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 Rome v0.4 Tutorial, Using Rome within a Servlet to create and return a feed
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 mkurz
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 2011-08-15 13:29:48.938
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Rome v0.4 Tutorial, Using Rome within a Servlet to create and return a feed


 <<Software requirements:>> J2SE 1.4\+, Servlet Container 2.3\+, JDOM 1.0 and Rome 0.4.


 This sample consists of a servlet that serves a feed as response. The feed type (RSS in any of its variants or Atom) can be specified as a URL parameter when requesting the feed. The returned feed is hardwired in the sample and it would be straight forward to modify the sample to generate the feed dynamically (i.e. from data stored in a database).


 The core logic of the <<<FeedServlet>>> is in the following fragment of code:



+------+

public class FeedServlet extends HttpServlet {
    ...

    public void doGet(HttpServletRequest req,HttpServletResponse res) throws IOException {
            ...
            SyndFeed feed = getFeed(req);

            String feedType = req.getParameter(FEED_TYPE);
            feedType = (feedType!=null) ? feedType : _defaultFeedType;
            feed.setFeedType(feedType);

            res.setContentType(MIME_TYPE);
            SyndFeedOutput output = new SyndFeedOutput();
            output.output(feed,res.getWriter());
            ...
    }

    protected SyndFeed getFeed(HttpServletRequest req) throws IOException,FeedException {
        SyndFeed feed = new SyndFeedImpl();
        feed = ...
        return feed;
    }

}

+------+

 The servlet returns a feed upon HTTP GET requests with the <<<doGet()>>> method.


 First the <<<SyndFeed>>> bean is obtained by invoking the <<<getFeed()>>> method, the request object is passed as it could be used to obtain request contextual information to create the feed. How to create a feed using SyndFeed bean is explained in detail in the {{{../../../HowRomeWorks/RomeV0.4TutorialUsingRomeToCreateAndWriteASyndicationFeed.html}Using Rome to create and write a feed}} Tutorial.


 Then the feed type of the response is determined, first looking at the request parameters and falling back to a default feed type (specified by a servlet init parameter) if the type is not indicated in the request parameters. Setting the feed type in the feed bean will indicate the <<<SyndFeedOutput>>> the feed type to output.


 Finally, the response is set with the proper content type (the MIME_TYPE constant is 'application/xml; charset\=UTF\-8') and the feed is written to response writer using the <<<SyndFeedOutput>>> output classes.


 Following is the full code for the servlet.



+------+

package com.sun.syndication.samples.servlet;

import com.sun.syndication.feed.synd.*;
import com.sun.syndication.io.FeedException;
import com.sun.syndication.io.SyndFeedOutput;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;

/**
 * Sample Servlet that serves a feed created with Rome.
 * <p>
 * The feed type is determined by the 'type' request parameter, if the parameter is missing it defaults
 * to the 'default.feed.type' servlet init parameter, if the init parameter is missing it defaults to 'atom_0.3'
 * <p>
 * @author Alejandro Abdelnur
 *
 */
public class FeedServlet extends HttpServlet {
    private static final String DEFAULT_FEED_TYPE = "default.feed.type";
    private static final String FEED_TYPE = "type";
    private static final String MIME_TYPE = "application/xml; charset=UTF-8";
    private static final String COULD_NOT_GENERATE_FEED_ERROR = "Could not generate feed";

    private static final DateFormat DATE_PARSER = new SimpleDateFormat("yyyy-MM-dd");

    private String _defaultFeedType;

    public void init() {
        _defaultFeedType = getServletConfig().getInitParameter(DEFAULT_FEED_TYPE);
        _defaultFeedType = (_defaultFeedType!=null) ? _defaultFeedType : "atom_0.3";
    }

    public void doGet(HttpServletRequest req,HttpServletResponse res) throws IOException {
        try {
            SyndFeed feed = getFeed(req);

            String feedType = req.getParameter(FEED_TYPE);
            feedType = (feedType!=null) ? feedType : _defaultFeedType;
            feed.setFeedType(feedType);

            res.setContentType(MIME_TYPE);
            SyndFeedOutput output = new SyndFeedOutput();
            output.output(feed,res.getWriter());
        }
        catch (FeedException ex) {
            String msg = COULD_NOT_GENERATE_FEED_ERROR;
            log(msg,ex);
            res.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,msg);
        }
    }

    protected SyndFeed getFeed(HttpServletRequest req) throws IOException,FeedException {
        SyndFeed feed = new SyndFeedImpl();

        feed.setTitle("Sample Feed (created with Rome)");
        feed.setLink("http://rome.dev.java.net");
        feed.setDescription("This feed has been created using Rome (Java syndication utilities");

