First the basics. If you want to try these examples yourself you need to request a key. More information can be found here:

http://open.nos.nl/

Because groovy is a very nice language to do this kind of experimentation I’ll show you de groovy code first. Just a few lines to print a JSON string:

def key = "Your Key"
nos = new RESTClient("http://open.nos.nl/v1/")
JSON newsItems = nos.get(path : "latest/article/key/$key/output/json/category/sport/").data
print newsItems

The result is a long string. If you want to convert a string to nice formatted json check the resources for a link. The following image gives you an idea of the structure of the returned JSON:

Now let us do the same thing in java. Usually this takes much more code. To be honest, it is not at all bad if you use the RESTTemplate of the Spring framework. Have a look at the following code:

public class SearchApiUsingSpring {
    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        String result = restTemplate.getForObject("http://open.nos.nl/v1/latest/article/key/{key}/output/json/category/sport/",
                String.class, "YOUR KEY");
        System.out.println(result);
    }
}

Of course the result is the same, not bad is it? Just three lines of real code. Nice, but not enough for my example. Of course I want to use the result as an object. Therefore I am going to use an object mapper called Jackson. Check resources for a link. Jackson is a framework that enables us to map JSON objects to actual java objects. Based on the structure of the returned JSON I created a java object and used jackson annotations to map it to the JSON structure. The spring RESTTemplate facilitates using mappers. A Jackson mapper is available. The following code shows the improved sample.

public class SearchApiUsingSpring {
    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        LatestArticle result = restTemplate.getForObject("http://open.nos.nl/v1/latest/article/key/{key}/output/json/category/sport/",
                LatestArticle.class, "Your Key");

        for (Article article : result.getItems().get(0)) {
            System.out.printf("Title : %s\n", article.getTitle());
            System.out.printf("Description : %s\n", article.getDescription());
            System.out.printf("Link : %s\n", article.getLink());
            System.out.println("_________________________________");
        }
    }
}

Just a very small difference, besides the printing stuff. The change is the type returned by the getForObject method. Now it is not a string anymore but a LatestArticle. To be able to use Jackson you do need to create the classes with a few annotations.

@JsonIgnoreProperties(ignoreUnknown = true)
public class LatestArticle {
    @JsonProperty("latest_article")
    private ArrayList<ArrayList<Article>> items = new ArrayList<ArrayList<Article>>();

	// getters and setters
}

@JsonIgnoreProperties(ignoreUnknown = true)
public class Article {
    private String id;
    private String type;
    private String title;
    private String description;
    private String link;

	// getters and setters
}

I use the annotation @JsonIgnoreProperties, I do not want to break my code if a property that is available in json is not available in my java class. I’ll remove it later on when I have all the properties mapped. Why not immediately? Well I want to explain what I did with the date fields first. Mapping a date is a bit different. We do need to map the date using the specific format. I include Joda time to the path and create a synchronizer for a Joda date time object. Jackson has support for joda time out of the box. But I used a different format and therefore I had to create my own. The class Article is slightly enhanced with a DateTime property called published. I only show the setter this time. This is where we have to assign our own deserializer. The code for my deserializer is also shown.

// from Article
    @JsonDeserialize(using = JsonDateDeserializer.class)
    public void setPublished(DateTime published) {
        this.published = published;
    }

public class JsonDateDeserializer extends JsonDeserializer<DateTime> {
    private final DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss");

    @Override
    public DateTime deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        return formatter.parseDateTime(jp.getText());
    }
}

Now we can also print the published date. Be sure not to put annotations on the field and on the setter. I had the problem with the last_update, I need JsonProperty annotation. First I put it on the field, but than the JsonDeserialize was not read anymore.

That is it for now, I will write more when I am ready. Than I will also publish the code. Some of the resources that were useful to me are written down below.

