AppEngine+Retrofit+OAuth

HttpRequestAdapter.java

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import oauth.signpost.http.HttpRequest;

import retrofit.client.Header;
import retrofit.client.Request;

public class HttpRequestAdapter implements HttpRequest {

    private static final String DEFAULT_CONTENT_TYPE = "application/json";

    private Request request;

    private String contentType;

    public HttpRequestAdapter(Request request) {
        this(request, request.getBody() != null ? request.getBody().mimeType() : DEFAULT_CONTENT_TYPE);
    }

    public HttpRequestAdapter(Request request, String contentType) {
        this.request = request;
        this.contentType = contentType;
    }

    @Override
    public Map<String, String> getAllHeaders() {
        HashMap<String, String> headers = new HashMap<String, String>();
        for(Header header : request.getHeaders()) {
            headers.put(header.getName(), header.getValue());
        }
        return headers;
    }

    @Override
    public String getContentType() {
        return contentType;
    }

    @Override
    public String getHeader(String key) {
        for(Header header : request.getHeaders()) {
            if(key.equals(header.getName())) {
                return header.getValue();
            }
        }
        return null;
    }

    @Override
    public InputStream getMessagePayload() throws IOException {
        final String contentType = getContentType();
        if (null != contentType && contentType.startsWith("application/x-www-form-urlencoded")) {
            long contentLength = request.getBody().length();
            ByteArrayOutputStream output = new ByteArrayOutputStream(Long.valueOf(contentLength)
                    .intValue());
            request.getBody().writeTo(output);
            return new ByteArrayInputStream(output.toByteArray());
        }

        throw new UnsupportedOperationException("The content type" + (contentType != null ? " " +
                contentType : "") + " is not supported.");
    }

    @Override
    public String getMethod() {
        return request.getMethod();
    }

    @Override
    public String getRequestUrl() {
        return request.getUrl();
    }

    @Override
    public void setHeader(String key, String value) {
        ArrayList<Header> headers = new ArrayList<Header>();
        headers.addAll(request.getHeaders());
        headers.add(new Header(key, value));
        Request copy = new Request(request.getMethod(), request.getUrl(), headers, request.getBody());
        request = copy;
    }

    @Override
    public void setRequestUrl(String url) {
        Request copy = new Request(request.getMethod(), url, request.getHeaders(), request.getBody());
        request = copy;
    }

    @Override
    public Object unwrap() {
        return request;
    }

}

RetrofitOAuthConsumer.java

import oauth.signpost.AbstractOAuthConsumer;
import oauth.signpost.http.HttpRequest;
import retrofit.client.Request;

public class RetrofitHttpOAuthConsumer extends AbstractOAuthConsumer {
    public RetrofitHttpOAuthConsumer(String consumerKey, String consumerSecret) {
        super(consumerKey, consumerSecret);
    }

    @Override
    protected HttpRequest wrap(Object request) {
        if (!(request instanceof retrofit.client.Request)) {
            throw new IllegalArgumentException("This consumer expects requests of type " + retrofit.client.Request.class.getCanonicalName());
        }
        return new HttpRequestAdapter((Request) request);
    }

}

SigningUrlFetchClient.java

import oauth.signpost.exception.OAuthCommunicationException;
import oauth.signpost.exception.OAuthExpectationFailedException;
import oauth.signpost.exception.OAuthMessageSignerException;
import retrofit.appengine.UrlFetchClient;
import retrofit.client.Request;
import retrofit.client.Response;

import java.io.IOException;

public class SigningUrlFetchClient extends UrlFetchClient {
    private final RetrofitHttpOAuthConsumer oAuthConsumer;

    public SigningUrlFetchClient(RetrofitHttpOAuthConsumer consumer) {
        oAuthConsumer = consumer;
    }

    @Override
    public Response execute(Request request) throws IOException {
        Request requestToSend = request;
        try {
            HttpRequestAdapter signedAdapter = (HttpRequestAdapter) oAuthConsumer.sign(request);
            requestToSend = (Request) signedAdapter.unwrap();
        } catch (OAuthMessageSignerException e) {
            e.printStackTrace();
        } catch (OAuthExpectationFailedException e) {
            e.printStackTrace();
        } catch (OAuthCommunicationException e) {
            e.printStackTrace();
        }

        return super.execute(requestToSend);
    }
}