Jackson is "the Java JSON library" or "the best JSON parser for Java". Or simply as "JSON for Java".

Jackson Core Source Code files are provided in the source packge (jackson-core-2.14.0-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Core Source Code below:

⏎ com/fasterxml/jackson/core/util/ByteArrayBuilder.java

/* Jackson JSON-processor.
 *
 * Copyright (c) 2007- Tatu Saloranta, tatu.saloranta@iki.fi
 */

package com.fasterxml.jackson.core.util;

import java.io.OutputStream;
import java.util.*;

/**
 * Helper class that is similar to {@link java.io.ByteArrayOutputStream}
 * in usage, but more geared to Jackson use cases internally.
 * Specific changes include segment storage (no need to have linear
 * backing buffer, can avoid reallocations, copying), as well API
 * not based on {@link java.io.OutputStream}. In short, a very much
 * specialized builder object.
 *<p>
 * Also implements {@link OutputStream} to allow
 * efficient aggregation of output content as a byte array, similar
 * to how {@link java.io.ByteArrayOutputStream} works, but somewhat more
 * efficiently for many use cases.
 *<p>
 * NOTE: maximum size limited to Java Array maximum, 2 gigabytes: this
 * because usage pattern is to collect content for a `byte[]` and so although
 * theoretically this builder can aggregate more content it will not be usable
 * as things are. Behavior may be improved if we solve the access problem.
 */
public final class ByteArrayBuilder extends OutputStream
{
    public final static byte[] NO_BYTES = new byte[0];
    
    // Size of the first block we will allocate.
    private final static int INITIAL_BLOCK_SIZE = 500;
    
    // Maximum block size we will use for individual non-aggregated blocks.
    // For 2.10, let's limit to using 128k chunks (was 256k up to 2.9)
    private final static int MAX_BLOCK_SIZE = (1 << 17);

    final static int DEFAULT_BLOCK_ARRAY_SIZE = 40;

    // Optional buffer recycler instance that we can use for allocating the first block.
    private final BufferRecycler _bufferRecycler;
    private final LinkedList<byte[]> _pastBlocks = new LinkedList<byte[]>();
    
    // Number of bytes within byte arrays in {@link _pastBlocks}.
    private int _pastLen;
    private byte[] _currBlock;
    private int _currBlockPtr;

    public ByteArrayBuilder() { this(null); }
    public ByteArrayBuilder(BufferRecycler br) { this(br, INITIAL_BLOCK_SIZE); }
    public ByteArrayBuilder(int firstBlockSize) { this(null, firstBlockSize); }

    public ByteArrayBuilder(BufferRecycler br, int firstBlockSize) {
        _bufferRecycler = br;
        // 04-Sep-2020, tatu: Let's make this bit more robust and refuse to allocate
        //    humongous blocks even if requested
        if (firstBlockSize > MAX_BLOCK_SIZE) {
            firstBlockSize = MAX_BLOCK_SIZE;
        }
        _currBlock = (br == null) ? new byte[firstBlockSize] : br.allocByteBuffer(BufferRecycler.BYTE_WRITE_CONCAT_BUFFER);
    }

    private ByteArrayBuilder(BufferRecycler br, byte[] initialBlock, int initialLen) {
        _bufferRecycler = null;
        _currBlock = initialBlock;
        _currBlockPtr = initialLen;
    }

    public static ByteArrayBuilder fromInitial(byte[] initialBlock, int length) {
        return new ByteArrayBuilder(null, initialBlock, length);
    }
    
    public void reset() {
        _pastLen = 0;
        _currBlockPtr = 0;

        if (!_pastBlocks.isEmpty()) {
            _pastBlocks.clear();
        }
    }

    /**
     * @return Number of bytes aggregated so far
     *
     * @since 2.9
     */
    public int size() {
        return _pastLen + _currBlockPtr;
    }

    /**
     * Clean up method to call to release all buffers this object may be
     * using. After calling the method, no other accessors can be used (and
     * attempt to do so may result in an exception)
     */
    public void release() {
        reset();
        if (_bufferRecycler != null && _currBlock != null) {
            _bufferRecycler.releaseByteBuffer(BufferRecycler.BYTE_WRITE_CONCAT_BUFFER, _currBlock);
            _currBlock = null;
        }
    }

    public void append(int i) {
        if (_currBlockPtr >= _currBlock.length) {
            _allocMore();
        }
        _currBlock[_currBlockPtr++] = (byte) i;
    }

    public void appendTwoBytes(int b16) {
        if ((_currBlockPtr + 1) < _currBlock.length) {
            _currBlock[_currBlockPtr++] = (byte) (b16 >> 8);
            _currBlock[_currBlockPtr++] = (byte) b16;
        } else {
            append(b16 >> 8);
            append(b16);
        }
    }

    public void appendThreeBytes(int b24) {
        if ((_currBlockPtr + 2) < _currBlock.length) {
            _currBlock[_currBlockPtr++] = (byte) (b24 >> 16);
            _currBlock[_currBlockPtr++] = (byte) (b24 >> 8);
            _currBlock[_currBlockPtr++] = (byte) b24;
        } else {
            append(b24 >> 16);
            append(b24 >> 8);
            append(b24);
        }
    }

