HeapByteBuffer 源码

HeapByteBuffer 源码分析

package java.nio;

class HeapByteBuffer extends ByteBuffer
{
    // ByteBuffer继承自Buffer
    // 实际是个byte数组
    protected final byte[] hb;
    // 偏移量，是byteBuffer用来控制从哪一个位置开始存储数组的标志
    protected final int offset;
    
    // 以下变量定义在父类里，ByteBuffer或Buffer里
    // 标记位，reset之后positon会跳到这里，进行重复读
    private int mark = -1;
    // 实际下一次读写的位置
    private int position = 0;
    // 有效数据的位置，读的时候为有效位置，写的时候为容量
    // limit后的数据不可读写，并且小于cap，必须大于mark
    private int limit;
    // 最大容量
    private int capacity;
    // 是否只读
    boolean isReadOnly;
    // 大端模式：数据的高位存储在低地址处，低位存储在高地址处
    boolean bigEndian = true;

    // 构造器，mark=-1，lim=cap，positon=0，offset=0
    HeapByteBuffer(int cap, int lim) {            
        super(-1, 0, lim, cap, new byte[cap], 0);
        /*
        hb = new byte[cap];
        offset = 0;
        */
    }

    // position为off，lim为off+len
    HeapByteBuffer(byte[] buf, int off, int len) { 

        super(-1, off, off + len, buf.length, buf, 0);
        /*
        hb = buf;
        offset = 0;
        */
    }

    protected HeapByteBuffer(byte[] buf,
                                   int mark, int pos, int lim, int cap,
                                   int off)
    {
        super(mark, pos, lim, cap, buf, off);
        /*
        hb = buf;
        offset = off;
        */
    }

    // this.remaining = lim - position
    public ByteBuffer slice() {
        return new HeapByteBuffer(hb,
                                        -1,
                                        0,
                                        this.remaining(),
                                        this.remaining(),
                                        this.position() + offset);
    }
    
    // 复制一个新的ByteBuffer
    public ByteBuffer duplicate() {
        return new HeapByteBuffer(hb,
                                        this.markValue(),
                                        this.position(),
                                        this.limit(),
                                        this.capacity(),
                                        offset);
    }

    public ByteBuffer asReadOnlyBuffer() {

        return new HeapByteBufferR(hb,
                                     this.markValue(),
                                     this.position(),
                                     this.limit(),
                                     this.capacity(),
                                     offset);
    }
    
    // 读取字节数组的偏移量
    protected int ix(int i) {
        return i + offset;
    }

    // 获取下一个字节
    public byte get() {
        return hb[ix(nextGetIndex())];
    }

    // 获取指定下标i的字节
    public byte get(int i) {
        return hb[ix(checkIndex(i))];
    }

    // 获取数组，实际是从postion位置跟进offset复制的
    public ByteBuffer get(byte[] dst, int offset, int length) {
        checkBounds(offset, length, dst.length);
        if (length > remaining())
            throw new BufferUnderflowException();
        // 系统数组复制
        System.arraycopy(hb, ix(position()), dst, offset, length);
        // 由于复制了offset个字符，所以下次position的位置变了，增加offset
        // position始终表示下次读写的位置
        position(position() + length);
        return this;
    }

    // 是否是直接存储的，不是，在堆上，GC自动回收
    // DirectByteBuffer就是堆外内存，不需要拷贝到内核读取，但是需要单独回收
    public boolean isDirect() {
        return false;
    }

