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Common functionality for HBase
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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.
 */
package org.apache.hadoop.hbase.util;

import org.apache.hadoop.hbase.classification.InterfaceAudience;

/**
 * Utility for Strings.
 */
@InterfaceAudience.Private
public class Strings {
  public final static String DEFAULT_SEPARATOR = "=";
  public final static String DEFAULT_KEYVALUE_SEPARATOR = ", ";

  /**
   * Append to a StringBuilder a key/value.
   * Uses default separators.
   * @param sb StringBuilder to use
   * @param key Key to append.
   * @param value Value to append.
   * @return Passed sb populated with key/value.
   */
  public static StringBuilder appendKeyValue(final StringBuilder sb,
      final String key, final Object value) {
    return appendKeyValue(sb, key, value, DEFAULT_SEPARATOR,
      DEFAULT_KEYVALUE_SEPARATOR);
  }

  /**
   * Append to a StringBuilder a key/value.
   * Uses default separators.
   * @param sb StringBuilder to use
   * @param key Key to append.
   * @param value Value to append.
   * @param separator Value to use between key and value.
   * @param keyValueSeparator Value to use between key/value sets.
   * @return Passed sb populated with key/value.
   */
  public static StringBuilder appendKeyValue(final StringBuilder sb,
      final String key, final Object value, final String separator,
      final String keyValueSeparator) {
    if (sb.length() > 0) {
      sb.append(keyValueSeparator);
    }
    return sb.append(key).append(separator).append(value);
  }

  /**
   * Given a PTR string generated via reverse DNS lookup, return everything
   * except the trailing period. Example for host.example.com., return
   * host.example.com
   * @param dnPtr a domain name pointer (PTR) string.
   * @return Sanitized hostname with last period stripped off.
   *
   */
  public static String domainNamePointerToHostName(String dnPtr) {
    if (dnPtr == null)
      return null;
    return dnPtr.endsWith(".") ? dnPtr.substring(0, dnPtr.length()-1) : dnPtr;
  }

  /**
   * Null-safe length check.
   * @param input
   * @return true if null or length==0
   */
  public static boolean isEmpty(String input) {
    return input == null || input.length() == 0;
  }

  /**
   * Push the input string to the right by appending a character before it, usually a space.
   * @param input the string to pad
   * @param padding the character to repeat to the left of the input string
   * @param length the desired total length including the padding
   * @return padding characters + input
   */
  public static String padFront(String input, char padding, int length) {
    if (input.length() > length) {
      throw new IllegalArgumentException("input \"" + input + "\" longer than maxLength=" + length);
    }
    int numPaddingCharacters = length - input.length();
    return repeat(padding, numPaddingCharacters) + input;
  }

  /**
   * @param c repeat this character
   * @param reapeatFor the length of the output String
   * @return c, repeated repeatFor times
   */
  public static String repeat(char c, int reapeatFor) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < reapeatFor; ++i) {
      sb.append(c);
    }
    return sb.toString();
  }
}