uk.ac.starlink.table.formats.LineSequence Maven / Gradle / Ivy
package uk.ac.starlink.table.formats;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
* Utility class which can read lines from an ASCII input stream.
* You can also push lines back if you want to unread them.
*
* @author Mark Taylor
* @since 7 Feb 2006
*/
class LineSequence {
private final InputStream in_;
private final StringBuffer sbuf_;
private final List readyLines_;
/**
* Constructs a new LineSequence.
*
* @param in input stream providing the data
*/
public LineSequence( InputStream in ) {
in_ = in;
sbuf_ = new StringBuffer();
readyLines_ = new ArrayList();
}
/**
* Returns the next line to read from the stream.
* If the stream is empty, null is returned.
* The line will not contain a terminating newline.
* Lines terminated by a "\n" or "\r\n" are recognised.
* Characters are assumed 8-bit.
* The line which is returned is either a newly-read one, or one which
* has previously been read and then pushed back using
* {@link #replaceLine}.
*
* @return next unread line, or null for end of stream
*/
public String nextLine() throws IOException {
if ( readyLines_.size() > 0 ) {
return readyLines_.remove( 0 );
}
else {
sbuf_.setLength( 0 );
for ( int v; ( v = in_.read() ) >= 0; ) {
char c = (char) v;
if ( c == '\n' ) {
return trimCr( sbuf_ );
}
else {
sbuf_.append( c );
}
}
if ( sbuf_.length() > 0 ) {
return trimCr( sbuf_ );
}
else {
return null;
}
}
}
/**
* Unreads a line. The submitted string line is replaced
* in the input so that a subsequent invocation of {@link #nextLine}
* will retrieve it before doing a new read from the stream.
* line doesn't actually have to be a line which was
* previously read, though that's generally what this method is intended
* for.
*
* @param line line to push back
*/
public void replaceLine( String line ) {
readyLines_.add( line );
}
/**
* Returns the string content of a character sequence, with any trailing
* CR ("\r") character removed.
* This can be used on input lines so that "\r\n" line endings
* are treated the same as "\n" line endings.
*
* @param sbuf character sequence that may or may not end
* with a single CR
* @return string value that does not include any single trailing CR
* from the input
* @see Goldfarb's First Law of Text Processing
*/
private String trimCr( CharSequence line ) {
int leng = line.length();
int iEnd = leng > 0 && line.charAt( leng - 1 ) == '\r'
? leng - 1
: leng;
return line.subSequence( 0, iEnd ).toString();
}
}