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.checkNotNull; import static com.google.common.base.Preconditions.checkState; import static org.apache.hadoop.yarn.util.StringHelper.djoin; import static org.apache.hadoop.yarn.util.StringHelper.join; import static org.apache.hadoop.yarn.util.StringHelper.pjoin; import java.lang.reflect.Method; import java.util.EnumSet; import java.util.List; import java.util.Map; import java.util.TreeMap; import java.util.regex.Pattern; import org.apache.commons.lang.StringUtils; import org.apache.hadoop.classification.InterfaceAudience; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.google.common.base.CharMatcher; import com.google.common.collect.ImmutableList; import com.google.common.collect.Maps; /** * Manages path info to controller#action routing. */ @InterfaceAudience.LimitedPrivate({ "YARN", "MapReduce" }) class Router { static final Logger LOG = LoggerFactory.getLogger(Router.class); static final ImmutableList<String> EMPTY_LIST = ImmutableList.of(); static final CharMatcher SLASH = CharMatcher.is('/'); static final Pattern controllerRe = Pattern.compile("^/[A-Za-z_]\\w*(?:/.*)?"); static class Dest { final String prefix; final ImmutableList<String> pathParams; final Method action; final Class<? extends Controller> controllerClass; Class<? extends View> defaultViewClass; final EnumSet<WebApp.HTTP> methods; Dest(String path, Method method, Class<? extends Controller> cls, List<String> pathParams, WebApp.HTTP httpMethod) { prefix = checkNotNull(path); action = checkNotNull(method); controllerClass = checkNotNull(cls); this.pathParams = pathParams != null ? ImmutableList.copyOf(pathParams) : EMPTY_LIST; methods = EnumSet.of(httpMethod); } } Class<?> hostClass; // starting point to look for default classes final TreeMap<String, Dest> routes = Maps.newTreeMap(); // path->dest /** * Add a route to the router. * e.g., add(GET, "/foo/show", FooController.class, "show", [name...]); * The name list is from /foo/show/:name/... */ synchronized Dest add(WebApp.HTTP httpMethod, String path, Class<? extends Controller> cls, String action, List<String> names) { LOG.debug("adding {}({})->{}#{}", new Object[] { path, names, cls, action }); Dest dest = addController(httpMethod, path, cls, action, names); addDefaultView(dest); return dest; } private Dest addController(WebApp.HTTP httpMethod, String path, Class<? extends Controller> cls, String action, List<String> names) { try { // Look for the method in all public methods declared in the class // or inherited by the class. // Note: this does not distinguish methods with the same signature // but different return types. // TODO: We may want to deal with methods that take parameters in the future Method method = cls.getMethod(action, null); Dest dest = routes.get(path); if (dest == null) { method.setAccessible(true); // avoid any runtime checks dest = new Dest(path, method, cls, names, httpMethod); routes.put(path, dest); return dest; } dest.methods.add(httpMethod); return dest; } catch (NoSuchMethodException nsme) { throw new WebAppException(action + "() not found in " + cls); } catch (SecurityException se) { throw new WebAppException("Security exception thrown for " + action + "() in " + cls); } } private void addDefaultView(Dest dest) { String controllerName = dest.controllerClass.getSimpleName(); if (controllerName.endsWith("Controller")) { controllerName = controllerName.substring(0, controllerName.length() - 10); } dest.defaultViewClass = find(View.class, dest.controllerClass.getPackage().getName(), join(controllerName + "View")); } void setHostClass(Class<?