9. HandlerMapping 组件（三）之 AbstractHandlerMethodMapping

概述

右半边黄色的部分

注解

org.springframework.web.bind.annotation.@RequestMapping
org.springframework.web.bind.annotation.@GetMapping
org.springframework.web.bind.annotation.@PostMapping
org.springframework.web.bind.annotation.@PutMapping
org.springframework.web.bind.annotation.@DeleteMapping
org.springframework.web.bind.annotation.@PatchMapping

AbstractHandlerMethodMapping

实现 InitializingBean 接口，继承 AbstractHandlerMapping 抽���类，以 Method 作为 Handler 的 HandlerMapping 抽象类，提供 Mapping 的初始化、注册等通用的骨架方法。这就是我们常说的“模板方法模式” 。

AbstractHandlerMethodMapping 定义为了  泛型，交给子类做决定。

例如，子类 RequestMappingInfoHandlerMapping 使用 RequestMappingInfo 类作为  泛型。

构造方法

// AbstractHandlerMethodMapping.java

public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean {

    /**
     * Mapping 注册表
     */
    private final MappingRegistry mappingRegistry = new MappingRegistry();

    /**
     * Mapping 命名策略
     */
    @Nullable
    private HandlerMethodMappingNamingStrategy<T> namingStrategy;
}

• mappingRegistry 属性，Mapping 注册表
• namingStrategy 属性，org.springframework.web.servlet.handler.HandlerMethodMappingNamingStrategy 接口，Handler 的 Method 的 Mapping 的名字生成策略接口。

// HandlerMethodMappingNamingStrategy.java

@FunctionalInterface
public interface HandlerMethodMappingNamingStrategy<T> {

/**
 * 获得名字
 *
 * Determine the name for the given HandlerMethod and mapping.
 * @param handlerMethod the handler method
 * @param mapping the mapping
 * @return the name
 */
	String getName(HandlerMethod handlerMethod, T mapping);

}

我们就可以根据 Mapping 的名字，获得 Handler

该策略模式，只有一个实现策略。代码如下：

// RequestMappingInfoHandlerMethodMappingNamingStrategy.java

public class RequestMappingInfoHandlerMethodMappingNamingStrategy
        implements HandlerMethodMappingNamingStrategy<RequestMappingInfo> {

    /** Separator between the type and method-level parts of a HandlerMethod mapping name. */
    public static final String SEPARATOR = "#";

    @Override
    public String getName(HandlerMethod handlerMethod, RequestMappingInfo mapping) {
        // 情况一，mapping 名字非空，则使用 mapping 的名字
        if (mapping.getName() != null) {
            return mapping.getName();
        }
        // 情况二，使用类名大写 + "#" + 方法名
        StringBuilder sb = new StringBuilder();
        String simpleTypeName = handlerMethod.getBeanType().getSimpleName();
        for (int i = 0 ; i < simpleTypeName.length(); i++) {
            if (Character.isUpperCase(simpleTypeName.charAt(i))) {
                sb.append(simpleTypeName.charAt(i));
            }
        }
        sb.append(SEPARATOR).append(handlerMethod.getMethod().getName());
        return sb.toString();
    }

}

• 如果 Mapping 已经配置名字，则直接返回

  • @RequestMapping(name = “login”, value = “user/login”) 注解的方法，它对应的 Mapping 的名字就是 “login”

• 如果 Mapping 未配置名字，则使用使用类名大写 + “#” + 方法名

  • @RequestMapping(value = “user/login”) 注解的方法，假设它所在的类为 UserController ，对应的方法名为 login ，则它对应的 Mapping 的名字就是 USERCONTROLLER#login

MappingRegistry

MappingRegistry ，是 AbstractHandlerMethodMapping 的私有类，Mapping 注册表。

构造方法

// AbstractHandlerMethodMapping.java#MappingRegistry

/**
 * 注册表
 *
 * KEY: Mapping
 */
private final Map<T, MappingRegistration<T>> registry = new HashMap<>();

/**
 * 注册表2
 *
 * KEY：Mapping
 */
private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>();

/**
 * 直接 URL 的映射
 *
 * KEY：直接 URL
 * VALUE：Mapping 数组
 */
private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>();

/**
 * Mapping 的名字与 HandlerMethod 的映射
 *
 * KEY：Mapping 的名字
 * VALUE：HandlerMethod 数组
 */
private final Map<String, List<HandlerMethod>> nameLookup = new ConcurrentHashMap<>();

/**
 * TODO 1012 cors
 */
private final Map<HandlerMethod, CorsConfiguration> corsLookup = new ConcurrentHashMap<>();

/**
 * 读写锁
 */
private final ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();

读写锁

/**
 * 获得读锁
 *
 * Acquire the read lock when using getMappings and getMappingsByUrl.
 */
public void acquireReadLock() {
	this.readWriteLock.readLock().lock();
}

/**
 * 获得写锁
 *
 * Release the read lock after using getMappings and getMappingsByUrl.
 */
public void releaseReadLock() {
	this.readWriteLock.readLock().unlock();
}

register

register(T mapping, Object handler, Method method) 方法，注册

// AbstractHandlerMethodMapping.java#MappingRegistry

public void register(T mapping, Object handler, Method method) {
    // <1> 获得写锁
    this.readWriteLock.writeLock().lock();
    try {
        // <2.1> 创建 HandlerMethod 对象
        HandlerMethod handlerMethod = createHandlerMethod(handler, method);
        // <2.2> 校验当前 mapping 不存在，否则抛出 IllegalStateException 异常
        assertUniqueMethodMapping(handlerMethod, mapping);
        // <2.3> 添加 mapping + HandlerMethod 到 mappingLookup 中
        this.mappingLookup.put(mapping, handlerMethod);

