    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.text.translate;
    018
    019import java.io.IOException;
    020import java.io.StringWriter;
    021import java.io.Writer;
    022import java.util.Locale;
    023
    024import org.apache.commons.lang3.Validate;
    025
    026/**
    027 * An API for translating text.
    028 * Its core use is to escape and unescape text. Because escaping and unescaping
    029 * is completely contextual, the API does not present two separate signatures.
    030 *
    031 * @since 1.0
    032 */
    033public abstract class CharSequenceTranslator {
    034
    035    /**
    036     * Array containing the hexadecimal alphabet.
    037     */
    038    static final char[] HEX_DIGITS = new char[] {'0', '1', '2', '3',
    039                                                 '4', '5', '6', '7',
    040                                                 '8', '9', 'A', 'B',
    041                                                 'C', 'D', 'E', 'F'};
    042
    043    /**
    044     * Translate a set of codepoints, represented by an int index into a CharSequence,
    045     * into another set of codepoints. The number of codepoints consumed must be returned,
    046     * and the only IOExceptions thrown must be from interacting with the Writer so that
    047     * the top level API may reliably ignore StringWriter IOExceptions.
    048     *
    049     * @param input CharSequence that is being translated
    050     * @param index int representing the current point of translation
    051     * @param out Writer to translate the text to
    052     * @return int count of codepoints consumed
    053     * @throws IOException if and only if the Writer produces an IOException
    054     */
    055    public abstract int translate(CharSequence input, int index, Writer out) throws IOException;
    056
    057    /**
    058     * Helper for non-Writer usage.
    059     * @param input CharSequence to be translated
    060     * @return String output of translation
    061     */
    062    public final String translate(final CharSequence input) {
    063        if (input == null) {
    064            return null;
    065        }
    066        try {
    067            final StringWriter writer = new StringWriter(input.length() * 2);
    068            translate(input, writer);
    069            return writer.toString();
    070        } catch (final IOException ioe) {
    071            // this should never ever happen while writing to a StringWriter
    072            throw new RuntimeException(ioe);
    073        }
    074    }
    075
    076    /**
    077     * Translate an input onto a Writer. This is intentionally final as its algorithm is
    078     * tightly coupled with the abstract method of this class.
    079     *
    080     * @param input CharSequence that is being translated
    081     * @param out Writer to translate the text to
    082     * @throws IOException if and only if the Writer produces an IOException
    083     */
    084    public final void translate(final CharSequence input, final Writer out) throws IOException {
    085        Validate.isTrue(out != null, "The Writer must not be null");
    086        if (input == null) {
    087            return;
    088        }
    089        int pos = 0;
    090        final int len = input.length();
    091        while (pos < len) {
    092            final int consumed = translate(input, pos, out);
    093            if (consumed == 0) {
    094                // inlined implementation of Character.toChars(Character.codePointAt(input, pos))
    095                // avoids allocating temp char arrays and duplicate checks
    096                final char c1 = input.charAt(pos);
    097                out.write(c1);
    098                pos++;
    099                if (Character.isHighSurrogate(c1) && pos < len) {
    100                    final char c2 = input.charAt(pos);
    101                    if (Character.isLowSurrogate(c2)) {
    102                      out.write(c2);
    103                      pos++;
    104                    }
    105                }
    106                continue;
    107            }
    108            // contract with translators is that they have to understand codepoints
    109            // and they just took care of a surrogate pair
    110            for (int pt = 0; pt < consumed; pt++) {
    111                pos += Character.charCount(Character.codePointAt(input, pos));
    112            }
    113        }
    114    }
    115
    116    /**
    117     * Helper method to create a merger of this translator with another set of
    118     * translators. Useful in customizing the standard functionality.
    119     *
    120     * @param translators CharSequenceTranslator array of translators to merge with this one
    121     * @return CharSequenceTranslator merging this translator with the others
    122     */
    123    public final CharSequenceTranslator with(final CharSequenceTranslator... translators) {
    124        final CharSequenceTranslator[] newArray = new CharSequenceTranslator[translators.length + 1];
    125        newArray[0] = this;
    126        System.arraycopy(translators, 0, newArray, 1, translators.length);
    127        return new AggregateTranslator(newArray);
    128    }
    129
    130    /**
    131     * <p>Returns an upper case hexadecimal <code>String</code> for the given
    132     * character.</p>
    133     *
    134     * @param codepoint The codepoint to convert.
    135     * @return An upper case hexadecimal <code>String</code>
    136     */
    137    public static String hex(final int codepoint) {
    138        return Integer.toHexString(codepoint).toUpperCase(Locale.ENGLISH);
    139    }
    140
    141}