CustomAnnotation.java

/*
 * Copyright (C) 2018 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.retrofit;

import java.io.IOException;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.util.concurrent.TimeUnit;
import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.Invocation;
import retrofit2.Retrofit;
import retrofit2.http.GET;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.util.concurrent.TimeUnit.MILLISECONDS;

public final class CustomAnnotation {
  public interface Browse {
    @GET("/")
    @WarnIfSlow(max = 500, timeUnit = MILLISECONDS)
    Call<ResponseBody> home();
  }

  @Documented
  @Target(METHOD)
  @Retention(RUNTIME)
  public @interface WarnIfSlow {
    long max();
    TimeUnit timeUnit();
  }

  static final class WarnIfSlowInterceptor implements Interceptor {
    @Override public Response intercept(Chain chain) throws IOException {
      Request request = chain.request();
      long startNanos = System.nanoTime();
      Response response = chain.proceed(request);
      long elapsedNanos = System.nanoTime() - startNanos;

      Invocation invocation = request.tag(Invocation.class);
      WarnIfSlow warnIfSlow = invocation.method().getAnnotation(WarnIfSlow.class);

      if (warnIfSlow != null && elapsedNanos > warnIfSlow.timeUnit().toNanos(warnIfSlow.max())) {
        System.out.printf("SLOW METHOD WARNING: %s.%s %s HTTP %s (%.0f ms)%n",
            invocation.method().getDeclaringClass().getSimpleName(),
            invocation.method().getName(),
            invocation.arguments(),
            response.code(),
            elapsedNanos / 1_000_000.0);
      }

      return response;
    }
  }

  public static void main(String... args) throws IOException {
    WarnIfSlowInterceptor warnIfSlowInterceptor = new WarnIfSlowInterceptor();

    OkHttpClient okHttpClient = new OkHttpClient.Builder()
        .addInterceptor(warnIfSlowInterceptor)
        .build();

    Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("https://square.com/")
        .callFactory(okHttpClient)
        .build();

    Browse browse = retrofit.create(Browse.class);

    browse.home().execute();
  }
}

Invocation invocation = request.tag(Invocation.class);

invocation may be null, so add if (invocation != null) {}

When i share a singleton OkHttpClient with glide to load image, invocation is null
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.reflect.Method retrofit2.Invocation.method()' on a null object reference