Atom Feeds with Spring MVC

How to add feeds (Atom) to your web application with just two classes?
How about Spring MVC?

Here are my assumptions:

• you are using Spring framework
• you have some entity, say “News”, that you want to publish in your feeds
• your "News" entity has creationDate, title, and shortDescription
• you have some repository/dao, say "NewsRepository", that will return the news from your database
  
• you want to write as little as possible
• you don't want to format Atom (xml) by hand

You actually do NOT need to use Spring MVC in your application already. If you do, skip to step 3.

Step 1: add Spring MVC dependency to your application
With maven that will be:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>3.1.0.RELEASE</version>
</dependency>

Step 2: add Spring MVC DispatcherServlet
With web.xml that would be:

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:spring-mvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/feed</url-pattern>
</servlet-mapping>

Notice, I set the url-pattern to “/feed” which means I don't want Spring MVC to handle any other urls in my app (I'm using a different web framework for the rest of the app). I also give it a brand new contextConfigLocation, where only the mvc configuration is kept.

Remember that, when you add a DispatcherServlet to an app that already has Spring (from ContextLoaderListener for example), your context is inherited from the global one, so you should not create beans that exist there again, or include xml that defines them. Watch out for Spring context getting up twice, and refer to spring or servlet documentation to understand what's happaning.

Step 3. add ROME – a library to handle Atom format
With maven that is:

<dependency>
    <groupId>net.java.dev.rome</groupId>
    <artifactId>rome</artifactId>
    <version>1.0.0</version>
</dependency>

Step 4. write your very simple controller

@Controller
public class FeedController {
    static final String LAST_UPDATE_VIEW_KEY = "lastUpdate";
    static final String NEWS_VIEW_KEY = "news";
    private NewsRepository newsRepository;
    private String viewName;

    protected FeedController() {} //required by cglib

    public FeedController(NewsRepository newsRepository, String viewName) {
        notNull(newsRepository); hasText(viewName);
        this.newsRepository = newsRepository;
        this.viewName = viewName;
    }

    @RequestMapping(value = "/feed", method = RequestMethod.GET)        
    @Transactional
    public ModelAndView feed() {
        ModelAndView modelAndView = new ModelAndView();
        modelAndView.setViewName(viewName);
        List<News> news = newsRepository.fetchPublished();
        modelAndView.addObject(NEWS_VIEW_KEY, news);
        modelAndView.addObject(LAST_UPDATE_VIEW_KEY, getCreationDateOfTheLast(news));
        return modelAndView;
    }

    private Date getCreationDateOfTheLast(List<News> news) {
        if(news.size() > 0) {
            return news.get(0).getCreationDate();
        }
        return new Date(0);
    }
}

And here's a test for it, in case you want to copy&paste (who doesn't?):

@RunWith(MockitoJUnitRunner.class)
public class FeedControllerShould {
    @Mock private NewsRepository newsRepository;
    private Date FORMER_ENTRY_CREATION_DATE = new Date(1);
    private Date LATTER_ENTRY_CREATION_DATE = new Date(2);
    private ArrayList<News> newsList;
    private FeedController feedController;

    @Before
    public void prepareNewsList() {
        News news1 = new News().title("title1").creationDate(FORMER_ENTRY_CREATION_DATE);
        News news2 = new News().title("title2").creationDate(LATTER_ENTRY_CREATION_DATE);
        newsList = newArrayList(news2, news1);
    }

    @Before
    public void prepareFeedController() {
        feedController = new FeedController(newsRepository, "viewName");
    }

    @Test
    public void returnViewWithNews() {
        //given
        given(newsRepository.fetchPublished()).willReturn(newsList);
        
        //when
        ModelAndView modelAndView = feedController.feed();
        
        //then
        assertThat(modelAndView.getModel())
                .includes(entry(FeedController.NEWS_VIEW_KEY, newsList));
    }

    @Test
    public void returnViewWithLastUpdateTime() {
        //given
        given(newsRepository.fetchPublished()).willReturn(newsList);

        //when
        ModelAndView modelAndView = feedController.feed();

