CharEscaperBuilder.java

/* Copyright (c) 2008 Google Inc.
 *
 * 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 com.google.gdata.util.common.base;

import java.util.HashMap;
import java.util.Map;

/**
 * Simple helper class to build a "sparse" array of objects based on the
 * indexes that were added to it.  The array will be from 0 to the maximum
 * index given.  All non-set indexes will contain null (so it's not really
 * a sparse array, just a pseudo sparse array).  The builder can also
 * return a CharEscaper based on the generated array.
 *
 * 
 */
public class CharEscaperBuilder {

  /**
   * Simple decorator that turns an array of replacement char[]s into
   * a CharEscaper, this results in a very fast escape method.
   */
  private static class CharArrayDecorator extends CharEscaper {

    private final char[][] replacements;
    private final int replaceLength;

    public CharArrayDecorator(char[][] replacements) {
      this.replacements = replacements;
      this.replaceLength = replacements.length;
    }

    /*
     * Overriding escape method to be slightly faster for this decorator.
     * We test the replacements array directly, saving a method call.
     */
    @Override
    public String escape(String s) {
      int slen = s.length();
      for (int index = 0; index < slen; index++) {
        char c = s.charAt(index);
        if (c < replacements.length && replacements[c] != null) {
          return escapeSlow(s, index);
        }
      }
      return s;
    }

    @Override protected char[] escape(char c) {
      return c < replaceLength ? replacements[c] : null;
    }
  }

  // Replacement mappings.
  private final Map<Character, String> map;

  // The highest index we've seen so far.
  private int max = -1;

  /**
   * Construct a new sparse array builder.
   */
  public CharEscaperBuilder() {
    this.map = new HashMap<Character, String>();
  }

  /**
   * Add a new mapping from an index to an object to the escaping.
   */
  public CharEscaperBuilder addEscape(char c, String r) {
    map.put(c, r);
    if (c > max) {
      max = c;
    }
    return this;
  }

  /**
   * Add multiple mappings at once for a particular index.
   */
  public CharEscaperBuilder addEscapes(char[] cs, String r) {
    for (char c : cs) {
      addEscape(c, r);
    }
    return this;
  }

  /**
   * Convert this builder into an array of char[]s where the maximum index
   * is the value of the highest character that has been seen.  The array will
   * be sparse in the sense that any unseen index will default to null.
   *
   * @return a "sparse" array that holds the replacement mappings.
   */
  public char[][] toArray() {
    char[][] result = new char[max + 1][];
    for (Map.Entry<Character, String> entry : map.entrySet()) {
      result[entry.getKey()] = entry.getValue().toCharArray();
    }
    return result;
  }

  /**
   * Convert this builder into a char escaper which is just a decorator
   * around the underlying array of replacement char[]s.
   *
   * @return an escaper that escapes based on the underlying array.
   */
  public CharEscaper toEscaper() {
    return new CharArrayDecorator(toArray());
  }
}