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JPEGBuffer.javaAPI DocJava SE 5 API7564Fri Aug 26 14:54:42 BST 2005com.sun.imageio.plugins.jpeg

JPEGBuffer

public class JPEGBuffer extends Object
A class wrapping a buffer and its state. For efficiency, the members are made visible to other classes in this package.

Fields Summary
private boolean
debug
final int
BUFFER_SIZE
The size of the buffer. This is large enough to hold all known marker segments (other than thumbnails and icc profiles)
byte[]
buf
The actual buffer.
int
bufAvail
The number of bytes available for reading from the buffer. Anytime data is read from the buffer, this should be updated.
int
bufPtr
A pointer to the next available byte in the buffer. This is used to read data from the buffer and must be updated to move through the buffer.
ImageInputStream
iis
The ImageInputStream buffered.
Constructors Summary
JPEGBuffer(ImageInputStream iis)


       
        buf = new byte[BUFFER_SIZE];
        bufAvail = 0;
        bufPtr = 0;
        this.iis = iis;
Methods Summary
longgetStreamPosition()
Return the stream position corresponding to the next available byte in the buffer.

        return (iis.getStreamPosition()-bufAvail);
voidloadBuf(int count)
Ensures that there are at least count bytes available in the buffer, loading more data and moving any remaining bytes to the front. A count of 0 means to just fill the buffer. If the count is larger than the buffer size, just fills the buffer. If the end of the stream is encountered before a non-0 count can be satisfied, an IIOException is thrown with the message "Image Format Error".

        if (debug) {
            System.out.print("loadbuf called with ");
            System.out.print("count " + count + ", ");
            System.out.println("bufAvail " + bufAvail + ", ");
        }
        if (count != 0) {
            if (bufAvail >= count) {  // have enough
                return;
            }
        } else {
            if (bufAvail == BUFFER_SIZE) {  // already full
                return;
            }
        }
        // First copy any remaining bytes down to the beginning
        if ((bufAvail > 0) && (bufAvail < BUFFER_SIZE)) {
            System.arraycopy(buf, bufPtr, buf, 0, bufAvail);
        }
        // Now fill the rest of the buffer
        int ret = iis.read(buf, bufAvail, buf.length - bufAvail);
        if (debug) {
            System.out.println("iis.read returned " + ret);
        }
        if (ret != -1) {
            bufAvail += ret;
        }
        bufPtr = 0;
        int minimum = Math.min(BUFFER_SIZE, count);
        if (bufAvail < minimum) {
            throw new IIOException ("Image Format Error");
        }
voidprint(int count)
Prints the contents of the buffer, in hex.

param
count the number of bytes to print, starting at the current available byte.

        System.out.print("buffer has ");
        System.out.print(bufAvail);
        System.out.println(" bytes available");
        if (bufAvail < count) {
            count = bufAvail;
        }
        for (int ptr = bufPtr; count > 0; count--) {
            int val = (int)buf[ptr++] & 0xff;
            System.out.print(" " + Integer.toHexString(val));
        }
        System.out.println();
voidpushBack()
Push back the remaining contents of the buffer by repositioning the input stream.

        iis.seek(iis.getStreamPosition()-bufAvail);
        bufAvail = 0;
        bufPtr = 0;
voidreadData(byte[] data)
Fills the data array from the stream, starting with the buffer and then reading directly from the stream if necessary. The buffer is left in an appropriate state. If the end of the stream is encountered, an IIOException is thrown with the message "Image Format Error".

        int count = data.length;
        // First see what's left in the buffer.
        if (bufAvail >= count) {  // It's enough
            System.arraycopy(buf, bufPtr, data, 0, count);
            bufAvail -= count;
            bufPtr += count;
            return;
        }
        int offset = 0;
        if (bufAvail > 0) {  // Some there, but not enough
            System.arraycopy(buf, bufPtr, data, 0, bufAvail);
            offset = bufAvail;
            count -= bufAvail;
            bufAvail = 0;
            bufPtr = 0;
        }
        // Now read the rest directly from the stream
        if (iis.read(data, offset, count) != count) {
            throw new IIOException ("Image format Error");
        }
booleanscanForFF(com.sun.imageio.plugins.jpeg.JPEGImageReader reader)
Scan the buffer until the next 0xff byte, reloading the buffer as necessary. The buffer position is left pointing to the first non-0xff byte after a run of 0xff bytes. If the end of the stream is encountered, an EOI marker is inserted into the buffer and true is returned. Otherwise returns false.

        boolean retval = false;
        boolean foundFF = false;
        while (foundFF == false) {
            while (bufAvail > 0) {
                if ((buf[bufPtr++] & 0xff) == 0xff) {
                    bufAvail--;
                    foundFF = true;
                    break;  // out of inner while
                }
                bufAvail--;
            }
            // Reload the buffer and keep going
            loadBuf(0);
            // Skip any remaining pad bytes
            if (foundFF == true) {
                while ((bufAvail > 0) && (buf[bufPtr] & 0xff) == 0xff) {
                    bufPtr++;  // Only if it still is 0xff
                    bufAvail--;
                }
            }
            if (bufAvail == 0) {  // Premature EOF
                // send out a warning, but treat it as EOI
                //reader.warningOccurred(JPEGImageReader.WARNING_NO_EOI);
                retval = true;
                buf[0] = (byte)JPEG.EOI;
                bufAvail = 1;
                bufPtr = 0;
                foundFF = true;
            }
        }
        return retval;
voidskipData(int count)
Skips count bytes, leaving the buffer in an appropriate state. If the end of the stream is encountered, an IIOException is thrown with the message "Image Format Error".

        // First see what's left in the buffer.
        if (bufAvail >= count) {  // It's enough
            bufAvail -= count;
            bufPtr += count;
            return;
        }
        if (bufAvail > 0) {  // Some there, but not enough
            count -= bufAvail;
            bufAvail = 0;
            bufPtr = 0;
        }
        // Now read the rest directly from the stream
        if (iis.skipBytes(count) != count) {
            throw new IIOException ("Image format Error");
        }