IndexController.java

package com.shin1ogawa.controller;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Map;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;

import org.codehaus.jackson.map.ObjectMapper;
import org.slim3.controller.Controller;
import org.slim3.controller.Navigation;
import org.slim3.util.StringUtil;

import com.google.common.io.ByteStreams;

public class IndexController extends Controller {
  static final String CLIENT_ID = ""; // FIXME
	static final String CLIENT_SECRET = ""; // FIXME
	static final String PROJECT_ID = ""; // FIXME

	static final String PATH = "/";

	static final String CHARCTER_ENCODING = "utf-8";
	static final String SCOPES = "https://www.googleapis.com/auth/glass.timeline"
			+ " https://www.googleapis.com/auth/glass.location"
			+ " https://www.googleapis.com/auth/userinfo.profile";

	@Override
	protected Navigation run() throws Exception {
		String refreshToken = loadRefreshTokenFromCookie();
		if (StringUtil.isEmpty(refreshToken) == false) {
			return doSomething(refreshToken);
		} else {
			String authorizationCode = request.getParameter("code");
			if (StringUtil.isEmpty(authorizationCode)) {
				return redirectToRetrieveAuthorizationCode();
			} else {
				return retrieveToken(authorizationCode);
			}
		}
	}

	Navigation doSomething(String refreshToken) throws IOException {
		String accessToken = Util.refreshAccessToken(CLIENT_ID, CLIENT_SECRET,
				refreshToken);
		// mirror API list timeline を実行する
		// https://developers.google.com/glass/v1/reference/timeline/list
		URL url = new URL("https://www.googleapis.com/mirror/v1/timeline");
		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setRequestProperty("Authorization", "Bearer " + accessToken);
		byte[] bytes = ByteStreams.toByteArray(connection.getInputStream());
		String responseAsString = new String(bytes, CHARCTER_ENCODING);

		saveRefreshTokenAsCookie(refreshToken);
		response.setContentType("text/plain");
		response.setCharacterEncoding(CHARCTER_ENCODING);
		PrintWriter writer = response.getWriter();
		writer.println("refreshToken=" + refreshToken);
		writer.println("refreshed accessToken=" + accessToken);
		writer.println();
		writer.print(responseAsString);
		writer.println();
		response.flushBuffer();
		return null;
	}

	Navigation retrieveToken(String authorizationCode) throws IOException {
		Map<String, String> tokens = Util.getTokensWithAuthorizationCode(
				request, authorizationCode);
		String refreshToken = tokens.get("refresh_token");
		saveRefreshTokenAsCookie(refreshToken);
		return new Navigation(PATH, true);
	}

	Navigation redirectToRetrieveAuthorizationCode()
			throws UnsupportedEncodingException {
		String redirectURI = Util.buildRedirectURIForOAuth2(request,
				IndexController.PATH);

		String redirectTo = new StringBuilder(
				"https://accounts.google.com/o/oauth2/auth?")
				.append("response_type=code").append("&client_id=")
				.append(URLEncoder.encode(CLIENT_ID, CHARCTER_ENCODING))
				.append("&redirect_uri=").append(redirectURI).append("&scope=")
				.append(URLEncoder.encode(SCOPES, CHARCTER_ENCODING))
				.append("&access_type=offline&approval_prompt=force")
				.toString();

		return redirect(redirectTo);
	}

	String loadRefreshTokenFromCookie() {
		String refreshToken = null;
		Cookie[] cookies = request.getCookies();
		if (cookies != null) {
			for (Cookie cookie : cookies) {
				if ("refresh_token".equals(cookie.getName()) == false) {
					continue;
				}
				refreshToken = cookie.getValue();
			}
		}
		return refreshToken;
	}

	void saveRefreshTokenAsCookie(String refreshToken) {
		Cookie cookie = new Cookie("refresh_token", refreshToken);
		response.addCookie(cookie);
	}

	static class Util {
		static String refreshAccessToken(String clientId, String clientSecret,
				String refreshToken) throws IOException {
			// パラメータを組み立てる
			StringBuilder b = new StringBuilder();
			b.append("&client_id=")
					.append(URLEncoder.encode(clientId, "utf-8"));
			b.append("&client_secret=").append(
					URLEncoder.encode(clientSecret, "utf-8"));
			b.append("&refresh_token=").append(
					URLEncoder.encode(refreshToken, "utf-8"));
			b.append("&grant_type=refresh_token");
			byte[] payload = b.toString().getBytes();

			// POST メソッドでリクエストする
			HttpURLConnection c = (HttpURLConnection) new URL(
					"https://accounts.google.com/o/oauth2/token")
					.openConnection();
			c.setRequestMethod("POST");
			c.setDoOutput(true);
			c.setRequestProperty("Content-Length",
					String.valueOf(payload.length));
			c.getOutputStream().write(payload);
			c.getOutputStream().flush();

			@SuppressWarnings("unchecked")
			Map<String, Object> map = new ObjectMapper().readValue(
					c.getInputStream(), Map.class);
			return (String) map.get("access_token");
		}

		static Map<String, String> getTokensWithAuthorizationCode(
				HttpServletRequest request, String authorizationCode)
				throws IOException {
			String redirectURI = buildRedirectURIForOAuth2(request,
					IndexController.PATH);

			String queryString = new StringBuilder().append("&code=")
					.append(URLEncoder.encode(authorizationCode, "utf-8"))
					.append("&client_id=")
					.append(URLEncoder.encode(CLIENT_ID, "utf-8"))
					.append("&client_secret=")
					.append(URLEncoder.encode(CLIENT_SECRET, "utf-8"))
					.append("&redirect_uri=").append(redirectURI)
					.append("&grant_type=authorization_code").toString();
			byte[] payload = queryString.getBytes("utf-8");

			URL url = new URL("https://accounts.google.com/o/oauth2/token");
			HttpURLConnection connection = (HttpURLConnection) url
					.openConnection();
			connection.setRequestMethod("POST");
			connection.setRequestProperty("Content-Length",
					String.valueOf(payload.length));

			connection.setDoOutput(true);
			connection.getOutputStream().write(payload);
			connection.getOutputStream().flush();

			@SuppressWarnings("unchecked")
			Map<String, String> responseAsMap = new ObjectMapper().readValue(
					connection.getInputStream(), Map.class);
			return responseAsMap;
		}

		static String buildRedirectURIForOAuth2(HttpServletRequest request,
				String path) throws UnsupportedEncodingException {
			StringBuilder b = new StringBuilder();
			b.append(request.getScheme()).append("://")
					.append(request.getServerName());
			if (request.getServerPort() != 443 && request.getServerPort() != 80) {
				b.append(":").append(request.getServerPort());
			}
			b.append(path);
			String redirectURI = URLEncoder.encode(b.toString(),
					CHARCTER_ENCODING);
			return redirectURI;
		}
	}
}

Slim3用。Jacksonに依存。
API ConsoleのClientIDのRedirectURIの設定に http://{YOUR-APP-ID}.appspot.com/ を追加する。