfiguration();
    		this.config.setUrlPathHelper(getUrlPathHelper());
    		this.config.setPathMatcher(getPathMatcher());
    		this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
    		this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
    		this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
    		this.config.setContentNegotiationManager(getContentNegotiationManager());
    		// 调用AbstractHandlerMethodMapping afterPropertiesSet 方法
    		super.afterPropertiesSet();
    	}

## isHandler ##

isHandler 方法作用是判断提供的handler是否有@Controller或@RequestMapping注解

/** * {@inheritDoc} * <p>Expects a handler to have either a type-level @{@link Controller} * annotation or a type-level @{@link RequestMapping} annotation. */
    	@Override
    	protected boolean isHandler(Class<?> beanType) { 
    		return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
    				AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
    	}

## getMappingForMethod ##

通过@RequestMapping 注解生成一个RequestMappingInfo 对象并返回，如果没有使用RequestMapping 注解会返回null，主要还是看createRequestMappingInfo 方法

@Override
    	@Nullable
    	protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) { 
    		RequestMappingInfo info = createRequestMappingInfo(method);
    		if (info != null) { 
    			RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
    			if (typeInfo != null) { 
    				info = typeInfo.combine(info);
    			}
    		}
    		return info;
    	}

## createRequestMappingInfo ##

createRequestMappingInfo 解析RequestMapping 注解 生成RequestMappingInfo对象。  
createRequestMappingInfo(AnnotatedElement element)这个方法会先判断参数类型，然后根据类型去查找是否有额外的请求条件，如果有就把条件RequestMapping 和 条件做为参数调用重载方法  
createRequestMappingInfo(RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition);

private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) { 
    		RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
    		// getCustomTypeCondition 和 getCustomMethodCondition return null 
    		RequestCondition<?> condition = (element instanceof Class ?
    				getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element));
    		return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);
    	}

getCustomTypeCondition和getCustomMethodCondition 这两个方法没有实现，它们的作用是自定义请求参数条件，如果需要可以继承AbstractRequestCondition 和使用CompositeRequestCondition 类来提供多个自定义条件。

重载方法createRequestMappingInfo，实际生成RequestMappingInfo 的方法，

/** * Create a {@link RequestMappingInfo} from the supplied * {@link RequestMapping @RequestMapping} annotation, which is either * a directly declared annotation, a meta-annotation, or the synthesized * result of merging annotation attributes within an annotation hierarchy. */
    	protected RequestMappingInfo createRequestMappingInfo(
    			RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition) { 
    
    		RequestMappingInfo.Builder builder = RequestMappingInfo
    				.paths(resolveEmbeddedValuesInPatterns(requestMapping.path()))
    				.methods(requestMapping.method())
    				.params(requestMapping.params())
    				.headers(requestMapping.headers())
    				.consumes(requestMapping.consumes())
    				.produces(requestMapping.produces())
    				.mappingName(requestMapping.name());
    		if (customCondition != null) { 
    			builder.customCondition(customCondition);
    		}
    		return builder.options(this.config).build();
    	}

上面就是简单的介绍了一下springmvc路径映射过程，有兴趣的还是看下源码吧，  
能力有限，水平一般，如有错误，请多指出。

[AbstractHandlerMethodMapping]: https://blog.csdn.net/qq_39654841/article/details/108695751