        List entries = new ArrayList();
        SyndEntry entry;
        SyndContent description;

        entry = new SyndEntryImpl();
        entry.setTitle("Rome v0.1");
        entry.setLink("http://wiki.java.net/bin/view/Javawsxml/Rome01");
        try {
            entry.setPublishedDate(DATE_PARSER.parse("2004-06-08"));
        }
        catch (ParseException ex) {
            // IT CANNOT HAPPEN WITH THIS SAMPLE
        }
        description = new SyndContentImpl();
        description.setType("text/plain");
        description.setValue("Initial release of Rome");
        entry.setDescription(description);
        entries.add(entry);

        entry = new SyndEntryImpl();
        entry.setTitle("Rome v0.2");
        entry.setLink("http://wiki.java.net/bin/view/Javawsxml/Rome02");
        try {
            entry.setPublishedDate(DATE_PARSER.parse("2004-06-16"));
        }
        catch (ParseException ex) {
            // IT CANNOT HAPPEN WITH THIS SAMPLE
        }
        description = new SyndContentImpl();
        description.setType("text/plain");
        description.setValue("Bug fixes, minor API changes and some new features"+
                             "<p>For details check the <a href=\"http://wiki.java.net/bin/view/Javawsxml/RomeChangesLog#RomeV02\">Changes Log for 0.2</a></p>");
        entry.setDescription(description);
        entries.add(entry);

        entry = new SyndEntryImpl();
        entry.setTitle("Rome v0.3");
        entry.setLink("http://wiki.java.net/bin/view/Javawsxml/Rome03");
        try {
            entry.setPublishedDate(DATE_PARSER.parse("2004-07-27"));
        }
        catch (ParseException ex) {
            // IT CANNOT HAPPEN WITH THIS SAMPLE
        }
        description = new SyndContentImpl();
        description.setType("text/html");
        description.setValue("<p>Bug fixes, API changes, some new features and some Unit testing</p>"+
                             "<p>For details check the <a href=\"http://wiki.java.net/bin/view/Javawsxml/RomeChangesLog#RomeV03\">Changes Log for 0.3</a></p>");
        entry.setDescription(description);
        entries.add(entry);

        entry = new SyndEntryImpl();
        entry.setTitle("Rome v0.4");
        entry.setLink("http://wiki.java.net/bin/view/Javawsxml/Rome04");
        try {
            entry.setPublishedDate(DATE_PARSER.parse("2004-09-24"));
        }
        catch (ParseException ex) {
            // IT CANNOT HAPPEN WITH THIS SAMPLE
        }
        description = new SyndContentImpl();
        description.setType("text/html");
        description.setValue("<p>Bug fixes, API changes, some new features, Unit testing completed</p>"+
                             "<p>For details check the <a href=\"http://wiki.java.net/bin/view/Javawsxml/RomeChangesLog#RomeV04\">Changes Log for 0.4</a></p>");
        entry.setDescription(description);
        entries.add(entry);

        feed.setEntries(entries);

        return feed;
    }

}

+------+

 To use the <<<FeedServlet>>> we need to create a Web Application. For the Web Application we need a deployment descriptor, the <<<web.xml>>> file:



+------+

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
    <display-name>Rome Samples</display-name>

    <servlet>
        <servlet-name>FeedServlet</servlet-name>
        <servlet-class>com.sun.syndication.samples.servlet.FeedServlet</servlet-class>
        <init-param>
            <param-name>default.feed.type</param-name>
            <param-value>rss_2.0</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
         <servlet-name>FeedServlet</servlet-name>
         <url-pattern>/feed</url-pattern>
    </servlet-mapping>

</web-app>

+------+

 To build the sample Web Application, just run maven war in the samples sub\-project. The WAR file, <<<rome\-samples.war>>>, will be created under the <<<target>>> directory. Deploy the WAR in a servlet container and the <<<FeedServlet>>> should be up an running. If you are using Tomcat 4 or Tomcat 5 and the WAR file was dropped in the <<<$\{TOMCAT\}/webapps>>> directory the URL for the <<<FeedServlet>>> would be {{{http://localhost:8080/rome\-samples/feed}http://localhost:8080/rome\-samples/feed}} in a default localhost Tomcat installation.