        //then
        assertThat(modelAndView.getModel())
                .includes(entry(FeedController.LAST_UPDATE_VIEW_KEY, LATTER_ENTRY_CREATION_DATE));
    }

    @Test
    public void returnTheBeginningOfTimeAsLastUpdateInViewWhenListIsEmpty() {
        //given
        given(newsRepository.fetchPublished()).willReturn(new ArrayList<News>());

        //when
        ModelAndView modelAndView = feedController.feed();

        //then
        assertThat(modelAndView.getModel())
                .includes(entry(FeedController.LAST_UPDATE_VIEW_KEY, new Date(0)));
    }
}

Notice: here, I'm using fest-assert and mockito. The dependencies are:

<dependency>
 <groupId>org.easytesting</groupId>
 <artifactId>fest-assert</artifactId>
 <version>1.4</version>
 <scope>test</scope>
</dependency>
<dependency>
 <groupId>org.mockito</groupId>
 <artifactId>mockito-all</artifactId>
 <version>1.8.5</version>
 <scope>test</scope>
</dependency>

Step 5. write your very simple view
Here's where all the magic formatting happens. Be sure to take a look at all the methods of Entry class, as there is quite a lot you may want to use/fill.

import org.springframework.web.servlet.view.feed.AbstractAtomFeedView;
[...]

public class AtomFeedView extends AbstractAtomFeedView {
    private String feedId = "tag:yourFantastiSiteName";
    private String title = "yourFantastiSiteName: news";
    private String newsAbsoluteUrl = "http://yourfanstasticsiteUrl.com/news/"; 

    @Override
    protected void buildFeedMetadata(Map<String, Object> model, Feed feed, HttpServletRequest request) {
        feed.setId(feedId);
        feed.setTitle(title);
        setUpdatedIfNeeded(model, feed);
    }

    private void setUpdatedIfNeeded(Map<String, Object> model, Feed feed) {
        @SuppressWarnings("unchecked")
        Date lastUpdate = (Date)model.get(FeedController.LAST_UPDATE_VIEW_KEY);
        if (feed.getUpdated() == null || lastUpdate != null || lastUpdate.compareTo(feed.getUpdated()) > 0) {
            feed.setUpdated(lastUpdate);
        }
    }

    @Override
    protected List<Entry> buildFeedEntries(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
        @SuppressWarnings("unchecked")
        List<News> newsList = (List<News>)model.get(FeedController.NEWS_VIEW_KEY);
        List<Entry> entries = new ArrayList<Entry>();
        for (News news : newsList) {
            addEntry(entries, news);
        }
        return entries;
    }

    private void addEntry(List<Entry> entries, News news) {
        Entry entry = new Entry();
        entry.setId(feedId + ", " + news.getId());
        entry.setTitle(news.getTitle());
        entry.setUpdated(news.getCreationDate());
        entry = setSummary(news, entry);
        entry = setLink(news, entry);
        entries.add(entry);
    }

    private Entry setSummary(News news, Entry entry) {
        Content summary = new Content();
        summary.setValue(news.getShortDescription());
        entry.setSummary(summary);
        return entry;
    }

    private Entry setLink(News news, Entry entry) {
        Link link = new Link();
        link.setType("text/html");
        link.setHref(newsAbsoluteUrl + news.getId()); //because I have a different controller to show news at http://yourfanstasticsiteUrl.com/news/ID
        entry.setAlternateLinks(newArrayList(link));
        return entry;
    }

}

Step 6. add your classes to your Spring context
I'm using xml approach. because I'm old and I love xml. No, seriously, I use xml because I may want to declare FeedController a few times with different views (RSS 1.0, RSS 2.0, etc.).

So this is the forementioned spring-mvc.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
        <property name="mediaTypes">
            <map>
                <entry key="atom" value="application/atom+xml"/>
                <entry key="html" value="text/html"/>
            </map>
        </property>
        <property name="viewResolvers">
            <list>
                <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
            </list>
        </property>
    </bean>

    <bean class="eu.margiel.pages.confitura.feed.FeedController">
        <constructor-arg index="0" ref="newsRepository"/>
        <constructor-arg index="1" value="atomFeedView"/>
    </bean>

    <bean id="atomFeedView" class="eu.margiel.pages.confitura.feed.AtomFeedView"/>
</beans>

And you are done.