        // <3.1> 获得 mapping 对应的普通 URL 数组
        List<String> directUrls = getDirectUrls(mapping);
        // <3.2> 添加到 url + mapping 到 urlLookup 集合中
        for (String url : directUrls) {
            this.urlLookup.add(url, mapping);
        }

        // <4> 初始化 nameLookup
        String name = null;
        if (getNamingStrategy() != null) {
            // <4.1> 获得 Mapping 的名字
            name = getNamingStrategy().getName(handlerMethod, mapping);
            // <4.2> 添加到 mapping 的名字 + HandlerMethod 到 nameLookup 中
            addMappingName(name, handlerMethod);
        }

        // <5> TODO 1012 cors
        CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
        if (corsConfig != null) {
            this.corsLookup.put(handlerMethod, corsConfig);
        }

        // <6> 创建 MappingRegistration 对象，并 mapping + MappingRegistration 添加到 registry 中
        this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod));
    } finally {
        // <7> 释放写锁
        this.readWriteLock.writeLock().unlock();
    }
}

校验不存在，抛出异常

// AbstractHandlerMethodMapping.java#MappingRegistry

private void assertUniqueMethodMapping(HandlerMethod newHandlerMethod, T mapping) {
	HandlerMethod handlerMethod = this.mappingLookup.get(mapping);
	if (handlerMethod != null && !handlerMethod.equals(newHandlerMethod)) { // 存在，且不相等，说明不唯一
		throw new IllegalStateException(
				"Ambiguous mapping. Cannot map '" + newHandlerMethod.getBean() + "' method \n" +
						newHandlerMethod + "\nto " + mapping + ": There is already '" +
						handlerMethod.getBean() + "' bean method\n" + handlerMethod + " mapped.");
	}
}

调用 #getDirectUrls(T mapping) 方法，获得 mapping 对应的直接 URL 数组

// AbstractHandlerMethodMapping.java#MappingRegistry

private List<String> getDirectUrls(T mapping) {
	List<String> urls = new ArrayList<>(1);
	// 遍历 Mapping 对应的路径
	for (String path : getMappingPathPatterns(mapping)) {
		// 非**模式**路径
		if (!getPathMatcher().isPattern(path)) {
			urls.add(path);
		}
	}
	return urls;
}

• 例如，@RequestMapping(“/user/login”) 注解对应的路径，就是直接路径
• 例如，@RequestMapping(“/user/${id}”) 注解对应的路径，不是直接路径

调用 #addMappingName(String name, HandlerMethod handlerMethod) 方法，添加 mapping 的名字 + HandlerMethod 到 nameLookup 中

// AbstractHandlerMethodMapping.java#MappingRegistry

private void addMappingName(String name, HandlerMethod handlerMethod) {
    // 获得 Mapping 的名字，对应的 HandlerMethod 数组
    List<HandlerMethod> oldList = this.nameLookup.get(name);
	if (oldList == null) {
		oldList = Collections.emptyList();
	}

	// 如果已经存在，则不用添加
	for (HandlerMethod current : oldList) {
		if (handlerMethod.equals(current)) {
			return;
		}
	}

	// 添加到 nameLookup 中
	List<HandlerMethod> newList = new ArrayList<>(oldList.size() + 1); // 重新创建的原因是，保证数组的大小固定。因为，基本不太存在扩容的可能性，申请大了就浪费了。
	newList.addAll(oldList);
	newList.add(handlerMethod);
	this.nameLookup.put(name, newList);
}

unregister

unregister(T mapping) 方法，取消注册

// AbstractHandlerMethodMapping.java#MappingRegistry

public void unregister(T mapping) {
    // 获得写锁
    this.readWriteLock.writeLock().lock();
    try {
        // 从 registry 中移除
        MappingRegistration<T> definition = this.registry.remove(mapping);
        if (definition == null) {
            return;
        }

        // 从 mappingLookup 中移除
        this.mappingLookup.remove(definition.getMapping());

        // 从 urlLookup 移除
        for (String url : definition.getDirectUrls()) {
            List<T> list = this.urlLookup.get(url);
            if (list != null) {
                list.remove(definition.getMapping());
                if (list.isEmpty()) {
                    this.urlLookup.remove(url);
                }
            }
        }

        // 从 nameLookup 移除
        removeMappingName(definition);

        // 从 corsLookup 中移除
        this.corsLookup.remove(definition.getHandlerMethod());
    } finally {
        // 释放写锁
        this.readWriteLock.writeLock().unlock();
    }
}

createHandlerMethod

创建 HandlerMethod 对象

// AbstractHandlerMethodMapping.java

protected HandlerMethod createHandlerMethod(Object handler, Method method) {
    HandlerMethod handlerMethod;
    // <1> 如果 handler 类型为 String， 说明对应一个 Bean 对象，例如 UserController 使用 @Controller 注解后，默认 handler 为它的 beanName ，即 `userController`
    if (handler instanceof String) {
        String beanName = (String) handler;
        handlerMethod = new HandlerMethod(beanName,
                obtainApplicationContext().getAutowireCapableBeanFactory(), method);
    // <2> 如果 handler 类型非 String ，说明是一个已经是一个 handler 对象，就无需处理，直接创建 HandlerMethod 对象
    } else {
        handlerMethod = new HandlerMethod(handler, method);
    }
    return handlerMethod;
}

