Exemplo de código para fazer o tracking do site dos Correios.

CorreiosCarrierTracker.java

import java.io.DataInputStream;
import java.io.File;
import java.io.FileWriter;
import java.io.PrintStream;
import java.net.URL;
import java.net.URLConnection;

public class CorreiosCarrierTracker {

	public static void main(String[] args) {
		new CorreiosCarrierTracker().saveXML("correios.xml");
	}

	@SuppressWarnings("deprecation")
	public void saveXML(String outputFile) {
		try {
			File outputXMLFile = new File(outputFile);

			String trackingCodes = "SW371675211BR";

			URL url = new URL(
					"http://websro.correios.com.br/sro_bin/sroii_xml.eventos");
			URLConnection connection = url.openConnection();
			connection.setDoOutput(true);
			connection.setUseCaches(false);
			connection.setRequestProperty("Content-Type",
					"application/x-www-form-urlencoded");
			connection.setAllowUserInteraction(false);
			PrintStream outStream = new PrintStream(
					connection.getOutputStream());
			outStream
					.println("usuario=ECT&senha=SRO&tipo=L&resultado=T&objetos="
							+ trackingCodes);
			outStream.close();

			DataInputStream inStream = new DataInputStream(
					connection.getInputStream());
			String inputLine;
			FileWriter f = new FileWriter(outputXMLFile);

			while ((inputLine = inStream.readLine()) != null) {
				f.write(inputLine);
			}

			f.close();
			inStream.close();

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}