DispatcherServlet之getHandlerAdapter
注: SpringFramework的版本是4.3.x。
1.DispatcherServlet的doService方法时序图
图1 DispatcherServlet的doService方法时序图
2.DispatcherServlet中默认会加载三个HandlerAdapter
一般情况下，我们不会自己指定HandlerAdapter，所以只需要分析默认的情况。首先看DispatcherServlet的方法initHandlerAdapters(ApplicationContext context)，该方法中加载文件DispatcherServlet.properties中指定的HandlerAdapter，如下图2所示，默认的HandlerAdapter有HttpRequestHandlerAdapter、SimpleControllerHandlerAdapter、AnnotationMethodHandlerAdapter。
图2 DispatcherServlet.properties指定的HandlerAdapter
2.1 HttpRequestHandlerAdapter
HttpRequestHandlerAdapter类在spring-webmvc模块，类图如下图3所示，较为简单。
图3 HttpRequestHandlerAdapter的类图
HttpRequestHandlerAdapter的源码如下List-1所示，由support的实现可知这个处理的情况是：controller类实现了接口HttpRequestHandler的情况。
List-1 HttpRequestHandlerAdapter的support和handle方法源码
public class HttpRequestHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof HttpRequestHandler);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((HttpRequestHandler) handler).handleRequest(request, response);
return null;
}
...
}2.2 SimpleControllerHandlerAdapter
SimpleControllerHandlerAdapter类在spring-webmvc模块中，它实现的HandlerAdapter接口是org.springframework.web.servlet.HandlerAdapter。
SimpleControllerHandlerAdapter的部分源码如下List-2所示，由其support方法可知，这个类处理的是我们定义的controller类实现了org.springframework.web.servlet.mvc.Controller接口的情况。
List-2 SimpleControllerHandlerAdapter的support及其它方法源码
@Override
public boolean supports(Object handler) {
return (handler instanceof Controller);
}
@Override
public void handleAction(ActionRequest request, ActionResponse response, Object handler)
throws Exception {
((Controller) handler).handleActionRequest(request, response);
}
@Override
public ModelAndView handleRender(RenderRequest request, RenderResponse response, Object handler)
throws Exception {
return ((Controller) handler).handleRenderRequest(request, response);
}
......2.3 AnnotationMethodHandlerAdapter
AnnotationMethodHandlerAdapter在spring-webmvc模块中，现在已经被Deprecated。
图4 AnnotationMethodHandlerAdapter的类继承图
AnnotationMethodHandlerAdapter的support方法及其它如下，一眼看上去比上面分析的俩个复杂多了。
List-3 AnnotationMethodHandlerAdapter的support方法及其它方法源码
@Override
public boolean supports(Object handler) {
return getMethodResolver(handler).hasHandlerMethods();
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
Class<?> clazz = ClassUtils.getUserClass(handler);
Boolean annotatedWithSessionAttributes = this.sessionAnnotatedClassesCache.get(clazz);
if (annotatedWithSessionAttributes == null) {
annotatedWithSessionAttributes = (AnnotationUtils.findAnnotation(clazz, SessionAttributes.class) != null);
this.sessionAnnotatedClassesCache.put(clazz, annotatedWithSessionAttributes);
}
if (annotatedWithSessionAttributes) {
checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
}
else {
checkAndPrepare(request, response, true);
}
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
return invokeHandlerMethod(request, response, handler);
}
}
}
return invokeHandlerMethod(request, response, handler);
}
......来看下AnnotationMethodHandlerAdapter的support方法时序图，原图在Github上。
图5 AnnotationMethodHandlerAdapter的support时序图
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