    // 默认读写均可
    public boolean isReadOnly() {
        return false;
    }

    public ByteBuffer put(byte x) {

        hb[ix(nextPutIndex())] = x;
        return this;
    }

    public ByteBuffer put(int i, byte x) {

        hb[ix(checkIndex(i))] = x;
        return this;
    }

    public ByteBuffer put(byte[] src, int offset, int length) {

        checkBounds(offset, length, src.length);
        if (length > remaining())
            throw new BufferOverflowException();
        System.arraycopy(src, offset, hb, ix(position()), length);
        position(position() + length);
        return this;
    }

    public ByteBuffer put(ByteBuffer src) {
        if (src instanceof HeapByteBuffer) {
            if (src == this)
                throw new IllegalArgumentException();
            HeapByteBuffer sb = (HeapByteBuffer)src;
            int n = sb.remaining();
            // 如果put的数组长于现有数组剩余长度，插不进，报错
            if (n > remaining())
                throw new BufferOverflowException();
            System.arraycopy(sb.hb, sb.ix(sb.position()),
                             hb, ix(position()), n);
            // 由于两个对象都是ByteBuffer，所以都要偏移position
            sb.position(sb.position() + n);
            position(position() + n);
        } else if (src.isDirect()) {
            int n = src.remaining();
            if (n > remaining())
                throw new BufferOverflowException();
            src.get(hb, ix(position()), n);
            position(position() + n);
        } else {
            super.put(src);
        }
        return this;
    }
    
    // 压缩缓冲区
    public ByteBuffer compact() {
        // 将当前数组的从position+offset的位置复制到从0开始，容量为remaining大小
        System.arraycopy(hb, ix(position()), hb, ix(0), remaining());
        // 将position的位置设置到remaining
        position(remaining());
        // 将lim的位置设置到remaining
        limit(capacity());
        // 将mark设置为初始值-1
        discardMark();
        return this;
    }

    byte _get(int i) {                          
        return hb[i];
    }

    void _put(int i, byte b) {               
        hb[i] = b;
    }

    public char getChar() {
        return Bits.getChar(this, ix(nextGetIndex(2)), bigEndian);
    }

    public char getChar(int i) {
        return Bits.getChar(this, ix(checkIndex(i, 2)), bigEndian);
    }

    public ByteBuffer putChar(char x) {

        Bits.putChar(this, ix(nextPutIndex(2)), x, bigEndian);
        return this;
    }

    public ByteBuffer putChar(int i, char x) {
        Bits.putChar(this, ix(checkIndex(i, 2)), x, bigEndian);
        return this;
    }

    public CharBuffer asCharBuffer() {
        int size = this.remaining() >> 1;
        int off = offset + position();
        return (bigEndian
                ? (CharBuffer)(new ByteBufferAsCharBufferB(this,
                                                               -1,
                                                               0,
                                                               size,
                                                               size,
                                                               off))
                : (CharBuffer)(new ByteBufferAsCharBufferL(this,
                                                               -1,
                                                               0,
                                                               size,
                                                               size,
                                                               off)));
    }

    public short getShort() {
        return Bits.getShort(this, ix(nextGetIndex(2)), bigEndian);
    }

    public short getShort(int i) {
        return Bits.getShort(this, ix(checkIndex(i, 2)), bigEndian);
    }

    public ByteBuffer putShort(short x) {

        Bits.putShort(this, ix(nextPutIndex(2)), x, bigEndian);
        return this;
    }

    public ByteBuffer putShort(int i, short x) {
        Bits.putShort(this, ix(checkIndex(i, 2)), x, bigEndian);
        return this;
    }

    public ShortBuffer asShortBuffer() {
        int size = this.remaining() >> 1;
        int off = offset + position();
        return (bigEndian
                ? (ShortBuffer)(new ByteBufferAsShortBufferB(this,
                                                                 -1,
                                                                 0,
                                                                 size,
                                                                 size,
                                                                 off))
                : (ShortBuffer)(new ByteBufferAsShortBufferL(this,
                                                                 -1,
                                                                 0,
                                                                 size,
                                                                 size,
                                                                 off)));
    }

    public int getInt() {
        return Bits.getInt(this, ix(nextGetIndex(4)), bigEndian);
    }

    public int getInt(int i) {
        return Bits.getInt(this, ix(checkIndex(i, 4)), bigEndian);
    }

