Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.yarn.webapp; import static com.google.common.base.Preconditions.checkState; import java.io.IOException; import java.util.Timer; import java.util.TimerTask; import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.http.HtmlQuoting; import org.apache.hadoop.yarn.webapp.Controller.RequestContext; import org.apache.hadoop.yarn.webapp.Router.Dest; import org.apache.hadoop.yarn.webapp.view.ErrorPage; import org.apache.hadoop.yarn.webapp.view.RobotsTextPage; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.google.common.collect.Iterables; import com.google.inject.Inject; import com.google.inject.Injector; import com.google.inject.Singleton; /** * The servlet that dispatch request to various controllers * according to the user defined routes in the router. */ @InterfaceAudience.LimitedPrivate({ "YARN", "MapReduce" }) @Singleton public class Dispatcher extends HttpServlet { private static final long serialVersionUID = 1L; static final Logger LOG = LoggerFactory.getLogger(Dispatcher.class); static final String ERROR_COOKIE = "last-error"; static final String STATUS_COOKIE = "last-status"; private transient final Injector injector; private transient final Router router; private transient final WebApp webApp; private volatile boolean devMode = false; @Inject Dispatcher(WebApp webApp, Injector injector, Router router) { this.webApp = webApp; this.injector = injector; this.router = router; } @Override public void doOptions(HttpServletRequest req, HttpServletResponse res) { // for simplicity res.setHeader("Allow", "GET, POST"); } @Override public void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setCharacterEncoding("UTF-8"); String uri = HtmlQuoting.quoteHtmlChars(req.getRequestURI()); if (uri == null) { uri = "/"; } if (devMode && uri.equals("/__stop")) { // quick hack to restart servers in dev mode without OS commands res.setStatus(res.SC_NO_CONTENT); LOG.info("dev mode restart requested"); prepareToExit(); return; } // if they provide a redirectPath go there instead of going to // "/" so that filters can differentiate the webapps. if (uri.equals("/")) { String redirectPath = webApp.getRedirectPath(); if (redirectPath != null && !redirectPath.isEmpty()) { res.sendRedirect(redirectPath); return; } } String method = req.getMethod(); if (method.equals("OPTIONS")) { doOptions(req, res); return; } if (method.equals("TRACE")) { doTrace(req, res); return; } if (method.equals("HEAD")) { doGet(req, res); // default to bad request return; } String pathInfo = req.getPathInfo(); if (pathInfo == null) { pathInfo = "/"; } Controller.RequestContext rc = injector.getInstance(Controller.RequestContext.class); //short-circuit robots.txt serving for all YARN webapps. if (uri.equals(RobotsTextPage.ROBOTS_TXT_PATH)) { rc.setStatus(HttpServletResponse.SC_FOUND); render(RobotsTextPage.class); return; } if (setCookieParams(rc, req) > 0) { Cookie ec = rc.cookies().get(ERROR_COOKIE); if (ec != null) { rc.setStatus(Integer.parseInt(rc.cookies().get(STATUS_COOKIE).getValue())); removeErrorCookies(res, uri); rc.set(Params.ERROR_DETAILS, ec.getValue()); render(ErrorPage.class); return; } } rc.prefix = webApp.name(); Router.Dest dest = null; try { dest = router.resolve(method, pathInfo); } catch (WebAppException e) { rc.error = e; if (!e.getMessage().contains("not found")) { rc.setStatus(res.SC_INTERNAL_SERVER_ERROR); render(ErrorPage.class); return; } } if (dest == null) { rc.setStatus(res.SC_NOT_FOUND); render(ErrorPage.class); return; } rc.devMode = devMode; setMoreParams(rc, pathInfo, dest); Controller controller = injector.getInstance(dest.controllerClass); try { // TODO: support args converted from /path/:arg1/... dest.action.invoke(controller, (Object[]) null); if (!rc.rendered) { if (dest.defaultViewClass != null) { render(dest.defaultViewClass); } else if (rc.status == 200) { throw new IllegalStateException("No view rendered for 200"); } } } catch (Exception e) { LOG.error("error handling URI: " + uri, e); // Page could be half rendered (but still not flushed). So redirect. redirectToErrorPage(res, e, uri, devMode); } } public static void redirectToErrorPage(HttpServletResponse res, Throwable e, String path, boolean devMode) { String st = devMode ? ErrorPage.toStackTrace(e, 1024 * 3) // spec: min 4KB : "See logs for stack trace"; res.setStatus(res.SC_FOUND); Cookie cookie = new Cookie(STATUS_COOKIE, String.valueOf(500)); cookie.setPath(path); res.addCookie(cookie); cookie = new Cookie(ERROR_COOKIE, st); cookie.setPath(path); res.addCookie(cookie); res.setHeader("Location", path); } public static void removeErrorCookies(HttpServletResponse res, String path) { removeCookie(res, ERROR_COOKIE, path); removeCookie(res, STATUS_COOKIE, path); } public static void removeCookie(HttpServletResponse res, String name, String path) { LOG.debug("removing cookie {} on {}", name, path); Cookie c = new Cookie(name, ""); c.setMaxAge(0); c.setPath(path); res.addCookie(c); } private void render(Class<? extends View> cls) { injector.getInstance(cls).render(); } // /path/foo/bar with /path/:arg1/:arg2 will set {arg1=>foo, arg2=>bar} private void setMoreParams(RequestContext rc, String pathInfo, Dest dest) { checkState(pathInfo.startsWith(dest.prefix), "prefix should match"); if (dest.pathParams.size() == 0 || dest.prefix.length() == pathInfo.length()) { return; } String[] parts = Iterables.toArray(WebApp.pathSplitter.split(pathInfo.substring(dest.prefix.length())), String.class); LOG.debug("parts={}, params={}", parts, dest.pathParams); for (int i = 0; i < dest.pathParams.size() && i < parts.length; ++i) { String key = dest.pathParams.get(i); if (key.charAt(0) == ':') { rc.moreParams().put(key.substring(1), parts[i]); } } } private int setCookieParams(RequestContext rc, HttpServletRequest req) { Cookie[] cookies = req.getCookies(); if (cookies != null) { for (Cookie cookie : cookies) { rc.cookies().put(cookie.getName(), cookie); } return cookies.length; } return 0; } public void setDevMode(boolean choice) { devMode = choice; } private void prepareToExit() { checkState(devMode, "only in dev mode"); new Timer("webapp exit", true).schedule(new TimerTask() { @Override public void run() { LOG.info("WebAppp /{} exiting...", webApp.name()); webApp.stop(); System.exit(0); // FINDBUG: this is intended in dev mode } }, 18); // enough time for the last local request to complete } }