• 如果 handler 类型为 String， 说明对应一个 Bean 对象

  • 例如 UserController 使用 @Controller 注解后， handler 为它的默认的 beanName = userController

• 如果 handler 类型非 String ，说明是一个已经是一个 handler 对象，就无需处理，直接创建 HandlerMethod 对象。

我们已经可以觉察，实际上，HandlerMethod 是 handler + method 的组合，一个对象的某个方法。

HandlerMethod

处理器的方法的封装对象

// HandlerMethod.java

/**
 * Bean 对象
 */
private final Object bean;

@Nullable
private final BeanFactory beanFactory;

/**
 * Bean 的类型
 */
private final Class<?> beanType;

/**
 * 方法
 */
private final Method method;

/**
 * {@link #method} 的桥接方法
 *
 * 详细说明
 *
 * 1. https://www.jianshu.com/p/250030ea9b28
 * 2. https://blog.csdn.net/mhmyqn/article/details/47342577
 */
private final Method bridgedMethod;

/**
 * 方法参数数组
 */
private final MethodParameter[] parameters;

/**
 * 响应的状态码，即 {@link ResponseStatus#code()}
 */
@Nullable
private HttpStatus responseStatus;
/**
 * 响应的状态码原因，即 {@link ResponseStatus#reason()}
 */
@Nullable
private String responseStatusReason;

/**
 * 解析自哪个 HandlerMethod 对象
 *
 * 仅构造方法中传入 HandlerMethod 类型的参数适用，例如 {@link #HandlerMethod(HandlerMethod)}
 */
@Nullable
private HandlerMethod resolvedFromHandlerMethod;

/**
 * 父接口的方法的参数注解数组
 */
@Nullable
private volatile List<Annotation[][]> interfaceParameterAnnotations;

构造方法

// HandlerMethod.java

/**
 * Create an instance from a bean name, a method, and a {@code BeanFactory}.
 * The method {@link #createWithResolvedBean()} may be used later to
 * re-create the {@code HandlerMethod} with an initialized bean.
 */
public HandlerMethod(String beanName, BeanFactory beanFactory, Method method) {
	Assert.hasText(beanName, "Bean name is required");
	Assert.notNull(beanFactory, "BeanFactory is required");
	Assert.notNull(method, "Method is required");
	// <1> 将 beanName 赋值给 bean 属性，说明 beanFactory + bean 的方式，获得 handler 对象
	this.bean = beanName;
	this.beanFactory = beanFactory;
	// <2> 初始化 beanType 属性
	Class<?> beanType = beanFactory.getType(beanName);
	if (beanType == null) {
		throw new IllegalStateException("Cannot resolve bean type for bean with name '" + beanName + "'");
	}
	this.beanType = ClassUtils.getUserClass(beanType);
	// <3> 初始化 method、bridgedMethod 属性
	this.method = method;
	this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
	// <4> 初始化 parameters 属性
	this.parameters = initMethodParameters();
	// <5> 初始化 responseStatus、responseStatusReason 属性
	evaluateResponseStatus();
}

evaluateResponseStatus() 方法，初始化 responseStatus、responseStatusReason 属性。

// HandlerMethod.java

private void evaluateResponseStatus() {
	ResponseStatus annotation = getMethodAnnotation(ResponseStatus.class);
	if (annotation == null) {
		annotation = AnnotatedElementUtils.findMergedAnnotation(getBeanType(), ResponseStatus.class);
	}
	if (annotation != null) {
		this.responseStatus = annotation.code();
		this.responseStatusReason = annotation.reason();
	}
}

调用 #initMethodParameters() 方法，初始化 parameters 属性。

// HandlerMethod.java

private MethodParameter[] initMethodParameters() {
	int count = this.bridgedMethod.getParameterCount();
	// 创建 MethodParameter 数组
	MethodParameter[] result = new MethodParameter[count];
	// 遍历 bridgedMethod 的参数，逐个解析参数类型
	for (int i = 0; i < count; i++) {
		HandlerMethodParameter parameter = new HandlerMethodParameter(i);
		GenericTypeResolver.resolveParameterType(parameter, this.beanType);
		result[i] = parameter;
	}
	return result;
}

MappingRegistration

MappingRegistration ，是 AbstractHandlerMethodMapping 的私有静态类，Mapping 注册登记。

// AbstractHandlerMethodMapping.java

private static class MappingRegistration<T> {

    /**
     * Mapping 对象
     */
    private final T mapping;

    /**
     * HandlerMethod 对象
     */
    private final HandlerMethod handlerMethod;

    /**
     * 直接 URL 数组
     */
    private final List<String> directUrls;

    /**
     * {@link #mapping} 的名字
     */
    @Nullable
    private final String mappingName;

    public MappingRegistration(T mapping, HandlerMethod handlerMethod,
            @Nullable List<String> directUrls, @Nullable String mappingName) {

        Assert.notNull(mapping, "Mapping must not be null");
        Assert.notNull(handlerMethod, "HandlerMethod must not be null");
        this.mapping = mapping;
        this.handlerMethod = handlerMethod;
        this.directUrls = (directUrls != null ? directUrls : Collections.emptyList());
        this.mappingName = mappingName;
    }

