Custom Datasource & Class Mediators

Quick Guide: Define and Access a Custom Datasource in WSO2 APIM & Class Mediator

Athiththan Kathirgamasegaran

3 min read

·

Dec 8, 2019

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Intro

This medium narrates on how to define an external data source and then access and use them within custom class mediators of WSO2 API-M Servers.

As an example, we have a use case in which we are required to fetch additional data from an external data source to process and retrieve related data for a particular API request.

The data source which is used to store and retrieve the additional data is maintained in-house, but we need to access them in order to retrieve all related data with the class mediator.

To fulfill the above-mentioned requirement/use-case we can implement and config the following

• Define our custom data source in the master-datasource.xml
• Develop a custom class mediator
• Develop an in-sequence and execute the developed class mediator

Guide

Define Custom Datasource

First, we will define our custom in-house data source configurations in the master-datasource.xml which is placed inside the <APIM>/repository/conf/datasource directory.

Given below is a sample JNDI data source configuration

<datasource>
  <name>InHouse_DB</name>
  <description>The datasource used for registry and user manager</description>
  <jndiConfig>
    <name>jdbc/InHouseDB</name>
  </jndiConfig>
  <definition type="RDBMS">
    <configuration>
      <url>jdbc:mysql://localhost:3306/custominhousedb?useSSL=false</url>
      <username>root</username>
      <password>root</password>
      <driverClassName>com.mysql.jdbc.Driver</driverClassName>
      <maxActive>80</maxActive>
      <maxWait>60000</maxWait>
      <minIdle>5</minIdle>
      <testOnBorrow>true</testOnBorrow>
      <validationQuery>SELECT 1</validationQuery>
      <validationInterval>30000</validationInterval>
    </configuration>
  </definition>
</datasource>

With the above-mentioned changes, we will be able to look up and access the JNDI source configurations programmatically.

Develop a Custom Class Mediator

Next, we will be developing a custom class mediator to create a connection with our in-house data source and to retrieve data.

Given below is a sample code block developed to create a database connection with the defined JNDI source configurations

@Override
public boolean mediate(MessageContext synCtx) {
  // sql connection variables
  Object jndiObj = null;
  Connection conn = null;
  Statement stmt = null;
  ResultSet rs = null;  try {
    jndiObj = new InitialContext().lookup("jdbc/WSO2ExternalDB");    DataSource externalDatasource = (DataSource) jndiObj;
    conn = externalDatasource.getConnection();
    stmt = conn.createStatement();    // given below is a sample block on using the datasource connection to connect
    // with the external datasource
    // rs = stmt.executeQuery("SELECT version()");
    // if (rs.next()) {
    // String version = rs.getString(1);
    // synCtx.setProperty("ExternalResults", version);
    // log.info("Database Version : " + version);
    // }    // TODO: implement mediation logic  } catch (NamingException e) {
    log.error("Error while getting datasource configurations", e);
  } catch (SQLException e) {
    log.error("Error while accessing DB connection", e);
  } finally {
    // close all the datasource connections
  }  return true;
}

Develop In-Sequence

At last, we will develop an in-sequence to invoke and execute our custom class mediator implementation for that particular API.

Given below is a sample sequence defined to invoke the custom class mediator …

<sequence xmlns="http://ws.apache.org/ns/synapse" name="in-sequence-sample">
  <log level="custom">
    <property name="TRACE" value="API Mediation Extension" />
  </log>  <!-- defining the class mediator -->
  <class name="com.sample.mediator.ClassMediatorJNDIDatasource" />  <!-- sample get-property -->
  <log level="custom">
    <property name="Database version from class mediator : " value="get-property('ExternalResults')"/>
  </log>
</sequence>

Add the in-sequence to the required API and invoke the flow.