me.chester.myretweetedtweets.RetrieveTweetsServlet.java Source code

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Here is the source code for me.chester.myretweetedtweets.RetrieveTweetsServlet.java

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package me.chester.myretweetedtweets;

/*
 * Copyright  2011 Carlos Duarte do Nascimento (Chester) <cd@pobox.com>
 * 
 * Licensed 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.
 */

import static org.apache.commons.lang.StringEscapeUtils.escapeHtml;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import net.sf.jsr107cache.Cache;
import net.sf.jsr107cache.CacheException;
import twitter4j.TwitterException;

import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.memcache.Expiration;
import com.google.appengine.api.memcache.MemcacheService;
import com.google.appengine.api.memcache.MemcacheServiceFactory;

@SuppressWarnings("serial")
public class RetrieveTweetsServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String path = request.getPathInfo();
        String callback = request.getParameter("callback");
        PrintWriter out = response.getWriter();
        if (path != null && path.length() > 1) {
            try {
                long id = Long.parseLong(path.substring(1));
                String json = getJsonWithCache(id, callback);
                response.setContentType("application/json");
                out.write(json);
                return;
            } catch (NumberFormatException e) {
                // Invalid id, will be treated as 404-not-found below
            } catch (EntityNotFoundException e) {
                // Invalid id, will be treated as 404-not-found below
            } catch (TwitterException e) {
                response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
                out.write("Error retrieving tweets. Maybe you should re-authorize?");
            } catch (CacheException e) {
                response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
                out.write("Error with Memcache. We are all doomed.");
            }
        }
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        out.write("Invalid URL. Try authorizing again to get a valid one");
    }

    private static final int TWO_HOURS_IN_SECONDS = 7200;

    private String getJsonWithCache(long id, String callback)
            throws EntityNotFoundException, TwitterException, CacheException {
        MemcacheService cache = MemcacheServiceFactory.getMemcacheService();
        String json;
        if (cache.contains(id)) {
            json = (String) cache.get(id);
        } else {
            User user = new User(id);
            List<String> statuses = user.getMyRetweetedTweets();
            StringBuilder sb = new StringBuilder();

            sb.append("{tweets:[");
            boolean first = true;
            for (String status : statuses) {
                sb.append(first ? "" : ",");
                sb.append("\"");
                sb.append(escapeHtml(status));
                sb.append("\"");
                first = false;
            }
            sb.append("]}");
            json = sb.toString();
            cache.put(id, json, Expiration.byDeltaSeconds(TWO_HOURS_IN_SECONDS));
        }
        if (callback != null) {
            return callback + "(" + json + ")";
        } else {
            return json;
        }
    }
}