Convert hexadecimal digits into byte array by encoding each two hexadecimal digits as a byte.

  
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 * 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
 * 
 *      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.
 */

import java.io.ByteArrayOutputStream;

/**
 * Library of utility methods useful in dealing with converting byte arrays to
 * and from strings of hexadecimal digits.
 * 
 * @author Craig R. McClanahan
 */

public class Utils {
  /**
   * Convert a String of hexadecimal digits into the corresponding byte array by
   * encoding each two hexadecimal digits as a byte.
   * 
   * @param digits
   *          Hexadecimal digits representation
   * 
   * @exception IllegalArgumentException
   *              if an invalid hexadecimal digit is found, or the input string
   *              contains an odd number of hexadecimal digits
   */
  public static byte[] convert(String digits) {

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    for (int i = 0; i < digits.length(); i += 2) {
      char c1 = digits.charAt(i);
      if ((i + 1) >= digits.length())
        throw new IllegalArgumentException("hexUtil.odd");
      char c2 = digits.charAt(i + 1);
      byte b = 0;
      if ((c1 >= '0') && (c1 <= '9'))
        b += ((c1 - '0') * 16);
      else if ((c1 >= 'a') && (c1 <= 'f'))
        b += ((c1 - 'a' + 10) * 16);
      else if ((c1 >= 'A') && (c1 <= 'F'))
        b += ((c1 - 'A' + 10) * 16);
      else
        throw new IllegalArgumentException("hexUtil.bad");
      if ((c2 >= '0') && (c2 <= '9'))
        b += (c2 - '0');
      else if ((c2 >= 'a') && (c2 <= 'f'))
        b += (c2 - 'a' + 10);
      else if ((c2 >= 'A') && (c2 <= 'F'))
        b += (c2 - 'A' + 10);
      else
        throw new IllegalArgumentException("hexUtil.bad");
      baos.write(b);
    }
    return (baos.toByteArray());

  }
}

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Convert hexadecimal digits into byte array by encoding each two hexadecimal digits as a byte. : Byte Array « File Input Output « Java

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