tomcat-valve通过servlet处理请求

上一节说到请求url定位servlet的过程，tomcat会把请求url和容器的映射关系保存到MappingData中，org.apache.catalina.connector.Request类实现了HttpServletRequest，其中定义了属性mappingDataprotected final MappingData mappingData = new MappingData();用于保存映射关系，其是在CoyoteAdapter.java#service()方法中创建。定位servlet对请求进行处理的入口是connector.getService().getContainer().getPipeline().getFirst().invoke(request, response);，就从这里往后面看。这里的逻辑就是调用Pipeline中的每个Valve进行处理。

StandardEngineValve
这是Engine的Valve，就是找到前面通过请求url定位的Host，获取Host的Valve进行处理。

    public void invoke(Request request, Response response) throws IOException, ServletException {// Select the Host to be used for this RequestHost host = request.getHost();......host.getPipeline().getFirst().invoke(request, response);}public Host getHost() {return mappingData.host;}
}

StandardHostValve
这个Valve也是跟Engine的Valve类似，沿着链表向后移动，找到下一个Valve进行处理。
StandardContextValve
从请求中获取StandardWrapperValve进行请求的处理。
StandardWrapperValve
前面铺垫了这么久，总算到正题了，请求的正式处理就是在StandardWrapperValve中进行的，前面的Valve做的还是对进行加工，没有进行正式的处理。怎么样，是不是看到熟悉的代码段，平时我们所说的过滤器链对请求过滤处理的代码!这块就是挨个调用每个过滤器Filter上的doFilter()方法进行处理。

    public void invoke(Request request, Response response) throws IOException, ServletException {......Servlet servlet = null;......servlet = wrapper.allocate();ApplicationFilterChain filterChain = ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);......filterChain.doFilter(request.getRequest(), response.getResponse());......        }

还是慢慢看吧，首先在Wrapper容器中取出Servlet，然后创建用来处理请求的servlet过滤器链。在调用每个过滤器的doFilter方法时，会通过HttpServlet中的模板方法internalDoFilter()调用内置的service方法，就是根据请求方式处理请求啦，也就是我们写的过滤器中处理请求的方法。

    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 logicdoGet(req, resp);} else {long ifModifiedSince;try {ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);} catch (IllegalArgumentException iae) {// Invalid date header - proceed as if none was setifModifiedSince = -1;}if (ifModifiedSince < (lastModified / 1000 * 1000)) {// 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 lessmaybeSetLastModified(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);}}