    // ... 省略 getting 方法
}

afterPropertiesSet

实现 #afterPropertiesSet() 方法，进行初始化

// AbstractHandlerMethodMapping.java

/**
 * 是否只扫描可访问的 HandlerMethod 们
 */
private boolean detectHandlerMethodsInAncestorContexts = false;

@Override
public void afterPropertiesSet() {
	// <x> 初始化处理器的方法们
	initHandlerMethods();
}

/**
 * Scan beans in the ApplicationContext, detect and register handler methods.
 * @see #getCandidateBeanNames()
 * @see #processCandidateBean
 * @see #handlerMethodsInitialized
 */
protected void initHandlerMethods() {
	// <1.1> 遍历 Bean ，逐个处理
	for (String beanName : getCandidateBeanNames()) {
		if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
			// <1.2> 处理 Bean
			processCandidateBean(beanName);
		}
	}
	// <2> 初始化处理器的方法们。目前是空方法，暂无具体的实现
	handlerMethodsInitialized(getHandlerMethods());
}

调用 #getCandidateBeanNames() 方法，获得所有 Bean 的名字们，然后进行遍历处理

// AbstractHandlerMethodMapping.java

/**
 * Determine the names of candidate beans in the application context.
 * @since 5.1
 * @see #setDetectHandlerMethodsInAncestorContexts
 * @see BeanFactoryUtils#beanNamesForTypeIncludingAncestors
 */
protected String[] getCandidateBeanNames() {
	return (this.detectHandlerMethodsInAncestorContexts ? // 可访问
			BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
			obtainApplicationContext().getBeanNamesForType(Object.class));
}

processCandidateBean

判断 Bean 是否为处理器，如果是，则扫描处理器方法。

// AbstractHandlerMethodMapping.java

/**
 * Determine the type of the specified candidate bean and call
 * {@link #detectHandlerMethods} if identified as a handler type.
 * <p>This implementation avoids bean creation through checking
 * {@link org.springframework.beans.factory.BeanFactory#getType}
 * and calling {@link #detectHandlerMethods} with the bean name.
 * @param beanName the name of the candidate bean
 * @since 5.1
 * @see #isHandler
 * @see #detectHandlerMethods
 */
protected void processCandidateBean(String beanName) {
    // <1> 获得 Bean 对应的类型
    Class<?> beanType = null;
    try {
        beanType = obtainApplicationContext().getType(beanName);
    } catch (Throwable ex) {
        // An unresolvable bean type, probably from a lazy bean - let's ignore it.
        if (logger.isTraceEnabled()) {
            logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
        }
    }
    // 判断 Bean 是否为处理器，如果是，则扫描处理器方法
    if (beanType != null && isHandler(beanType)) { // <2.1>
        detectHandlerMethods(beanName); // <2.2>
    }
}

detectHandlerMethods(Object handler) 方法， 扫描处理器的方法们

// AbstractHandlerMethodMapping.java

/**
 * 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) {
    // <1> 获得处理器类型
    Class<?> handlerType = (handler instanceof String ?
            obtainApplicationContext().getType((String) handler) : handler.getClass());

    if (handlerType != null) {
        // <2> 获得真实的类。因为，handlerType 可能是代理类
        final Class<?> userType = ClassUtils.getUserClass(handlerType);
        // <3> 获得匹配的方法的集合
        Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
                (MethodIntrospector.MetadataLookup<T>) method -> getMappingForMethod(method, userType)); // 抽象方法，子类实现
        if (logger.isTraceEnabled()) {
            logger.trace("Mapped " + methods.size() + " handler method(s) for " + userType + ": " + methods);
        }
        // <4> 遍历方法，逐个注册 HandlerMethod
        methods.forEach((key, mapping) -> {
            Method invocableMethod = AopUtils.selectInvocableMethod(key, userType);
            registerHandlerMethod(handler, invocableMethod, mapping);
        });
    }
}

ClassUtils#getUserClass(handlerType) 方法，获得真实的类。因为，handlerType 可能是代理类。

// ClassUtils.java

public static Class<?> getUserClass(Class<?> clazz) {
	// 如果 CG_CLASS 代理类，则获取其父类
	if (clazz.getName().contains(CGLIB_CLASS_SEPARATOR)) {
		Class<?> superclass = clazz.getSuperclass();
		if (superclass != null && superclass != Object.class) {
			return superclass;
		}
	}
	return clazz;
}

获得匹配的方法的集合。通过 #getMappingForMethod(Method method, Class<?> handlerType) 抽象方法，获得方法的 Mapping 信息。

@Nullable
protected abstract T getMappingForMethod(Method method, Class<?> handlerType);

该方法在 RequestMappingHandlerMapping 类中实现。

逐个调用 #registerHandlerMethod(Object handler, Method method, T mapping) 方法，注册 HandlerMethod

// AbstractHandlerMethodMapping.java

/**
 * 注册 HandlerMethod
 *
 * Register a handler method and its unique mapping. Invoked at startup for
 * each detected handler method.
 * @param handler the bean name of the handler or the handler instance
 * @param method the method to register
 * @param mapping the mapping conditions associated with the handler method
 * @throws IllegalStateException if another method was already registered
 * under the same mapping
 */
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
	this.mappingRegistry.register(mapping, handler, method);
}

