之前给大家介绍过@requestmapping注解方面的内容，那么接下来要给大家介绍的就是@RequestMapping原理，一起来了解一下吧。
首先我们要知道，springmvc启动的时候，会加载所有的Bean类，也就是加了@Controller，@Component等组件标识的类，之后，会将@RequestMapping的方法也加入到一个集合。
放入到上下文环境中。
下面是发起请求之后的执行流程：检查request类型--获取匹配的Handlemethod--查找拦截器--组成HandlerExecutionChain执行链--获取方法执行链对象的适配器(HandlerAdapter)--之后反射执行业务方法。
再来看一下源码分析：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception
{
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try
{
ModelAndView mv = null;
Exception dispatchException = null;
try
{
processedRequest = checkMultipart(request);
multipartRequestParsed = processedRequest != request;
// Determine handler for the current request.
//获取匹配的执行链
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null)
{
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//根据匹配到的执行链对象，获取合适的适配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method))
{
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled())
{
String requestUri = urlPathHelper.getRequestUri(request);
logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response)
.checkNotModified(lastModified) && isGet)
{
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response))
{
return;
}
try
{
// Actually invoke the handler.
//在这里面反射执行业务方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally
{
if (asyncManager.isConcurrentHandlingStarted())
{
return;
}
}
applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex)
{
dispatchException = ex;
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex)
{
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err)
{
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}
finally
{
if (asyncManager.isConcurrentHandlingStarted())
{
// Instead of postHandle and afterCompletion
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed)
{
cleanupMultipart(processedRequest);
}
}
}从标红部分点进去，到AbstractHandlerMethodAdapter类的handle方法--RequestMappingHandlerAdapter类的handleInternal方法--RequestMappingHandlerAdapter类的invokeHandleMethod--RequestMappingHandlerAdapter类的invokeAndHandle--ServletInvocableHandlerMethod类的invokeForRequest--InvocableHandlerMethod类的invokeForRequest。
方法代码：
public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer
, Object...providedArgs) throws Exception
{
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled())
{
StringBuilder sb = new StringBuilder("Invoking [");
sb.append(this.getBeanType()
.getSimpleName())
.append(".");
sb.append(getMethod()
.getName())
.append("] method with arguments ");
sb.append(Arrays.asList(args));
logger.trace(sb.toString());
}
//执行方法
Object returnValue = invoke(args);
if (logger.isTraceEnabled())
{
logger.trace("Method [" + getMethod()
.getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}之后，执行方法。
这里的话要注意一下匹配方法的时候，依据@RequestMapping里面的value路径来匹配的。
假如，匹配到的有多个，例如，匹配到了通配符，也配置了精确配置，就都会匹配到放在一个集合中，依据规则排序，之后取集合的第一个元素。
具体代码实现：
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception
{
List < Match > matches = new ArrayList < Match > ();
List < T > directPathMatches = this.urlMap.get(lookupPath);
if (directPathMatches != null)
{
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty())
{
// No choice but to go through all mappings
addMatchingMappings(this.handlerMethods.keySet(), matches, request);
}
if (!matches.isEmpty())
{
//排序规则
Comparator < Match > comparator = new MatchComparator(getMappingComparator(request));
//进行排序
Collections.sort(matches, comparator);
if (logger.isTraceEnabled())
{
logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);
}
Match bestMatch = matches.get(0);
if (matches.size() > 1)
{
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0)
{
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
throw new IllegalStateException(
"Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" +
m1 + ", " + m2 + "}");
}
}
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}
else
{
return handleNoMatch(handlerMethods.keySet(), lookupPath, request);
}
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