    001    /*
    002     * Copyright (C) 2007 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.io;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.base.Preconditions;
    021
    022    import java.io.IOException;
    023    import java.io.Reader;
    024    import java.nio.CharBuffer;
    025    import java.util.LinkedList;
    026    import java.util.Queue;
    027
    028    /**
    029     * A class for reading lines of text. Provides the same functionality
    030     * as {@link java.io.BufferedReader#readLine()} but for all {@link Readable}
    031     * objects, not just instances of {@link Reader}.
    032     *
    033     * @author Chris Nokleberg
    034     * @since 1.0
    035     */
    036    @Beta
    037    public final class LineReader {
    038      private final Readable readable;
    039      private final Reader reader;
    040      private final char[] buf = new char[0x1000]; // 4K
    041      private final CharBuffer cbuf = CharBuffer.wrap(buf);
    042
    043      private final Queue<String> lines = new LinkedList<String>();
    044      private final LineBuffer lineBuf = new LineBuffer() {
    045        @Override protected void handleLine(String line, String end) {
    046          lines.add(line);
    047        }
    048      };
    049
    050      /**
    051       * Creates a new instance that will read lines from the given
    052       * {@code Readable} object.
    053       */
    054      public LineReader(Readable readable) {
    055        Preconditions.checkNotNull(readable);
    056        this.readable = readable;
    057        this.reader = (readable instanceof Reader) ? (Reader) readable : null;
    058      }
    059
    060      /**
    061       * Reads a line of text. A line is considered to be terminated by any
    062       * one of a line feed ({@code '\n'}), a carriage return
    063       * ({@code '\r'}), or a carriage return followed immediately by a linefeed
    064       * ({@code "\r\n"}).
    065       *
    066       * @return a {@code String} containing the contents of the line, not
    067       *     including any line-termination characters, or {@code null} if the
    068       *     end of the stream has been reached.
    069       * @throws IOException if an I/O error occurs
    070       */
    071      public String readLine() throws IOException {
    072        while (lines.peek() == null) {
    073          cbuf.clear();
    074          // The default implementation of Reader#read(CharBuffer) allocates a
    075          // temporary char[], so we call Reader#read(char[], int, int) instead.
    076          int read = (reader != null)
    077              ? reader.read(buf, 0, buf.length)
    078              : readable.read(cbuf);
    079          if (read == -1) {
    080            lineBuf.finish();
    081            break;
    082          }
    083          lineBuf.add(buf, 0, read);
    084        }
    085        return lines.poll();
    086      }
    087    }