spring


23
Apr 15

Question Everything

Feeding Da Brain


In 90s you would say: “I am a programmer”. Some would reply with “o.. k”. More insightful would reply with a question “which programming language?”.

21st century.. socially accepted terminology has changed a bit, now you would say “I am a developer”. Some would ask “which programming language?”. More insightful would reply with a question “which out of these 42 languages do you use the most?”

The greatest thing about using several at the same time is that feeling of constant adjustment as I jump between the languages. It feels like my brain goes through exuberant synaptogenesis over and over again building those new formations.

   What's for dinner today honey?
   Asynchronous brain refactoring with a gentle touch of "mental polish"

With all these new synapses, I came to love the fact that something that seemed so holy and “crystal right” before, now gets questioned and can easily be dismissed. Was it wrong all along? No. Did it change? No. So what changed then? Well.. perception did.

Inmates of the “Gang of Four” Prison


Design patterns are these “ways” of doing things that cripple new programmers, and imprison many senior ones. Instead of having an ability to think freely, we have all these “software standard patterns” which mostly have to do with limitations of “technology at time”.

Take big guys, like C++ / Java / C#, while they have many great features and ideas, these languages have horrible story of “behavior and state”: you always have to guard something. Whether it is from multiple threads, or from other people misusing it. The languages themselves promote reuse vs. decoupling: i.e. “let’s inherit that behavior”, etc..

So how do we overcome these risks and limitations? Simple: let’s create dozens of “ways” that all developers will follow to fight this together. Oh, yea, and let’s make it industry standard, call them patterns, teach them in schools, and select people by how well they can “apply” these patterns to “any” problem at hand.

Not all developers bought into this cult of course. Here is Peter Norvig’s notes from 1996, where he “dismisses” 16 out of 23 patterns from Gang of Four, by just using functions, types, modules, etc.

Builder Pattern vs. Immutable Data Structures


Builder pattern makes sense unless.. several things. There is a great “Builders vs. Option Maps” short post that talks about builder patter limitations:

* Builders are too verbose
* Builders are not data structures
* Builders are mutable
* Builders can’t easily compose
* Builders are order dependent

Due to mutable data structures (in Java/C#/alike) Builders still make sense for things like Google protobufs with simple (i.e. primitive) types, but for most cases where immutable things need to be created it is best to use immutable data structures for the above reasons.

While jumping between the languages, I often need to create things in Clojure that are implemented in Java with Builders. This is not always easy, especially when Builders rely on external state or/and when Builders need to be passed around (i.e. to achieve a certain level of composition).

Let’s say I need to create a notification client that, by design (on the Java side of things), takes some initial state (i.e. an external system connection props), and then event handlers (callbacks) are registered on it one by one, before it gets built, i.e. builds a final, immutable notification client:

SomeClassBuilder builder = SomeClass.newBuilder()
                             .setState( state )
                             .setAnotherThing( thing );
 
builder.register( notificationHandlerOne );
builder.register( notificationHandlerTwo );
...
builder.register( notificationHandlerN );
 
builder.build();

In case you need to decouple “register events” logic from this monolithic piece above, you would pass that builder to the caller that would pass it down the chain. It is something that seems “normal” to do (at least to a “9 to 5″ developer), since methods with side effects do not really raise any eyebrows in OO languages. In fact most of methods in those languages have side effects.

I quite often see people designing builders such as the one above (with lots of external state), and when I need to use them in Clojure, it becomes very apparent that the above is not well designed:

;; creates a "mutable" builder..
(defn- make-bldr [state thing]
  (-> (SomeClass/newBuilder)
      (.withState state)
      (.withAnotherThing thing)))
 
;; wraps "builder.register(foo)" into a composable function
(defn register-event-handler! [bldr handler]
    ;; in case handler is just a Clojure function wrap it with something ".register" will accept
    (.register bldr handler))
 
(defn notification-client [state thing]
  (let [bldr (make-bldr state thing)]
    ;; ... do things that would call "register-event-handler!" passing them the "bldr"
    (.build bldr)))

Things that immediately feel “off” are: returning a mutable builder from “make-bldr”, mutating that builder in “register-event-handler!”, and returning that mutated builder back.. Not something common in Clojure at all.