这样，Mapping 和 handler + method ，就成功注册到 mappingRegistry 中。究竟 Mapping 是什么？实际上，在 RequestMappingHandlerMapping 中，就是 @RequestMapping 解析成的 RequestMappingInfo 对象。

getHandlerInternal

获得请求对应的 HandlerMethod 对象

// AbstractHandlerMethodMapping.java

// AbstractHandlerMethodMapping.java

/**
 * Look up a handler method for the given request.
 */
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
    // <1> 获得请求的路径
    String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
    // <2> 获得写锁
    this.mappingRegistry.acquireReadLock();
    try {
        // <3> 获得 HandlerMethod 对象
        HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
        // <4> 进一步，获得 HandlerMethod 对象
        return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
    } finally {
        // <5> 释放写锁
        this.mappingRegistry.releaseReadLock();
    }
}

调用 #lookupHandlerMethod(ServerWebExchange exchange) 方法，获得 HandlerMethod 对象

如果获得到 HandlerMethod 对象，则调用 HandlerMethod#createWithResolvedBean() 方法，进一步，获得 HandlerMethod 对象。

// HandlerMethod.java

/**
 * If the provided instance contains a bean name rather than an object instance,
 * the bean name is resolved before a {@link HandlerMethod} is created and returned.
 */
public HandlerMethod createWithResolvedBean() {
	Object handler = this.bean;
	// 如果是 bean 是 String类型，则获取对应的 handler 对象。例如，bean = userController 字符串，获取后，handler = UserController 对象
	if (this.bean instanceof String) {
		Assert.state(this.beanFactory != null, "Cannot resolve bean name without BeanFactory");
		String beanName = (String) this.bean;
		handler = this.beanFactory.getBean(beanName);
	}
	// 创建 HandlerMethod 对象
	return new HandlerMethod(this, handler);
}

lookupHandlerMethod

获得 HandlerMethod 对象。

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
    // <1> Match 数组，存储匹配上当前请求的结果
    List<Match> matches = new ArrayList<>();
    // <1.1> 优先，基于直接 URL 的 Mapping 们，进行匹配
    List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
    if (directPathMatches != null) {
        addMatchingMappings(directPathMatches, matches, request);
    }
    // <1.2> 其次，扫描注册表的 Mapping 们，进行匹配
    if (matches.isEmpty()) {
        // No choice but to go through all mappings...
        addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
    }

    // <2> 如果匹配到，则获取最佳匹配的 Match 对象的 handlerMethod 属性
    if (!matches.isEmpty()) {
        // <2.1> 创建 MatchComparator 对象，排序 matches 结果
        Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
        matches.sort(comparator);
        // <2.2> 获得首个 Match 对象
        Match bestMatch = matches.get(0);
        // <2.3> 处理存在多个 Match 对象的情况！！
        if (matches.size() > 1) {
            if (logger.isTraceEnabled()) {
                logger.trace(matches.size() + " matching mappings: " + matches);
            }
            // TODO 1012 cors
            if (CorsUtils.isPreFlightRequest(request)) {
                return PREFLIGHT_AMBIGUOUS_MATCH;
            }
            // 比较 bestMatch 和 secondBestMatch ，如果相等，说明有问题，抛出 IllegalStateException 异常
            // 因为，两个优先级一样高，说明无法判断谁更优先
            Match secondBestMatch = matches.get(1);
            if (comparator.compare(bestMatch, secondBestMatch) == 0) {
                Method m1 = bestMatch.handlerMethod.getMethod();
                Method m2 = secondBestMatch.handlerMethod.getMethod();
                String uri = request.getRequestURI();
                throw new IllegalStateException(
                        "Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
            }
        }
        // <2.4> 处理首个 Match 对象
        handleMatch(bestMatch.mapping, lookupPath, request);
        // <2.5> 返回首个 Match 对象的 handlerMethod 属性
        return bestMatch.handlerMethod;
    // <3> 如果匹配不到，则处理不匹配的情况
    } else {
        return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
    }
}

• 优先，基于直接 URL 的 Mapping 们，进行匹配
• 其次，基于扫描注册表的 Mapping 们，进行匹配

Match 数组，存储匹配上当前请求的结果。Match 是 AbstractHandlerMethodMapping 的内部类

private class Match {

    /**
     * Mapping 对象
     */
    private final T mapping;
    /**
     * HandlerMethod 对象
     */
    private final HandlerMethod handlerMethod;

    public Match(T mapping, HandlerMethod handlerMethod) {
        this.mapping = mapping;
        this.handlerMethod = handlerMethod;
    }

    @Override
    public String toString() {
        return this.mapping.toString();
    }

}

addMatchingMappings(Collection mappings, List matches, ServerWebExchange exchange) 方法，将当前请求和注册表中的 Mapping 进行匹配。若匹配成功，则生成 Mapping 记录，添加到 matches 中。

// AbstractHandlerMethodMapping.java

private void addMatchingMappings(Collection<T> mappings, List<Match> matches, ServerWebExchange exchange) {
    // 遍历 Mapping 数组
	for (T mapping : mappings) {
	    // <1> 执行匹配
		T match = getMatchingMapping(mapping, exchange);
		// <2> 如果匹配，则创建 Match 对象，添加到 matches 中
		if (match != null) {
			matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));
		}
	}
}

• 遍历 Mapping 数组，逐个调用 #getMatchingMapping(T mapping, ServerWebExchange exchange) 抽象方法，执行匹配。
• 如果匹配，则返回的结果非空。则创建 Match 对象，添加到 matches 中

创建 MatchComparator 对象，排序 matches 结果。其中 MatchComparator 实现 Comparator 接口，是 AbstractHandlerMethodMapping 的私有类，Match 排序器。

