上篇博客讲了DispathcerServlet的流转过程以及它是如何工作的，从这篇博客开始就开始深入到DispatcherServlet的内部看看它的几个主要的组件。那么这一篇就从HandlerMapping这个组件开始学习。
public class SimpleUrlHandlerMapping extends AbstractUrlHandlerMapping {
private final Map<String, Object> urlMap = new HashMap<String, Object>();
// 通过属性配置URL到Bean名的映射
public void setMappings(Properties mappings) {
CollectionUtils.mergePropertiesIntoMap(mappings, this.urlMap);
}
// 配置URL到Bean的映射
public void setUrlMap(Map<String, ?> urlMap) {
this.urlMap.putAll(urlMap);
}
public Map<String, ?> getUrlMap() {
return this.urlMap;
}
@Override
public void initApplicationContext() throws BeansException {
super.initApplicationContext();
// 初始化的时候注册处理器
registerHandlers(this.urlMap);
}
protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
// 如果配置的处理器映射为空，则警告
if (urlMap.isEmpty()) {
logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
}
else {
// 对于没一个配置的URL到处理器的映射，如果URL不是以斜线(/)开头，则追加斜线开头，则注册处理器
for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
String url = entry.getKey();
Object handler = entry.getValue();
// Prepend with slash if not already present.
if (!url.startsWith("/")) {
url = "/" + url;
}
// Remove whitespace from handler bean name.
if (handler instanceof String) {
handler = ((String) handler).trim();
}
registerHandler(url, handler);
}
}
}
} protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
//查找符合匹配规则的handler。可能的结果是HandlerExecutionChain对象或者是null
Object handler = lookupHandler(lookupPath, request);
//如果没有找到匹配的handler，则需要处理下default handler
if (handler == null) {
// 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();
}
//在getRootHandler和getDefaultHandler方法中，可能持有的是bean name。
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = getApplicationContext().getBean(handlerName);
}
validateHandler(rawHandler, request);
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
//如果handler还是为空，则抛出错误。
if (handler != null && this.mappedInterceptors != null) {
Set<HandlerInterceptor> mappedInterceptors =
this.mappedInterceptors.getInterceptors(lookupPath, this.pathMatcher);
if (!mappedInterceptors.isEmpty()) {
HandlerExecutionChain chain;
if (handler instanceof HandlerExecutionChain) {
chain = (HandlerExecutionChain) handler;
} else {
chain = new HandlerExecutionChain(handler);
}
chain.addInterceptors(mappedInterceptors.toArray(new HandlerInterceptor[mappedInterceptors.size()]));
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to handler '" + handler + "'");
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
} public interface HandlerMapping {
String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";
String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";
String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";
String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";
public abstract HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}Spring学习总结（2.3）-Spring MVC：handlermapping
原文：http://blog.csdn.net/zhuojiajin/article/details/46292125