Again the goal is to “decouple logic to register events from notification client creation“, if both can happen at the same time, the above Builder would work.

In Clojure it would just be a map. All data structures in Clojure are immutable, so there would be no intermediate mutable holder/builder, it would always be an immutable map. When all handlers are registered, this map would be passed to a function that would create a notification client with these handlers and start it with “state” and “thing”.

Mocking Suspicions


Another synapse formation, that was created from using many languages at the same time, convinced me that if I have to use а mock to test something, that something needs a close look, and would potentially welcome refactoring.

The most common case for mocking is:

A method of a component "A" takes a component "B" that depends on a component "C".

So if I want to test A’s method, I can just mock B and not to worry about C.

The flaw here is:

"B" that depends on a component "C".

These things are extremely beneficial to question. I used to use Spring a lot, and when I did, I loved it. Learned from it, taught it to others, and had a great sense of accomplishment when high complexity could be broken down to simple pieces and re wired together with Spring.

Time went on, and in Erlang or Clojure, or even Groovy for that matter, I used Spring less and less. I still use it for all my Java work, but not as much. So if 10 years ago:

"B" that depends on a component "C".

was a way of life, now, every time I see it, I ask why?. Does “B” have to depend on “C”? Can “B” be stateless and take “C” whenever it needed it, rather that be injected with it and carry that state burden?

If before “B” was:

public class B {
 
  private final C c;
 
  public B ( C c ) {
    this.c = c;
  }
 
  public Profit doBusiness() {
    return new Profit( c.doYourBusiness() + 42 );
  }
}

Can it instead just be:

public final class B {
  public static Profit doBusiness( C c ) {
    return new Profit( c.doYourBusiness() + 42 );
  }
}

In most cases it can! It really can, the problem is not enough of us question that dependency, but we should.

This does not mean “B” no longer depends on “C”, it means something more: there is no “B” (“there is no spoon..”) as it just becomes a module, which does not need to be passed around as an instance. The only thing that is left from “B” is “doBusiness( C c )”. Do we need to mock “C” now? Can it, its instance disappear the way “B” did? Most likely, and even if it can’t for whatever reason (i.e. someone else’s code), I did question it, and so should you.


The more synapse formations I go through the better I learn to question pretty much everything. It is fun, and it pays back with beautiful revelations. I love my brain :)


22
Jul 11

Having Cluster Fun @ Chariot Solutions

The best way to experiment with distributed computing is to have a distributed cluster of things to play with. One approach would of course be to spin off multiple Amazon EC2 instances, which would be wise and pretty cheap:

Micro instances provide 613 MB of memory and support 32-bit and 64-bit platforms on both Linux and Windows. Micro instance pricing for On-Demand instances starts at $0.02 per hour for Linux and $0.03 per hour for Windows”

However some problems are better solved/simulated by having real, “touchable” hardware, that would have real dedicated disks, dedicated cores, RAM, and would only share any kind of state with other nodes over network. Easier said that done though.. Do you have a dozen of spare (same spec’ed) PCs laying around?

But what if you had an awesome training room with, let’s say, 10 iMacs? That would look something like:

Chariot Solutions Training Room

This is in fact the real deal => “Chariot Solutions Training Room“, which is usually occupied by people learning about Scala, Clojure, Hadoop, Spring, Hibernate, Maven, Rails, etc..

So once upon a time, in after training hours, we decided to run some distributed simulations. As we were passing by the training room, we had a thought: “It’s Friday night, and as any other creatures, these beautiful machines would definitely like to hang out together”…

Cluster at Chariot Solutions

This is one of this night’s highlights: a MongoDB playground. The same Friday night we played with Riak, Cassandra, RabbitMQ and vanilla distributed Erlang. As you can imagine iMacs had a lot of fun in a process pumping data in and out via 10 Gigabit switch. And we geeked out like real men!


15
Mar 11

Spring Batch: CommandLineJobRunner to Run Multiple Jobs

Sometimes this requirement may jump at you: “I still want to have them as several jobs, but I want no operational overhead, and need to run them in sequence via a single launch…”.

