OkHttpClient throws exception after upgrading to OkHttp3

Question

I'm using following lines of code to add a default header to all of my requests sent using Retrofit2:

private static OkHttpClient defaultHttpClient = new OkHttpClient();
static {
    defaultHttpClient.networkInterceptors().add(new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Request request = chain.request().newBuilder()
                    .addHeader("Accept", "Application/JSON").build();
            return chain.proceed(request);
        }
    });
}

After upgrading retrofit to beta-3 version, I had to upgrade OkHttp to OkHttp3 also (actually I just changed package names from okhttp to okhttp3, the library is included inside retrofit). After that I get exceptions from this line:

defaultHttpClient.networkInterceptors().add(new Interceptor());

Caused by: java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableCollection.add(Collections.java:932)

---

Caused by: java.lang.ExceptionInInitializerError

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What is the problem here?

Answer 1

You have to use builder if you want to create OkHttp(3)Client object.

Try change this:

private static OkHttpClient defaultHttpClient = new OkHttpClient();

To something like this:

  OkHttpClient defaultHttpClient = new OkHttpClient.Builder()
       .addInterceptor(
           new Interceptor() {
             @Override
             public Response intercept(Interceptor.Chain chain) throws IOException {
                   Request request = chain.request().newBuilder()
                   .addHeader("Accept", "Application/JSON").build();
               return chain.proceed(request);
              }
           }).build();

Answer 2

compile 'com.squareup.retrofit2:retrofit:2.1.0'
compile "com.squareup.retrofit2:converter-gson:2.1.0"
compile "com.squareup.retrofit2:adapter-rxjava:2.1.0"
compile 'com.squareup.okhttp3:logging-interceptor:3.4.0'

You should probably use these versions. Just put them, sync your gradle, delete all imports, and try again.

import okhttp3.Interceptor;

import okhttp3.OkHttpClient;

import okhttp3.Request;

import okhttp3.Response;

import okhttp3.logging.HttpLoggingInterceptor;

import retrofit2.Retrofit;

import retrofit2.converter.gson.GsonConverterFactory;

Answer 3

To add up V.Sch's answer, with Java Lambda we can shorten this to

    OkHttpClient httpClient = new OkHttpClient.Builder()
        .addInterceptor(
                chain -> {
                    Request request = chain.request().newBuilder()
                            .addHeader("Accept", "Application/JSON").build();
                    return chain.proceed(request);
                }).build();