NullInputStream.java
/*
* 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 static org.apache.commons.io.IOUtils.EOF;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
/**
* A functional, light weight {@link InputStream} that emulates a stream of a specified size.
* <p>
* This implementation provides a light weight object for testing with an {@link InputStream} where the contents don't matter.
* </p>
* <p>
* One use case would be for testing the handling of large {@link InputStream} as it can emulate that scenario without the overhead of actually processing large
* numbers of bytes - significantly speeding up test execution times.
* </p>
* <p>
* This implementation returns zero from the method that reads a byte and leaves the array unchanged in the read methods that are passed a byte array. If
* alternative data is required the {@code processByte()} and {@code processBytes()} methods can be implemented to generate data, for example:
* </p>
*
* <pre>
* public class TestInputStream extends NullInputStream {
* public TestInputStream(int size) {
* super(size);
* }
* protected int processByte() {
* return ... // return required value here
* }
* protected void processBytes(byte[] bytes, int offset, int length) {
* for (int i = offset; i < length; i++) {
* bytes[i] = ... // set array value here
* }
* }
* }
* </pre>
*
* @since 1.3
*/
public class NullInputStream extends InputStream {
/**
* The singleton instance.
*
* @since 2.12.0
*/
public static final NullInputStream INSTANCE = new NullInputStream();
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;
/**
* Constructs an {@link InputStream} that emulates a size 0 stream which supports marking and does not throw EOFException.
*
* @since 2.7
*/
public NullInputStream() {
this(0, true, false);
}
/**
* Constructs an {@link InputStream} that emulates a specified size which supports marking and does not throw EOFException.
*
* @param size The size of the input stream to emulate.
*/
public NullInputStream(final long size) {
this(size, true, false);
}
/**
* Constructs an {@link InputStream} that emulates a specified size with option settings.
*
* @param size The size of the input stream 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 NullInputStream(final long size, final boolean markSupported, final boolean throwEofException) {
this.size = size;
this.markSupported = markSupported;
this.throwEofException = throwEofException;
}
/**
* Returns the number of bytes that can be read.
*
* @return The number of bytes that can be read.
*/
@Override
public int available() {
final long avail = size - position;
if (avail <= 0) {
return 0;
}
if (avail > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
}
return (int) avail;
}
/**
* Throws {@link EOFException} if {@code throwEofException} is enabled.
*
* @param message The {@link EOFException} message.
* @throws EOFException Thrown if {@code throwEofException} is enabled.
*/
private void checkThrowEof(final String message) throws EOFException {
if (throwEofException) {
throw new EOFException(message);
}
}
/**
* Closes this input stream - 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;
}
/**
* Gets the current position.
*
* @return the current position.
*/
public long getPosition() {
return position;
}
/**
* Gets the size this {@link InputStream} emulates.
*
* @return The size of the input stream to emulate.
*/
public long getSize() {
return size;
}
/**
* Handles End of File.
*
* @return {@code -1} if {@code throwEofException} is set to {@code false}
* @throws EOFException if {@code throwEofException} is set to {@code true}.
*/
private int handleEof() throws EOFException {
eof = true;
checkThrowEof("handleEof()");
return EOF;
}
/**
* Marks the current position.
*
* @param readLimit The number of bytes before this marked position is invalid.
* @throws UnsupportedOperationException if mark is not supported.
*/
@Override
public synchronized void mark(final int readLimit) {
if (!markSupported) {
throw UnsupportedOperationExceptions.mark();
}
mark = position;
this.readLimit = readLimit;
}
/**
* Tests whether <i>mark</i> is supported.
*
* @return Whether <i>mark</i> is supported or not.
*/
@Override
public boolean markSupported() {
return markSupported;
}
/**
* Returns a byte value for the {@code read()} method.
* <p>
* This implementation returns zero.
*
* @return This implementation always returns zero.
*/
protected int processByte() {
// do nothing - overridable by subclass
return 0;
}
/**
* Processes the bytes for the {@code read(byte[], offset, length)} method.
* <p>
* This implementation leaves the byte array unchanged.
* </p>
*
* @param bytes The byte array
* @param offset The offset to start at.
* @param length The number of bytes.
*/
protected void processBytes(final byte[] bytes, final int offset, final int length) {
// do nothing - overridable by subclass
}
/**
* Reads a byte.
*
* @return Either The byte value returned by {@code processByte()} or {@code -1} if the end of file has been reached and {@code throwEofException} is set to
* {@code false}.
* @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public int read() throws IOException {
if (eof) {
checkThrowEof("read()");
return EOF;
}
if (position == size) {
return handleEof();
}
position++;
return processByte();
}
/**
* Reads some bytes into the specified array.
*
* @param bytes The byte array to read into
* @return The number of bytes read or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
* @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public int read(final byte[] bytes) throws IOException {
return read(bytes, 0, bytes.length);
}
/**
* Reads the specified number bytes into an array.
*
* @param bytes The byte array to read into.
* @param offset The offset to start reading bytes into.
* @param length The number of bytes to read.
* @return The number of bytes read or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
* @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public int read(final byte[] bytes, final int offset, final int length) throws IOException {
if (eof) {
checkThrowEof("read(byte[], int, int)");
return EOF;
}
if (position == size) {
return handleEof();
}
position += length;
int returnLength = length;
if (position > size) {
returnLength = length - (int) (position - size);
position = size;
}
processBytes(bytes, offset, returnLength);
return returnLength;
}
/**
* Resets 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 exceeded since the last position was marked.
*/
@Override
public synchronized void reset() throws IOException {
if (!markSupported) {
throw UnsupportedOperationExceptions.reset();
}
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;
}
/**
* Skips a specified number of bytes.
*
* @param numberOfBytes The number of bytes to skip.
* @return The number of bytes skipped or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
* @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public long skip(final long numberOfBytes) throws IOException {
if (eof) {
checkThrowEof("skip(long)");
return EOF;
}
if (position == size) {
return handleEof();
}
position += numberOfBytes;
long returnLength = numberOfBytes;
if (position > size) {
returnLength = numberOfBytes - (position - size);
position = size;
}
return returnLength;
}
}