So if you were using CommandLineJobRunner to launch these jobs, it would only be natural to aggregate those calls under your own e.g. “CommandLineMultipleJobRunner” that just delegates its calls to “CommandLineJobRunner” for each job in a list..

The only caveat is the default SystemExiter which is set to JvmSystemExiter, which makes it imposible to make more than one launch using a “CommandLineJobRunner”, since “JvmSystemExiter” does:

public void exit(int status) {
    System.exit(status);
}

Fortunately, there is a static accessor to override this behavior:

// disabling a default "JvmSystemExiter" to be able to run several times
CommandLineJobRunner.presetSystemExiter( new SystemExiter() { public void exit( int status ) {} } );

Now, call “CommandLineJobRunner.main( String[] args )” as many times as you’d like.

If you have a choice, think about creating a single multi step job instead, but if you don’t have a luxury, “CommandLineMultipleJobRunner” should now be not all that hard to implement.

Batch Away! :)


12
Oct 10

Running Spring AspectJ Tests with Maven

You need to use a real AspectJ aspect with Spring, where you would like to inject some dependencies into this aspect as a Spring container starts up.

Here is an AspectJ aspect:

@Aspect
public class VeryImportantAspect {
    ...
    public void setSomeDependency( SomeDependency dependency ) {
        this.dependency = dependency;
    }
    ...
}

Now let’s define it as a bean and inject “someDependency”:

<bean id="veryImportantAspect" 
         class="org.dotkam.VeryImportantAspect"
         factory-method="aspectOf">
 
         <property name="someDependency" ref="someDependency"/>
</bean>

Notice factory-method=”aspectOf” that tells Spring to use a real AspectJ ( not Spring AOP ) aspect to create this bean. In reality, if the “VeryImportantAspect” was already woven in, it will have an “aspectOf” method.

Hence if you get this error at some point:

No matching factory method found: factory method 'aspectOf()'

That would mean that the aspect was not woven by AspectJ weaver.

We also need to tell Spring to use load time weaving:

<context:load-time-weaver/>

If you run with the above configuration without doing anything, you would get a following error:

ClassLoader does NOT provide an 'addTransformer(ClassFileTransformer)' method

That tells you ( well not explicitly :) ) to include a “spring-instrument.jar” javaagent.

So at this point two things need to be added: AspectJ weaver and Spring Instrument agent. Build / Continues integration server does not use any IDE, so it is not as simple as downloading AspectJ plugin for IDEA / Eclipse and including VM arguments in Run Configurations… It is simpler: just add the two in your POM file.

Adding an AspectJ plugin:

<plugin>
     <groupId>org.codehaus.mojo</groupId>
     <artifactId>aspectj-maven-plugin</artifactId>
     <version>1.3</version>
     <executions>
         <execution>
             <configuration>
                <source>1.6</source>
                <target>1.6</target>
            </configuration>                     
             <goals>
                 <goal>compile</goal>       <!-- use this goal to weave all your main classes -->
                 <goal>test-compile</goal>  <!-- use this goal to weave all your test classes -->
             </goals>
         </execution>
    </executions>
</plugin>

Adding a Spring Instrument agent to participate in a test execution:

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-surefire-plugin</artifactId>
	<version>2.4</version>
	<configuration>
            <forkMode>once</forkMode>
            <argLine>
                 -javaagent:"${settings.localRepository}/org/springframework/spring-instrument/${spring.framework.version}/spring-instrument-${spring.framework.version}.jar"
	    </argLine>
            <useSystemClassloader>true</useSystemClassloader>
	</configuration>
</plugin>

And all that work, just too see a couple of lines from Maven:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------

26
Sep 10

Money Making Project

For the past several years most of my projects were based on Spring and Hibernate. And what I keep seeing is how people struggle to understand how the two are working together.

So going from project to project, I have to repeat the same spiel over and over again to get people up to speed.

Since I believe that the most effective way to LEARN is to DO, I create simple examples for people to play with / to complete / to analyze, etc..

So “Money Making Project” is one of such examples. It comfortably lives at github’s luxury apartments, so anybody can “git clone” / “fork” and play with it.

