SpringMVC源码解读之HandlerMapping - AbstractUrlHandlerMapping系列request分发

AbstractHandlerMapping实现HandlerMapping接口定的getHandler

　　1. 提供getHandlerInternal模板方法给子类实现

　     2. 如果没有获取Handler,则使用默认的defaultHandler

　　3. 如果handler是string类型,从context获取实例

　　4. 通过getHandlerExecutionChain封装handler,添加interceptor

// AbstractHandlerMapping
/**
* 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
*/
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
return getHandlerExecutionChain(handler, request);
} 
// AbstractHandlerMapping
/**
* Build a HandlerExecutionChain for the given handler, including applicable interceptors.
* <p>The default implementation simply builds a standard HandlerExecutionChain with
* the given handler, the handler mapping's common interceptors, and any {@link MappedInterceptor}s
* matching to the current request URL. Subclasses may
* override this in order to extend/rearrange the list of interceptors.
* <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a pre-built
* HandlerExecutionChain. This method should handle those two cases explicitly,
* either building a new HandlerExecutionChain or extending the existing chain.
* <p>For simply adding an interceptor, consider calling {@code super.getHandlerExecutionChain}
* and invoking {@link HandlerExecutionChain#addInterceptor} on the returned chain object.
* @param handler the resolved handler instance (never {@code null})
* @param request current HTTP request
* @return the HandlerExecutionChain (never {@code null})
* @see #getAdaptedInterceptors()
*/
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain =
(handler instanceof HandlerExecutionChain) ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler);
chain.addInterceptors(getAdaptedInterceptors());
String lookupPath = urlPathHelper.getLookupPathForRequest(request);
for (MappedInterceptor mappedInterceptor : mappedInterceptors) {
if (mappedInterceptor.matches(lookupPath, pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
return chain;
}

接下来看看AbstractUrlHandlerMapping实现的getHandlerInternal

// AbstractUrlHandlerMapping
/**
* Look up a handler for the URL path of the given request.
* @param request current HTTP request
* @return the handler instance, or {@code null} if none found
*/
@Override
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
// 根据request获取url
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
// 根据url查找handler
Object handler = lookupHandler(lookupPath, request);
if (handler == null) {
// 如果没有匹配到handler需要查找默认的,下面需要将PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE缓存到request
// We need to care for the default handler directly, since we need to
// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
Object rawHandler = null;
if ("/".equals(lookupPath)) {
rawHandler = getRootHandler();
}
if (rawHandler == null) {
rawHandler = getDefaultHandler();
}
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = getApplicationContext().getBean(handlerName);
}
// 预留的校验handler模板方法,没有使用
validateHandler(rawHandler, request);
// 添加expose属性到request的拦截器
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to " + handler);
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
} 
// AbstractUrlHandlerMapping
/**
* Look up a handler instance for the given URL path.
* <p>Supports direct matches, e.g. a registered "/test" matches "/test",
* and various Ant-style pattern matches, e.g. a registered "/t*" matches
* both "/test" and "/team". For details, see the AntPathMatcher class.
* <p>Looks for the most exact pattern, where most exact is defined as
* the longest path pattern.
* @param urlPath URL the bean is mapped to
* @param request current HTTP request (to expose the path within the mapping to)
* @return the associated handler instance, or {@code null} if not found
* @see #exposePathWithinMapping
* @see org.springframework.util.AntPathMatcher
*/
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
// Direct match? 直接根据url进行查找handler
Object handler = this.handlerMap.get(urlPath);
if (handler != null) {
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
return buildPathExposingHandler(handler, urlPath, urlPath, null);
}
// Pattern match? 通过表达式进行匹配具体通过AntPathMatcher实现,具体后面分析
List<String> matchingPatterns = new ArrayList<String>();
for (String registeredPattern : this.handlerMap.keySet()) {
if (getPathMatcher().match(registeredPattern, urlPath)) {
matchingPatterns.add(registeredPattern);
}
}
String bestPatternMatch = null;
Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
if (!matchingPatterns.isEmpty()) {
Collections.sort(matchingPatterns, patternComparator);
if (logger.isDebugEnabled()) {
logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
}
// order序号最小的优先级最高
bestPatternMatch = matchingPatterns.get();
}
if (bestPatternMatch != null) {
handler = this.handlerMap.get(bestPatternMatch);
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);
// There might be multiple 'best patterns', let's make sure we have the correct URI template variables
// for all of them
Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
for (String matchingPattern : matchingPatterns) {
if (patternComparator.compare(bestPatternMatch, matchingPattern) == ) {
Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
uriTemplateVariables.putAll(decodedVars);
}
}
if (logger.isDebugEnabled()) {
logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
}
return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
}
// No handler found...
return null;
}

设计用于校验Handler,实际什么都没做,包括子类.

/**
* Validate the given handler against the current request.
* <p>The default implementation is empty. Can be overridden in subclasses,
* for example to enforce specific preconditions expressed in URL mappings.
* @param handler the handler object to validate
* @param request current HTTP request
* @throws Exception if validation failed
*/
protected void validateHandler(Object handler, HttpServletRequest request) throws Exception {
}

封装handler为HandlerExecutionChain,并添加PathExposingHandlerInterceptor和UriTemplateVariablesHandlerInterceptor拦截器.

/**
* Build a handler object for the given raw handler, exposing the actual
* handler, the {@link #PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE}, as well as
* the {@link #URI_TEMPLATE_VARIABLES_ATTRIBUTE} before executing the handler.
* <p>The default implementation builds a {@link HandlerExecutionChain}
* with a special interceptor that exposes the path attribute and uri template variables
* @param rawHandler the raw handler to expose
* @param pathWithinMapping the path to expose before executing the handler
* @param uriTemplateVariables the URI template variables, can be {@code null} if no variables found
* @return the final handler object
*/
protected Object buildPathExposingHandler(Object rawHandler, String bestMatchingPattern,
String pathWithinMapping, Map<String, String> uriTemplateVariables) {
HandlerExecutionChain chain = new HandlerExecutionChain(rawHandler);
chain.addInterceptor(new PathExposingHandlerInterceptor(bestMatchingPattern, pathWithinMapping));
if (!CollectionUtils.isEmpty(uriTemplateVariables)) {
chain.addInterceptor(new UriTemplateVariablesHandlerInterceptor(uriTemplateVariables));
}
return chain;
}

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