Resources

http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/remoting.html#rest-resttemplate

http://jackson.codehaus.org/

http://jsonviewer.stack.hu/

http://java.dzone.com/articles/how-serialize-javautildate

What are the tasks that we focus on right now:

• Create a new contact
• Remove a contact
• Change the name of a contact
• Register an address of a certain type for a specific contact
• Remove an address from a contact

But before we step into creating the front-end, we install some plugins that I discussed in previous posts.

Plugins

• Db-util – mainly used for testing
• Navigation – change the templates as well as add navigation stuff to the controller

Get our grails hands dirty

Task driven – Create a new contact, remove a contact, change name of a contact

Time to start working on the tasks. The first is a basic one: Create a new contact. This is one that comes out of the box, but we now have different navigation and I only want to show the fields that can actually be entered. For a contact that is only the name.

When creating new views I like to generate the views and start from the result. I took the list view first, removed the navigation part and shuffled the columns.

We move on to the create.gsp and the edit.gsp. Again we remove the input fields for items we do not need. In this case this is purely the identifier field. Of course I also remove the navigation. After testing the create screen, now without the identifier field I found out we need to change the constraints of the Contact object. We have to add nullable is true.

Let us move on to a more interesting task

Register an address of a certain type for a specific contact

At the moment we use the AddressEntryController to have a look at the addresses. This is about to change. Now we are going to show the available addresses in the contact details screen. This is also the screen where we present the tasks to remove an address and to register a new one.

We start with creating the button to add an address. We reuse the add button as provided by grails. There is a difference, the add button usually is presented in the top bar, we however want it in the bottom bar. Therefore we must add a class to the stylesheet and the following button to the bottom button bar:

<span class="button">
  <g:actionSubmit class="add" action="registerAddress"
      value="${message(code: 'orderEntry.button.registerAddress.label', default: 'Register Address')}"/>
</span>

Another part of the show Contact page we need to change is the part where we actually show the addresses of the contact. I use the generated code for the list.gsp of address entries. I remove the pagination part, but other than that it is the same. Except for one column. We do want to be able to delete addresses. Therefore I have added an image with the a link to the delete action. This link with an image is shown in the next line of code.

<g:link action="deleteAddress" id="${addressEntryInstance.id}">
    &ltimg src="${resource(dir:'images/skin',file:'database_delete.png')}" alt="delete">
</g:link>

Check out the way to create the link, just define the action and pass it an id. That is enough to be wired to the actual action method on the controller. I also like the way to create a link to an image. The resource method is used to point to a directory and the actual file. No need to think about web context url or things like that.

The final screen we need is the registerAddress form. It is mostly a copy of the edit.gsp of the address entry. I also do not want the contact name and contact identifier to be editable. Finally I changed the action of the form into saveAddress.

The final thing I want to have a look at is the groovy code of the controllers. The following code block shows all three methods that are important with respect to the addresses. The code is pretty straightforward.

    def registerAddress = {
        def contactEntryInstance = ContactEntry.get(params.id)
        def addressEntryInstance = new AddressEntry();
        addressEntryInstance.contactIdentifier = contactEntryInstance.identifier
        addressEntryInstance.contactName = contactEntryInstance.name
        [addressEntryInstance: addressEntryInstance]
    }

    def saveAddress = {
        def addressEntryInstance = new AddressEntry(params)
        if (addressEntryInstance.validate()) {
            def foundContact = ContactEntry.findByIdentifier(addressEntryInstance.contactIdentifier)
            contactCommandHandlerService.registerAddress(
                    addressEntryInstance.addressType,
                    addressEntryInstance.contactIdentifier,
                    addressEntryInstance.streetAndNumber,
                    addressEntryInstance.zipCode,
                    addressEntryInstance.city)
            flash.message = "${message(code: 'default.created.message', args: [message(code: 'addressEntry.label', default: 'AddressEntry'), addressEntryInstance.city])}"
            redirect(action: "show", params:[id:foundContact.id])
        }
        else {
            render(view: "registerAddress", model: [addressEntryInstance: addressEntryInstance])
        }
    }

    def deleteAddress = {
        def addressEntryInstance = AddressEntry.get(params.id)
        if (addressEntryInstance) {
            contactCommandHandlerService.removeAddress(addressEntryInstance.addressType, addressEntryInstance.contactIdentifier)
        }
        def foundContact = ContactEntry.findByIdentifier(addressEntryInstance.contactIdentifier)
        redirect(action: "show", id: foundContact.id)
    }

