Shared OkHttp application Interceptor that will add or intercept E-Tag hash for ALL requests on client instance

gistfile1.java

// by Nikola Despotoski

import android.content.Context;
import android.text.TextUtils;

import com.squareup.okhttp.Headers;
import com.squareup.okhttp.Interceptor;
import com.squareup.okhttp.Request;
import com.squareup.okhttp.Response;

import java.io.IOException;


/**
 * Created by nikola on 1/27/15.
 */
public class OkHttpSharedEtagNetworkInterceptor implements Interceptor{
    private static final java.lang.String IF_NONE_MATCH = "If-None-Match";
    private static final java.lang.String ETAG = "ETag";
    private final Context mContext;

    public OkHttpSharedEtagNetworkInterceptor(Context context){
        mContext = context;
    }
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        //----rebuild request from scratch---
        Request.Builder newRequest = request.newBuilder();
        newRequest.cacheControl(request.cacheControl());
        newRequest.url(request.url());
        if(request.method().equals("GET"))
           newRequest.get();
        else
           newRequest.method(request.method(), request.body());
           
        //----retrieve last stored hash
        String etag = getEtag();
    
        Headers headers = request.headers();
        Headers.Builder newHeaders = headers.newBuilder();
        //---if exists add it to headers--- 
        if(!TextUtils.isEmpty(etag)){
            newHeaders.add(IF_NONE_MATCH, etag);
        }

        for(int i = 0; i < headers.size(); i++){
            newHeaders.add(headers.name(i), headers.value(i));
        }
        headers = newHeaders.build();
        newRequest.headers(headers);
        request = newRequest.build();
        Response response = chain.proceed(request);
        //---- if received Not modified 304 code, store it to preferences for later ----
        if(response.code() == 304){
            storeEtag(response.header(ETAG));
        }
        return response;
    }

    private void storeEtag(String header) {
        SharedPreferencesUtil.writeString(mContext, ETAG, header);
    }

    public String getEtag() {
        return SharedPreferencesUtil.getString(mContext, ETAG);
    }
}