    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 *      https://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 static org.apache.commons.io.IOUtils.EOF;
    020
    021import java.io.IOException;
    022import java.io.Reader;
    023import java.io.SequenceInputStream;
    024import java.util.Arrays;
    025import java.util.Iterator;
    026import java.util.Objects;
    027
    028import org.apache.commons.io.IOUtils;
    029import org.apache.commons.io.function.Uncheck;
    030
    031/**
    032 * Provides the contents of multiple {@link Reader}s in sequence.
    033 * <p>
    034 * Like {@link SequenceInputStream} but for {@link Reader} arguments.
    035 * </p>
    036 *
    037 * @since 2.7
    038 */
    039public class SequenceReader extends Reader {
    040
    041    private Reader reader;
    042    private final Iterator<? extends Reader> readers;
    043
    044    /**
    045     * Constructs a new instance with readers
    046     *
    047     * @param readers the readers to read.
    048     */
    049    public SequenceReader(final Iterable<? extends Reader> readers) {
    050        this.readers = Objects.requireNonNull(readers, "readers").iterator();
    051        this.reader = Uncheck.get(this::nextReader);
    052    }
    053
    054    /**
    055     * Constructs a new instance with readers
    056     *
    057     * @param readers the readers to read.
    058     */
    059    public SequenceReader(final Reader... readers) {
    060        this(Arrays.asList(readers));
    061    }
    062
    063    /*
    064     * (non-Javadoc)
    065     *
    066     * @see Reader#close()
    067     */
    068    @Override
    069    public void close() throws IOException {
    070        do { // NOPMD
    071             // empty
    072        } while (nextReader() != null);
    073    }
    074
    075    /**
    076     * Returns the next available reader or null if done.
    077     *
    078     * @return the next available reader or null.
    079     * @throws IOException IOException  If an I/O error occurs.
    080     */
    081    private Reader nextReader() throws IOException {
    082        if (reader != null) {
    083            reader.close();
    084        }
    085        if (readers.hasNext()) {
    086            reader = readers.next();
    087        } else {
    088            reader = null;
    089        }
    090        return reader;
    091    }
    092
    093    /*
    094     * (non-Javadoc)
    095     *
    096     * @see Reader#read(char[], int, int)
    097     */
    098    @Override
    099    public int read() throws IOException {
    100        int c = EOF;
    101        while (reader != null) {
    102            c = reader.read();
    103            if (c != EOF) {
    104                break;
    105            }
    106            nextReader();
    107        }
    108        return c;
    109    }
    110
    111    @Override
    112    public int read(final char[] cbuf, int off, int len) throws IOException {
    113        IOUtils.checkFromIndexSize(cbuf, off, len);
    114        if (len == 0) {
    115            return 0;
    116        }
    117        int count = 0;
    118        while (reader != null) {
    119            final int readLen = reader.read(cbuf, off, len);
    120            if (readLen == EOF) {
    121                nextReader();
    122            } else {
    123                count += readLen;
    124                off += readLen;
    125                len -= readLen;
    126                if (len <= 0) {
    127                    break;
    128                }
    129            }
    130        }
    131        if (count > 0) {
    132            return count;
    133        }
    134        return EOF;
    135    }
    136}