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.io.input;
018
019import java.io.FilterReader;
020import java.io.IOException;
021import java.io.Reader;
022
023/**
024 * A filter reader that filters out characters where subclasses decide which characters to filter out.
025 */
026public abstract class AbstractCharacterFilterReader extends FilterReader {
027
028    /**
029     * Constructs a new reader.
030     *
031     * @param reader
032     *            the reader to filter
033     */
034    protected AbstractCharacterFilterReader(final Reader reader) {
035        super(reader);
036    }
037
038    @Override
039    public int read() throws IOException {
040        int ch;
041        do {
042            ch = in.read();
043        } while (filter(ch));
044        return ch;
045    }
046
047    /**
048     * Returns true if the given character should be filtered out, false to keep the character.
049     *
050     * @param ch
051     *            the character to test.
052     * @return true if the given character should be filtered out, false to keep the character.
053     */
054    protected abstract boolean filter(int ch);
055
056    @Override
057    public int read(final char[] cbuf, final int off, final int len) throws IOException {
058        final int read = super.read(cbuf, off, len);
059        if (read == -1) {
060            return -1;
061        }
062        int pos = off - 1;
063        for (int readPos = off; readPos < off + read; readPos++) {
064            if (filter(read)) {
065                continue;
066            }
067            pos++;
068            if (pos < readPos) {
069                cbuf[pos] = cbuf[readPos];
070            }
071        }
072        return pos - off + 1;
073    }
074}