I've been asked a few times before to put all the working code in some public repo, so this time it's the other way around. I've describe things that I had already published, and you can grab the commit from the bitbucket.

Hope that helps.

Spring Security by example: OpenID (login via gmail)

This is a part of a simple Spring Security tutorial:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social

OpenID is to form authentication, what DVCS is to centralized version control system.

Ok, but without the technical mumbo-jumbo: OpenID allows the user to use one account (like Gmail) to login to other services (websites) without having to remember anything and without worries about password security.

Easy enough?

And the best part is: chances are, you already have an account which is a provider to OpenID. Are you registered on Gmail, Yahoo, or even Blogger? You can already use it to login to other sites.

But why would you? Isn't login/password good enough?

Have you ever wondered whether the service you are logging to, uses one-way password hashing or keeps the password as open text? Most users do not create password per site because they cannot remember more than, let's say, three passwords. If one site keeps their password as open text, they are practically screwed. And more often than not, it's the site that has the worst (or non-existing) security. Welcome to hell: all your bases are belong to us.

By the way, I know of only one site, which does SHA hashing on the client side (in javascript), so that the server has no way of knowing what the real password is: sprezentuj.pl

Kudos for that, though it smells like overengineering a bit :)

OpenID is pretty simple, and the process description at Wikipedia is practically everything you need, but as they say, one picture is worth 1000 words, so let's look at a  picture. There is a loot you can find with google, but most of them are in big-arrows-pointing-some-boxes-notation, and I find easier to read a sequence diagram, so here is my take on it:

Read emails from imap with Spring Intergration

What's the easiest way to read emails from IMAP account in Java? Depends what your background is. If you have any experience in Apache Camel, ServiceMix, Mule, you already know the answer. If you don't, and your application is using Spring already, Spring-Integration may be the solution for you.

It's not a one-liner like what you could do with Camel, but it's still quite easy to understand.

Spring Integration has great docs and there are nice tutorials around, but if you just want to get it running first and dig into the docs later, here is a quick example for you.

To make it work, you need three steps:

Spring Security by example: securing methods

This is a part of a simple Spring Security tutorial:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social

Securing web resources is all nice and cool, but in a well designed application it's more natural to secure methods (for example on backend facade or even domain objects). While we may get away with role-based authorization in many intranet business applications, nobody will ever handle assigning roles to users in a public, free to use Internet service. We need authorization based on rules described in our domain.

For example: there is a service AlterStory, that allows cooperative writing of stories, where one user is a director (like a movie director), deciding which chapter proposed by other authors should make it to the final story.

The method for accepting chapters, looks like this:

Spring Security by example: securing web resources

This is a part of a simple Spring Security tutorial:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social

Securing web resources means making sure that only users with granted authority will be able to visit given URL.

Let's say we have a page “protected.html” that should be accessed only by our admin. First thing we have to do, is to define which URLs are protected and which are accessible for anonymous user. We do that by adding intercept-url tags and a decision manager to the http tag:

Spring Security by example: user in the backend, testing

This is a part of a simple Spring Security tutorial:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social

While login by form, OpenID, OAuth2 and so on may be cool, we may often need to do login/logout in the backend. Finally, we will need a way to get currently logged user. Working with Spring Security, we may do all of that using two classes: SecurityContextHolder and AuthenticationManager. Instead of explaining their API (docs are better) let me show you an implementation of an easy to use service. Our interface looks like this:

Spring Security by example: set up and form authentication

Spring Security (former Acegi) is a Java library that handles authorization and authentication in web applications. Documentation on the project web site is, as expected from Spring Source, easy to read and use. I have a feeling though, that most of us first search Google for a fast, technology tutorial, before reading the docs, so in this little article I'm going to show you a few things Spring Security can do, give you a few hints and code snippets I have, after using it a little bit here and there. I'm not going to explain everything throughly, that's what docs are for, but what is here should help to get you started (or decide whether you want to).

Since this is quite a lot of text for a blog post.

Here is the plan:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social