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Feign Hystrix
There is a newer version: 9.2.0
/*
 * Copyright © 2012 The Feign Authors ([email protected])
 *
 * 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 feign.hystrix;

import static feign.Util.checkNotNull;

import feign.FeignException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Used to control the fallback given its cause.
 *
 * Ex.
 *
 * 
{@code
 * // This instance will be invoked if there are errors of any kind.
 * FallbackFactory fallbackFactory = cause -> (owner, repo) -> {
 *   if (cause instanceof FeignException && ((FeignException) cause).status() == 403) {
 *     return Collections.emptyList();
 *   } else {
 *     return Arrays.asList("yogi");
 *   }
 * };
 *
 * GitHub github = HystrixFeign.builder()
 *                             ...
 *                             .target(GitHub.class, "https://api.github.com", fallbackFactory);
 * }
 *
 * @param  the feign interface type
 */
public interface FallbackFactory {

  /**
   * Returns an instance of the fallback appropriate for the given cause
   *
   * @param cause corresponds to {@link com.netflix.hystrix.AbstractCommand#getExecutionException()}
   *     often, but not always an instance of {@link FeignException}.
   */
  T create(Throwable cause);

  /** Returns a constant fallback after logging the cause to FINE level. */
  final class Default implements FallbackFactory {
    // jul to not add a dependency
    final Logger logger;
    final T constant;

    public Default(T constant) {
      this(constant, Logger.getLogger(Default.class.getName()));
    }

    Default(T constant, Logger logger) {
      this.constant = checkNotNull(constant, "fallback");
      this.logger = checkNotNull(logger, "logger");
    }

    @Override
    public T create(Throwable cause) {
      if (logger.isLoggable(Level.FINE)) {
        logger.log(Level.FINE, "fallback due to: " + cause.getMessage(), cause);
      }
      return constant;
    }

    @Override
    public String toString() {
      return constant.toString();
    }
  }
}