DDevelopment & Design

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.
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: 


    org.springframework
    spring-webmvc
    3.1.0.RELEASE

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


    dispatcher
    org.springframework.web.servlet.DispatcherServlet
    
        contextConfigLocation
        classpath:spring-mvc.xml
    
    1


    dispatcher
    /feed

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: 


    net.java.dev.rome
    rome
    1.0.0

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 = newsRepository.fetchPublished();
        modelAndView.addObject(NEWS_VIEW_KEY, news);
        modelAndView.addObject(LAST_UPDATE_VIEW_KEY, getCreationDateOfTheLast(news));
        return modelAndView;
    }

    private Date getCreationDateOfTheLast(List 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 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());

        //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: 


 org.easytesting
 fest-assert
 1.4
 test


 org.mockito
 mockito-all
 1.8.5
 test

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 model, Feed feed, HttpServletRequest request) {
        feed.setId(feedId);
        feed.setTitle(title);
        setUpdatedIfNeeded(model, feed);
    }

    private void setUpdatedIfNeeded(Map 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 buildFeedEntries(Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {
        @SuppressWarnings("unchecked")
        List newsList = (List)model.get(FeedController.NEWS_VIEW_KEY);
        List entries = new ArrayList();
        for (News news : newsList) {
            addEntry(entries, news);
        }
        return entries;
    }

    private void addEntry(List 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

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.

Solution Architect @ TouK

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DDevelopment & Design

Using WsLite in practice

TL;DR

There is a example working GitHub project which covers unit testing and request/response logging when using WsLite.

Why Groovy WsLite ?

I’m a huge fan of Groovy WsLite project for calling SOAP web services. Yes, in a real world you have to deal with those - big companies have huge amount of “legacy” code and are crazy about homogeneous architecture - only SOAP, Java, Oracle, AIX…

But I also never been comfortable with XFire/CXF approach of web service client code generation. I wrote a bit about other posibilites in this post. With JAXB you can also experience some freaky classloading errors - as Tomek described on his blog. In a large commercial project the “the less code the better” principle is significant. And the code generated from XSD could look kinda ugly - especially more complicated structures like sequences, choices, anys etc.

Using WsLite with native Groovy concepts like XmlSlurper could be a great choice. But since it’s a dynamic approach you have to be really careful - write good unit tests and log requests. Below are my few hints for using WsLite in practice.

Unit testing

Suppose you have some invocation of WsLite SOAPClient (original WsLite example):

def getMothersDay(long _year) {
    def response = client.send(SOAPAction: action) {
       body {
           GetMothersDay('xmlns':'http://www.27seconds.com/Holidays/US/Dates/') {
              year(_year)
           }
       }
    }
    response.GetMothersDayResponse.GetMothersDayResult.text()
}

How can the unit test like? My suggestion is to mock SOAPClient and write a simple helper to test that builded XML is correct. Example using great SpockFramework: 

void setup() {
   client = Mock(SOAPClient)
   service.client = client
}

def "should pass year to GetMothersDay and return date"() {
  given:
      def year = 2013
  when:
      def date = service.getMothersDay(year)
  then:
      1 * client.send(_, _) >> { Map params, Closure requestBuilder ->
            Document doc = buildAndParseXml(requestBuilder)
            assertXpathEvaluatesTo("$year", '//ns:GetMothersDay/ns:year', doc)
            return mockResponse(Responses.mothersDay)
      }
      date == "2013-05-12T00:00:00"
}

This uses a real cool feature of Spock - even when you mock the invocation with “any mark” (_), you are able to get actual arguments. So we can build XML that would be passed to SOAPClient's send method and check that specific XPaths are correct:

void setup() {
    engine = XMLUnit.newXpathEngine()
    engine.setNamespaceContext(new SimpleNamespaceContext(namespaces()))
}

protected Document buildAndParseXml(Closure xmlBuilder) {
    def writer = new StringWriter()
    def builder = new MarkupBuilder(writer)
    builder.xml(xmlBuilder)
    return XMLUnit.buildControlDocument(writer.toString())
}

protected void assertXpathEvaluatesTo(String expectedValue,
                                      String xpathExpression, Document doc) throws XpathException {
    Assert.assertEquals(expectedValue,
            engine.evaluate(xpathExpression, doc))
}

protected Map namespaces() {
    return [ns: 'http://www.27seconds.com/Holidays/US/Dates/']
}

The XMLUnit library is used just for XpathEngine, but it is much more powerful for comparing XML documents. The NamespaceContext is needed to use correct prefixes (e.g. ns:GetMothersDay) in your Xpath expressions.

Finally - the mock returns SOAPResponse instance filled with envelope parsed from some constant XML:

protected SOAPResponse mockResponse(String resp) {
    def envelope = new XmlSlurper().parseText(resp)
    new SOAPResponse(envelope: envelope)
}

Request and response logging

The WsLite itself doesn’t use any logging framework. We usually handle it by adding own sendWithLogging method:

private SOAPResponse sendWithLogging(String action, Closure cl) {
    SOAPResponse response = client.send(SOAPAction: action, cl)
    log(response?.httpRequest, response?.httpResponse)
    return response
}

private void log(HTTPRequest request, HTTPResponse response) {
    log.debug("HTTPRequest $request with content:\n${request?.contentAsString}")
    log.debug("HTTPResponse $response with content:\n${response?.contentAsString}")
}

This logs the actual request and response send through SOAPClient. But it logs only when invocation is successful and errors are much more interesting… So here goes withExceptionHandler method:

private SOAPResponse withExceptionHandler(Closure cl) {
    try {
        cl.call()
    } catch (SOAPFaultException soapEx) {
        log(soapEx.httpRequest, soapEx.httpResponse)
        def message = soapEx.hasFault() ? soapEx.fault.text() : soapEx.message
        throw new InfrastructureException(message)
    } catch (HTTPClientException httpEx) {
        log(httpEx.request, httpEx.response)
        throw new InfrastructureException(httpEx.message)
    }
}
def send(String action, Closure cl) {
    withExceptionHandler {
        sendWithLogging(action, cl)
    }
}

XmlSlurper gotchas

Working with XML document with XmlSlurper is generally great fun, but is some cases could introduce some problems. A trivial example is parsing an id with a number to Long value:

def id = Long.valueOf(edit.'@id' as String)

The Attribute class (which edit.'@id' evaluates to) can be converted to String using as operator, but converting to Long requires using valueOf.

The second example is a bit more complicated. Consider following XML fragment:

<edit id="3">
   <params>
      <param value="label1" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>123</value>
</edit>
<edit id="6">
   <params>
      <param value="label2" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>456</value>
</edit>

We want to find id of edit whose label is label1. The simplest solution seems to be:

def param = doc.edit.params.param.find { it['@value'] == 'label1' }
def edit = params.parent().parent()

But it doesn’t work! The parent method returns multiple edits, not only the one that is parent of given param…

Here’s the correct solution:

doc.edit.find { edit ->
    edit.params.param.find { it['@value'] == 'label1' }
}

Example

The example working project covering those hints could be found on GitHub.

DDevelopment & Design

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