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Timer Service is a mechanism by which scheduled application can be build. For example, salary slip generation on the 1st of every month. EJB 3.0 specification has specified @Timeout annotation, which helps in programming the EJB service in a stateless or message driven bean. EJB Container calls the method, which is annotated by @Timeout.
EJB Timer Service is a service provided by EJB container, which helps to create timer and to schedule callback when timer expires.
Steps to Create Timer
Inject SessionContext in bean using @Resource annotation −
@Stateless public class TimerSessionBean { @Resource private SessionContext context; ... }
Use SessionContext object to get TimerService and to create timer. Pass time in milliseconds and message.
public void createTimer(long duration) { context.getTimerService().createTimer(duration, "Hello World!"); }
Steps to Use Timer
Use @Timeout annotation to a method. Return type should be void and pass a parameter of type Timer. We are canceling the timer after first execution otherwise it will keep running after fix intervals.
@Timeout public void timeOutHandler(Timer timer) { System.out.println("timeoutHandler : " + timer.getInfo()); timer.cancel(); }
Example Application
Let us create a test EJB application to test Timer Service in EJB.
Step | Description |
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1 |
Create a project with a name EjbComponent under a package com.tutorialspoint.timer as explained in the EJB – Create Application chapter. |
2 |
Create TimerSessionBean.java and TimerSessionBeanRemote as explained in the EJB – Create Application chapter. Keep rest of the files unchanged. |
3 |
Clean and Build the application to make sure business logic is working as per the requirements. |
4 |
Finally, deploy the application in the form of jar file on JBoss Application Server. JBoss Application server will get started automatically if it is not started yet. |
5 |
Now create the EJB client, a console based application in the same way as explained in the EJB – Create Application chapter under topic Create Client to access EJB. |
EJBComponent (EJB Module)
TimerSessionBean.java
package com.tutorialspoint.timer; import javax.annotation.Resource; import javax.ejb.SessionContext; import javax.ejb.Timer; import javax.ejb.Stateless; import javax.ejb.Timeout; @Stateless public class TimerSessionBean implements TimerSessionBeanRemote { @Resource private SessionContext context; public void createTimer(long duration) { context.getTimerService().createTimer(duration, "Hello World!"); } @Timeout public void timeOutHandler(Timer timer) { System.out.println("timeoutHandler : " + timer.getInfo()); timer.cancel(); } }
TimerSessionBeanRemote.java
package com.tutorialspoint.timer; import javax.ejb.Remote; @Remote public interface TimerSessionBeanRemote { public void createTimer(long milliseconds); }
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As soon as you deploy the EjbComponent project on JBOSS, notice the jboss log.
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JBoss has automatically created a JNDI entry for our session bean − TimerSessionBean/remote.
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We will using this lookup string to get remote business object of type −
com.tutorialspoint.timer.TimerSessionBeanRemote
JBoss Application Server Log Output
... 16:30:01,401 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: TimerSessionBean/remote - EJB3.x Default Remote Business Interface TimerSessionBean/remote-com.tutorialspoint.timer.TimerSessionBeanRemote - EJB3.x Remote Business Interface 16:30:02,723 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=TimerSessionBean,service=EJB3 16:30:02,723 INFO [EJBContainer] STARTED EJB: com.tutorialspoint.timer.TimerSessionBeanRemote ejbName: TimerSessionBean ...
EJBTester (EJB Client)
jndi.properties
java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces java.naming.provider.url=localhost
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These properties are used to initialize the InitialContext object of java naming service.
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InitialContext object will be used to lookup stateless session bean.
EJBTester.java
package com.tutorialspoint.test; import com.tutorialspoint.stateful.TimerSessionBeanRemote; import java.io.BufferedReader; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.util.List; import java.util.Properties; import javax.naming.InitialContext; import javax.naming.NamingException; public class EJBTester { BufferedReader brConsoleReader = null; Properties props; InitialContext ctx; { props = new Properties(); try { props.load(new FileInputStream("jndi.properties")); } catch (IOException ex) { ex.printStackTrace(); } try { ctx = new InitialContext(props); } catch (NamingException ex) { ex.printStackTrace(); } brConsoleReader = new BufferedReader(new InputStreamReader(System.in)); } public static void main(String[] args) { EJBTester ejbTester = new EJBTester(); ejbTester.testTimerService(); } private void showGUI() { System.out.println("**********************"); System.out.println("Welcome to Book Store"); System.out.println("**********************"); System.out.print("Options n1. Add Bookn2. Exit nEnter Choice: "); } private void testTimerService() { try { TimerSessionBeanRemote timerServiceBean = (TimerSessionBeanRemote)ctx.lookup("TimerSessionBean/remote"); System.out.println("["+(new Date()).toString()+ "]" + "timer created."); timerServiceBean.createTimer(2000); } catch (NamingException ex) { ex.printStackTrace(); } } }
EJBTester is doing the following tasks.
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Load properties from jndi.properties and initialize the InitialContext object.
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In testTimerService() method, jndi lookup is done with the name – “TimerSessionBean/remote” to obtain the remote business object (timer stateless EJB).
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Then createTimer is invoked passing 2000 milliseconds as schedule time.
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EJB Container calls the timeoutHandler method after 2 seconds.
Run Client to Access EJB
Locate EJBTester.java in project explorer. Right click on EJBTester class and select run file.
Verify the following output in Netbeans console.
run: [Wed Jun 19 11:35:47 IST 2013]timer created. BUILD SUCCESSFUL (total time: 0 seconds)
JBoss Application Server Log Output
You can find the following callback entries in JBoss log
... 11:35:49,555 INFO [STDOUT] timeoutHandler : Hello World! ...
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