// AbstractHandlerMethodMapping.java

private class MatchComparator implements Comparator<Match> {

	private final Comparator<T> comparator;

	public MatchComparator(Comparator<T> comparator) {
		this.comparator = comparator;
	}

	@Override
	public int compare(Match match1, Match match2) {
		return this.comparator.compare(match1.mapping, match2.mapping);
	}
}

• 获得首个 Match 对象 bestMatch 变量
• 处理存在多个 Match 对象的情况！！获得第二 Match 对象 secondBestMatch 变量。通过 bestMatch 和 secondBestMatch 的比较，如果一样的优先级，则抛出 IllegalStateException 异常。因为，两个优先级一样高，说明无法判断谁更优先。

调用 #handleMatch(T mapping, String lookupPath, HttpServletRequest request) 方法，设置匹配的路径 lookupPath 到请求属性种。

// AbstractHandlerMethodMapping.java

protected void handleMatch(T mapping, String lookupPath, HttpServletRequest request) {
	request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, lookupPath);
}

如果匹配不到，调用 #handleNoMatch(Set mappings, String lookupPath, HttpServletRequest request) 方法，处理不匹配的情况。

@Nullable
protected HandlerMethod handleNoMatch(Set<T> mappings, String lookupPath, HttpServletRequest request)
		throws Exception {
	return null;
}

RequestMappingInfoHandlerMapping

org.springframework.web.servlet.mvc.method.RequestMappingInfoHandlerMapping ，继承 AbstractHandlerMethodMapping 抽象类，定义了使用的泛型  为 org.springframework.web.servlet.mvc.method.RequestMappingInfo 类，即 ==Mapping 类型就是 RequestMappingInfo ==

好处

RequestMappingInfoHandlerMapping 定义了使用了 RequestMappingInfo 对象，而 其子类 RequestMappingHandlerMapping 使用了 @RequestMapping 注解，来生成 RequestMappingInfo 对象。

这样，如果未来我们自己定义了自己的注解，或者其他方式来生成 RequestMappingHandlerMapping 对象，未尝不可。

构造方法

// RequestMappingInfoHandlerMapping.java

public abstract class RequestMappingInfoHandlerMapping extends AbstractHandlerMethodMapping<RequestMappingInfo> {

	protected RequestMappingInfoHandlerMapping() {
		setHandlerMethodMappingNamingStrategy(new RequestMappingInfoHandlerMethodMappingNamingStrategy());
	}

}

• 泛型，为 RequestMappingInfo 类型
• 设置了 AbstractHandlerMethodMapping.namingStrategy 属性，为 RequestMappingInfoHandlerMethodMappingNamingStrategy 对象。

RequestMappingInfo

RequestMappingInfo 不是 RequestMappingInfoHandlerMapping 的内部类，但是是 RequestMappingInfo-HandlerMapping 的前缀。

构造方法

// RequestMappingInfo.java

/**
 * 名字
 */
@Nullable
private final String name;

/**
 * 请求路径的条件
 */
private final PatternsRequestCondition patternsCondition;

/**
 * 请求方法的条件
 */
private final RequestMethodsRequestCondition methodsCondition;

/**
 * 参数的条件
 */
private final ParamsRequestCondition paramsCondition;

/**
 * 请求头的条件
 */
private final HeadersRequestCondition headersCondition;

/**
 * 可消费的 Content-Type 的条件
 */
private final ConsumesRequestCondition consumesCondition;

/**
 * 可生产的 Content-Type 的条件
 */
private final ProducesRequestCondition producesCondition;

/**
 * 自定义的条件
 */
private final RequestConditionHolder customConditionHolder;

• 我们可以看到各种条件。实际上，和 @RequestMapping 注解是一一对应的。
• 日常使用最多的还是 patternsCondition 请求路径条件，和 methodsCondition 请求方法条件。

getMatchingCondition

从当前 RequestMappingInfo 获得匹配的条件。如果匹配，则基于其匹配的条件，创建新的 RequestMappingInfo 对象。如果不匹配，则返回 null

// RequestMappingInfo.java

@SuppressWarnings("Duplicates")
@Override
@Nullable
public RequestMappingInfo getMatchingCondition(HttpServletRequest request) {
    // 匹配 methodsCondition、paramsCondition、headersCondition、consumesCondition、producesCondition
	RequestMethodsRequestCondition methods = this.methodsCondition.getMatchingCondition(request);
	ParamsRequestCondition params = this.paramsCondition.getMatchingCondition(request);
	HeadersRequestCondition headers = this.headersCondition.getMatchingCondition(request);
	ConsumesRequestCondition consumes = this.consumesCondition.getMatchingCondition(request);
	ProducesRequestCondition produces = this.producesCondition.getMatchingCondition(request);
	// 如果任一为空，则返回 null ，表示匹配失败
	if (methods == null || params == null || headers == null || consumes == null || produces == null) {
		return null;
	}

	// 匹配 patternsCondition
	PatternsRequestCondition patterns = this.patternsCondition.getMatchingCondition(request);
	if (patterns == null) { // 如果 patterns 为空，则返回 null ，表示匹配失败
		return null;
	}

	// 匹配 customConditionHolder
	RequestConditionHolder custom = this.customConditionHolder.getMatchingCondition(request);
	if (custom == null) { // 如果 custom 为空，则返回 null ，表示匹配失败
		return null;
	}

