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package com.peterphi.std.io;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
/**
* A Reader whose source is a CharSequence (such as a StringBuilder or a StringBuffer).
* This is slightly faster than new StringReader(str.toString()) although it creates a greater number of (small) garbage
* objects
* Implementation based on that of {@link StringReader}
*/
public class CharSequenceReader extends Reader
{
private CharSequence str;
private int next = 0;
private int mark = 0;
public CharSequenceReader(final CharSequence str)
{
this.str = str;
}
private final int length()
{
return str.length();
}
/**
* Check to make sure that the stream has not been closed
*/
private void ensureOpen() throws IOException
{
if (str == null)
throw new IOException("Stream closed");
}
/**
* Reads a single character.
*
* @return The character read, or -1 if the end of the stream has been reached
*
* @throws IOException
* If an I/O error occurs
*/
@Override
public int read() throws IOException
{
synchronized (lock)
{
ensureOpen();
if (next >= length())
return -1;
return str.charAt(next++);
}
}
/**
* Reads characters into a portion of an array.
*
* @param cbuf
* Destination buffer
* @param off
* Offset at which to start writing characters
* @param len
* Maximum number of characters to read
*
* @return The number of characters read, or -1 if the end of the stream has been reached
*
* @throws IOException
* If an I/O error occurs
*/
@Override
public int read(char cbuf[], int off, int len) throws IOException
{
synchronized (lock)
{
ensureOpen();
if ((off < 0) || (off > cbuf.length) || (len < 0) || ((off + len) > cbuf.length) || ((off + len) < 0))
{
throw new IndexOutOfBoundsException();
}
else if (len == 0)
{
return 0;
}
if (next >= length())
return -1;
final int n = Math.min(length() - next, len);
// str.getChars(next, next + n, cbuf, off);
final String subsequence = str.subSequence(next, next + n).toString();
subsequence.getChars(0, n, cbuf, off);
next += n;
return n;
}
}
/**
* Skips the specified number of characters in the stream. Returns the number of characters that were skipped.
*
*
* The ns parameter may be negative, even though the skip method of the {@link Reader} superclass
* throws an exception in this case. Negative values of ns cause the stream to skip backwards. Negative return
* values indicate a skip backwards. It is not possible to skip backwards past the beginning of the string.
*
*
* If the entire string has been read or skipped, then this method has no effect and always returns 0.
*
* @throws IOException
* If an I/O error occurs
*/
@Override
public long skip(long ns) throws IOException
{
synchronized (lock)
{
ensureOpen();
if (next >= length())
return 0;
// Bound skip by beginning and end of the source
long n = Math.min(length() - next, ns);
n = Math.max(-next, n);
next += n;
return n;
}
}
/**
* Tells whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input
*
* @throws IOException
* If the stream is closed
*/
@Override
public boolean ready() throws IOException
{
synchronized (lock)
{
ensureOpen();
return true;
}
}
/**
* Tells whether this stream supports the mark() operation, which it does.
*/
@Override
public boolean markSupported()
{
return true;
}
/**
* Marks the present position in the stream. Subsequent calls to reset() will reposition the stream to this point.
*
* @param readAheadLimit
* Limit on the number of characters that may be read while still preserving the mark. Because the stream's input comes from
* a string, there is no actual limit, so this argument must not be negative, but is otherwise ignored.
*
* @throws IllegalArgumentException
* If readAheadLimit is < 0
* @throws IOException
* If an I/O error occurs
*/
@Override
public void mark(int readAheadLimit) throws IOException
{
if (readAheadLimit < 0)
{
throw new IllegalArgumentException("Read-ahead limit < 0");
}
synchronized (lock)
{
ensureOpen();
mark = next;
}
}
/**
* Resets the stream to the most recent mark, or to the beginning of the string if it has never been marked.
*
* @throws IOException
* If an I/O error occurs
*/
@Override
public void reset() throws IOException
{
synchronized (lock)
{
ensureOpen();
next = mark;
}
}
/**
* Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(),
* ready(), mark(), or reset() invocations will throw an IOException. Closing a previously closed stream has no effect.
*/
@Override
public void close()
{
str = null;
}
}