I wrote a server in 90 lines (it only handles OAuth callbacks).

OAuthCallbackServer.java

package scholl.both.analyzer.social;

import java.io.*;
import java.net.*;

/**
 * An HTTP server.
 * 
 * NOTE: I modified this from http://fragments.turtlemeat.com/javawebserver.php
 * 
 * @author Jackson
 */
public class OAuthCallbackServer {
    private final int port; // port we are going to listen to

    /**
     * Sole constructor.
     * 
     * @param listenPort port to bind to (default 80)
     */
    public OAuthCallbackServer(int listenPort) {
        port = listenPort;
    }

    /**
     * Get a request on the set port and return the verifier as a string.
     * 
     * @return the OAuth verifier
     * @throws IOException
     */
    public String handleRequest() throws IOException {
        System.out.printf("A simple HTTP server, used for OAuth callback.%n%n");
        System.out.printf("Trying to bind to localhost on port %d...", port);

        ServerSocket serverSocket = new ServerSocket(port);

        System.out.printf("Ready, Waiting for requests...%n");

        try {
            // this call waits/blocks until someone connects to the port we are listening to
            Socket connectionSocket = serverSocket.accept();

            return getOAuthVerifier(new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())),
                    new DataOutputStream(connectionSocket.getOutputStream()));
        } finally {
            serverSocket.close();
        }
    }

    private String getOAuthVerifier(BufferedReader input, DataOutputStream output) throws IOException {
        PrintStream print = new PrintStream(new BufferedOutputStream(output));
        String tmp = input.readLine();

        if (!tmp.toUpperCase().startsWith("GET")) { // Unsupported operation
            output.writeBytes(constructHeader(501)); // HTTP "Not Implemented" response
            output.close();
            throw new UnsupportedOperationException();
        }

        print.print(constructHeader(200));

        String verifier = tmp.replaceAll("GET /callback\\?oauth_token=\\w+&oauth_verifier=(\\w+) HTTP/1.1", "$1");
        // print.printf("%nVerifier: %s%n", verifier);
        print.close();

        return verifier;
    }

    /**
     * This method makes the HTTP header for the response.
     * 
     * @param returnCode HTTP response code
     * @return HTTP header
     */
    private String constructHeader(int returnCode) {
        String responseString = "";
        if (returnCode == 200) {
            responseString = "OK";
        } else if (returnCode == 501) {
            responseString = "Not Implemented";
        } else {
            responseString = "(return code unknown)";
        }

        String s = String.format("HTTP/1.0 %d %s%s", returnCode, responseString,
                "%nConnection: close%nServer: SimpleHTTPtutorial v0%nContent-Type: text/html%n%n");

        return s;
    }
}