	// 创建匹配的 RequestMappingInfo 对象。
	// 为什么要创建 RequestMappingInfo 对象呢？因为当前 RequestMappingInfo 对象，一个 methodsCondition 可以配置 GET、POST、DELETE 等等条件，但是实际就匹配一个请求类型，此时 methods 只代表其匹配的那个。
	return new RequestMappingInfo(this.name, patterns,
			methods, params, headers, consumes, produces, custom.getCondition());
}

• 实际都是调用每个属性对应的 #getMatchingCondition(HttpServletRequest request) 方法，获得其匹配的真正的条件。
• 如果一个 @RequestMapping(value = “user/login”) 注解，并未写 RequestMethod 的条件，岂不是会报空？实际上不会。在这种情况下，会创建一个 RequestMethodsRequestCondition 对象，并且在匹配时，直接返回自身。

private final Set<RequestMethod> methods;

@Override
@Nullable
public RequestMethodsRequestCondition getMatchingCondition(HttpServletRequest request) {
	if (CorsUtils.isPreFlightRequest(request)) {
		return matchPreFlight(request);
	}

	// 空的情况下，就返回自身
	if (getMethods().isEmpty()) {
		if (RequestMethod.OPTIONS.name().equals(request.getMethod()) &&
				!DispatcherType.ERROR.equals(request.getDispatcherType())) {
			return null; // No implicit match for OPTIONS (we handle it)
		}
		return this;
	}

	// 非空，逐个匹配
	return matchRequestMethod(request.getMethod());
}

compareTo

比较优先级

@Override
public int compareTo(RequestMappingInfo other, HttpServletRequest request) {
	int result;
	// Automatic vs explicit HTTP HEAD mapping
	// 针对 HEAD 请求方法，特殊处理
	if (HttpMethod.HEAD.matches(request.getMethod())) {
		result = this.methodsCondition.compareTo(other.getMethodsCondition(), request);
		if (result != 0) {
			return result;
		}
	}
	// 比较 patternsCondition
	result = this.patternsCondition.compareTo(other.getPatternsCondition(), request);
	if (result != 0) {
		return result;
	}
	// 比较 paramsCondition
	result = this.paramsCondition.compareTo(other.getParamsCondition(), request);
	if (result != 0) {
		return result;
	}
	// 比较 headersCondition
	result = this.headersCondition.compareTo(other.getHeadersCondition(), request);
	if (result != 0) {
		return result;
	}
	// 比较 consumesCondition
	result = this.consumesCondition.compareTo(other.getConsumesCondition(), request);
	if (result != 0) {
		return result;
	}
	// 比较 producesCondition
	result = this.producesCondition.compareTo(other.getProducesCondition(), request);
	if (result != 0) {
		return result;
	}
	// Implicit (no method) vs explicit HTTP method mappings
	// 比较 methodsCondition
	result = this.methodsCondition.compareTo(other.getMethodsCondition(), request);
	if (result != 0) {
		return result;
	}
	// 比较 customConditionHolder
	result = this.customConditionHolder.compareTo(other.customConditionHolder, request);
	if (result != 0) {
		return result;
	}
	return 0;
}

PatternsRequestCondition

继承 AbstractRequestCondition 抽象类，请求路径条件。

https://www.cnblogs.com/fangjian0423/p/springMVC-request-mapping.html

getMappingPathPatterns

获得 Mapping 对应的请求路径集合

@Override
protected Set<String> getMappingPathPatterns(RequestMappingInfo info) {
	return info.getPatternsCondition().getPatterns();
}

getMatchingMapping

@Override
protected RequestMappingInfo getMatchingMapping(RequestMappingInfo info, HttpServletRequest request) {
	return info.getMatchingCondition(request);
}

handleMatch

覆写父类的方法，设置更多的属性，到请求中

@Override
protected void handleMatch(RequestMappingInfo info, String lookupPath, HttpServletRequest request) {
	super.handleMatch(info, lookupPath, request);

	// 获得 bestPattern 和 uriVariables
	String bestPattern; // 最佳路径
	Map<String, String> uriVariables; // 路径上的变量集合
	Set<String> patterns = info.getPatternsCondition().getPatterns();
	if (patterns.isEmpty()) {
		bestPattern = lookupPath;
		uriVariables = Collections.emptyMap();
	} else {
		bestPattern = patterns.iterator().next();
		uriVariables = getPathMatcher().extractUriTemplateVariables(bestPattern, lookupPath);
	}
	request.setAttribute(BEST_MATCHING_PATTERN_ATTRIBUTE, bestPattern);

	// 设置 MATRIX_VARIABLES_ATTRIBUTE 属性，到请求中
	if (isMatrixVariableContentAvailable()) {
		Map<String, MultiValueMap<String, String>> matrixVars = extractMatrixVariables(request, uriVariables);
		request.setAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, matrixVars);
	}

	// 设置 URI_TEMPLATE_VARIABLES_ATTRIBUTE 属性，到请求中
	Map<String, String> decodedUriVariables = getUrlPathHelper().decodePathVariables(request, uriVariables);
	request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, decodedUriVariables);

	// 设置 PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE 属性，到请求中
	if (!info.getProducesCondition().getProducibleMediaTypes().isEmpty()) {
		Set<MediaType> mediaTypes = info.getProducesCondition().getProducibleMediaTypes();
		request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes);
	}
}

handleNoMatch

覆写父类方法，处理无匹配 Mapping 的情况

@Override
protected HandlerMethod handleNoMatch(
        Set<RequestMappingInfo> infos, String lookupPath, HttpServletRequest request) throws ServletException {
    // <1> 创建 PartialMatchHelper 对象，解析可能的错误
    PartialMatchHelper helper = new PartialMatchHelper(infos, request);
    if (helper.isEmpty()) {
        return null;
    }

