Configure Different Database Connections in Wildfly/JBoss Application Server

1. download and copy the database driver libraries
   For Oralce, search ojdbc from Oracle, https://www.oracle.com/technetwork/database/features/jdbc/jdbc-ucp-122-3110062.html
   For MS SQL Server, https://www.microsoft.com/en-us/download/details.aspx?id=56615
   For MySQL, https://dev.mysql.com/downloads/connector/j/
   For PostgreSQL, https://jdbc.postgresql.org/download.html

2. install and configure the database drivers in Wildfly/JBoss system modules
   For Oracle, copy ojdbc?.jar (e.g. ojdbc7.jar) to %JBOSS_HOME%/modules/system/layers/base/com/oracle/main (create folders when necessary). Create a configuration file, module.xml in the same folder with the driver file.
       <?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.1" name="com.oracle">
  <resources>
<resource-root path="ojdbc5.jar"/>
  </resources>
  <dependencies>
<module name="javax.api"/>
<module name="javax.transaction.api"/>
  </dependencies>
</module>

   For MS SQL Server, copy mssql-jdbc-x.x.x.jre?.jar (e.g. mssql-jdbc-6.2.2.jre7) into %JBOSS_HOME%/modules/system/layers/base/com/microsoft/sqlserver/main. Create a configuration file, module.xml in the same folder with the driver file.
       <?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.1" name="com.microsoft.sqlserver">
  <resources>
<resource-root path="mssql-jdbc-6.2.2.jre7.jar"/>
  </resources>
  <dependencies>
<module name="javax.api"/>
<module name="javax.transaction.api"/>
<module name="javax.xml.bind.api"/>
  </dependencies>
</module>

   For MySQL, copy mysql-connector-java-x.x.x.jar (e.g. mysql-connector-java-5.1.44.jar) into %JBOSS_HOME%/modules/system/layers/base/com/mysql/main. Create a configuration file, module.xml in the same folder with the driver file.
   <?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.1" name="com.mysql">
  <resources>
<resource-root path="mysql-connector-java-5.1.44.jar"/>
  </resources>
  <dependencies>
<module name="javax.api"/>
<module name="javax.transaction.api"/>
  </dependencies>
</module>

For PostgreSQL, copy postgresql-x.x.x.jre?.jar (e.g. postgresql-9.4.1209.jre6.jar) into %JBOSS_HOME%/modules/system/layers/base/org/postgresql/main. Create a configuration file, module.xml in the same folder with the driver file.
    <?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.1" name="org.postgresql">
  <resources>
<resource-root path="postgresql-9.4.1209.jre6.jar"/>
  </resources>
  <dependencies>
<module name="javax.api"/>
<module name="javax.transaction.api"/>
  </dependencies>
</module>

3. Configure the database drivers and data sources in Wild/JBoss Application Server.
    Open and update the Wildfly/JBoss configuration file (e.g. standalone.xml) by adding the database driver and data source information like the following: (Note: make sure the driver name, module name and etc. match with the configuration previously mentioned)

        <subsystem xmlns="urn:jboss:domain:datasources:2.0">
            <datasources>
                ... ...
<!-- // Connection Pool of Oracle. java:/jdbc/myoracle is used in applications -->
                <datasource jndi-name="java:/jdbc/myoracle" pool-name="myOraclePool" enabled="true" use-java-context="true">
                    <connection-url>jdbc:oracle:thin:@server_name:1521:SID</connection-url>
                    <driver>oracle_driver</driver>
                    <security>
                        <user-name>db_user_name</user-name>
                        <password>db_user_password</password>
                    </security>
                </datasource>

