content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one or more
   *  contributor license agreements.  See the NOTICE file distributed with
   *  this work for additional information regarding copyright ownership.
   *  The ASF 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 org.apache.tools.ant.types.selectors.modifiedselector;
  
  import java.io.File;
  import java.io.FileReader;
  import java.io.Reader;
  
  import org.apache.tools.ant.util.FileUtils;
  
  /**
   * Computes a 'hashvalue' for the content of file using String.hashValue().
   * Use of this algorithm doesn't require any additional nested &lt;param&gt;s and
   * doesn't support any.
   *
   * @version 2003-09-13
   * @since  Ant 1.6
   */
  public class HashvalueAlgorithm implements Algorithm {
  
      /**
       * This algorithm doesn't need any configuration.
       * Therefore it's always valid.
       * @return always true
       */
      public boolean isValid() {
          return true;
      }
  
      /**
       * Computes a 'hashvalue' for a file content.
       * It reads the content of a file, convert that to String and use the
       * String.hashCode() method.
       * @param file  The file for which the value should be computed
       * @return the hashvalue or <i>null</i> if the file couldn't be read
       */
       // Because the content is only read the file will not be damaged. I tested
       // with JPG, ZIP and PDF as binary files.
      public String getValue(File file) {
          if (!file.canRead()) {
              return null;
          }
          try (Reader r = new FileReader(file)) {
              int hash = FileUtils.readFully(r).hashCode();
              return Integer.toString(hash);
          } catch (Exception e) {
              return null;
          }
      }
  
  
      /**
       * Override Object.toString().
       * @return information about this comparator
       */
      public String toString() {
          return "HashvalueAlgorithm";
      }
  
  }
  