Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## The jobs Concurrency Example

This section describes a very basic example that shows how to use some of the basic concurrency features in an enterprise application. Specifically, this example uses one of the main components of Concurrency Utilities for Java EE, a Managed Executor Service.

The example demonstrates a scenario where a RESTful web service, exposed as a public API, is used to submit generic jobs for execution. These jobs are processed in the background. Each job prints a "Starting" and a "Finished" message at the beginning and end of the execution. Also, to simulate background processing, each job takes 10 seconds to execute.

The RESTful service exposes two methods:

- `/token`: Exposed as a GET method that registers and returns valid API tokens

- `/process`: Exposed as a POST method that receives a `jobID` query parameter, which is the identifier for the job to be executed, and a custom HTTP header named `X-REST-API-Key,` which will be used internally to validate requests with tokens

The token is used to differentiate the Quality of Service (QoS) offered by the API. Users that provide a token in a service request can process multiple concurrent jobs. However, users that do not provide a token can process only one job at a time. Since every job takes 10 seconds to execute, users that provide no token will be able to execute only one call to the service every 10 seconds. For users that provide a token, processing will be much faster.

This differentiation is made possible by the use of two different Managed Executor Services, one for each type of request.

### Running the jobs Example

After configuring GlassFish Server by adding two Managed Executor Services, you can use either NetBeans IDE or Maven to build, package, deploy, and run the `jobs` example.

The following topics are addressed here:

- To Configure GlassFish Server for the Basic Concurrency Example

- To Build, Package, and Deploy the jobs Example Using NetBeans IDE

- To Build, Package, and Deploy the jobs Example Using Maven

- To Run the jobs Example and Submit Jobs with Low Priority

- To Run the jobs Example and Submit Jobs with High Priority

#### To Configure GlassFish Server for the Basic Concurrency Example

To configure GlassFish Server, follow these steps.

1. Open the Administration Console at `http://localhost:4848`.

2. Expand the Resources node.

3. Expand the Concurrent Resources node.

4. Click Managed Executor Services.

5. On the Managed Executor Services page, click New to open the New Managed Executor Services page.

6. In the JNDI Name field, enter `MES_High` to create the high-priority Managed Executor Service. Use the following settings (keep the default values for other settings):

   - Thread Priority: 10

   - Core Size: 2

   - Maximum Pool Size: 5

   - Task Queue Capacity: 2

7. Click OK.

8. On the On the Managed Executor Services page, click New again.

9. In the JNDI Name field, enter `MES_Low` to create the low-priority Managed Executor Service. Use the following settings (keep the default values for other settings):

   - Thread Priority: 1

   - Core Size: 1

   - Maximum Pool Size: 1

   - Task Queue Capacity: 0

10. Click OK.

#### To Build, Package, and Deploy the jobs Example Using NetBeans IDE

1. Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

2. From the File menu, choose Open Project.

3. In the Open Project dialog box, navigate to:

       tut-install/examples/concurrency

4. Select the `jobs` folder.

5. Click Open Project.

6. In the Projects tab, right-click the `jobs` project and select Build.

   This command builds and deploys the application.

#### To Build, Package, and Deploy the jobs Example Using Maven

1. Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

2. In a terminal window, go to:

       tut-install/examples/concurrency/jobs

3. Enter the following command to build and deploy the application:

       mvn install

#### To Run the jobs Example and Submit Jobs with Low Priority

To run the example as a user who submits jobs with low priority, follow these steps:

1. In a web browser, enter the following URL:

       http://localhost:8080/jobs

2. In the Jobs Client page, enter the value 1 in the Enter a JobID field, enter nothing in the Enter a Token field, then click Submit Job.

   The following message should be displayed at the bottom of the page:

       Job 1 successfully submitted

   The server log includes the following messages:

       INFO:   Invalid or missing token!
       INFO:   Task started LOW-1
       INFO:   Job 1 successfully submitted
       INFO:   Task finished LOW-1

   You submitted a job with low priority. This means that you cannot submit another job for 10 seconds. If you try to do so, the RESTful API will return a service unavailable (HTTP 503) response and the following message will be displayed at the bottom of the page:

       Job 2 was NOT submitted

   The server log will include the following messages:

       INFO:   Invalid or missing token!
       INFO:   Job 1 successfully submitted
       INFO:   Task started LOW-1
       INFO:   Invalid or missing token!
       INFO:   Job 2 was NOT submitted
       INFO:   Task finished LOW-1

#### To Run the jobs Example and Submit Jobs with High Priority

To run the example as a user who submits jobs with high priority, follow these steps:

1. In a web browser, enter the following URL:

       http://localhost:8080/jobs

2. In the Jobs Client page, enter a value of one to ten digits in the Enter a JobID field.

3. Click the here link on the line "Get a token here" to get a token. The page that displays the token will open in a new tab.

4. Copy the token and return to the Jobs Client page.

5. Paste the token in the Enter a Token field, then click Submit Job.

   A message like the following should be displayed at the bottom of the page:

       Job 11 successfully submitted

   The server log includes the following messages:

       INFO:   Token accepted. Execution with high priority.
       INFO:   Task started HIGH-11
       INFO:   Job 11 successfully submitted
       INFO:   Task finished HIGH-11

   You submitted a job with high priority. This means that you can submit multiple jobs, each with a token, and not face the 10 second per job restriction that the low priority submitters face. If you submit 3 jobs with tokens in rapid succession, messages like the following will be displayed at the bottom of the page:

       Job 1 was submitted
       Job 2 was submitted
       Job 3 was submitted

   The server log will include the following messages:

       INFO:   Token accepted. Execution with high priority.
       INFO:   Task started HIGH-1
       INFO:   Job 1 successfully submitted
       INFO:   Token accepted. Execution with high priority.
       INFO:   Task started HIGH-2
       INFO:   Job 2 successfully submitted
       INFO:   Task finished HIGH-1
       INFO:   Token accepted. Execution with high priority.
       INFO:   Task started HIGH-3
       INFO:   Job 3 successfully submitted
       INFO:   Task finished HIGH-2
       INFO:   Task finished HIGH-3

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