SpringMVC DispatcherServles分析
web请求最先到达就是DispatcherServlet。他是springmvc的核心控制。再DispatcherServlet类中通过源码可看到：他是继承FrameworkServlet，HttpServletBean，HttpServlet， ApplicationContextAware EnvironmentCapable，EnvironmentAware 接口
HttpServlet 类中 我们 可以看到 service 方法的实现
1、通用servlet 可以接受任意类型的请求
将 ServletRequest、ServletResponse 转换成 HttpServletRequest 、HttpServletResponse
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException
{
HttpServletRequest request;
HttpServletResponse response;
if (!(req instanceof HttpServletRequest &&
res instanceof HttpServletResponse)) {
throw new ServletException("non-HTTP request or response");
}
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
service(request, response);
}
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String method = req.getMethod();
if (method.equals(METHOD_GET)) {
long lastModified = getLastModified(req);
if (lastModified == -1) {
// servlet doesn't support if-modified-since, no reason
// to go through further expensive logic
doGet(req, resp);
} else {
long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
if (ifModifiedSince < lastModified) {
// If the servlet mod time is later, call doGet()
// Round down to the nearest second for a proper compare
// A ifModifiedSince of -1 will always be less
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
} else if (method.equals(METHOD_HEAD)) {
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else if (method.equals(METHOD_POST)) {
doPost(req, resp);
} else if (method.equals(METHOD_PUT)) {
doPut(req, resp);
} else if (method.equals(METHOD_DELETE)) {
doDelete(req, resp);
} else if (method.equals(METHOD_OPTIONS)) {
doOptions(req,resp);
} else if (method.equals(METHOD_TRACE)) {
doTrace(req,resp);
} else {
//
// Note that this means NO servlet supports whatever
// method was requested, anywhere on this server.
//
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
}
}
这里职责主要是先拿到一个请求，然后又做了一个判断请求方式。
FrameworkServlet 类中的 Service 方法 处理请求
DEBUG 可以看到，Service 最终调用了super.servic
在HttpServlet中，最开始是按类型将请求分开的。但是，SpringMVC又将他们统一用 processRequest 来处理，是因为SpringMVC是将不同类型请求使用不同的Handler来处理。
调用doGet 方法
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
调用 processRequest() 方法
在processRequest() 再调用 doService()
在doService () 再调用doDispatch()
查询handler来处理请求
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
决定使用那个适配器处理请求（适配器模式）
执行预处理方法
使用适配器执行目标方法，返回ModleAndView
执行目标后处理方法
业务逻辑执行以后的返回结果，调用本类的processDispatchResult方法
渲染视图
调用AbstractView类中的render方法
调用InternalResourceView类中的renderMergedOutputModel方法进行渲染模型、转发操作：