org.apache.commons.io.LineIterator Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of commons-io Show documentation
Show all versions of commons-io Show documentation
The Apache Commons IO library contains utility classes, stream implementations, file filters,
file comparators, endian transformation classes, and much more.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.io;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* An Iterator over the lines in a Reader.
*
* LineIterator holds a reference to an open Reader.
* When you have finished with the iterator you should close the reader
* to free internal resources. This can be done by closing the reader directly,
* or by calling the {@link #close()} or {@link #closeQuietly(LineIterator)}
* method on the iterator.
*
* The recommended usage pattern is:
*
* LineIterator it = FileUtils.lineIterator(file, "UTF-8");
* try {
* while (it.hasNext()) {
* String line = it.nextLine();
* // do something with line
* }
* } finally {
* it.close();
* }
*
*
* @version $Id: LineIterator.java 1471767 2013-04-24 23:24:19Z sebb $
* @since 1.2
*/
public class LineIterator implements Iterator {
// N.B. This class deliberately does not implement Iterable, see https://issues.apache.org/jira/browse/IO-181
/** The reader that is being read. */
private final BufferedReader bufferedReader;
/** The current line. */
private String cachedLine;
/** A flag indicating if the iterator has been fully read. */
private boolean finished = false;
/**
* Constructs an iterator of the lines for a Reader.
*
* @param reader the Reader to read from, not null
* @throws IllegalArgumentException if the reader is null
*/
public LineIterator(final Reader reader) throws IllegalArgumentException {
if (reader == null) {
throw new IllegalArgumentException("Reader must not be null");
}
if (reader instanceof BufferedReader) {
bufferedReader = (BufferedReader) reader;
} else {
bufferedReader = new BufferedReader(reader);
}
}
//-----------------------------------------------------------------------
/**
* Indicates whether the Reader has more lines.
* If there is an IOException then {@link #close()} will
* be called on this instance.
*
* @return {@code true} if the Reader has more lines
* @throws IllegalStateException if an IO exception occurs
*/
public boolean hasNext() {
if (cachedLine != null) {
return true;
} else if (finished) {
return false;
} else {
try {
while (true) {
final String line = bufferedReader.readLine();
if (line == null) {
finished = true;
return false;
} else if (isValidLine(line)) {
cachedLine = line;
return true;
}
}
} catch(final IOException ioe) {
close();
throw new IllegalStateException(ioe);
}
}
}
/**
* Overridable method to validate each line that is returned.
* This implementation always returns true.
* @param line the line that is to be validated
* @return true if valid, false to remove from the iterator
*/
protected boolean isValidLine(final String line) {
return true;
}
/**
* Returns the next line in the wrapped Reader.
*
* @return the next line from the input
* @throws NoSuchElementException if there is no line to return
*/
public String next() {
return nextLine();
}
/**
* Returns the next line in the wrapped Reader.
*
* @return the next line from the input
* @throws NoSuchElementException if there is no line to return
*/
public String nextLine() {
if (!hasNext()) {
throw new NoSuchElementException("No more lines");
}
final String currentLine = cachedLine;
cachedLine = null;
return currentLine;
}
/**
* Closes the underlying Reader quietly.
* This method is useful if you only want to process the first few
* lines of a larger file. If you do not close the iterator
* then the Reader remains open.
* This method can safely be called multiple times.
*/
public void close() {
finished = true;
IOUtils.closeQuietly(bufferedReader);
cachedLine = null;
}
/**
* Unsupported.
*
* @throws UnsupportedOperationException always
*/
public void remove() {
throw new UnsupportedOperationException("Remove unsupported on LineIterator");
}
//-----------------------------------------------------------------------
/**
* Closes the iterator, handling null and ignoring exceptions.
*
* @param iterator the iterator to close
*/
public static void closeQuietly(final LineIterator iterator) {
if (iterator != null) {
iterator.close();
}
}
}