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    /**
080     * Indicates whether the {@code Reader} has more lines.
081     * If there is an {@code IOException} then {@link #close()} will
082     * be called on this instance.
083     *
084     * @return {@code true} if the Reader has more lines
085     * @throws IllegalStateException if an IO exception occurs
086     */
087    @Override
088    public boolean hasNext() {
089        if (cachedLine != null) {
090            return true;
091        }
092        if (finished) {
093            return false;
094        }
095        try {
096            while (true) {
097                final String line = bufferedReader.readLine();
098                if (line == null) {
099                    finished = true;
100                    return false;
101                }
102                if (isValidLine(line)) {
103                    cachedLine = line;
104                    return true;
105                }
106            }
107        } catch(final IOException ioe) {
108            IOUtils.closeQuietly(this, ioe::addSuppressed);
109            throw new IllegalStateException(ioe);
110        }
111    }
112
113    /**
114     * Overridable method to validate each line that is returned.
115     * This implementation always returns true.
116     * @param line  the line that is to be validated
117     * @return true if valid, false to remove from the iterator
118     */
119    protected boolean isValidLine(final String line) {
120        return true;
121    }
122
123    /**
124     * Returns the next line in the wrapped {@code Reader}.
125     *
126     * @return the next line from the input
127     * @throws NoSuchElementException if there is no line to return
128     */
129    @Override
130    public String next() {
131        return nextLine();
132    }
133
134    /**
135     * Returns the next line in the wrapped {@code Reader}.
136     *
137     * @return the next line from the input
138     * @throws NoSuchElementException if there is no line to return
139     */
140    public String nextLine() {
141        if (!hasNext()) {
142            throw new NoSuchElementException("No more lines");
143        }
144        final String currentLine = cachedLine;
145        cachedLine = null;
146        return currentLine;
147    }
148
149    /**
150     * Closes the underlying {@code Reader}.
151     * This method is useful if you only want to process the first few
152     * lines of a larger file. If you do not close the iterator
153     * then the {@code Reader} remains open.
154     * This method can safely be called multiple times.
155     *
156     * @throws IOException if closing the underlying {@code Reader} fails.
157     */
158    @Override
159    public void close() throws IOException {
160        finished = true;
161        cachedLine = null;
162        IOUtils.close(bufferedReader);
163    }
164
165    /**
166     * Unsupported.
167     *
168     * @throws UnsupportedOperationException always
169     */
170    @Override
171    public void remove() {
172        throw new UnsupportedOperationException("remove not supported");
173    }
174
175    //-----------------------------------------------------------------------
176    /**
177     * Closes a {@code LineIterator} quietly.
178     *
179     * @param iterator The iterator to close, or {@code null}.
180     * @deprecated As of 2.6 deprecated without replacement. Please use the try-with-resources statement or handle
181     * suppressed exceptions manually.
182     * @see Throwable#addSuppressed(java.lang.Throwable)
183     */
184    @Deprecated
185    public static void closeQuietly(final LineIterator iterator) {
186        IOUtils.closeQuietly(iterator);
187    }
188
189}