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   /*
    * Copyright 2020 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.codec.http.multipart;
  
  import java.io.File;
  import java.util.Collections;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * DeleteFileOnExitHook.
   */
  final class DeleteFileOnExitHook {
      private static final Set<String> FILES = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
  
      private DeleteFileOnExitHook() {
      }
  
      static {
          // DeleteOnExitHook must be the last shutdown hook to be invoked.
          // Application shutdown hooks may add the first file to the
          // delete on exit list and cause the DeleteOnExitHook to be
          // registered during shutdown in progress.
          Runtime.getRuntime().addShutdownHook(new Thread() {
  
              @Override
              public void run() {
                  runHook();
              }
          });
      }
  
      /**
       * Remove from the pool to reduce space footprint.
       *
       * @param file tmp file path
       */
      public static void remove(String file) {
          FILES.remove(file);
      }
  
      /**
       * Add to the hook and clean up when the program exits.
       *
       * @param file tmp file path
       */
      public static void add(String file) {
          FILES.add(file);
      }
  
      /**
       * Check in the hook files.
       *
       * @param file target file
       * @return true or false
       */
      public static boolean checkFileExist(String file) {
          return FILES.contains(file);
      }
  
      /**
       * Clean up all the files.
       */
      static void runHook() {
          for (String filename : FILES) {
              new File(filename).delete();
          }
      }
  }