Trace InputStream : Debug « Development Class « Java

Trace InputStream

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 * @(#)  1.8 07/05/04


 * This class is a FilterInputStream that writes the bytes
 * being read from the given input stream into the given output
 * stream. This class is typically used to provide a trace of
 * the data that is being retrieved from an input stream.
 * @author John Mani

public class TraceInputStream extends FilterInputStream {
    private boolean trace = false;
    private boolean quote = false;
    private OutputStream traceOut;

     * Creates an input stream filter built on top of the specified
     * input stream.
     * @param   in   the underlying input stream.
     * @param   out  the trace stream
    public TraceInputStream(InputStream in, OutputStream traceOut) {
  this.traceOut = traceOut;

     * Set trace mode.
     * @param trace the trace mode
    public void setTrace(boolean trace) {
  this.trace = trace;

     * Set quote mode.
     * @param quote the quote mode
    public void setQuote(boolean quote) {
  this.quote = quote;

     * Reads the next byte of data from this input stream. Returns
     * <code>-1</code> if no data is available. Writes out the read
     * byte into the trace stream, if trace mode is <code>true</code>
    public int read() throws IOException {
  int b =;
  if (trace && b != -1) {
      if (quote)
  return b;

     * Reads up to <code>len</code> bytes of data from this input stream
     * into an array of bytes. Returns <code>-1</code> if no more data
     * is available. Writes out the read bytes into the trace stream, if 
     * trace mode is <code>true</code>
    public int read(byte b[], int off, int len) throws IOException {
  int count =, off, len);
  if (trace && count != -1) {
      if (quote) {
    for (int i = 0; i < count; i++)
        writeByte(b[off + i]);
      } else
    traceOut.write(b, off, count);
  return count;

     * Write a byte in a way that every byte value is printable ASCII.
    private final void writeByte(int b) throws IOException {
  b &= 0xff;
  if (b > 0x7f) {
      b &= 0x7f;
  if (b == '\r') {
  } else if (b == '\n') {
  } else if (b == '\t') {
  } else if (b < ' ') {
      traceOut.write('@' + b);
  } else {


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