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How to use DataSource in Tomcat 8

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Introduction

This works for Tomcat 7, 8 and 9, but here I will use Tomcat 8.

Installation

Copy wanted jdbc driver to $TOMCAT_HOME/lib.


$ cp ~/.m2/repository/com/h2database/h2/1.4.185/h2-1.4.185.jar ~/bin/apache-tomcat-8.5.15/lib/

$ cp ~/.m2/repository/mysql/mysql-connector-java/5.1.34/mysql-connector-java-5.1.34.jar ~/bin/apache-tomcat-8.5.15/lib/

DataSource Configuration

Add global datasource configuration in $TOMCAT_HOME/conf/server.xml. Here is a minimal server.xml with H2 database.


<?xml version="1.0" encoding="UTF-8"?>
<Server port="8005" shutdown="SHUTDOWN">

<Listener className="org.apache.catalina.startup.VersionLoggerListener" />
<Listener className="org.apache.catalina.core.AprLifecycleListener"
SSLEngine="on" />
<Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
<Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
<Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />

<GlobalNamingResources>

<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml" />

<Resource name="ExampleDS" auth="Container" type="javax.sql.DataSource"
driverClassName="org.h2.Driver" url="jdbc:h2:mem:example" username="sa"
password="" maxTotal="20" maxIdle="10" maxWaitMillis="-1" />
</GlobalNamingResources>

<Service name="Catalina">

<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000"
redirectPort="8443" />

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

<Engine name="Catalina" defaultHost="localhost">

<Host name="localhost" appBase="webapps" unpackWARs="true"
autoDeploy="true">

<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="logs" prefix="localhost_access_log" suffix=".txt"
pattern="%h %l %u %t "%r" %s %b" />

</Host>
</Engine>
</Service>
</Server>

And here is for MySQL


<Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/javatest"
username="javauser" password="javadude"
maxTotal="20" maxIdle="10" maxWaitMillis="-1" />

For a complete list of configuration for Apache Commons DBCP, see http://commons.apache.org/proper/commons-dbcp/configuration.html.

Application

Now add a resource link in you application $APP_HOME/META-INF/context.xml.


<?xml version="1.0" encoding="UTF-8"?>
<Context path="/example-tomcat">

<!-- java:/comp/env/jdbc/ExampleDS -->
<ResourceLink name="jdbc/ExampleDS" global="ExampleDS"
type="javax.sql.DataSource" />
</Context>

And to access inside your tomcat app.


package se.magnuskkarlsson.example.tomcat;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

@WebServlet(name = "HelloServlet", urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
try {
resp.getWriter().println("Data from database " + getDBValue());
} catch (Exception e) {
super.log("FAILED to read from database. Cause " + e.getMessage());
resp.getWriter().println("FAILED to read from database. Cause " + e.getMessage());
}
}

protected int getDBValue() throws NamingException, SQLException {
Connection conn = null;
PreparedStatement prepstmt = null;
ResultSet rs = null;
try {
Context ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup("java:/comp/env/jdbc/ExampleDS");
conn = ds.getConnection();
prepstmt = conn.prepareStatement("SELECT 1");
rs = prepstmt.executeQuery();
rs.next();
return rs.getInt(1);
} finally {
closeQuietly(rs);
closeQuietly(prepstmt);
closeQuietly(conn);
}
}

protected void closeQuietly(AutoCloseable closeable) {
if (closeable != null) {
try {
closeable.close();
} catch (Exception IGNORE) {
}
}
}

}

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