<!-- // Connection Pool for MS SQL Server Express -->
                <datasource jndi-name="java:/jdbc/MsSQLSvrDS" pool-name="MsSQLPool" enabled="true" use-java-context="true">
                    <connection-url>jdbc:sqlserver://server_name\SQLEXPRESS:54126;databaseName=TestDB;integratedSecurity=true;</connection-url>
                    <driver-class>com.microsoft.sqlserver.jdbc.SQLServerDriver</driver-class>
                    <driver>sqlserver_driver</driver>
                    <pool>
                        <min-pool-size>5</min-pool-size>
                        <max-pool-size>10</max-pool-size>
                    </pool>
                    <security>
                        <user-name>db_user_name</user-name>
                        <password>db_user_password</password>
                    </security>
                </datasource>

<!-- // Connection Pool for MySQL -->
                <datasource jndi-name="java:/jdbc/MySQLDS" pool-name="MySQLDS" enabled="true" use-java-context="true">
                    <connection-url>jdbc:mysql://server_name:3306/my_test_db</connection-url>
                    <driver>mysql_driver</driver>
                    <pool>
                        <min-pool-size>1</min-pool-size>
                        <max-pool-size>5</max-pool-size>
                    </pool>
                    <security>
                        <user-name>db_user_name</user-name>
                        <password>db_user_password</password>
                    </security>
                </datasource>

                <!-- // Connection Pool for MySQL -->
                <datasource jta="false" jndi-name="java:/jdbc/PostgreSQLDS" pool-name="PostgreSQLDS" enabled="true" use-ccm="false">
                    <connection-url>jdbc:postgresql://server_name:5432/my_test_db</connection-url>
                    <driver-class>org.postgresql.Driver</driver-class>
                    <driver>postgresql_driver</driver>
                    <pool>
                        <min-pool-size>1</min-pool-size>
                        <max-pool-size>5</max-pool-size>
                    </pool>
                    <security>
                        <user-name>db_user_name</user-name>
                        <password>db_user_password</password>
                    </security>
                </datasource>
                <drivers>
                    ... ...
                    <!-- // Oracle Driver -->
    <driver name="oracle_driver" module="com.oracle">
                        <driver-class>oracle.jdbc.OracleDriver</driver-class>
                    </driver>

                    <!-- // MS SQL Server Driver -->
                    <driver name="sqlserver_driver" module="com.microsoft.sqlserver">
                        <driver-class>com.microsoft.sqlserver.jdbc.SQLServerDriver</driver-class>
                    </driver>
                   
                    <!-- // MySQL Driver -->
                    <driver name="mysql_driver" module="com.mysql">
                        <driver-class>com.mysql.jdbc.Driver</driver-class>
                    </driver>

                    <!-- // PostgreSQL Driver -->
                    <driver name="postgresql_driver" module="org.postgresql">
                        <driver-class>org.postgresql.Driver</driver-class>
                    </driver>
                </drivers>
            </datasources>
        </subsystem>

4. Start the Wildfly/JBoss application server and verify the database connectivities from the server logs.

5. Use the connection pool for JPA.
    Find and update persistence.xml as following in the application folder, /src/main/resources/META-INF/persistence.xml.

<persistence-unit name="Persistence_Unit_Name"> <!-- referenced in application //-->
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <jta-data-source>PostgreSQLDS</jta-data-source> <!-- // for example of PostgreSQL datasource defined in Wildfly/JBoss -->
<properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
            <property name="hibernate.show_sql" value="false" /> <!-- Debugging purpose //-->
            <property name="hibernate.generate_statistics" value="false"/> <!-- Debugging purpose //-->
        </properties>
</persistence-unit>

If not use Connection Pool defined in Wildfly/JBoss application server, need to specify the database connection information in preperties as well.
<persistence-unit name="Persistence_Unit_Name" transaction-type="RESOURCE_LOCAL"> <!-- referenced in application //-->
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
<property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://server_name:5432/my_test_db" />
            <property name="javax.persistence.jdbc.user" value="db_user_name" />
            <property name="javax.persistence.jdbc.password" value="db_user_password" />

     <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
        </properties>
</persistence-unit>