Again a lot of copy paste from the generated controller. But here we use the contactCommandHandlerService to create the commands that are send back to the server. In all three methods we use the query datasource to obtain the contact data. As you can see, we do not store anything in the query database. That is all handled by the commands and events. Than in the event listener we receive the domain events and update the query database. The following and last code block gives you the action that handles the AddressDeletedEvent.

    private void doHandle(AddressRemovedEvent event) {
        ContactEntry foundContact = ContactEntry.findByIdentifier(event.aggregateIdentifier.toString())
        AddressEntry foundAddress = AddressEntry.findByAddressTypeAndContactIdentifier(event.addressType,foundContact.identifier)
        if (foundAddress) {
            foundAddress.delete()
        }
    }

Oke because I actually forgot to implement this correct at first, the listener for ContactDeletedEvent. I forgot to remove the addresses for the contact. We have a table with contacts and a table that combines the contact information with the address information. Therefore we have to do two delete actions.

    private void doHandle(ContactDeletedEvent event) {
        ContactEntry foundContact = ContactEntry.findByIdentifier(event.aggregateIdentifier.toString())
        List<AddressEntry> foundAddresses = AddressEntry.findAllByContactName(foundContact.name)

        foundContact.delete()

        foundAddresses.each {address ->
            address.delete()
        }
    }

The following image gives you an idea about the screen.

That is it for now, in my next and final blogpost about this example I will show the advantage of having these simple screen oriented tables.

The best learning source for me consists of a number of manning books:

• Grails in Action
• Groovy in Action (2nd edition)

The first thing I did was creating some scripts, I mainly copied some sources from others. I also wrote a blog post about the groovy goodness:

http://www.gridshore.nl/2009/11/20/analyzing-beet-results-with-groovy/

Again I was amazed by the way groovy is used to obtain a webpage and print the contents of the page. The following code block shows the script.

#!/usr/bin/env groovy
def NEW_LINE = System.getProperty("line.separator")
def address = "http://www.applenieuws.nl/?feed=rss"
def urlInfo = address.toURL()
println "URL: ${address}${NEW_LINE}"
println "URL Text: ${urlInfo.text}${NEW_LINE}"
println "Host/Port: ${urlInfo.host}/${urlInfo.port}${NEW_LINE}"
println "Protocol: ${urlInfo.protocol}${NEW_LINE}"
println "User Info: ${urlInfo.userInfo}${NEW_LINE}"
println "File: ${urlInfo.file}${NEW_LINE}"

But since you are reading this I guess you are already interested in groovy. This post is not for experts in groovy. It is more focussed on people trying to find out if groovy is going to help them work more effectively or just for the fun of it.

Integration

I love the integration of groovy and java. You can implement a java interface with groovy. You can call a groovy class from java code. One of the things you are able to do is use spring annotations like @Autowired and @Component in groovy. The following code block shows a listener that can function within an Axon application to receive events. Nice stuff isn’t it?

@Component
class GroovyAddressListener implements org.axonframework.core.eventhandler.EventListener {

  @Autowired
  GroovyAddressListener(SimpleEventBus eventBus) {
    eventBus.subscribe this
  }

  void handle(Event event) {
    if (event instanceof AddressRegisteredEvent) {
      println "a new address in city ${event.address.getCity()} is received."
    }
  }
}

If you are not familiar with the Axon Framework, check the website www.axonframework.org. I am also planning a blog post around a sample I am creating with a tight integration of Axon and Grails.