Besides making money, this project also demos things such as:

A way to structure a project

Maven based structure ( hence can be easily used by gradle ). Configuration and property files organized under “META-INF/conf”, “META-INF/props”, etc..

A way to separate Spring configs

“tx-spring-config.xml”, “persistence-spring-config.xml”, “service-spring-config.xml”, “repository-spring-config.xml” and “application-context.xml” that includes them all

Properties via PropertyPlaceholderConfigurer

<context:property-placeholder location="classpath:META-INF/props/env.properties"/>

Hibernate overall configuration file

That is injected into AnnotationSessionFactoryBean

Hibernate Named Queries

That are linked to the Hibernate overall config

<mapping resource="META-INF/conf/hibernate/mapping/startup-bank-named-queries.xml"/>

Spring’s DAO / Hibernate Exception Translation

Via @Repository and “PersistenceExceptionTranslationPostProcessor”

Simple CRUD Repository

public interface MoneyRepository {
 
    public void make( MoneyRoll moneyRoll );        // C
    public MoneyRoll find( Long id );                       // R
    public void update( MoneyRoll moneyRoll );     // U
    public void takeOut( MoneyRoll moneyRoll );    // D
}

with a Hibernate based implementation

Transaction Management with Spring AOP

Declarative, on a Service Level, using “aop:config”, “tx:advice” namespaces

Spring Testing

With SpringJUnit4ClassRunner, ContextConfiguration, etc..

Using Embeded in-memory H2 Database for Testing

<jdbc:embedded-database id="dataSource" type="H2"/>

Hibernate Logging

Most useful hibernate “log4j.logger” properties

Demoing how important Transaction is for Hibernate Sessions

“HibernateSessionNotBoundToThreadIntegrationTest” for the second (after LazyInitializationException ) most common Hibernate exception: “No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here”


10
Sep 10

Spring Expression Language: Calling a Method with Parameters

Have you ever wanted to win $1,000,000 with a single SpEL ( Spring Expression Language ) call? Well, now you can, and here is how.

Let’s say there is a Lottery that deposits money to a winner’s bank account and congratulates the winner:

private class Lottery {
    // ...
    public String congratulateWinner( String name, BigDecimal amount, Date date ) {
    	String now = new SimpleDateFormat( "MM-dd-yyyy" ).format( date );
    	String cash = new DecimalFormat( "$#,###,###" ).format( amount.doubleValue() );
 
    	return "Congratulations " + name + "! " +
    	       "Today is " + now + ", and it's your lucky day, because " +
    	       "you just won " + cash + "!";
    }
}

Here is how to make Anatoly win money with SpEL:

"congratulateWinner( 'Anatoly', #amount, #date )"

( of course, let’s not forget to set an amount to at least a million dollars ).

And here is a million dollar unit test:

@Test
public void shouldInvokeMethodWithParameters() {
 
    Lottery lottery = new Lottery();
 
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set( 2010, 8, 10 );
 
    BigDecimal amount = BigDecimal.valueOf( 1000000.00 );
 
    // letting SPEL know about the "lottery", the "amount" won, and the "date"
    EvaluationContext context = new StandardEvaluationContext( lottery );
    context.setVariable( "amount", amount );
    context.setVariable( "date", calendar.getTime() );
 
    ExpressionParser parser = new SpelExpressionParser();
 
    // using '#' to identify a variable ( NOTE: #this, #root are reserved variables )
    Expression exp = parser.parseExpression( "congratulateWinner( 'Anatoly', #amount, #date )" );
 
    String congratulations = ( String ) exp.getValue( context );	
    assertEquals( "Congratulations Anatoly! " + 
                  "Today is 09-10-2010, and it's your lucky day, because you just won $1,000,000!", 
                  congratulations );
}

(!) Do not write code that does not earn you money :)


6
Apr 10

Spring Batch: Quick Start

Spring Source Logo

You heard about Spring Batch, but have this “uneasy” feeling about where/how/what you should start with? A year ago it was truly difficult for a non geek developer (most of the developers) to start with projects like Spring Batch, Spring Integration, Spring Webflow, Spring MVC, etc.. But now..

