Writing Tasks

The following diagram illustrates the process of creating and scheduling a custom task implementation.

The main steps while writing a task are as follows:

1. Write the Task class
2. Customize the task
3. Compile and bundle the task
4. Add the task to the WSO2 ESB class path
5. Configure and schedule the task in ESB Console

Step 1. Write the Task Class

The custom Task class should implement org.apache.synapse.startup.Task. Each task should therefore implement the Task interface. This interface has a single execute() method. This method contains the code that is to be run at the specified intervals.

package org.apache.synapse.task;

/*** Represents an executable Task*/

public interface Task {

   /*** Execute method will be invoked by the QuartzJOb.
   */
   public void execute();
}

The execute() method contains following actions:

1. Check whether the file exists at the desired location.
2. If it does, then read the file line by line composing place order messages for each line in the text file.
3. Individual messages are then injected to the synapse environment with the given To endpoint reference.
4. Set each message as OUT_ONLY since it is not expected any response for messages.

In addition to the execute() method, it is also possible to make the class implement a JavaBean interface. The WSO2 ESB console can then be used to configure the properties of this JavaBean.

See Writing Tasks Sample to learn more information on how to write tasks in Java. You can also use JavaScript, Ruby, Groovy or other Apache BSF scripting languages for this purpose.

Step 2. Customize the Task

It is possible to pass values to a task at run time using property elements. When creating a Task object, WSO2 ESB will initialize the properties with the given values in the configuration file. For those properties given as XML elements, properties need to be defined within the Task class using the following format:

public void setMessage(_property_ elem) {
message = elem;}

It can be initialized with an XML element as follows:

<property name="message">
<m0:getQuote xmlns:m0="http://services.samples/xsd">
<m0:request>
<m0:symbol>IBM</m0:symbol>
</m0:request>
</m0:getQuote>
</property>

Step 3. Compile and bundle the task

Assemble the compiled class Task as a JAR file.

Step 4. Add to the WSO2 ESB Class Path

After compiling and bundling the Task class, you need to add it to the WSO2 ESB class path. Place the JAR file to the repository/components/lib directory of the ESB.

The Task class will be available for use from the next time you start WSO2 ESB.

Step 5. Configure and Schedule in ESB Console

See Adding and Scheduling Tasks.

For more information see http://wso2.org/library/2900.