SSM-SpringMVC-17：SpringMVC中深度剖析HandlerAdapter处理器适配器底层
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先放一张图
很熟悉啊，之前就看过，我们之前已经把handlerMapping剖了个底朝天，顺着上次的进度，继续跟，把HandlerAdapter处理器适配器剖一下
它同样是由中央调度器DispatcherServlet调度到的，所以，还是这个类中找doDispatch(request,response)这个方法，我把有用的代码，扒下来
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { try { ModelAndView err = null; Exception dispatchException = null; try { processedRequest = this.checkMultipart(request); multipartRequestParsed = processedRequest != request; mappedHandler = this.getHandler(processedRequest); if(mappedHandler == null || mappedHandler.getHandler() == null) { this.noHandlerFound(processedRequest, response); return; } //上面的是我说的HandleMapping的执行 流程 //所以从后面的第一行开始看 HandlerAdapter ex = this.getHandlerAdapter(mappedHandler.getHandler());
HandlerExecutionChain mappedHandler这个变量，是处理器执行链，它的getHandler方法，就是获取它里面的处理器
它外面的this.getHandlerAdpter
点过去追踪
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { //迭代器 Iterator var2 = this.handlerAdapters.iterator(); //一会要返回去的适配器对象 HandlerAdapter ha; do { //如果没有下一个的话。就抛异常 if(!var2.hasNext()) { throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"); } //将此强转成为处理器适配器 ha = (HandlerAdapter)var2.next(); if(this.logger.isTraceEnabled()) { this.logger.trace("Testing handler adapter [" + ha + "]"); } } while(!ha.supports(handler)); //这儿有个适配器模式 return ha; }
这是下载源码后的最直观的源码
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { for (HandlerAdapter ha : this.handlerAdapters) { if (logger.isTraceEnabled()) { logger.trace("Testing handler adapter [" + ha + "]"); } if (ha.supports(handler)) { return ha; } } throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"); }
看ha.sipports(handler)这个方法
找到HandlerAdapter接口
public interface HandlerAdapter { boolean supports(Object handler); ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception; long getLastModified(HttpServletRequest request, Object handler); }
再来看一下自己写的控制器实现了Controller。这样就看DispatcherServlet属性中的HandlerApater谁支持Controller类型的处理器了。在运行的过程中发现SimpleControllerHandlerAdapter是支持Controller类型的控制器的。
来看一下SimpleControllerHandlerAdapter的代码
找它的实现类：Ctrl+H SimpleControllerHandlerAdapter
public class SimpleControllerHandlerAdapter implements HandlerAdapter { public boolean supports(Object handler) { return (handler instanceof Controller); } public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return ((Controller) handler).handleRequest(request, response); } public long getLastModified(HttpServletRequest request, Object handler) { if (handler instanceof LastModified) { return ((LastModified) handler).getLastModified(request); } return -1L; } }
它support来判断是否是处理器
拿到处理器在中央调度器一处调用了handle方法
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. mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. 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()) { logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //就是上面这处
看看handle方法,因为被执行调用到，它返回ModelAndView
里面return走的handleRequest是Controller接口的，找它的实现类
AbstractController抽象类，它有实现handleRequest
@Override public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception { // Delegate to WebContentGenerator for checking and preparing. checkRequest(request); prepareResponse(response); // Execute handleRequestInternal in synchronized block if required. if (this.synchronizeOnSession) { HttpSession session = request.getSession(false); if (session != null) { Object mutex = WebUtils.getSessionMutex(session); synchronized (mutex) { return handleRequestInternal(request, response); } } } return handleRequestInternal(request, response); }
看到最后面的那个返回值了吗？是ModelAndView对象，它调用了handleRequestInternal(request,respone)这个方法
还记得AbstractController的实现类吗？不是有种处理器的定义方法就是继承AbstractController
package cn.dawn.day04abstractController; import org.springframework.web.servlet.ModelAndView; import org.springframework.web.servlet.mvc.AbstractController; import org.springframework.web.servlet.mvc.Controller; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Created by Dawn on 2018/3/19. */ //处理器 public class FirstController extends AbstractController { protected ModelAndView handleRequestInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception { ModelAndView me=new ModelAndView(); me.setViewName("index"); return me; } }
它的实现类默认要求必须实现handleRequestInternal（request,response）这个方法
所以，理清了吧，再一步步return回去，最后回到了中央调度器
结论，中央处理器DispatcherServlet通过处理器执行链找到handlerAdapter处理器适配器，后者调度了它的处理器，通过处理器处理，返回一个ModelAndView模型和视图对象，一路返回，到中央调度器