Now, you have no excuse: it is extremely simple to build a sample Spring project, of pretty much any “flavour”, that comes pre-built with unit and integration tests, that you can run right after those 12 seconds that you spent downloading the project, and resolving dependencies.

Does it sound helpful? Well, not really, since I just said what will happen, and how easy it is to make it happen, but there was no how part… I hate when people do that :)

So without further ado, here comes the “how” part:

Step 1. DON’T PANIC :)

After successful completion of Step 1, it is time for…

Step 2. Download Spring Tool Suite

As I already mentioned in “Spring Insight in Action – 5 Minutes From Scratch“, I like to think about Spring Tool Suite as Eclipse on Spring rocks (Spring IDE, Spring Interactive Tutorials, Exception Resolution, Grails support, Spring Insight, Spring tc Server, Spring Template Projects, and much more): http://www.springsource.com/products/springsource-tool-suite-download

Step 3. Create New Spring Template Project

After Spring Tool Suite is started (remember, it is just a Spring version of Eclipse, so it should look very familiar), press Ctrl+n to create “something” new, and start typing “spring temp…”:

Spring Tool Suite: New Spring Template Project

As you type, Eclipse will narrow down selection to “Spring Template Project”. Select it, and click Next:

Spring Tool Suite: New Spring Batch Template Project

Here you can see many hot and ready to go Spring template projects that you can explore. The purpose of this article is to show how easy it is to start with Spring Batch, but for the most part, you can follow these steps to create all of the projects from the list above. (as an extra credit, try to create a Spring Integration Template project, once we done here).

Select “Simple Spring Batch Project”, and click Next:

new spring batch template project name

Name your fresh and ready to go Spring Batch project, and click Finish, here is what your own Spring Batch project will look like:

spring batch template project live

You are actually done right here, but, since curiosity is what makes us humans, let’s take a look at what’s inside:

spring batch template project structure

As you can see, it is a Maven structured project with all the goodies: source, tests, pom, configs, etc..

Let’s look at your first real Batch Job. Double click on “module-context.xml”:

spring batch template project job config

In order to make sense of what you are looking at, you can refer to a very good and extensive Spring Batch documentation: http://static.springsource.org/spring-batch/reference/html/index.html

Step 4. Make Sure It Works

But hey, don’t just believe me that it works => make sure it does! And how would you do that? Well, again, simple: just run a test:

spring batch template project run test

Now you should see some green, which actually tells you: “it works indeed”.

Now you see, that starting to work on any major Spring Project is only a couple of mouse clicks away. You can really feel how close and accessible all that knowledge is. So be brave and take it all!

Good Luck!


10
Feb 10

Multiple Around Advices Applied to the Same Join Point

Spring and AspectJ

So, what do you think will happen if you apply two around advices to the same join point? They both call “proceedingJoinPoint.proceed()” which calls their target object.

But then if the target object is the same, then it is going to be called twice.. Hmm.. not something you would want to happen especially if that target object is a service that withdraws money from your bank account..

According to the Spring documentation, you may specify the order in which these advices are applied, using Ordered interface, so in case the target object (that service that withdraws money from your account) is called twice, you have an opportunity to specify the order of who calls it first:)

To free the minds of many from unnecessary worries, I’ll show you what really happens when two around advices are applied to the same join point.

Here is this target object (transfer money service):

public class WireTransferMoneyService implements TransferMoneyService {
 
	public void transferMoney( Money money, 
			         Account sourceAccount,
			         Account targetAccount) {
 
		// Start the "Wire Transfer" manager
		// ...
 
