{"id":533,"date":"2011-09-26T15:26:00","date_gmt":"2011-09-26T15:26:00","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/2012\/10\/jboss-modules-example-modular-web-application.html"},"modified":"2012-10-21T20:11:18","modified_gmt":"2012-10-21T20:11:18","slug":"jboss-modules-example-modular-web","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2011\/09\/jboss-modules-example-modular-web.html","title":{"rendered":"JBoss Modules Example – Modular Web Application"},"content":{"rendered":"
Recently I read Why there is no standard for developing real modular web applications?<\/a> by Patroklos Papapetrou (also featured in Java Code Geeks<\/a>). Inspired by this article I decided to check JBoss Modules<\/a> in action. This post describes my experiment step by step.<\/p>\n

I’ve started with the following goal in mind – to create a web application using some service defined by my own JBoss module. The service prepared by me was pretty simple. I named it Echo Service:<\/p>\n

package warlock.echo;\r\n\r\npublic interface EchoService {\r\n\r\n    String echo(String param);\r\n    \r\n}\r\n<\/pre>\n
and placed into a separate jar file, named echo-api. Then I implemented this service:<\/p>\n
package warlock.echo.impl;\r\n\r\nimport warlock.echo.EchoService;\r\n\r\npublic class DefaultEchoService implements EchoService {\r\n    \r\n    public String echo(String param) {\r\n        return param;\r\n    }\r\n        \r\n}\r\n<\/pre>\n
and placed the implementation in a new jar file, named echo-module. Having in mind that my web application should have knowledge of the service API only, not the specific implementation, I decided to go with the way described in Creating Extensible Applications With the Java Platform<\/a> – that choice required adding to echo-module jar special file under: META-INF\/services\/warlock.echo.EchoService, holding the “pointer” to the service implementation (fully qualified name of implementing class).<\/p>\n
At this point, I retrieved and unpacked JBoss Application Server 7<\/a>, stepped into the unpacked JBoss, and then into the modules directory. In this directory I’ve added the following structure:
 
<\/div> <\/div><\/p>\n
\"\"<\/a><\/p>\n
Two jar files visible here are mentioned above, module.xml file is the definition of my JBoss Module – named ‘warlock.echo’, and has the following content:<\/p>\n
<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n\r\n<module xmlns=\"urn:jboss:module:1.0\" name=\"warlock.echo\">\r\n\r\n    <resources>\r\n        <resource-root path=\"echo-module-1.0.0-SNAPSHOT.jar\" \/>\r\n        <resource-root path=\"echo-api-1.0.0-SNAPSHOT.jar\" \/>\r\n    <\/resources>\r\n\r\n<\/module>\r\n<\/pre>\n
After the completion of the JBoss Module definition, I’ve prepared a simple Spring Framework based application (which uses echo-api jar only during the compilation of project and doesn’t use the echo-module jar at all) with only one Controller:<\/p>\n
package warlock;\r\n\r\nimport org.springframework.beans.factory.annotation.Autowired;\r\nimport org.springframework.stereotype.Controller;\r\nimport org.springframework.web.bind.annotation.RequestMapping;\r\nimport org.springframework.web.bind.annotation.RequestMethod;\r\nimport org.springframework.web.bind.annotation.ResponseBody;\r\n\r\nimport warlock.echo.EchoService;\r\n\r\n@Controller\r\n@RequestMapping(\"\/echo.html\")\r\npublic class EchoController {\r\n\r\n    @Autowired\r\n    private EchoService service;\r\n    \r\n    @RequestMapping(method = RequestMethod.GET)\r\n    @ResponseBody\r\n    public String handleGet() {\r\n        return service.echo(\"It workzzzzz!\");\r\n    }\r\n}\r\n<\/pre>\n
As you can see, the Controller returns as response body the result of Echo Service call for some string. Now to the most important part – Echo Service definition in Web Application:<\/p>\n
<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<beans xmlns=\"http:\/\/www.springframework.org\/schema\/beans\"\r\nxmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\r\nxsi:schemaLocation=\"http:\/\/www.springframework.org\/schema\/beans http:\/\/www.springframework.org\/schema\/beans\/spring-beans-3.0.xsd\">\r\n\r\n    ...\r\n\r\n    <bean class=\"org.springframework.beans.factory.serviceloader.ServiceFactoryBean\">\r\n        <property name=\"serviceType\" value=\"warlock.echo.EchoService\" \/>\r\n    <\/bean>\r\n\r\n    ...\r\n    \r\n<\/beans>\r\n<\/pre>\n
I know, one thing is bothering you :) – how the hell will Echo Service implementation be found if we don’t add either echo-api and echo-module jars to the Web Application?!<\/p>\n
Well, this is the beauty itself ;) – We just need one more thing – WEB-INF\/jboss-deployment-structure.xml file:<\/p>\n
<jboss-deployment-structure>\r\n    <deployment>\r\n        <dependencies>\r\n            <module name=\"warlock.echo\" services=\"export\" \/>\r\n        <\/dependencies>\r\n    <\/deployment>\r\n<\/jboss-deployment-structure>\r\n<\/pre>\n
This way we tell JBoss that this application depends on the ‘warlock.echo’ module and the services defined in this module. The rest is pure JBoss Module magic ;)<\/p>\n
Lectures for the dessert:<\/p>\n