Example usage for javax.imageio.stream MemoryCacheImageOutputStream writeBits

Introduction

In this page you can find the example usage for javax.imageio.stream MemoryCacheImageOutputStream writeBits.

Prototype

public void writeBits(long bits, int numBits) throws IOException 

Source Link

Usage

From source file:org.apache.pdfbox.filter.LZWFilter.java

/**
 * {@inheritDoc}//from  ww w  .jav  a 2  s.c om
 */
@Override
protected void encode(InputStream rawData, OutputStream encoded, COSDictionary parameters) throws IOException {
    List<byte[]> codeTable = createCodeTable();
    int chunk = 9;

    byte[] inputPattern = null;
    final MemoryCacheImageOutputStream out = new MemoryCacheImageOutputStream(encoded);
    out.writeBits(CLEAR_TABLE, chunk);
    int foundCode = -1;
    int r;
    while ((r = rawData.read()) != -1) {
        byte by = (byte) r;
        if (inputPattern == null) {
            inputPattern = new byte[] { by };
            foundCode = by & 0xff;
        } else {
            inputPattern = Arrays.copyOf(inputPattern, inputPattern.length + 1);
            inputPattern[inputPattern.length - 1] = by;
            int newFoundCode = findPatternCode(codeTable, inputPattern);
            if (newFoundCode == -1) {
                // use previous
                chunk = calculateChunk(codeTable.size() - 1, 1);
                out.writeBits(foundCode, chunk);
                // create new table entry
                codeTable.add(inputPattern);

                if (codeTable.size() == 4096) {
                    // code table is full
                    out.writeBits(CLEAR_TABLE, chunk);
                    codeTable = createCodeTable();
                }

                inputPattern = new byte[] { by };
                foundCode = by & 0xff;
            } else {
                foundCode = newFoundCode;
            }
        }
    }
    if (foundCode != -1) {
        chunk = calculateChunk(codeTable.size() - 1, 1);
        out.writeBits(foundCode, chunk);
    }

    // PPDFBOX-1977: the decoder wouldn't know that the encoder would output 
    // an EOD as code, so he would have increased his own code table and 
    // possibly adjusted the chunk. Therefore, the encoder must behave as 
    // if the code table had just grown and thus it must be checked it is
    // needed to adjust the chunk, based on an increased table size parameter
    chunk = calculateChunk(codeTable.size(), 1);

    out.writeBits(EOD, chunk);

    // pad with 0
    out.writeBits(0, 7);

    // must do or file will be empty :-(
    out.flush();
    out.close();
}

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