		System.err.println( this.getClass().getSimpleName() + " is called" );
 
		sourceAccount.withdraw( money );
		targetAccount.deposit( money );	
	}
}

And here are the two around advices that are applied to this transfer service:

@Around("com.xmen.iii.aspect.SystemArchitecture.businessService()")
public Object doSomethingOnTransfer(ProceedingJoinPoint pjp) throws Throwable {
 
	System.err.println( Thread.currentThread().getStackTrace()[1].getMethodName() +
			" \t\twas called before " + pjp.getTarget().getClass().getSimpleName() );
 
	Object retVal = pjp.proceed();
 
	System.err.println( Thread.currentThread().getStackTrace()[1].getMethodName() +
			" \t\twas called after " + pjp.getTarget().getClass().getSimpleName());
 
	return retVal;
}
 
@Around("com.xmen.iii.aspect.SystemArchitecture.businessService()")
public Object doSomethingElseOnTransfer(ProceedingJoinPoint pjp) throws Throwable {
 
	System.err.println( Thread.currentThread().getStackTrace()[1].getMethodName() +
			" \twas called before " + pjp.getTarget().getClass().getSimpleName() );
 
	Object retVal = pjp.proceed();
 
	System.err.println( Thread.currentThread().getStackTrace()[1].getMethodName() +
			" \twas called after " + pjp.getTarget().getClass().getSimpleName() );
 
	return retVal;
}

Now it’s simple: let’s run it and see what happens… And that is what happens:

2010-02-10 19:52:47,542 INFO [org.springframework.test.context.TestContextManager] - <@TestExecutionListeners is not present for class [class com.xmen.iii.integration.TransferLoggingAspectTest]: using defaults.>
2010-02-10 19:52:47,667 INFO [org.springframework.beans.factory.xml.XmlBeanDefinitionReader] - <Loading XML bean definitions from class path resource [com/xmen/iii/integration/TransferLoggingAspectTest-context.xml]>
2010-02-10 19:52:47,808 INFO [org.springframework.beans.factory.xml.XmlBeanDefinitionReader] - <Loading XML bean definitions from class path resource [META-INF/spring/aspect-context.xml]>
2010-02-10 19:52:47,839 INFO [org.springframework.beans.factory.xml.XmlBeanDefinitionReader] - <Loading XML bean definitions from class path resource [META-INF/spring/app-context.xml]>
2010-02-10 19:52:47,917 INFO [org.springframework.context.support.GenericApplicationContext] - <Refreshing org.springframework.context.support.GenericApplicationContext@1820dda: display name [org.springframework.context.support.GenericApplicationContext@1820dda]; startup date [Wed Feb 10 19:52:47 EST 2010]; root of context hierarchy>
2010-02-10 19:52:47,917 INFO [org.springframework.context.support.GenericApplicationContext] - <Bean factory for application context [org.springframework.context.support.GenericApplicationContext@1820dda]: org.springframework.beans.factory.support.DefaultListableBeanFactory@1126b07>
2010-02-10 19:52:48,355 INFO [org.springframework.beans.factory.support.DefaultListableBeanFactory] - <Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1126b07: defining beans [transferMoneyService,messageSource,org.springframework.aop.config.internalAutoProxyCreator,com.xmen.iii.aspect.logging.ServiceLoggingAspect#0,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor]; root of factory hierarchy>
"
doSomethingOnTransfer                   was called before WireTransferMoneyService
doSomethingElseOnTransfer               was called before WireTransferMoneyService
WireTransferMoneyService is called
doSomethingElseOnTransfer               was called after WireTransferMoneyService
doSomethingOnTransfer                   was called after WireTransferMoneyService
"
2010-02-10 19:52:48,433 INFO [org.springframework.context.support.GenericApplicationContext] - <Closing org.springframework.context.support.GenericApplicationContext@1820dda: display name [org.springframework.context.support.GenericApplicationContext@1820dda]; startup date [Wed Feb 10 19:52:47 EST 2010]; root of context hierarchy>
2010-02-10 19:52:48,433 INFO [org.springframework.beans.factory.support.DefaultListableBeanFactory] - <Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1126b07: defining beans [transferMoneyService,messageSource,org.springframework.aop.config.internalAutoProxyCreator,com.xmen.iii.aspect.logging.ServiceLoggingAspect#0,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor]; root of factory hierarchy>

So, as you can see, AspectJ and Spring are modest but smart, they chain those around advices for you, which is of course niice.

Happy Advising!


28
Oct 09

Spring Insight in Action – 5 Minutes From Scratch

Spring Source Logo

Spring Insight gives deep visibility into your application’s real activity on a request-by-request basis. For any request you can see all the JDBC queries it made, how much time it took to render, or timings for any of your major Spring beans.” – said Jon Travis in his article on a Spring blog.

