LineInputStream.java Source code

Introduction

Here is the source code for LineInputStream.java

Source

import java.io.*;

/**
 * This class is to support reading CRLF terminated lines that
 * contain only US-ASCII characters from an input stream. Provides
 * functionality that is similar to the deprecated 
 * <code>DataInputStream.readLine()</code>. Expected use is to read
 * lines as String objects from a RFC822 stream.
 *
 * It is implemented as a FilterInputStream, so one can just wrap 
 * this class around any input stream and read bytes from this filter.
 * 
 * @author John Mani
 */

public class LineInputStream extends FilterInputStream {

    private char[] lineBuffer = null; // reusable byte buffer

    public LineInputStream(InputStream in) {
        super(in);
    }

    /**
     * Read a line containing only ASCII characters from the input 
     * stream. A line is terminated by a CR or NL or CR-NL sequence.
     * A common error is a CR-CR-NL sequence, which will also terminate
     * a line.
     * The line terminator is not returned as part of the returned 
     * String. Returns null if no data is available. <p>
     *
     * This class is similar to the deprecated 
     * <code>DataInputStream.readLine()</code>
     */
    public String readLine() throws IOException {
        InputStream in = this.in;
        char[] buf = lineBuffer;

        if (buf == null)
            buf = lineBuffer = new char[128];

        int c1;
        int room = buf.length;
        int offset = 0;

        while ((c1 = in.read()) != -1) {
            if (c1 == '\n') // Got NL, outa here.
                break;
            else if (c1 == '\r') {
                // Got CR, is the next char NL ?
                int c2 = in.read();
                if (c2 == '\r') // discard extraneous CR
                    c2 = in.read();
                if (c2 != '\n') {
                    // If not NL, push it back
                    if (!(in instanceof PushbackInputStream))
                        in = this.in = new PushbackInputStream(in);
                    ((PushbackInputStream) in).unread(c2);
                }
                break; // outa here.
            }

            // Not CR, NL or CR-NL ...
            // .. Insert the byte into our byte buffer
            if (--room < 0) { // No room, need to grow.
                buf = new char[offset + 128];
                room = buf.length - offset - 1;
                System.arraycopy(lineBuffer, 0, buf, 0, offset);
                lineBuffer = buf;
            }
            buf[offset++] = (char) c1;
        }

        if ((c1 == -1) && (offset == 0))
            return null;

        return String.copyValueOf(buf, 0, offset);
    }
}