Scheduling a Task Using a Custom Implementation

When you create a task using the default task implementation of the ESB, the task can inject messages to a proxy service, or to a sequence. If you have a specific task-handling requirement, you can write your own task-handling implementation by creating a custom Java Class that implements the org.apache.synapse.startup.Task interface.

For example, the below sections demonstrate how you can create and schedule a task to receive stock quotes by invoking a back-end service, which exposes stock quotes. The scheduled task will read stock order information from a text file, and print the stock quotes.

Starting the Back End Service

Follow the steps below to start the backend service.

Download the backend service from Git Hub.
Copy the JAR file you downloaded to the <EI_HOME>/wso2/msf4j/deployment/microservices directory.
Start the MSF4J profile. For instructions, see Starting the product profiles.

Creating the custom Task implementation

Follow the steps below to create the implementation of the custom Task.

Creating the Maven Project

Create a Maven Project using the following information. For instructions, see Creating the Maven project.

You can skip step 5 since you do not need to add external JAR files in this example.
- Group Id: org.wso2.task
- Artifact Id : StockQuoteTaskMavenProject
Creating the Java Package
Create a Java Package inside the Maven Project using the following information. For instructions, see Creating the Java Package for the Maven Project.
- Name: org.wso2.task.stockquote.v1
Creating the Java Class
Create a Java Class inside the Maven Project using the following information. For instructions, see Creating the Java Class for the Maven Project.
- Name: StockQuoteTaskV1

In the Project Explorer , double-click on the StockQuoteTaskV1.java file and replace its source with the below content.

package org.wso2.task.stockquote.v1;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.synapse.ManagedLifecycle;
import org.apache.synapse.MessageContext;
import org.apache.synapse.SynapseException;
import org.apache.synapse.core.SynapseEnvironment;
import org.apache.synapse.startup.Task;
import org.apache.synapse.util.PayloadHelper;

public class StockQuoteTaskV1 implements Task, ManagedLifecycle {
    private Log log = LogFactory.getLog(StockQuoteTaskV1.class);
    private String to;
    private String stockFile;
    private SynapseEnvironment synapseEnvironment;

    public void execute() {
        log.debug("PlaceStockOrderTask begin");

        if (synapseEnvironment == null) {
            log.error("Synapse Environment not set");
            return;
        }

        if (to == null) {
            log.error("to not set");
            return;
        }

        File existFile = new File(stockFile);

        if (!existFile.exists()) {
            log.debug("waiting for stock file");
            return;
        }

        try {

            // file format IBM,100,120.50

            BufferedReader reader = new BufferedReader(new FileReader(stockFile));
            String line = null;

            while ((line = reader.readLine()) != null) {
                line = line.trim();

                if (line == "") {
                    continue;
                }

                String[] split = line.split(",");
                String symbol = split[0];
                String quantity = split[1];
                String price = split[2];
                MessageContext mc = synapseEnvironment.createMessageContext();
                mc.setTo(new EndpointReference(to));
                mc.setSoapAction("urn:placeOrder");
                mc.setProperty("OUT_ONLY", "true");
                OMElement placeOrderRequest = createPlaceOrderRequest(symbol, quantity, price);
                PayloadHelper.setXMLPayload(mc, placeOrderRequest);
                synapseEnvironment.injectMessage(mc);
                log.info("placed order symbol:" + symbol + " quantity:" + quantity + " price:" + price);
            }

            reader.close();
        } catch (IOException e) {
            throw new SynapseException("error reading file", e);
        }

        File renamefile = new File(stockFile);
        renamefile.renameTo(new File(stockFile + "." + System.currentTimeMillis()));
        log.debug("PlaceStockOrderTask end");
    }

    public static OMElement createPlaceOrderRequest(String symbol, String qty, String purchPrice) {
        OMFactory factory = OMAbstractFactory.getOMFactory();
        OMNamespace ns = factory.createOMNamespace("http://services.samples/xsd", "m0");
        OMElement placeOrder = factory.createOMElement("placeOrder", ns);
        OMElement order = factory.createOMElement("order", ns);
        OMElement price = factory.createOMElement("price", ns);
        OMElement quantity = factory.createOMElement("quantity", ns);
        OMElement symb = factory.createOMElement("symbol", ns);
        price.setText(purchPrice);
        quantity.setText(qty);
        symb.setText(symbol);
        order.addChild(price);
        order.addChild(quantity);
        order.addChild(symb);
        placeOrder.addChild(order);
        return placeOrder;
    }