That is such a great idea I though, and watched Jon’s screencast.

What actually surprised me is how simple and quick it is to try the Spring Insight in action. Here are these 3 simple steps:

Step 1. Download Spring Tool Suite

I like to think about Spring Tool Suite as an Eclipse on Spring rocks (Spring IDE, Spring Interactive Tutorials, Exception Resolution, and much more). And now ( since version 2.2 ), it comes with tc Server Developer Edition that includes Spring Insight, so the easiest way to try out Spring Insight is to download Spring Tool Suite, since it comes with it: http://www.springsource.com/products/springsource-tool-suite-download

Note that “tc Development Edition” can be downloaded and run on its own, Spring Tool Suite (STS) gives us something extra: “ready to go” sample applications that we can deploy to tc Server – all in one.

Step 2. Import a sample web application

About those sample applications… Now as you have STS unpacked/unzipped, you can run it and go to “File” –> “Import” –> “Spring Tool Suite” –> “Sample Projects”. You should see three sample applications “Hotel Booking”, “PetClinic” and “SpringTravel”. I chose “PetClinic”, but it does not really matter, we can use any sample application to play with Spring Insight.

Once you click “Ok”, STS will ask you if that is ok to download 20+ MB of JARs, you, of course, having a huge HD, would say yes, and.. here you go 1 minute later you have yourself a fully functional ready to deploy web app!

Step 3. Deploy a web application to tc Server Developer Edition

Now right click on PetClinic app, -> Run on server -> Choose Spring tc Server (it is not going to say anything about Insight, but it’s there :) ).

At this point STS will ask you to browse to the location of your tc server, it should be under the directory you installed STS, e.g in my case it was: “/opt/springsource/tc-server-6.0.20.C”

After you click “Finish”, you should see “INFO: Deploying web application archive insight.war” as one of your deployment messages in STS console.

After another minute, once your app (PetClinic in my case) is deployed, go to http://localhost:8080/insight and you should be good to go:

Spring Insight

Insight Away!


26
Jul 09

Apache Chain with Spring

“A popular technique for organizing the execution of complex processing flows is the “Chain of Responsibility” pattern, as described (among many other places) in the classic “Gang of Four” design patterns book. Although the fundamental API contracts required to implement this design patten are extremely simple, it is useful to have a base API that facilitates using the pattern, and (more importantly) encouraging composition of command implementations from multiple diverse sources.”

That is what Apache has to say as an intro to its Commons Chain API

It is no brainer, really, but Apache APIs do make it simpler to configure, implement and execute multiple Chains of Responsibilities. One thing, however, that feels “off”, when (if) implementing “Commons Chain” side by side with Spring, is there is no flexible, consistent (with Spring) way to setup Command objects: inject Command properties / refer to a single Command class as a bean, instead of duplicating the class name in Apache Chains, and Spring configuration, if Command object needs to be reused, etc…

Here is a simple way to utilize all the power that Apache offers + make it Spring friendly. Five components will be used in this example – 1 core class, 2 command classes, 1 test (driver) and Spring configuration file. Let’s see if you can figure out which is which :):

apache commons chain on spring: components

As you can see we are going to play an ultra short session of table tennis, or how it is sometimes called “Ping Pong”. It is going to be quite short, because we have two command objects: Ping and Pong, which are going to be chained, and run (by ChainRunner) once each: “Ping -> Pong”.

First, instead of relying on Apache way to configure chains, to make it consistent with all other application beans (classes) we’ll keep chain(s) configuration in Spring:

chain-config.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"
	xmlns:util="http://www.springframework.org/schema/util"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/util
http://www.springframework.org/schema/util/spring-util-2.5.xsd">
 
	<bean name="pingPongChain" class="org.apache.commons.chain.impl.ChainBase">
		<constructor-arg>
			<util:list>
				<ref bean="pingCommand" />
				<ref bean="pongCommand" />
			</util:list>
		</constructor-arg>
	</bean>
 
	<bean name="pingCommand" class="org.dotkam.samples.chain.command.PingCommand">
		<constructor-arg value="ping"/>
	</bean>
 
	<bean name="pongCommand" class="org.dotkam.samples.chain.command.PongCommand">
		<constructor-arg value="pong"/>
	</bean>
 
	<bean id="chainRunner" class="org.dotkam.samples.chain.ChainRunner"/>
 
</beans>

A “pingPongChain” is configured as “org.apache.commons.chain.impl.ChainBase”, and have two Commad classes, that implement “org.apache.commons.chain.Command” interface, wired in.

