Using headers from a WebView.load(...) response. Kinda ugly implementation since it requires exposing the networking implementation at the "view" level.

gistfile1.txt

package io.mercury.monkeybutt.webviewintercept;

import android.annotation.TargetApi;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebResourceRequest;
import android.webkit.WebResourceResponse;
import android.webkit.WebView;
import android.webkit.WebViewClient;

import okhttp3.Call;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class WebViewActivity extends AppCompatActivity {

    private OkHttpClient okHttpClient = new OkHttpClient.Builder().build(); // TODO: Make this a singleton for the app

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_web_view);

        WebView webView = (WebView) findViewById(R.id.webView);
        webView.setWebViewClient(new WebViewClient() {
            @SuppressWarnings("deprecation") // From API 21 we should use another overload
            @Override
            public WebResourceResponse shouldInterceptRequest(WebView view, String url) {
                return handleRequest(url);
            }

            @TargetApi(Build.VERSION_CODES.LOLLIPOP)
            @Override
            public WebResourceResponse shouldInterceptRequest(@NonNull WebView view, @NonNull WebResourceRequest request) {
                return handleRequest(request.getUrl().toString());
            }

            private WebResourceResponse handleRequest(String url) {
                try {
                    final Call call = okHttpClient.newCall(new Request.Builder()
                            .url(url)
                            // TODO: Add custom headers
                            .build()
                    );

                    final Response response = call.execute();

                    // TODO: Probably need to go back to the UI thread, verify first
                    // TODO: Get the title from some custom "x-" header instead of using the response code
                    updateScreenTitle(Integer.toString(response.code()));

                    return new WebResourceResponse(
                            response.header("content-type", "text/plain"), // You can set something other as default content-type
                            response.header("content-encoding", "utf-8"),  // Again, you can set another encoding as default
                            response.body().byteStream()
                    );
                } catch (Exception e) {
                    // TODO: Figure out how to show a custom error screen when we fail
                    return null;
                }
            }
        });

        webView.loadUrl("http://www.google.com");
    }


    private void updateScreenTitle(String title) {
        setTitle(title);
    }
}