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;
018
019import java.io.BufferedReader;
020import java.io.Closeable;
021import java.io.IOException;
022import java.io.Reader;
023import java.util.Iterator;
024import java.util.NoSuchElementException;
025
026/**
027 * An Iterator over the lines in a {@code Reader}.
028 * <p>
029 * {@code LineIterator} holds a reference to an open {@code Reader}.
030 * When you have finished with the iterator you should close the reader
031 * to free internal resources. This can be done by closing the reader directly,
032 * or by calling the {@link #close()} or {@link #closeQuietly(LineIterator)}
033 * method on the iterator.
034 * <p>
035 * The recommended usage pattern is:
036 * <pre>
037 * LineIterator it = FileUtils.lineIterator(file, "UTF-8");
038 * try {
039 *   while (it.hasNext()) {
040 *     String line = it.nextLine();
041 *     // do something with line
042 *   }
043 * } finally {
044 *   it.close();
045 * }
046 * </pre>
047 *
048 * @since 1.2
049 */
050public class LineIterator implements Iterator<String>, Closeable {
051
052    // N.B. This class deliberately does not implement Iterable, see https://issues.apache.org/jira/browse/IO-181
053
054    /** The reader that is being read. */
055    private final BufferedReader bufferedReader;
056    /** The current line. */
057    private String cachedLine;
058    /** A flag indicating if the iterator has been fully read. */
059    private boolean finished;
060
061    /**
062     * Constructs an iterator of the lines for a {@code Reader}.
063     *
064     * @param reader the {@code Reader} to read from, not null
065     * @throws IllegalArgumentException if the reader is null
066     */
067    public LineIterator(final Reader reader) throws IllegalArgumentException {
068        if (reader == null) {
069            throw new IllegalArgumentException("Reader must not be null");
070        }
071        if (reader instanceof BufferedReader) {
072            bufferedReader = (BufferedReader) reader;
073        } else {
074            bufferedReader = new BufferedReader(reader);
075        }
076    }
077
078    /**
079     * Indicates whether the {@code Reader} has more lines.
080     * If there is an {@code IOException} then {@link #close()} will
081     * be called on this instance.
082     *
083     * @return {@code true} if the Reader has more lines
084     * @throws IllegalStateException if an IO exception occurs
085     */
086    @Override
087    public boolean hasNext() {
088        if (cachedLine != null) {
089            return true;
090        }
091        if (finished) {
092            return false;
093        }
094        try {
095            while (true) {
096                final String line = bufferedReader.readLine();
097                if (line == null) {
098                    finished = true;
099                    return false;
100                }
101                if (isValidLine(line)) {
102                    cachedLine = line;
103                    return true;
104                }
105            }
106        } catch(final IOException ioe) {
107            IOUtils.closeQuietly(this, ioe::addSuppressed);
108            throw new IllegalStateException(ioe);
109        }
110    }
111
112    /**
113     * Overridable method to validate each line that is returned.
114     * This implementation always returns true.
115     * @param line  the line that is to be validated
116     * @return true if valid, false to remove from the iterator
117     */
118    protected boolean isValidLine(final String line) {
119        return true;
120    }
121
122    /**
123     * Returns the next line in the wrapped {@code Reader}.
124     *
125     * @return the next line from the input
126     * @throws NoSuchElementException if there is no line to return
127     */
128    @Override
129    public String next() {
130        return nextLine();
131    }
132
133    /**
134     * Returns the next line in the wrapped {@code Reader}.
135     *
136     * @return the next line from the input
137     * @throws NoSuchElementException if there is no line to return
138     */
139    public String nextLine() {
140        if (!hasNext()) {
141            throw new NoSuchElementException("No more lines");
142        }
143        final String currentLine = cachedLine;
144        cachedLine = null;
145        return currentLine;
146    }
147
148    /**
149     * Closes the underlying {@code Reader}.
150     * This method is useful if you only want to process the first few
151     * lines of a larger file. If you do not close the iterator
152     * then the {@code Reader} remains open.
153     * This method can safely be called multiple times.
154     *
155     * @throws IOException if closing the underlying {@code Reader} fails.
156     */
157    @Override
158    public void close() throws IOException {
159        finished = true;
160        cachedLine = null;
161        IOUtils.close(bufferedReader);
162    }
163
164    /**
165     * Unsupported.
166     *
167     * @throws UnsupportedOperationException always
168     */
169    @Override
170    public void remove() {
171        throw new UnsupportedOperationException("remove not supported");
172    }
173
174    /**
175     * Closes a {@code LineIterator} quietly.
176     *
177     * @param iterator The iterator to close, or {@code null}.
178     * @deprecated As of 2.6 deprecated without replacement. Please use the try-with-resources statement or handle
179     * suppressed exceptions manually.
180     * @see Throwable#addSuppressed(java.lang.Throwable)
181     */
182    @Deprecated
183    public static void closeQuietly(final LineIterator iterator) {
184        IOUtils.closeQuietly(iterator);
185    }
186
187}