Java Programming Code Examples
Java > Servlets Code Examples
Accessing a data source from a servlet
Accessing a data source from a servlet
package com.ack.web.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.Date;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
/**
* web.xml configuration part of the a data source
*
* <web-app>
...
<resource-ref>
<description>the database for this app</description>
<res-ref-name>jdbc/thedatabase</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>CONTAINER</res-auth>
</resource-ref>
...
</web-app>
*
* the vendor-specific mapping of the res-ref-name into their
* own application server space, eg weblogic does the following
* in a weblogic.xml file
*
<weblogic-web-app>
...
<reference-descriptor>
...
<resource-description>
<res-ref-name>jdbc/thedatabase</res-ref-name>
<jndi-name>jdbc/gangland</jndi-name>
</resource-description>
...
</reference-descriptor>
...
</weblogic-web-app>
*/
public class AccessingADataSourceFromAServlet extends HttpServlet {
public void init() {
System.out.println( "### loading -> " + getServletName() + " at " +
new Date( System.currentTimeMillis() ).toString() );
}
public void doGet( HttpServletRequest req, HttpServletResponse res )
throws ServletException, IOException {
res.setContentType( "text/html" );
PrintWriter pw = res.getWriter();
Connection con = null;
try {
Context ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup( "java:comp/env/jdbc/thedatabase" );
con = ds.getConnection();
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery( "select * from enemies" );
while( rs.next() ) {
pw.println( rs.getString( "name" ) + "<br>" );
}
}
catch( Exception ex ) {
log( "problem accessing database", ex );
res.sendError( res.SC_INTERNAL_SERVER_ERROR, ex.getMessage() );
}
finally {
if( con != null ) {
try {
con.close();
}
catch( SQLException ex ) {
log( "problem closing connection", ex );
}
}
}
}
}