    public ByteBuffer putInt(int x) {

        Bits.putInt(this, ix(nextPutIndex(4)), x, bigEndian);
        return this;
    }

    public ByteBuffer putInt(int i, int x) {

        Bits.putInt(this, ix(checkIndex(i, 4)), x, bigEndian);
        return this;
    }

    public IntBuffer asIntBuffer() {
        int size = this.remaining() >> 2;
        int off = offset + position();
        return (bigEndian
                ? (IntBuffer)(new ByteBufferAsIntBufferB(this,
                                                             -1,
                                                             0,
                                                             size,
                                                             size,
                                                             off))
                : (IntBuffer)(new ByteBufferAsIntBufferL(this,
                                                             -1,
                                                             0,
                                                             size,
                                                             size,
                                                             off)));
    }

    public long getLong() {
        return Bits.getLong(this, ix(nextGetIndex(8)), bigEndian);
    }

    public long getLong(int i) {
        return Bits.getLong(this, ix(checkIndex(i, 8)), bigEndian);
    }

    public ByteBuffer putLong(long x) {

        Bits.putLong(this, ix(nextPutIndex(8)), x, bigEndian);
        return this;
    }

    public ByteBuffer putLong(int i, long x) {

        Bits.putLong(this, ix(checkIndex(i, 8)), x, bigEndian);
        return this;
    }

    public LongBuffer asLongBuffer() {
        int size = this.remaining() >> 3;
        int off = offset + position();
        return (bigEndian
                ? (LongBuffer)(new ByteBufferAsLongBufferB(this,
                                                               -1,
                                                               0,
                                                               size,
                                                               size,
                                                               off))
                : (LongBuffer)(new ByteBufferAsLongBufferL(this,
                                                               -1,
                                                               0,
                                                               size,
                                                               size,
                                                               off)));
    }

    public float getFloat() {
        return Bits.getFloat(this, ix(nextGetIndex(4)), bigEndian);
    }

    public float getFloat(int i) {
        return Bits.getFloat(this, ix(checkIndex(i, 4)), bigEndian);
    }

    public ByteBuffer putFloat(float x) {
        Bits.putFloat(this, ix(nextPutIndex(4)), x, bigEndian);
        return this;
    }

    public ByteBuffer putFloat(int i, float x) {

        Bits.putFloat(this, ix(checkIndex(i, 4)), x, bigEndian);
        return this;
    }

    public FloatBuffer asFloatBuffer() {
        int size = this.remaining() >> 2;
        int off = offset + position();
        return (bigEndian
                ? (FloatBuffer)(new ByteBufferAsFloatBufferB(this,
                                                                 -1,
                                                                 0,
                                                                 size,
                                                                 size,
                                                                 off))
                : (FloatBuffer)(new ByteBufferAsFloatBufferL(this,
                                                                 -1,
                                                                 0,
                                                                 size,
                                                                 size,
                                                                 off)));
    }

    public double getDouble() {
        return Bits.getDouble(this, ix(nextGetIndex(8)), bigEndian);
    }

    public double getDouble(int i) {
        return Bits.getDouble(this, ix(checkIndex(i, 8)), bigEndian);
    }

    public ByteBuffer putDouble(double x) {

        Bits.putDouble(this, ix(nextPutIndex(8)), x, bigEndian);
        return this;
    }

    public ByteBuffer putDouble(int i, double x) {

        Bits.putDouble(this, ix(checkIndex(i, 8)), x, bigEndian);
        return this;
    }

    public DoubleBuffer asDoubleBuffer() {
        int size = this.remaining() >> 3;
        int off = offset + position();
        return (bigEndian
                ? (DoubleBuffer)(new ByteBufferAsDoubleBufferB(this,
                                                                   -1,
                                                                   0,
                                                                   size,
                                                                   size,
                                                                   off))
                : (DoubleBuffer)(new ByteBufferAsDoubleBufferL(this,
                                                                   -1,
                                                                   0,
                                                                   size,
                                                                   size,
                                                                   off)));
    }











































}