ch.inftec.ju.util.io.LineIterator Maven / Gradle / Ivy

Go to download
package ch.inftec.ju.util.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;
import java.util.NoSuchElementException;

import ch.inftec.ju.util.IOUtil;

/**
 * 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();
 * }
 * 
 *
 * @author Stephen Colebourne
 * @author Sandy McArthur
 * @version $Id: LineIterator.java 1102128 2011-05-11 23:05:22Z sebb $
 * @since Commons IO 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 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) {
					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);
			}
		}
	}

	/**
	 * 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 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");
		}
		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;
		IOUtil.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();
		}
	}

}