springmvc中对业务的具体处理是通过HandlerAdapter适配器操作的

HandlerAdapter接口方法

列表如下

/**
* Given a handler instance, return whether or not this {@code HandlerAdapter}
* can support it. Typical HandlerAdapters will base the decision on the handler
* type. HandlerAdapters will usually only support one handler type each.
* <p>A typical implementation:
* <p>{@code
* return (handler instanceof MyHandler);
* }
* @param handler handler object to check
* @return whether or not this object can use the given handler
*/
boolean supports(Object handler); /**
* Use the given handler to handle this request.
* The workflow that is required may vary widely.
* @param request current HTTP request
* @param response current HTTP response
* @param handler handler to use. This object must have previously been passed
* to the {@code supports} method of this interface, which must have
* returned {@code true}.
* @throws Exception in case of errors
* @return ModelAndView object with the name of the view and the required
* model data, or {@code null} if the request has been handled directly
*/
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception; /**
* Same contract as for HttpServlet's {@code getLastModified} method.
* Can simply return -1 if there's no support in the handler class.
* @param request current HTTP request
* @param handler handler to use
* @return the lastModified value for the given handler
* @see javax.servlet.http.HttpServlet#getLastModified
* @see org.springframework.web.servlet.mvc.LastModified#getLastModified
*/
long getLastModified(HttpServletRequest request, Object handler);

下面针对以上接口对springmvc内置的实现类作下简析

AbstractHandlerMethodAdapter-处理HandlerMethod业务

处理handler类型为HandlerMethod.class的请求,这是常用的请求方式,一般都是返回视图给前台页面

	@Override
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler)); @Override
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
//供子类实现调用
return handleInternal(request, response, (HandlerMethod) handler);
} @Override
public final long getLastModified(HttpServletRequest request, Object handler) {
//供子类实现调用
return getLastModifiedInternal(request, (HandlerMethod) handler);
}

以下看下主要实现类RequestMappingHandlerAdapter的具体实现代码

RequestMappingHandlerAdapter#supportsInternal()

直接返回true,表明handler为HandlerMethod对象即可

	@Override
protected boolean supportsInternal(HandlerMethod handlerMethod) {
return true;
}

RequestMappingHandlerAdapter#handleInternal()-业务处理逻辑

	protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ModelAndView mav;
//确定请求是否符合,比如是否为GET/POST请求,可配置
checkRequest(request); // 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) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
//最终通过invokeHandlerMethod()方法创建ModelAndView视图对象,这里涉及到反射机制使用
mav = invokeHandlerMethod(request, response, handlerMethod);
}
//设置关于cache的头部信息
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
} return mav;
}

RequestMappingHandlerAdapter的关键方法invokeHandlerMethod(),采用的是反射的思想来获取视图对象,有兴趣的可自行查阅分析

HttpRequestHandlerAdapter-处理HttpRequestHandler接口业务

处理handler类型为HttpRequestHandler.class的请求,简单的http请求,常用的有静态资源映射请求ResourceHttpRequestHandler,其包装在SimpleUrlHandlerMapping中,具体可看>>>SpringMVC源码情操陶冶-ResourcesBeanDefinitionParser静态资源解析器

	@Override
public boolean supports(Object handler) {
return (handler instanceof HttpRequestHandler);
} @Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
//调用handleRequest()接口方法直接返回内容给前端
//ResourceHttpRequestHandler返回请求的静态资源文件给前端
((HttpRequestHandler) handler).handleRequest(request, response);
return null;
} @Override
public long getLastModified(HttpServletRequest request, Object handler) {
if (handler instanceof LastModified) {
return ((LastModified) handler).getLastModified(request);
}
return -1L;
}

SimpleControllerHandlerAdapter-处理Controller接口业务

处理handler类型为Controller.class的请求,一般不采用

@Override
public boolean supports(Object handler) {
return (handler instanceof Controller);
} @Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
//调用Controller接口类的接口方法handleRequest()方法直接响应给前端
return ((Controller) handler).handleRequest(request, response);
} @Override
public long getLastModified(HttpServletRequest request, Object handler) {
if (handler instanceof LastModified) {
return ((LastModified) handler).getLastModified(request);
}
return -1L;
}

SimpleServletHandlerAdapter-处理Servlet接口业务

处理handler类型为Servlet.class的请求,一般不采用

	@Override
public boolean supports(Object handler) {
return (handler instanceof Servlet);
} @Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
//直接调用Servlet的service接口返回
((Servlet) handler).service(request, response);
return null;
} @Override
public long getLastModified(HttpServletRequest request, Object handler) {
return -1;
}