Spring中HandlerMapping接口源码详解
作者：立小研先森
这篇文章主要介绍了Spring中HandlerMapping接口源码详解,RequestMappingHandlerMapping类就是实现此接口并将容器中所有的控制器的RequestMappingInfo请求和HandlerMethod注册到内存之中,需要的朋友可以参考下
前言
实现HandlerMapping接口的类用来定义request请求和handler object之间的映射关系；request请求可以理解为路由url、RequestMappingInfo，handler object理解为控制器类；
RequestMappingHandlerMapping类就是实现此接口并将容器中所有的控制器的RequestMappingInfo请求和HandlerMethod注册到内存之中，方便真实的请求发送过来调用具体的控制器方法；
本文将以RequestMappingHandlerMapping为主线来讲解。
接口源码如下：
public interface HandlerMapping {
/**
* 返回一个包含handler Object和所有拦截器的HandlerExecutionChain
*/
@Nullable
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}
1.HandlerMapping的初始化
容器加载时DispatcherServlet中的初始化方法initStrategies会被调用，里面的initHandlerMappings(context)方法会被执行，源码如下：
//容器中HandlerMapping接口实现类集合
@Nullable
private List<HandlerMapping> handlerMappings;
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
//判定是否检测所有的HandlerMapping
if (this.detectAllHandlerMappings) {
//查看容器中所有的实现了HandlerMapping的bean
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// 使用实现类的order进行优先级排序，升序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
//加载缺省的HandlerMapping
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerMapping later.
}
}
// Ensure we have at least one HandlerMapping, by registering
// a default HandlerMapping if no other mappings are found.
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
上面的源码是从容器中获取HandlerMapping接口的实现类，其中包括RequestMappingHandlerMapping类实例，那这个类实例实在哪里加载的呢？
2.RequestMappingHandlerMapping处理reques请求
前端发送过来一个request请求首先进入DispatcherServlet的doService方法，再进入doDispatch方法
本文的重点是通过request请求如何获取HandlerExecutionChain处理程序执行器链;HandlerExecutionChain是一个很重要的类，所有的HandlerMethod最终都要包装成HandlerExecutionChain后才可以使用；
跳出正文主题分析下HandlerExecutionChain类：
Handler execution chain, consisting of handler object and any handler interceptors. Returned by HandlerMapping’s {@link HandlerMapping#getHandler} method.
上面官方说明已经说的很清楚了，该类包含handler object(HandlerMethod)和所有的handler interceptors；而且该类的生成只能通过HandlerMapping接口的getHandler方法，具体由AbstractHandlerMapping抽象类实现；AbstractHandlerMapping类实现源码：
/**
* 根据request请求获取HandlerExecutionChain处理程序执行器链
* Look up a handler for the given request, falling back to the default
* handler if no specific one is found.
* @param request current HTTP request
* @return the corresponding handler instance, or the default handler
* @see #getHandlerInternal
*/
@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//获取Handler object即HandlerMethod对象
Object handler = getHandlerInternal(request);
if (handler == null) {
//如果没有找到匹配的HandlerMethod对象，那么就获取默认的handler
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
//根据上面获取的handler object获取处理程序执行器链类HandlerExecutionChain
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (logger.isTraceEnabled()) {
logger.trace("Mapped to " + handler);
}
else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
logger.debug("Mapped to " + executionChain.getHandler());
}
//有跨域相关配置时执行如下代码
if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {
CorsConfiguration config = (this.corsConfigurationSource != null ? this.corsConfigurationSource.getCorsConfiguration(request) : null);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
config = (config != null ? config.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
看下getHandlerInternal方法如何获取HandlerMethod对象：
/**
* 通过request请求获取对应的HandlerMethod类
*/
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
//获取请求URL
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
request.setAttribute(LOOKUP_PATH, lookupPath);
this.mappingRegistry.acquireReadLock();
try {
//获取URL对应的HandlerMethod,重点是我们如何获取HandlerMethod对象？
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
}
看lookupHandlerMethod源码：
/**
* 通过URL获取HandlerMethod对象
*/
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
//通过URL获取RequestMappingInfo集合
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
if (directPathMatches != null) {
//将RequestMappingInfo对象和HandlerMethod对象封装到Match对象中存到matches集合
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
if (!matches.isEmpty()) {
//获取集合中第一个Match对象
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
matches.sort(comparator);
bestMatch = matches.get(0);
if (logger.isTraceEnabled()) {
logger.trace(matches.size() + " matching mappings: " + matches);
}
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
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 + "}");
}
}
request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
handleMatch(bestMatch.mapping, lookupPath, request);
//返回HandlerMethod对象
return bestMatch.handlerMethod;
}
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}
上面的代码有一个this.mappingRegistry.getMappingsByUrl(lookupPath)方法获取url对应的RequestMappingInfo对象，源码如下：
//URL和RequestMappingInfo集合
private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>();
/**
* 返回与URL匹配的RequestMappingInfo集合
*/
@Nullable
public List<T> getMappingsByUrl(String urlPath) {
return this.urlLookup.get(urlPath);
}
上面的源码显示RequestMappingInfo对象是从urlLookup集合中获取的，那urlLookup集合中的数据又是从哪里来的呢？请看我的另外一篇文章RequestMappingHandlerMapping源码分析。
上面代码有一个addMatchingMappings方法，是通过这个方法获取到的HandlerMethod对象，看下源码：
private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
//循环遍历RequestMappingInfo对象
for (T mapping : mappings) {
//
T match = getMatchingMapping(mapping, request);
if (match != null) {
//通过this.mappingRegistry.getMappings()获取HandlerMethod对象
matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));
}
}
}
//RequestMappingInfo和HandlerMethod集合
private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>();
/**
* Return all mappings and handler methods. Not thread-safe.
* @see #acquireReadLock()
*/
public Map<T, HandlerMethod> getMappings() {
return this.mappingLookup;
}
上面源码获取HandlerMethod对象实际上是从mappingLookUp集合之中获取的，那你可能会问mappingLookup集合中的数据又是从哪里获取到的呢？请看我的另外一篇文章RequestMappingHandlerMapping源码分析；
回到正文，我们看下mappedHandler = getHandler(processedRequest);方法，源码如下：
/**
* Return the HandlerExecutionChain for this request.
* <p>Tries all handler mappings in order.
* @param request current HTTP request
* @return the HandlerExecutionChain, or {@code null} if no handler could be found
*/
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
//循环HandlerMapping实现类集合，其中包括RequestMappingHandlerMapping
for (HandlerMapping mapping : this.handlerMappings) {
//调用HandlerMapping实现类的getHandler方法，并获取程序执行器链类对象
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
//如果匹配直接返回，否则返回null
return handler;
}
}
}
return null;
}
通过上面我们一步步的分析源码，知道了HandlerExecutionChain处理程序执行器链是如何获取的，HandlerExecutionChain里面包含了请求对应的HandlerMethod对象和所有有关的连接器；
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