Due to the easy integration of groovy and java, people that like groovy create wrappers around existing java libraries to make them better useable. On of those examples is the HttpBuilder project. This is a project that wraps the apache http client.

Building groovy

Using maven

What is with software that it needs to be build. In java land we have maven. Nowadays (maven 3), maven is even powered by groovy. If you want to integrate groovy with java, a maven build seems very logical. There is a good maven plugin for building groovy. Checkout the following page to learn about the maven configuration.

http://btilford.blogspot.com/2010/02/groovy-170-and-gmaven-12-multi-module.html

If you want to compile groovy classes into java classes and use them in your own application, you need to add the groovy library to your classpath. The groovy maven plugin itself is easy to configure. The following code block shows an example that makes use of the groovy maven plugin.

<dependencies>
    <dependency>
        <groupId>org.codehaus.gmaven.runtime</groupId>
        <artifactId>gmaven-runtime-1.7</artifactId>
        <version>1.2</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-all</artifactId>
        <version>1.7.0</version>
    </dependency>
<dependencies>
<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.gmaven</groupId>
            <artifactId>gmaven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>generateStubs</goal>
                        <goal>generateTestStubs</goal>
                        <goal>compile</goal>
                        <goal>testCompile</goal>
                    </goals>
                    <configuration>
                        <providerSelection>1.7</providerSelection>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Using grails

Cannot get easier than this, just create a project and use the grails commands. Grails also makes it very easy to add libraries to the project. These libraries can be used in the normal grails classes: domain, controller, service. But you can also use them in your own groovy classes. I use this extensively in the grails/axon integration sample.

In your grails project go to the directory grails-app/conf. There you can find the BuildConfig.groovy. Within this file you can find the dependencies. The following code block gives you an example to include the axon framework as a compile time dependency and xstream as a runtime dependency. To be able to use this you have to uncomment the mavenLocal() in de dependencies part of the same file.

  dependencies {
    compile 'org.axonframework:axon-core:0.5-SNAPSHOT'
    runtime 'com.thoughtworks.xstream:xstream:1.3.1'
  }

Of course you could obtain libraries from other maven repositories, but since we use the snapshot that is not available in a repository we use the local maven repository.

The complete dependency model of grails is pretty extensive and a bit to much to discuss in detail.

Using Gradle

If you are only doing groovy, maven might not be the best choice. Even if you are combining java and groovy some people say maven is not the right choice. I think it is a matter of taste although I do think maven is pretty verbose. An alternative in groovy landscape is Gradle. Gradle uses convention over configuration. It needs less lines of code than ant (without custom libraries) and gives more freedom than maven. Maybe the best about grails is that it does not use xml, but it uses groovy instead.

Peter Ledbrook is doing a good job in using gradle to build grails projects. Read his blog post : http://www.cacoethes.co.uk/blog/groovyandgrails/building-a-grails-project-with-gradle. Personally I do think this is one step to far. For me the grails build system is good enough. I also had a lot of tooling problems when combining gradle and grails in intellij. I did not get the classpath like I wanted to. Using the mechanism as described in the grails part of build works for me. I do think they borrowed some good ideas (dependency management) from gradle.

Grapes

The last tool you can use when running groovy I would like to mention is Grapes. I like the idea for dependency management in scripts. There is a very easy way to add libraries to your classpath by using the grab mechanism. I like the example as published on the page about the groovy Http builder. I am not going to reprint the example here. It all has to do with the grab annotation. The following line only shows the grab command.

@Grab(group='org.codehaus.groovy.modules.http-builder', module='http-builder', version='0.5.0-RC2' )

So even in a command line script you can now use libraries managed by Grapes.

That is it for now, more to follow the next months.

In this blog post I go step-to-step through a solution that analyzes the xml file and plots the results in a chart generated with jfreechart.

