Thursday, May 9, 2019

Spring DataSource JNDI with Tomcat Example

 Step - 1:  Create database in MySQL
create database myExampleDB
use myExampleDB
CREATE TABLE `users` (
  `user_id` int(11) NOT NULL AUTO_INCREMENT,
  `firstName` varchar(45) NOT NULL,
  `lastName` varchar(45) NOT NULL,
  `username` varchar(45) NOT NULL,
  `password` varchar(45) NOT NULL,
  `email` varchar(45) NOT NULL,
  PRIMARY KEY (`user_id`)

 Step -2:  Go to Configuring context of tomcat -- inside $CATALINA_BASE/conf/context.xml
To create JNDI DataSource in tomcat for  MySQL database,  create a Resource XML element as given below.

Add the above code inside the root element <Context> in a context.xml file. Apache Tomcat provide three ways to configure DataSource in JNDI context.

Application (in /META-INF directory of a web application) context.xml : the JNDI DataSource is only available for the application itself, thus this will not be shared among other applications. In addition, this configuration is dependent on the application.

Server context.xml (in $CATALINA_BASE/conf directory): In tomacte this is the preferred place because where we can create JNDI DataSource. it will be available for all web applications and it is independent of any applications. The scope of server context.xml file is application. So if we define a DataSource connection pool size of 100 connections and we have 20 applications then the datasource will be created for each of the application. This will result in 2000 connections that will obviously consume all the database server resources and hurt application performance.

server.xml and context.xml : We should define DataSource at global level by defining here in the server.xml   GlobalNamingResources  element. If we use this approach, then we need to define a   ResourceLink    from context.xml file of server or application specific. This is the preferred way while we are looking to share a common resource pool across multiple applications running on the server. Regarding resource link, whether to define it at server level context xml file or application level depends on your requirement.

<Resource name="jdbc/myExampleDB

Tomcat DataSource JNDI Resource Link Configuration – context.xml
Add below code in the server context.xml file.

<ResourceLink name="jdbc/myExampleDB"
                type="javax.sql.DataSource" />

The following table describes the attributes specified in the above configuration:
Attribute name
  name   Name of the resource example  "jdbc/myExampleDB"
  auth   Specify authentication mechanism for the application code, can be Application or Container.
  type   The fully qualified name of Java class expected by the web application when it performs a lookup for this resource.
  Example "javax.sql.DataSource"
  maxActive   Max number of active database connections required in pool.
  We can set to -1 for no limit.
  maxIdle   Max number of idle database connections to retain in pool.
  We can set to -1 for no limit.
  maxWait   Maximum waiting time for a database connection to become available in ms. example 10 seconds in my my example. If database not connected in 10 seconds.  if this timeout is exceeded an Exception is thrown.
We can set to -1 to wait indefinitely. But we must set some time in this.
  driverClassName   The fully qualified name of Java class the database driver.
  Example like MySQL Connector/J, it is "com.mysql.jdbc.Driver".
  url   Connection URL for JDBC as we provide while connect with database in any application.
  Example "jdbc:mysql://localhost:3306/myExampleDB".
  username   UserName of database for which we have to connect.
  As we are using MySQL database. 
  password   Password of databse for which we have to connect.
  As we are using MySQL database.

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