    // @since 2.9
    public void appendFourBytes(int b32) {
        if ((_currBlockPtr + 3) < _currBlock.length) {
            _currBlock[_currBlockPtr++] = (byte) (b32 >> 24);
            _currBlock[_currBlockPtr++] = (byte) (b32 >> 16);
            _currBlock[_currBlockPtr++] = (byte) (b32 >> 8);
            _currBlock[_currBlockPtr++] = (byte) b32;
        } else {
            append(b32 >> 24);
            append(b32 >> 16);
            append(b32 >> 8);
            append(b32);
        }
    }
    
    /**
     * Method called when results are finalized and we can get the
     * full aggregated result buffer to return to the caller
     *
     * @return Aggregated contents as a {@code byte[]}
     */
    public byte[] toByteArray()
    {
        int totalLen = _pastLen + _currBlockPtr;
        
        if (totalLen == 0) { // quick check: nothing aggregated?
            return NO_BYTES;
        }
        byte[] result = new byte[totalLen];
        int offset = 0;

        for (byte[] block : _pastBlocks) {
            int len = block.length;
            System.arraycopy(block, 0, result, offset, len);
            offset += len;
        }
        System.arraycopy(_currBlock, 0, result, offset, _currBlockPtr);
        offset += _currBlockPtr;
        if (offset != totalLen) { // just a sanity check
            throw new RuntimeException("Internal error: total len assumed to be "+totalLen+", copied "+offset+" bytes");
        }
        // Let's only reset if there's sizable use, otherwise will get reset later on
        if (!_pastBlocks.isEmpty()) {
            reset();
        }
        return result;
    }

    /*
    /**********************************************************
    /* Non-stream API (similar to TextBuffer)
    /**********************************************************
     */

    /**
     * Method called when starting "manual" output: will clear out
     * current state and return the first segment buffer to fill
     *
     * @return Segment to use for writing
     */
    public byte[] resetAndGetFirstSegment() {
        reset();
        return _currBlock;
    }

    /**
     * Method called when the current segment buffer is full; will
     * append to current contents, allocate a new segment buffer
     * and return it
     *
     * @return Segment to use for writing
     */
    public byte[] finishCurrentSegment() {
        _allocMore();
        return _currBlock;
    }

    /**
     * Method that will complete "manual" output process, coalesce
     * content (if necessary) and return results as a contiguous buffer.
     * 
     * @param lastBlockLength Amount of content in the current segment
     * buffer.
     * 
     * @return Coalesced contents
     */
    public byte[] completeAndCoalesce(int lastBlockLength) {
        _currBlockPtr = lastBlockLength;
        return toByteArray();
    }

    public byte[] getCurrentSegment() { return _currBlock; }
    public void setCurrentSegmentLength(int len) { _currBlockPtr = len; }
    public int getCurrentSegmentLength() { return _currBlockPtr; }

    /*
    /**********************************************************
    /* OutputStream implementation
    /**********************************************************
     */

    @Override
    public void write(byte[] b) {
        write(b, 0, b.length);
    }

    @Override
    public void write(byte[] b, int off, int len)
    {
        while (true) {
            int max = _currBlock.length - _currBlockPtr;
            int toCopy = Math.min(max, len);
            if (toCopy > 0) {
                System.arraycopy(b, off, _currBlock, _currBlockPtr, toCopy);
                off += toCopy;
                _currBlockPtr += toCopy;
                len -= toCopy;
            }
            if (len <= 0) break;
            _allocMore();
        }
    }

    @Override
    public void write(int b) {
        append(b);
    }

    @Override public void close() { /* NOP */ }
    @Override public void flush() { /* NOP */ }

    /*
    /**********************************************************
    /* Internal methods
    /**********************************************************
     */

    private void _allocMore()
    {
        final int newPastLen = _pastLen + _currBlock.length;

        // 13-Feb-2016, tatu: As per [core#351] let's try to catch problem earlier;
        //     for now we are strongly limited by 2GB limit of Java arrays        
        if (newPastLen < 0) {
            throw new IllegalStateException("Maximum Java array size (2GB) exceeded by `ByteArrayBuilder`");
        }

        _pastLen = newPastLen;

        /* Let's allocate block that's half the total size, except
         * never smaller than twice the initial block size.
         * The idea is just to grow with reasonable rate, to optimize
         * between minimal number of chunks and minimal amount of
         * wasted space.
         */
        int newSize = Math.max((_pastLen >> 1), (INITIAL_BLOCK_SIZE + INITIAL_BLOCK_SIZE));
        // plus not to exceed max we define...
        if (newSize > MAX_BLOCK_SIZE) {
            newSize = MAX_BLOCK_SIZE;
        }
        _pastBlocks.add(_currBlock);
        _currBlock = new byte[newSize];
        _currBlockPtr = 0;
    }
}

⏎ com/fasterxml/jackson/core/util/ByteArrayBuilder.java

Or download all of them as a single archive file:

File name: jackson-core-2.14.0-sources.jar
File size: 497693 bytes
Release date: 2022-11-05
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