    // <2> 方法错误
    if (helper.hasMethodsMismatch()) {
        Set<String> methods = helper.getAllowedMethods();
        if (HttpMethod.OPTIONS.matches(request.getMethod())) {
            HttpOptionsHandler handler = new HttpOptionsHandler(methods);
            return new HandlerMethod(handler, HTTP_OPTIONS_HANDLE_METHOD);
        }
        throw new HttpRequestMethodNotSupportedException(request.getMethod(), methods);
    }

    // 可消费的 Content-Type 错误
    if (helper.hasConsumesMismatch()) {
        Set<MediaType> mediaTypes = helper.getConsumableMediaTypes();
        MediaType contentType = null;
        if (StringUtils.hasLength(request.getContentType())) {
            try {
                contentType = MediaType.parseMediaType(request.getContentType());
            } catch (InvalidMediaTypeException ex) {
                throw new HttpMediaTypeNotSupportedException(ex.getMessage());
            }
        }
        throw new HttpMediaTypeNotSupportedException(contentType, new ArrayList<>(mediaTypes));
    }

    // 可生产的 Content-Type 错误
    if (helper.hasProducesMismatch()) {
        Set<MediaType> mediaTypes = helper.getProducibleMediaTypes();
        throw new HttpMediaTypeNotAcceptableException(new ArrayList<>(mediaTypes));
    }

    // <5> 参数错误
    if (helper.hasParamsMismatch()) {
        List<String[]> conditions = helper.getParamConditions();
        throw new UnsatisfiedServletRequestParameterException(conditions, request.getParameterMap());
    }

    return null;
}

• 核心代码在 PartialMatchHelper 中实现

RequestMappingHandlerMapping

实现 MatchableHandlerMapping 接口、EmbeddedValueResolverAware 接口，继承 RequestMappingInfoHandlerMapping 抽象类，基于 @RequestMapping 注解来构建 RequestMappingInfo 对象。

构造方法

// RequestMappingHandlerMapping.java

private boolean useSuffixPatternMatch = true;

private boolean useRegisteredSuffixPatternMatch = false;

private boolean useTrailingSlashMatch = true;

private Map<String, Predicate<Class<?>>> pathPrefixes = new LinkedHashMap<>();

private ContentNegotiationManager contentNegotiationManager = new ContentNegotiationManager();

@Nullable
private StringValueResolver embeddedValueResolver;

/**
 * RequestMappingInfo.BuilderConfiguration 配置
 */
private RequestMappingInfo.BuilderConfiguration config = new RequestMappingInfo.BuilderConfiguration();

afterPropertiesSet

// RequestMappingHandlerMapping.java

@Override
public void afterPropertiesSet() {
	// 构建 RequestMappingInfo.BuilderConfiguration 对象
	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());

	// 调用父类，初始化
	super.afterPropertiesSet();
}

isHandler

判断是否为处理器

@Override
protected boolean isHandler(Class<?> beanType) {
	return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
			AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}

getMappingForMethod

获得方法上的 RequestMappingInfo 对象，基于 @RequestMapping 构造。

@Override
@Nullable
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
    // <1> 基于方法上的 @RequestMapping 注解，创建 RequestMappingInfo 对象
    RequestMappingInfo info = createRequestMappingInfo(method);
    if (info != null) {
        // <2> 基于类上的 @RequestMapping 注解，合并进去
        RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
        if (typeInfo != null) {
            info = typeInfo.combine(info);
        }
        // <3> 如果有前缀，则设置到 info 中
        String prefix = getPathPrefix(handlerType);
        if (prefix != null) {
            info = RequestMappingInfo.paths(prefix).build().combine(info);
        }
    }
    return info;
}

createRequestMappingInfo

@Nullable
private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) {
	// <1> 获得 @RequestMapping 注解
	RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
	// <2> 获得自定义的条件。目前都是空方法，可以无视
	RequestCondition<?> condition = (element instanceof Class ?
			getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element));
	// <3> 基于 @RequestMapping 注解，创建 RequestMappingInfo 对象
	return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);
}

• 获得 @RequestMapping 注解。当然，@GetMapping、@PostMapping 等等注解，也可以被扫描到。
• 获得自定义的条件。目前都是空方法，可以无视。

createRequestMappingInfo

protected RequestMappingInfo createRequestMappingInfo(RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition) {
// 创建 RequestMappingInfo.Builder 对象，设置对应属性
	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);
	}
	// 创建 RequestMappingInfo 对象
	return builder.options(this.config).build();
}

基于类上的 @RequestMapping 注解，创建 RequestMappingInfo 对象，并合并进去。

match

执行匹配

@Override
public RequestMatchResult match(HttpServletRequest request, String pattern) {
	// 创建 RequestMappingInfo 对象
	RequestMappingInfo info = RequestMappingInfo.paths(pattern).options(this.config).build();
	// 获得匹配的 RequestMappingInfo 对象
	RequestMappingInfo matchingInfo = info.getMatchingCondition(request);
	if (matchingInfo == null) { // 如果不匹配，则返回 null
		return null;
	}
	// 获得请求路径的集合
	Set<String> patterns = matchingInfo.getPatternsCondition().getPatterns();
	// 获得请求的路径
	String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
	// 创建 RequestMatchResult 结果
	return new RequestMatchResult(patterns.iterator().next(), lookupPath, getPathMatcher());
}