Tutorial: Creation of a "Hello World - SE"

This tutorial describes how to create a very simple "Hello world" JBI service engine (SE) component, pack it into a Service Unit (SU) which will be packed to a Service Assambly (SA), and finally how to run the SE inside ServiceMix. The SE will answer received messages with "Hello, I received xyz bytes!", so we literally see that it works. As it has the same structure as real, useful SE, the given hints help to use the presented code as a blueprint to create own SE-SA-SUs. Still, the example is as minimalistic as possible, so readers shall not get lost in too many details but get an idea of the big picture.

This tutorial shows the desired/best practices or "clean" way to create a SE-SA-SU using Maven archetypes, so how the workflow shall be - of course, other possibilities exist and may be better suited for certain situations. Furthermore, it will explain the reasons for critical choices and how required information can be retrieved. Where appropriate, additional reading will be suggested. To make it as easy as possible to follow the descriptions, they contain only the relevant code snippets, while the full code is available in the SVN repository. Please note that the code snippets are fetched directly from the full code in the SVN repository, thus the wiki and the code share always at the same, up to date state.

Prerequisites

The following is required:

• Around 15 minutes of time
• A running copy of ServiceMix 3.0 and Maven 2.0.4 or higher
• A connection to the Internet to download dependencies
• A text editor to alter XML files
• An editor or IDE for Java files

Overview SE-SU-SA

JBI components are can be tought of as the "smallest applications" you can access in an ESB. They have a very specific purpose, thus a narrow scope and set of functionallity. Components come in two flavours: Service Engine (SE) and Binding Components (BC).

Components are enriched by metadata (which?) and the whole is packed into a Service Unit (SU) - basically a JAR archive.

Several SUs are packed into a Service Assambly (SA). An SA is a complete "application" consisting of multiple components (reminder: the "smallest appliactions") interacting with each other and making up the big "application".

Further reading: JSR 208

Creating the SE

Creating the stub of the SE

First, a JBI component has to be created. Here, we use archetypes, just like shown at Creating a Standard JBI Component and Notes on Creating JBI Component using maven2 and Creating a protocol bridge. The Maven 2 archetypes are a kind of pattern, generic model, blueprint or template, or as Merriam-Webster defines "the original pattern or model of which all things of the same type are representations or copies". Using archetypes, Maven creates the basis for components, settings and so on, thus archetypes spare developers repetetive work and avoid errors like typos etc.

Note: As this text describes how to create a "Hello World" Service Engine and pack it into an SU and SA, the project name is hello-world-SE-SU-SA and the single pieces are named analogous. For a custom project, the IDs and names shall be altered such that they describe the purpose or function of the given piece of the SA.

First, we create a directory hello-world-SE-SU-SA and open a command line in this folder. Now we execute the following command (it has to be one line but was split to be readable):

The first three parameters identify the maven 2 archetype to use, while the last two parameters define the generated maven 2 project. The version information "3.0-incubating" may have to be changed; a look at any of ServiceMix' pom.xml reveals the version to use. Maven uses the group ID (printed in pink) as default Java package (see output below as well), thus invalid characters like minus, percent etc. must be avoided or a custom package name has to be given as parameter. Mavens output following the command looks like this (only relevant information preserved):

Maven creates a new folder having the same name as the artifact ID provided (printed in green in the command and output). Inside this folder, a file called pom.xml is created. This contains the Project Object Model providing Maven with all needed information for building (see Introduction to the POM at the Maven website). Moreover, Java source files and tests were created. The full structure of files created by Maven looks like this (some directories are grouped together for better readability):

\hello-world-SE-SU-SA\hello-world-SE\
      pom.xml
      src\main\
            java\
                  org\apache\servicemix\
                        samples\helloWorldSE\
                              MyBootstrap.java
                              MyComponent.java
                              MyDeployer.java
                              MyEndpoint.java
                              MyLifeCycle.java
                              MySpringComponent.java
      test\
            java\
                  org\apache\servicemix\
                        samples\helloWorldSE\
                              MySpringComponentTest.java
            resources\
                  spring.xml

All the classes have the word "My" prefixed to them due to the template. We can just rename the prefix to whatever we want to, as long as we make sure we change the corresponding resource files (all tests and the pom.xml) as well.

Compiling the code

From now on, we can build the code by executing

cd hello-world-SE

mvn compile

which shall present us as one of the last lines of output

[INFO] BUILD SUCCESSFUL

In case this success information is not appearing, the output shall give further information on the reasons. Further information can be found in the ServiceMix mailing lists archive and the Maven website.

Testing the code

Doing automated testing of the code is possible as well. As ServiceMix' root POM disables testing, we have to be activate it for the subprojects that shall be tested. To do so, the <build> entity of our pom.xml has to be enriched by

<pluginManagement>
	  <plugins>
			<plugin>
				  <groupId>org.apache.maven.plugins</groupId>
				  <artifactId>maven-surefire-plugin</artifactId>
				  <configuration>
						<skip>false</skip><!-- this overrides ServiceMix' root POM and forces to execute the tests -->
				  </configuration>
			</plugin>
	  </plugins>
</pluginManagement>

where <skip>false</skip> is the relevant line of code. Now, when executing

mvn test

tests will be done and Maven outputs the following (truncated to the relevant information):

[INFO] Scanning for projects...
[INFO] ----------------------------------------------------------------------------
[INFO] Building A custom project
[INFO]    task-segment: [test]
[INFO] ----------------------------------------------------------------------------
...
[INFO] [compiler:compile]
...
[INFO] [surefire:test]
[INFO] Setting reports dir: c:\java\tmp\servicemix-helloWorldSE\target/surefire-reports
-------------------------------------------------------
 T E S T S
-------------------------------------------------------
[surefire] Running org.apache.servicemix.samples.helloWorldSE.MySpringComponentTest
...
[surefire] Tests run: 1, Failures: 0, Errors: 0, Time elapsed: 1,422 sec
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
...

Adding functionality to the stub of the SE

The default implementation of the component accepts InOut MEPs and return the input content as the out message.

Using an IDE to add meat to the component. You can either use IDEA or Eclipse, I tried it with Eclipse so I guess I am going to stick it for now. <TODO>

This shall already include everything stated at
http://www.servicemix.org/site/maven-jbi-plugin.html#MavenJBIplugin-GettingStarted
and
http://www.servicemix.org/site/working-with-components.html

Packing into the SU

The archetypes for SUs and SAs do not contain much code, but rather help with tasks related to Maven. You will only need to adapt the generated POMs to your project - just little work, but requiring some guidiance. Here we go:

use the SU archetype like in http://www.servicemix.org/site/creating-a-protocol-bridge.html

manually editing http://goopen.org/confluence/display/SM/Working+with+Service+Units

Packing into the SA

As mentioned above\, the archetypes for SUs and SAs mainly help with tasks related to Maven.

use the SA archetype like in http://www.servicemix.org/site/creating-a-protocol-bridge.html
mvn archetype:create -DarchetypeGroupId=org.apache.servicemix.tooling -DarchetypeArtifactId=servicemix-service-assembly -DarchetypeVersion=3.0-incubating-SNAPSHOT -DgroupId=org.apache.servicemix.samples.helloWorldSE -DartifactId=hello-world-SA

manually editing http://www.servicemix.org/site/working-with-service-assemblies.html