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Commons IO example source code file (NullReader.java)

This example Commons IO source code file (NullReader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons IO tags/keywords

eofexception, io, ioexception, ioexception, mark, mark, no, nullreader, nullreader, override, override, read, reader, skip, unsupportedoperationexception

The Commons IO NullReader.java source code

/*
 * 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.input;

import java.io.EOFException;
import java.io.IOException;
import java.io.Reader;

/**
 * A functional, light weight {@link Reader} that emulates
 * a reader of a specified size.
 * <p>
 * This implementation provides a light weight
 * object for testing with an {@link Reader}
 * where the contents don't matter.
 * <p>
 * One use case would be for testing the handling of
 * large {@link Reader} as it can emulate that
 * scenario without the overhead of actually processing
 * large numbers of characters - significantly speeding up
 * test execution times.
 * <p>
 * This implementation returns a space from the method that
 * reads a character and leaves the array unchanged in the read
 * methods that are passed a character array.
 * If alternative data is required the <code>processChar() and
 * <code>processChars() methods can be implemented to generate
 * data, for example:
 *
 * <pre>
 *  public class TestReader extends NullReader {
 *      public TestReader(int size) {
 *          super(size);
 *      }
 *      protected char processChar() {
 *          return ... // return required value here
 *      }
 *      protected void processChars(char[] chars, int offset, int length) {
 *          for (int i = offset; i < length; i++) {
 *              chars[i] = ... // set array value here
 *          }
 *      }
 *  }
 * </pre>
 *
 * @since Commons IO 1.3
 * @version $Revision: 736890 $
 */
public class NullReader extends Reader {

    private final long size;
    private long position;
    private long mark = -1;
    private long readlimit;
    private boolean eof;
    private final boolean throwEofException;
    private final boolean markSupported;

    /**
     * Create a {@link Reader} that emulates a specified size
     * which supports marking and does not throw EOFException.
     *
     * @param size The size of the reader to emulate.
     */
    public NullReader(long size) {
       this(size, true, false);
    }

    /**
     * Create a {@link Reader} that emulates a specified
     * size with option settings.
     *
     * @param size The size of the reader to emulate.
     * @param markSupported Whether this instance will support
     * the <code>mark() functionality.
     * @param throwEofException Whether this implementation
     * will throw an {@link EOFException} or return -1 when the
     * end of file is reached.
     */
    public NullReader(long size, boolean markSupported, boolean throwEofException) {
       this.size = size;
       this.markSupported = markSupported;
       this.throwEofException = throwEofException;
    }

    /**
     * Return the current position.
     *
     * @return the current position.
     */
    public long getPosition() {
        return position;
    }

    /**
     * Return the size this {@link Reader} emulates.
     *
     * @return The size of the reader to emulate.
     */
    public long getSize() {
        return size;
    }

    /**
     * Close this Reader - resets the internal state to
     * the initial values.
     *
     * @throws IOException If an error occurs.
     */
    @Override
    public void close() throws IOException {
        eof = false;
        position = 0;
        mark = -1;
    }

    /**
     * Mark the current position.
     *
     * @param readlimit The number of characters before this marked position
     * is invalid.
     * @throws UnsupportedOperationException if mark is not supported.
     */
    @Override
    public synchronized void mark(int readlimit) {
        if (!markSupported) {
            throw new UnsupportedOperationException("Mark not supported");
        }
        mark = position;
        this.readlimit = readlimit;
    }

    /**
     * Indicates whether <i>mark is supported.
     *
     * @return Whether <i>mark is supported or not.
     */
    @Override
    public boolean markSupported() {
        return markSupported;
    }

    /**
     * Read a character.
     *
     * @return Either The character value returned by <code>processChar()
     * or <code>-1 if the end of file has been reached and
     * <code>throwEofException is set to false.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException is set to true.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read() throws IOException {
        if (eof) {
            throw new IOException("Read after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position++;
        return processChar();
    }

    /**
     * Read some characters into the specified array.
     *
     * @param chars The character array to read into
     * @return The number of characters read or <code>-1
     * if the end of file has been reached and
     * <code>throwEofException is set to false.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException is set to true.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read(char[] chars) throws IOException {
        return read(chars, 0, chars.length);
    }

    /**
     * Read the specified number characters into an array.
     *
     * @param chars The character array to read into.
     * @param offset The offset to start reading characters into.
     * @param length The number of characters to read.
     * @return The number of characters read or <code>-1
     * if the end of file has been reached and
     * <code>throwEofException is set to false.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException is set to true.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read(char[] chars, int offset, int length) throws IOException {
        if (eof) {
            throw new IOException("Read after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position += length;
        int returnLength = length;
        if (position > size) {
            returnLength = length - (int)(position - size);
            position = size;
        }
        processChars(chars, offset, returnLength);
        return returnLength;
    }

    /**
     * Reset the stream to the point when mark was last called.
     *
     * @throws UnsupportedOperationException if mark is not supported.
     * @throws IOException If no position has been marked
     * or the read limit has been exceed since the last position was
     * marked.
     */
    @Override
    public synchronized void reset() throws IOException {
        if (!markSupported) {
            throw new UnsupportedOperationException("Mark not supported");
        }
        if (mark < 0) {
            throw new IOException("No position has been marked");
        }
        if (position > (mark + readlimit)) {
            throw new IOException("Marked position [" + mark +
                    "] is no longer valid - passed the read limit [" +
                    readlimit + "]");
        }
        position = mark;
        eof = false;
    }

    /**
     * Skip a specified number of characters.
     *
     * @param numberOfChars The number of characters to skip.
     * @return The number of characters skipped or <code>-1
     * if the end of file has been reached and
     * <code>throwEofException is set to false.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException is set to true.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public long skip(long numberOfChars) throws IOException {
        if (eof) {
            throw new IOException("Skip after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position += numberOfChars;
        long returnLength = numberOfChars;
        if (position > size) {
            returnLength = numberOfChars - (position - size);
            position = size;
        }
        return returnLength;
    }

    /**
     * Return a character value for the  <code>read() method.
     * <p>
     * This implementation returns zero.
     *
     * @return This implementation always returns zero.
     */
    protected int processChar() {
        // do nothing - overridable by subclass
        return 0;
    }

    /**
     * Process the characters for the <code>read(char[], offset, length)
     * method.
     * <p>
     * This implementation leaves the character array unchanged.
     *
     * @param chars The character array
     * @param offset The offset to start at.
     * @param length The number of characters.
     */
    protected void processChars(char[] chars, int offset, int length) {
        // do nothing - overridable by subclass
    }

    /**
     * Handle End of File.
     *
     * @return <code>-1 if throwEofException is
     * set to <code>false
     * @throws EOFException if <code>throwEofException is set
     * to <code>true.
     */
    private int doEndOfFile() throws EOFException {
        eof = true;
        if (throwEofException) {
            throw new EOFException();
        }
        return -1;
    }

}

Other Commons IO examples (source code examples)

Here is a short list of links related to this Commons IO NullReader.java source code file:



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