MockWebServerProxy.java

import java.io.IOException;
import java.io.PrintStream;
import okhttp3.Headers;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.mockwebserver.Dispatcher;
import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.MockWebServer;
import okhttp3.mockwebserver.RecordedRequest;
import okio.Buffer;

public final class MockWebServerProxy {
  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    MockWebServer proxy = new MockWebServer();
    proxy.setDispatcher(new Dispatcher() {
      @Override public MockResponse dispatch(RecordedRequest proxyRequest) {
        try {
          Request request = new Request.Builder()
              .url(proxyRequest.getRequestUrl()
                  .newBuilder()
                  .scheme("https")
                  .host("square.com")
                  .port(443)
                  .build())
              .headers(proxyRequest.getHeaders()).build();

          Response response = client.newCall(request).execute();

          MockResponse proxyResponse = new MockResponse();
          proxyResponse.setHeaders(response.headers());
          proxyResponse.setResponseCode(response.code());

          Buffer responseBody = new Buffer();
          responseBody.writeAll(response.body().source());

          proxyResponse.setBody(responseBody);
          return proxyResponse;
        } catch (IOException e) {
          Buffer responseBody = new Buffer();
          e.printStackTrace(new PrintStream(responseBody.outputStream()));

          MockResponse proxyResponse = new MockResponse();
          proxyResponse.setResponseCode(500);
          proxyResponse.setBody(responseBody);
          return proxyResponse;
        }
      }
    });


    Request request = new Request.Builder()
        .url(proxy.url("/robots.txt"))
        .build();

    try (Response response = client.newCall(request).execute()) {
      //if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      Headers responseHeaders = response.headers();
      for (int i = 0; i < responseHeaders.size(); i++) {
        System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
      }

      System.out.println(response.body().string());
    }
  }

  public static void main(String... args) throws Exception {
    new MockWebServerProxy().run();
  }
}