    public void destroy() {}

    public void init(SynapseEnvironment synapseEnvironment) {
        this.synapseEnvironment = synapseEnvironment;
    }

    public SynapseEnvironment getSynapseEnvironment() {
        return synapseEnvironment;
    }

    public void setSynapseEnvironment(SynapseEnvironment synapseEnvironment) {
        this.synapseEnvironment = synapseEnvironment;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    public String getStockFile() {
        return stockFile;
    }

    public void setStockFile(String stockFile) {
        this.stockFile = stockFile;
    }
}

In the Project Explorer, double-click on the pom.xml file and replace its source with the below content.
pom.xml
```
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.wso2.task</groupId>
    <artifactId>StockQuoteTask</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <repositories>
        <repository>
            <id>wso2.releases</id>
            <name>WSO2 internal Repository</name>
            <url>http://maven.wso2.org/nexus/content/repositories/releases/</url>
            <releases>
                <enabled>true</enabled>
                <updatePolicy>daily</updatePolicy>
                <checksumPolicy>ignore</checksumPolicy>
            </releases>
        </repository>
    </repositories>
    <dependencies>
        <dependency>
            <groupId>org.apache.synapse</groupId>
            <artifactId>synapse-core</artifactId>
            <version>2.1.7-wso2v65</version>
        </dependency>
    </dependencies>
</project>
```
Writing the custom Task
Step 1: Writing the Task Class
You can create a custom task class, which implements the org.apache.synapse.startup.Task interface as follows. This interface has a single execute() method, which contains the code that will be executed according to the defined schedule.
The execute() method contains the 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.
When creating customized task schedules, if the injecting sequence of the message flow contains Publish Event mediators, set the following property in the Synapse message context:

mc.setProperty("CURRENT_TASK_EXECUTING_TENANT_IDENTIFIER",PrivilegedCarbonContext.getThreadLocalCarbonContext().getTenantId());

Also, add the following dependency to the POM file of the custom task project: WSO2 Carbon - Utilities bundle (symbolic name: org.wso2.carbon.utils)
When creating customized task schedules, if the injecting sequence of the message flow contains Publish Event mediators, set the following property in the Synapse message context:

mc.setProperty("CURRENT_TASK_EXECUTING_TENANT_IDENTIFIER",PrivilegedCarbonContext.getThreadLocalCarbonContext().getTenantId());

Also, add the following dependency to the POM file of the custom task project: WSO2 Carbon - Utilities bundle (symbolic name: org.wso2.carbon.utils)
This is a bean implementing two properties: To and StockFile. These are used to configure the task.
Implementing ManagedLifecycle for Initialization and Clean-up
Since a task implements ManagedLifecyle interface, the ESB profile will call the init() method at the initialization of a Task object and destroy() method when a Task object is destroyed:
public interface ManagedLifecycle { public void init(SynapseEnvironment se); public void destroy(); }
The PlaceStockOrderTask stores the Synapse environment object reference in an instance variable for later use with the init() method. The SynapseEnvironment is needed for injecting messages into the ESB.
Step 2: Customizing the Task
It is possible to pass values to a task at runtime using property elements. In this example, the location of the stock order file and its address was given using two properties within the Task object:
- String type
- OMElement type
Tip

For OMElement type, it is possible to pass XML elements as values in the configuration file.
When creating a Task object, the ESB will initialize the properties with the given values in the configuration file.
public String getStockFile() { return stockFile; } public void setStockFile(String stockFile) { this.stockFile = stockFile; }
For example, the following properties in the Task class are initialized with the given values within the property element of the task in the configuration.
<syn:property xmlns="http://ws.apache.org/ns/synapse" name="stockFile"value="/home/upul/test/stock.txt"/>
For those properties given as XML elements, properties need to be defined within the Task class using the format given below. OMElement comes from Apache AXIOM, which is used by the ESB profile. AXIOM is an object model similar to DOM. To learn more about AXIOM, see the tutorial in the AXIOM user guide.
public void setMessage(OMElement 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>

Deploying the custom Task implementation

For instructions on deploying the custom Task implementation, see Deploying artifacts of the Maven Project.

You can skip step 1 since you already added the dependencies above.

