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.waveprotocol.wave.client.gadget.renderer; import com.google.gwt.core.client.Duration; import com.google.gwt.http.client.Response; import com.google.gwt.http.client.Request; import com.google.gwt.http.client.RequestBuilder; import com.google.gwt.http.client.RequestCallback; import com.google.gwt.http.client.RequestException; import com.google.gwt.json.client.JSONArray; import com.google.gwt.json.client.JSONObject; import com.google.gwt.json.client.JSONParser; import com.google.gwt.json.client.JSONString; import org.waveprotocol.wave.model.id.WaveletName; import java.util.HashMap; import java.util.Iterator; import java.util.Map; /** * Gadget data store implementation. * * Please see the initial metadata call spec at: * https://cwiki.apache.org/SHINDIG/shindigs-metadata-call.html * *<p> * <li>TODO(user): Add unit tests.</li> * <li>TODO(vadimg): Consider batching gadget requests to improve performance. * </li> * <li>TODO(vadimg): Work out how to gracefully renew expired security tokens. * </li> * */ public class GadgetDataStoreImpl implements GadgetDataStore { /** * Lifetime of a cache element in milliseconds. The cache elements can be * evicted after this time period. WFE also gets long-life security tokens (1 * hour) to support this cache expiration time. */ private static final double CACHE_EXPIRATION_TIME_MS = 3600000; /** Gadget Metadata path. */ public static final String GADGET_METADATA_PATH = "/gadgets/metadata"; /** * Cache element class that contains both cached gadget metadata and * expiration time. */ private static class CacheElement { private final GadgetMetadata metadata; private final String securityToken; private final double expirationTime; CacheElement(GadgetMetadata metadata, String securityToken) { this.metadata = metadata; this.securityToken = securityToken; expirationTime = Duration.currentTimeMillis() + CACHE_EXPIRATION_TIME_MS; } GadgetMetadata getMetadata() { return metadata; } String getSecurityToken() { return securityToken; } boolean expired() { return Duration.currentTimeMillis() > expirationTime; } } /** Metadata cache. Maps the gadget instance key to cache element objects. */ private final Map<String, CacheElement> metadataMap = new HashMap<String, CacheElement>(); private static GadgetDataStoreImpl singleton = null; /** Private singleton constructor. */ private GadgetDataStoreImpl() { } /** * Retrieves the class singleton. * * @return singleton instance of the class. */ static GadgetDataStore getInstance() { if (singleton == null) { singleton = new GadgetDataStoreImpl(); } return singleton; } private void cleanupExpiredCache() { Iterator<CacheElement> i = metadataMap.values().iterator(); while (i.hasNext()) { if (i.next().expired()) { i.remove(); } } } private boolean fetchDataByKey(String key, DataCallback receiveDataCommand) { if (metadataMap.containsKey(key)) { CacheElement cache = metadataMap.get(key); receiveDataCommand.onDataReady(cache.getMetadata(), cache.getSecurityToken()); return true; } return false; } @Override public void getGadgetData(final String gadgetSpecUrl, WaveletName waveletName, int instanceId, final DataCallback receiveDataCommand) { cleanupExpiredCache(); final String secureGadgetDataKey = waveletName.waveId + " " + waveletName.waveletId + " " + instanceId + " " + gadgetSpecUrl; if (fetchDataByKey(secureGadgetDataKey, receiveDataCommand)) { return; } final String nonSecureGadgetDataKey = gadgetSpecUrl; if (fetchDataByKey(nonSecureGadgetDataKey, receiveDataCommand)) { return; } JSONObject request = new JSONObject(); JSONObject requestContext = new JSONObject(); JSONArray gadgets = new JSONArray(); JSONObject gadget = new JSONObject(); try { gadget.put("url", new JSONString(gadgetSpecUrl)); gadgets.set(0, gadget); requestContext.put("container", new JSONString("wave")); request.put("context", requestContext); request.put("gadgets", gadgets); RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, GADGET_METADATA_PATH); builder.sendRequest(request.toString(), new RequestCallback() { public void onError(Request request, Throwable exception) { receiveDataCommand.onError("Error retrieving metadata from the server.", exception); } public void onResponseReceived(Request request, Response response) { JSONObject gadgetMetadata = null; try { gadgetMetadata = JSONParser.parseLenient(response.getText()).isObject().get("gadgets") .isArray().get(0).isObject(); } catch (NullPointerException exception) { receiveDataCommand.onError("Error in gadget metadata JSON.", exception); } if (gadgetMetadata != null) { GadgetMetadata metadata = new GadgetMetadata(gadgetMetadata); // TODO: Security token is unused therefore the gadget is stored // under the non secure key. String securityToken = null; metadataMap.put(nonSecureGadgetDataKey, new CacheElement(metadata, securityToken)); receiveDataCommand.onDataReady(metadata, securityToken); } else { receiveDataCommand.onError("Error in gadget metadata JSON.", null); } } }); } catch (RequestException e) { receiveDataCommand.onError("Unable to process gadget request.", e); } } }