panda.io.stream.NullReader Maven / Gradle / Ivy
package panda.io.stream;
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.
*
* This implementation provides a light weight object for testing with an {@link Reader} where the
* contents don't matter.
*
* 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.
*
* 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 processChar() and processChars() methods can be implemented to
* generate data, for example:
*
*
* 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
* }
* }
* }
*
*
*/
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(final 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 mark()
* functionality.
* @param throwEofException Whether this implementation will throw an {@link EOFException} or
* return -1 when the end of file is reached.
*/
public NullReader(final long size, final boolean markSupported, final 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(final int readlimit) {
if (!markSupported) {
throw new UnsupportedOperationException("Mark not supported");
}
mark = position;
this.readlimit = readlimit;
}
/**
* Indicates whether mark is supported.
*
* @return Whether mark is supported or not.
*/
@Override
public boolean markSupported() {
return markSupported;
}
/**
* Read a character.
*
* @return Either The character value returned by processChar() or -1
* if the end of file has been reached and throwEofException is set to
* {@code false}.
* @throws EOFException if the end of file is reached and 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) {
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 -1 if the end of file has been reached
* and throwEofException is set to {@code false}.
* @throws EOFException if the end of file is reached and throwEofException is set
* to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public int read(final 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 -1 if the end of file has been reached
* and throwEofException is set to {@code false}.
* @throws EOFException if the end of file is reached and throwEofException is set
* to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public int read(final char[] chars, final int offset, final 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 -1 if the end of file has been
* reached and throwEofException is set to {@code false}.
* @throws EOFException if the end of file is reached and throwEofException is set
* to {@code true}.
* @throws IOException if trying to read past the end of file.
*/
@Override
public long skip(final 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 read() method.
*
* 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 read(char[], offset, length) method.
*
* 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(final char[] chars, final int offset, final int length) {
// do nothing - overridable by subclass
}
/**
* Handle End of File.
*
* @return -1 if throwEofException is set to {@code false}
* @throws EOFException if throwEofException is set to {@code true}.
*/
private int doEndOfFile() throws EOFException {
eof = true;
if (throwEofException) {
throw new EOFException();
}
return -1;
}
}