Introduction

In one of my previous posts I have discussed a nice framework for easy performance measurement called Beet. You can find this post here: Using beet to monitor your (springframework) application. The result of a monitor session with beet can be an xml file. Nice, but how do you analyze this file? By hand? No way, you need a tool. Excel or Numbers can be fine, but it can be a lot faster. Therefore I decided to create a small groovy application.

The first requirement for me was very easy, read the events in the xml file and calculate the average of all events of a certain type. I asked a few of my collegues about their estimated effort when having to do it in java. They varied from 1 hour (pretty optimistic) to half a day. Curious how much time it took me?

First iteration

The first iteration was to calculate the overall average, an optimist of 2 hour java work. First you locate the file, than you slurp the xml out of the file. With the xml file in your hand, you obtain all events with a child element type with the value method. The following code block shows these three lines of code, yes for real, three lines.

def file = new File("beet-integration-web-perf.xml")
def xml = new XmlSlurper().parse(file)
def methodEvents = xml.event.findAll {it.type == "method"}

The next step is to take all durations from the found events. Using these durations, calculating the average is very easy.

def file = new File("beet-integration-web-perf.xml")
def xml = new XmlSlurper().parse(file)
def methodEvents = xml.event.findAll {it.type == "method"}
def durations = methodEvents*."duration-ms"
println "Average duration is ${durations.sum {it.toBigDecimal()} / durations.size()}"

That is it, this took me 10 minutes. And yes for 5 lines of code that is still a lot, but cut me some slag man, I am still learning groovy . What I forgot to mention is that I use the groovyConsole to create and run the application.

Second iteration

The total average is nice, but with hundreds of measurements, not very useful. Of course we want more information on the data. To stretch myself a little bit, I had the idea to take the average of each minute and print that on screen. The next code block does just that, it calculates the averages of all measurements in the same minute and prints the result on the screen. When reading the code, take this tip. We create an array with all durations for each minute and put the result in a map with the minute as a key and the array with durations as a value.

def averages = [:]
def start = methodEvents[0].start.text()[0..16]
def minuteItems = []
methodEvents.each {
    def duration = it."duration-ms".toBigDecimal()
    def currentStart = it.start.text()[0..16]

    if (start == currentStart) {
        minuteItems.add duration
    } else {
        averages.put ((start),minuteItems)
        minuteItems = [duration]
        start = currentStart
    }
}

averages.each {key,value ->
    println "Minute : ${key} has average duration of ${value.sum {it.toBigDecimal()} / value.size()}"
}

Third and final iteration

Having this data written to the screen is oke, but a nice graph would be even better. For this I used a sample I found via google. Since the code is pretty straightforward, I just copy it in here.

def dataset = new DefaultCategoryDataset()
dataset.with{
    avarages.each {key,values ->
    def value = (values.sum {it.toInteger()} / values.size())
        addValue value , "average", key[-3..-1]
    }
}

def labels = ["Registered events total ${methodEvents.size()}", "Minute", "Average"]
def options = [true, true, true]
def chart = ChartFactory.createLineChart(*labels, dataset,Orientation.VERTICAL, *options)
def swing = new SwingBuilder()
def frame = swing.frame(title:'Groovy LineChart',
        defaultCloseOperation:WC.EXIT_ON_CLOSE) {
    panel(id:'canvas') { widget(new ChartPanel(chart)) }
}
frame.pack()
frame.show()

For those java people, check the way you can work with arrays in line 5. Counting from the end of the array, nice.

The result is shown in the next image.

That is about it, just two last things. First you need to add two jars to the classpath of groovy: jcommon-1.0.16.jar, jfreechart-1.0.13.jar. These are in the jfreechart download package. I used the mechanism to create a folder .groovy/lib in your root and add the jars to that folder.

The other thing I wanted to mention is the option to create a shell script from groovy. Just add the following line at the top and make your file executable and you are good to go.

#!/usr/bin/env groovy

That is it, in total 2 hours of work, not bad I think for a beginner in groovy with access to google. If you are good at groovy and you spot improvements, please let me know, I am eager to learn more.