Problem Connecting Oracle DB in Java

the SID you gave it to the database of data when creating it, it is the name of the database.

This is an example to connect through localhost:

import java.sql.*;

public class OracleConnection {
    public static void main(String args[]) {

        String usuario = "nombre_usuario";
        String password = "secreta";

        String host = "localhost"; // tambien puede ser una ip
        String puerto = "1521";
        String sid = "prueba";

        String driver = "oracle.jdbc.driver.OracleDriver";

        String urljdbc = "jdbc:oracle:thin:" + usuario + "/" + password + "@" + host + ":" + puerto + ":" + sid;

        Connection connection = null;
        try {
            Class.forName(driver).newInstance();
            connection = DriverManager.getConnection(urljdbc);

            // Ya tenemos el objeto connection creado

            ResultSet result = connection.createStatement().executeQuery("SELECT 'hola mundo' FROM DUAL");
            result.next();
            System.out.println(result.getString(1));

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                }
            }
        }
    }
}

Although the correct way is to connect through jdbc, that is, a pool of connections. Go into GlassFish, create a pool of connections and the resource.

In your web project, in the web.xml file, you have to add this:

<listener>
    <description>ServletContextListener</description>
    <listener-class>Listener.Oyente</listener-class>
</listener>
<resource-ref>
    <description>jdbc:oracle:thin:@localhost:1521:orcl</description>
    <res-ref-name>ds</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
    <res-sharing-scope>Shareable</res-sharing-scope>
</resource-ref>

Create a file glassfish-resources.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE resources PUBLIC "-//GlassFish.org//DTD GlassFish Application Server 3.1 Resource Definitions//EN" "http://glassfish.org/dtds/glassfish-resources_1_5.dtd">
<resources>
    <jdbc-resource enabled="true" jndi-name="jdbc/oracle" pool-name="ORCL">
        <description/>
    </jdbc-resource>
    <jdbc-connection-pool 
        allow-non-component-callers="false" 
        associate-with-thread="false" 
        connection-creation-retry-attempts="0" 
        connection-creation-retry-interval-in-seconds="10" 
        connection-leak-reclaim="false" 
        connection-leak-timeout-in-seconds="0" 
        connection-validation-method="auto-commit" 
        datasource-classname="oracle.jdbc.pool.OracleDataSource" 
        fail-all-connections="false" 
        idle-timeout-in-seconds="300" 
        is-connection-validation-required="false" 
        is-isolation-level-guaranteed="true" 
        lazy-connection-association="false" 
        lazy-connection-enlistment="false" 
        match-connections="false" 
        max-connection-usage-count="0" 
        max-pool-size="32" 
        max-wait-time-in-millis="60000" 
        name="ORCL" 
        non-transactional-connections="false" 
        ping="false" 
        pool-resize-quantity="2" 
        pooling="true" 
        res-type="javax.sql.DataSource" 
        statement-cache-size="0" 
        statement-leak-reclaim="false" 
        statement-leak-timeout-in-seconds="0" 
        statement-timeout-in-seconds="-1" 
        steady-pool-size="8" 
        validate-atmost-once-period-in-seconds="0" 
        wrap-jdbc-objects="false">
        <property name="URL" value="jdbc:oracle:thin:@localhost:1521:orcl"/>
        <property name="User" value="NOMBRE_USUARIO"/>
        <property name="Password" value="PASSWORD"/>
    </jdbc-connection-pool>
</resources>

Create a Model class:

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.sql.DataSource;

public class Modelo {

    private DataSource ds;

    public Modelo(DataSource ds) {
        this.ds = ds;
    }

    public boolean existeUsuario(String USUARIO, String CONTRASENA) {
        Connection con = null;
        boolean resultado = true;

        try {
            con = ds.getConnection();
            resultado = false;
            PreparedStatement ps = con.prepareStatement("SELECT * FROM USUARIOS WHERE USUARIO=? AND CONTRASENA=?");
            ps.setString(1, USUARIO);
            ps.setString(2, CONTRASENA);
            ResultSet rs = ps.executeQuery();
            rs.next();
            if (rs.getString(1).length() > 0 && rs.getString(2).length() > 0) {
                resultado = true;
            } else {
                resultado = false;
            }

        } catch (SQLException ex) {
            resultado = false;
        } finally {
            try {
                con.close();
            } catch (SQLException ex) {
                Logger.getLogger(Modelo.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

        return resultado;
    }
}

Finally, create a Listener:

import Modelo.Modelo;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.sql.DataSource;

public class Oyente implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        try {

            Context ctx = new InitialContext();
            DataSource ds = (DataSource) ctx.lookup("jdbc/oracle");
            Modelo m = new Modelo(ds);
            sce.getServletContext().setAttribute("modelo", m);
        } catch (NamingException ex) {
            Logger.getLogger(Oyente.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
    }

}