NOTE: The best practice is to keep Commands either stateless, or, if they have to have a state – immutable. If this practice is followed, these Commands can be safely reused throughout many chains (or even as stand alone utilities). That is the reason, in configuration above, parameters are injected at Command’s creation time via constructor injection.

In this example Commands are ultra simple for clarity:

PingCommand.java:

package org.dotkam.samples.chain.command;
 
import org.apache.commons.chain.Command;
import org.apache.commons.chain.Context;
 
public class PingCommand implements Command {
 
	private String message;
 
	public PingCommand( String message ) {
		this.message = message;
	}
 
	public boolean execute( Context context ) throws Exception {
 
		System.err.println( message );
		return false;
	}
}

and PongCommand.java:

package org.dotkam.samples.chain.command;
 
import org.apache.commons.chain.Command;
import org.apache.commons.chain.Context;
 
public class PongCommand implements Command {
 
	private String message;
 
	public PongCommand( String message ) {
		this.message = message;
	}
 
	public boolean execute( Context context ) throws Exception {
 
		System.err.println( message );
		return false;
	}
}

Now let’s look at the heart of the “Spring Chainer” – the “ChainRunner.java”:

package org.dotkam.samples.chain;
 
import org.apache.commons.chain.impl.ChainBase;
import org.apache.commons.chain.impl.ContextBase;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
 
public class ChainRunner implements BeanFactoryAware {
 
	private BeanFactory beanFactory;
 
	public void runChain( String chainName ) {
		try {
			createChain ( chainName ).execute( new ContextBase() );
		}
		catch ( Exception exc ) {
			throw new RuntimeException(
					"Chain \"" + chainName + "\": Execution failed.", exc );
		}
	}
 
	public void setBeanFactory( BeanFactory beanFactory ) throws BeansException {
		this.beanFactory = beanFactory;
	}
 
	protected ChainBase createChain( String chainName ) {
		return ( ChainBase ) this.beanFactory.getBean( chainName );
	}
}

It only does a couple of things, really.

By implementing Spring’s “BeanFactoryAware” interface, at runtime ChainRunner will have a reference to a “beanFactory” which it is going to use to obtain a reference to the requested chain via “createChain” method.

“ChainRunner” has an entry point which is a “runChain” method, that executes a chain by chain name (bean name in configuration file). For example, in the configuration shown above “pingPongChain” name can be provided.

It would ideally need to use a couple of custom runtime exceptions: e.g. ChainNotFoundException, IsNotChainException and ChainExecutionException, but we’ll keep it short here for clarity.

Alternatively, to strong type chains a bit, “ChainRunner” could take a Map of chains with keys as chain names, and corresponding “ChainBase” chain objects as values.

“ChainRunner” is pretty much everything that is needed in order to configure an Apache chain in Spring. We can run it by creating a JUnit (not really a test, just a driver):

ChainTest.java:

package org.dotkam.samples.chain;
 
import javax.annotation.Resource;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
@RunWith( SpringJUnit4ClassRunner.class )
@ContextConfiguration( locations={ "/conf/chain-config.xml"} )
public class ChainTest {
 
	@Resource
	ChainRunner chainRunner;
 
	@Test
	public void driveTheChain() {
		System.out.println("Starting up...      [Ok]");
		chainRunner.runChain( "pingPongChain" );
		System.out.println("Finised...          [Ok]");
	}
}

And here is the test/driver result:

apache commons chain on spring: results

Good start! Now it is time to sign up and see your name at the top of The International Table Tennis Federation (ITTF) World Ranking. Good Luck! :)