> cls) { hostClass = cls; } /** * Resolve a path to a destination. */ synchronized Dest resolve(String httpMethod, String path) { WebApp.HTTP method = WebApp.HTTP.valueOf(httpMethod); // can throw Dest dest = lookupRoute(method, path); if (dest == null) { return resolveDefault(method, path); } return dest; } private Dest lookupRoute(WebApp.HTTP method, String path) { String key = path; do { Dest dest = routes.get(key); if (dest != null && methodAllowed(method, dest)) { if ((Object) key == path) { // shut up warnings LOG.debug("exact match for {}: {}", key, dest.action); return dest; } else if (isGoodMatch(dest, path)) { LOG.debug("prefix match2 for {}: {}", key, dest.action); return dest; } return resolveAction(method, dest, path); } Map.Entry<String, Dest> lower = routes.lowerEntry(key); if (lower == null) { return null; } dest = lower.getValue(); if (prefixMatches(dest, path)) { if (methodAllowed(method, dest)) { if (isGoodMatch(dest, path)) { LOG.debug("prefix match for {}: {}", lower.getKey(), dest.action); return dest; } return resolveAction(method, dest, path); } // check other candidates int slashPos = key.lastIndexOf('/'); key = slashPos > 0 ? path.substring(0, slashPos) : "/"; } else { key = "/"; } } while (true); } static boolean methodAllowed(WebApp.HTTP method, Dest dest) { // Accept all methods by default, unless explicity configured otherwise. return dest.methods.contains(method) || (dest.methods.size() == 1 && dest.methods.contains(WebApp.HTTP.GET)); } static boolean prefixMatches(Dest dest, String path) { LOG.debug("checking prefix {}{} for path: {}", new Object[] { dest.prefix, dest.pathParams, path }); if (!path.startsWith(dest.prefix)) { return false; } int prefixLen = dest.prefix.length(); if (prefixLen > 1 && path.length() > prefixLen && path.charAt(prefixLen) != '/') { return false; } // prefix is / or prefix is path or prefix/... return true; } static boolean isGoodMatch(Dest dest, String path) { if (SLASH.countIn(dest.prefix) > 1) { return true; } // We want to match (/foo, :a) for /foo/bar/blah and (/, :a) for /123 // but NOT / for /foo or (/, :a) for /foo or /foo/ because default route // (FooController#index) for /foo and /foo/ takes precedence. if (dest.prefix.length() == 1) { return dest.pathParams.size() > 0 && !maybeController(path); } return dest.pathParams.size() > 0 || // /foo should match /foo/ (path.endsWith("/") && SLASH.countIn(path) == 2); } static boolean maybeController(String path) { return controllerRe.matcher(path).matches(); } // Assume /controller/action style path private Dest resolveDefault(WebApp.HTTP method, String path) { List<String> parts = WebApp.parseRoute(path); String controller = parts.get(WebApp.R_CONTROLLER); String action = parts.get(WebApp.R_ACTION); // NameController is encouraged default Class<? extends Controller> cls = find(Controller.class, join(controller, "Controller")); if (cls == null) { cls = find(Controller.class, controller); } if (cls == null) { throw new WebAppException(join(path, ": controller for ", controller, " not found")); } return add(method, defaultPrefix(controller, action), cls, action, null); } private String defaultPrefix(String controller, String action) { if (controller.equals("default") && action.equals("index")) { return "/"; } if (action.equals("index")) { return join('/', controller); } return pjoin("", controller, action); } private <T> Class<? extends T> find(Class<T> cls, String cname) { String pkg = hostClass.getPackage().getName(); return find(cls, pkg, cname); } private <T> Class<? extends T> find(Class<T> cls, String pkg, String cname) { String name = StringUtils.capitalize(cname); Class<? extends T> found = load(cls, djoin(pkg, name)); if (found == null) { found = load(cls, djoin(pkg, "webapp", name)); } if (found == null) { found = load(cls, join(hostClass.getName(), '$', name)); } return found; } @SuppressWarnings("unchecked") private <T> Class<? extends T> load(Class<T> cls, String className) { LOG.debug("trying: {}", className); try { Class<?> found = Class.forName(className); if (cls.isAssignableFrom(found)) { LOG.debug("found {}", className); return (Class<? extends T>) found; } LOG.warn("found a {} but it's not a {}", className, cls.getName()); } catch (ClassNotFoundException e) { // OK in this case. } return null; } // Dest may contain a candidate controller private Dest resolveAction(WebApp.HTTP method, Dest dest, String path) { if (dest.prefix.length() == 1) { return null; } checkState(!isGoodMatch(dest, path), dest.prefix); checkState(SLASH.countIn(path) > 1, path); List<String> parts = WebApp.parseRoute(path); String controller = parts.get(WebApp.R_CONTROLLER); String action = parts.get(WebApp.R_ACTION); return add(method, pjoin("", controller, action), dest.controllerClass, action, null); } }