Erro ao connectar Oracle

Connection connection = null;
try {
    // Load the JDBC driver
    String driverName = "oracle.jdbc.driver.OracleDriver";
    Class.forName(driverName);

    // Create a connection to the database
    String serverName = "127.0.0.1";
    String portNumber = "1521";
    String sid = "mydatabase";
    String url = "jdbc:oracle:thin:@" + serverName + ":" + portNumber + ":" + sid;
    String username = "username";
    String password = "password";
    connection = DriverManager.getConnection(url, username, password);
} catch (ClassNotFoundException e) {
    // Could not find the database driver
} catch (SQLException e) {
    // Could not connect to the database
}

java.sql.SQLException: The Network Adapter could not establish the connection
	at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:412)
	at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:531)
	at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:221)
	at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
	at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:503)
	at java.sql.DriverManager.getConnection(DriverManager.java:579)
	at java.sql.DriverManager.getConnection(DriverManager.java:221)
	at gestorpos.ligaORA.ligarOra(ligaORA.java:37)
	at gestorpos.Main.main(Main.java:21)
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
	at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:359)
	at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:422)
	at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:672)
	at oracle.net.ns.NSProtocol.connect(NSProtocol.java:237)
	at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1042)
	at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:301)
	... 8 more