Poll Scope in Mule

  Poll Scope in Mule

As integration developers, we are always faced with the need to poll a legacy resource to retrieve new data and to sync it over to another destination endpoint. MuleSoft allows developers to do this via "Poll Scope." The poll scope allows the developer to poll a particular source endpoint based on a timed interval. The poll scope also has this neat caching function known as "Watermark."

While some connectors, such as HTTP and FTP, utilize a polling process to actively retrieve messages from an external resource, most message processors in Mule are triggered when called by a previous element in a flow. If you want to arrange for a message processor to actively call a resource at regular intervals, use a Poll scope.

Here we are using Message Enricher in mule 3 in Anypoint studio 6.2

Poll scope polls the nested message processor for some new messages.


Here in our flow we have placed db connector in poll scope. Poll scope will poll data from db table by the given frequency in the scope.I have given frequency of 10 seconds means in every 10 seconds it checks the table for new data and writes the data in the file by file connector.



Poll scope settings :


we used fixed frequency scheduler with freq. of 10 seconds.We can also use cron scheduler with cron expressions. And we have disabled watermarking for now in watermark section.



File connector settings :



Here no need to make data.txt manually as we have given path and name of file in file connector so it will automatically generate the file data.txt. So, just configure it correctly as mentioned below.



Once you start the server and project gets deployed, it will start polling with given frequency.

XML project code :

<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:tracking="http://www.mulesoft.org/schema/mule/ee/tracking" xmlns:json="http://www.mulesoft.org/schema/mule/json" xmlns:db="http://www.mulesoft.org/schema/mule/db" xmlns:file="http://www.mulesoft.org/schema/mule/file" xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns:quartz="http://www.mulesoft.org/schema/mule/quartz" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/quartz http://www.mulesoft.org/schema/mule/quartz/current/mule-quartz.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/file http://www.mulesoft.org/schema/mule/file/current/mule-file.xsd
http://www.mulesoft.org/schema/mule/db http://www.mulesoft.org/schema/mule/db/current/mule-db.xsd
http://www.mulesoft.org/schema/mule/json http://www.mulesoft.org/schema/mule/json/current/mule-json.xsd
http://www.mulesoft.org/schema/mule/ee/tracking http://www.mulesoft.org/schema/mule/ee/tracking/current/mule-tracking-ee.xsd">
    <http:request-config name="HTTP_Request_Configuration" host="localhost" port="8083" doc:name="HTTP Request Configuration"/>
    <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8084" doc:name="HTTP Listener Configuration"/>
    <quartz:connector name="Quartz" validateConnections="true" doc:name="Quartz"/>
    <file:connector name="File" autoDelete="true" streaming="true" validateConnections="true" doc:name="File"/>
    <db:mysql-config name="MySQL_Configuration" host="localhost" port="3306" user="root" password="*******" database="demodata" doc:name="MySQL Configuration"/>
    <flow name="test_poll">
        <poll doc:name="Poll">
            <fixed-frequency-scheduler frequency="10" timeUnit="SECONDS"/>
            <db:select config-ref="MySQL_Configuration" doc:name="Database">
                <db:parameterized-query><![CDATA[select * from info]]></db:parameterized-query>
            </db:select>
        </poll>
        <json:object-to-json-transformer doc:name="Object to JSON"/>
        <file:outbound-endpoint path="src/main/resources" responseTimeout="10000" doc:name="File" outputPattern="data.txt" connector-ref="File"/>
    </flow>
</mule>