1.1成員變量

private final ByteBufAllocator alloc;

private ByteBuffer buffer; private ByteBuffer tmpNioBuf; private int capacity; private boolean doNotFree;

1.2構造方法

protected UnpooledDirectByteBuf(ByteBufAllocator alloc, int initialCapacity, int maxCapacity) {super(maxCapacity);if (alloc == null) {throw new NullPointerException("alloc");}if (initialCapacity < 0) {throw new IllegalArgumentException("initialCapacity: " + initialCapacity);}if (maxCapacity < 0) {throw new IllegalArgumentException("maxCapacity: " + maxCapacity);}if (initialCapacity > maxCapacity) {throw new IllegalArgumentException(String.format("initialCapacity(%d) > maxCapacity(%d)", initialCapacity, maxCapacity));}this.alloc = alloc;setByteBuffer(ByteBuffer.allocateDirect(initialCapacity));}

2.動態擴展緩存

聯系一下上文的UploadHeapByteBuf的實現，其實發現好簡單的

3.寫操作

public ByteBuf setBytes(int index, ByteBuf src, int srcIndex, int length) {checkSrcIndex(index, length, srcIndex, src.capacity());if (src.nioBufferCount() > 0) {for (ByteBuffer bb: src.nioBuffers(srcIndex, length)) {int bbLen = bb.remaining();setBytes(index, bb);index += bbLen;}} else {src.getBytes(srcIndex, this, index, length);}return this;} public ByteBuf setBytes(int index, ByteBuffer src) {ensureAccessible();ByteBuffer tmpBuf = internalNioBuffer();if (src == tmpBuf) {src = src.duplicate();}tmpBuf.clear().position(index).limit(index + src.remaining());tmpBuf.put(src);return this;}

和Heap進行對比，非常容易發現，heap因為它就是堆，直接對array進行讀寫操作就行了，和內存的直接對索引操作形成了對比。
讀寫操作差不多，不再贅述。

總結

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