Mega Code Archive
An Iterator over the lines in a Reader
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//package com.qlogic.commons.utils.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 <code>Reader</code>.
* <p>
* <code>LineIterator</code> holds a reference to an open <code>Reader</code>.
* 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.
* <p>
* The recommended usage pattern is:
* <pre>
* LineIterator it = FileUtils.lineIterator(file, "UTF-8");
* try {
* while (it.hasNext()) {
* String line = it.nextLine();
* /// do something with line
* }
* } finally {
* LineIterator.closeQuietly(iterator);
* }
* </pre>
*
* @author Niall Pemberton
* @author Stephen Colebourne
* @author Sandy McArthur
* @version $Id$
* @since Commons IO 1.2
*/
public class LineIterator implements Iterator {
/** 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 <code>Reader</code>.
*
* @param reader the <code>Reader</code> 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 <code>Reader</code> has more lines.
* If there is an <code>IOException</code> then {@link #close()} will
* be called on this instance.
*
* @return <code>true</code> 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) {
String line = bufferedReader.readLine();
if (line == null) {
finished = true;
return false;
} else if (isValidLine(line)) {
cachedLine = line;
return true;
}
}
} catch(IOException ioe) {
close();
throw new IllegalStateException(ioe.toString());
}
}
}
/**
* Overridable method to validate each line that is returned.
*
* @param line the line that is to be validated
* @return true if valid, false to remove from the iterator
*/
protected boolean isValidLine(String line) {
return true;
}
/**
* Returns the next line in the wrapped <code>Reader</code>.
*
* @return the next line from the input
* @throws NoSuchElementException if there is no line to return
*/
public Object next() {
return nextLine();
}
/**
* Returns the next line in the wrapped <code>Reader</code>.
*
* @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");
}
String currentLine = cachedLine;
cachedLine = null;
return currentLine;
}
/**
* Closes the underlying <code>Reader</code> 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 <code>Reader</code> remains open.
* This method can safely be called multiple times.
*/
public void close() {
finished = true;
//BinaryStreamsUtils.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(LineIterator iterator) {
if (iterator != null) {
iterator.close();
}
}
}
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