Creating the Task

Follow the steps below to create the task and schedule it.

Creating the ESB Project

Create a ESB Solution Project using the following information. For instructions, see Creating the ESB Project.
- Name: PrintStockQuote
Creating the Sequence
Create a Sequence using the following information. For instructions, see Creating the Sequence.
- Name: PrintStockQuoteSequence
Add a Log Mediator and a Drop Mediator to the sequence and configure them. For instructions, see Creating the Sequence.
Configuration of the Sequence
The below is the complete source configuration of the Sequence (i.e., the PrintStockQuoteSequence.xml file).
<?xml version="1.0" encoding="UTF-8"?> <sequence name="PrintStockQuoteSequence" trace="disable" xmlns="http://ws.apache.org/ns/synapse"> <log level="custom"/> <drop/> </sequence>
Creating the Scheduled Task
Create a Scheduled Task using the following information. For instructions, see Creating the Scheduled Task.
- Task Name: PrintStockQuoteScheduledTask
- Count: 1
- Interval (in seconds): 5
Defining the properties of the Task

In the Project Explorer, double-click on the PrintStockQuoteScheduledTask.xml file and replace its source with the below content.

<task class="org.apache.synapse.startup.tasks.MessageInjector" group="synapse.simple.quartz" name="PrintStockQuoteScheduledTask" xmlns="http://ws.apache.org/ns/synapse">
    <trigger count="1" interval="5" />
    <property name="to" value="http://localhost:9000/soap/SimpleStockQuoteService" xmlns:task="http://www.wso2.org/products/wso2commons/tasks" />
    <property name="stockFile" value="/Users/praneesha/Desktop/stockfile.txt" xmlns:task="http://www.wso2.org/products/wso2commons/tasks" />
    <property name="synapseEnvironment" value="" xmlns:task="http://www.wso2.org/products/wso2commons/tasks" />
</task>

The task properties will change according to the custom implementation. Therefore, you need to enter values for your custom properties. This sets the below properties.

Parameter Name	Value
to	http://localhost:9000/soap/SimpleStockQuoteService
stockFile	The directory path to the `stockfile.txt` file.
synapseEnvironment	Do not enter a value. This will be used during runtime.

Currently, you cannot set properties of a custom task using the Design View due to a known issue, which will be fixed in the future WSO2 EI versions.

Configuration of the Scheduled Task

The below is the complete source configuration of the Sequence (i.e., the PrintStockQuoteScheduledTask.xml file).

<?xml version="1.0" encoding="UTF-8"?>
<task class="org.apache.synapse.startup.tasks.MessageInjector" group="synapse.simple.quartz" name="PrintStockQuoteScheduledTask" xmlns="http://ws.apache.org/ns/synapse">
    <trigger interval="3" />
    <property name="to" value="http://localhost:9000/soap/SimpleStockQuoteService" xmlns:task="http://www.wso2.org/products/wso2commons/tasks" />
    <property name="stockFile" value="/Users/praneesha/Desktop/stockfile.txt" xmlns:task="http://www.wso2.org/products/wso2commons/tasks" />
</task>

Deploying the Task

For instructions on deploying the Task, see Deploying the Task.

Creating the text file

Create a text file named stockfile.txt with the following content and save it to a preferred location on your machine. This will include the information to be read by the scheduled task to pass to the backend service.

stockfile.txt

IBM,100,120.50
MSFT,200,70.25
SUN,400,60.758

Each line in the text file contains details for a stock order:

symbol
quantity
price

A task that is scheduled using this custom implementation will read the text file, a line at a time, and create orders using the given values to be sent to the back-end service. The text file will then be tagged as processed to include a system time stamp. The task will be scheduled to run every 15 seconds.

Viewing the output

You will view the stock quotes sent by the backend service printed every 3 seconds by the scheduled task in the below format.

INFO - StockQuoteTask placed order symbol:IBM quantity:100 price:120.50

Scheduling a Task Using a Custom Implementation

Starting the Back End Service

Creating the custom Task implementation

Creating the Maven Project

Creating the Java Package

Creating the Java Class

Step 1: Writing the Task Class

Step 2: Customizing the Task

Deploying the custom Task implementation

Creating the Task

Creating the ESB Project

Creating the Sequence

Creating the Scheduled Task

Defining the properties of the Task

Deploying the Task

Creating the text file

Viewing the output