ByteBuf 笔记

/**
 * Netty 内存分配容器 ByteBuf
 */
public class ByteBufDemo {

    public void doAlloc(ChannelHandlerContext ctx, UserModel userModel) {
        // 初始化容器内存大小,
        ByteBuf byteBuf = ctx.alloc().directBuffer().capacity(1024);
        /**
         * 经验表明，Bytebuf的最佳实践是在IO通信线程的读写缓冲区使用DirectByteBuf，后端业务使用HeapByteBuf
         */
//        ByteBuf byteBurWriter = ctx.alloc().directBuffer().writeBytes(userModel.getProtoData().toByteArray);

    }

    public static void main(String[] args) throws Exception {
//        testUnpooledHeapBuffer();
//        testUnpooledDirectBuffer();
        testComposite();

    }

    // 直接缓冲区
    public static void testUnpooledDirectBuffer() throws Exception {
        // 未池化的直接缓冲区
        ByteBuf directBuffer = Unpooled.directBuffer(100);
        directBuffer.writeBytes("directBUffer".getBytes());
        //检查 ByteBuf 是否由数组支撑。如果不是，则这是一个直接缓冲区，是数组则应该放在堆内存
        if (!directBuffer.hasArray()) {
            int length = directBuffer.readableBytes();
            byte[] array = new byte[length];
            /**
             * 先读取两个字节
             * 结果如下： [114, 101, 99, 66, 85, 102, 102, 101, 114, 0, 0]
             * 11
             */
            directBuffer.readerIndex(2);
            /**
             * 将字节复制到数组
             * 未读取之前结果如下： [100, 105, 114, 101, 99, 66, 85, 102, 102, 101, 114]
             */
            directBuffer.getBytes(directBuffer.readerIndex(), array);
            System.out.println(Arrays.toString(array));
            System.out.println(length);
        }
    }

    // 堆缓冲区
    public static void testUnpooledHeapBuffer() {
        ByteBuf heapBuf = Unpooled.copiedBuffer("heap buffer", CharsetUtil.UTF_8);
        if (heapBuf.hasArray()) {
            byte[] array = heapBuf.array();
            int offerset = heapBuf.arrayOffset() + heapBuf.readerIndex();
            int length = heapBuf.readableBytes();

            System.out.println(Arrays.toString(array));
            System.out.println(offerset);
            System.out.println(length);
            /**
             * 结果如下：
             * [104, 101, 97, 100, 32, 98, 117, 102, 102, 101, 114, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
             * 0
             * 11
             */
        }
    }

    /**
     * 复合缓冲区
     * Netty 通过一个 ByteBuf 子类——CompositeByteBuf——实现了组合模式，它提供了一
     *  个将多个缓冲区表示为单个合并缓冲区的虚拟表示
     */
    public static void printCompositeBuf(CompositeByteBuf compbuf) {
        // 可读字节数
        int length = compbuf.readableBytes();
        byte[] array = new byte[length];
        compbuf.getBytes(compbuf.readerIndex(), array);
        System.out.println("array: " + Arrays.toString(array));
        System.out.println("length: " + length);
    }

    public static void testComposite() {
        // 复合缓冲区
        CompositeByteBuf messageBuf = Unpooled.compositeBuffer();
        ByteBuf headBuf = Unpooled.directBuffer(1024);
        headBuf.writeBytes("head buffer".getBytes(StandardCharsets.UTF_8));
//        ByteBuf headBuf = Unpooled.copiedBuffer("head buffer", StandardCharsets.UTF_8);
        ByteBuf bodyBuf = Unpooled.copiedBuffer("body buffer", StandardCharsets.UTF_8);

        //
        messageBuf.addComponents(headBuf, bodyBuf);
        System.out.println("headBuf 可读字节数： " + headBuf.readableBytes());
        System.out.println("BodyBuf 可读字节数： " + bodyBuf.readableBytes());
        System.out.println("messgeBuf可读字节数：  " + messageBuf.readableBytes());
        System.out.println("remove head before -------------");

        printCompositeBuf(messageBuf);

        for (ByteBuf buf : messageBuf) {
            System.out.println(buf.toString(StandardCharsets.UTF_8));
        }

        // 根据数组下标删除元素
        messageBuf.removeComponent(0);

        System.out.println("remove head after-------------");

        printCompositeBuf(messageBuf);

        for (ByteBuf buf : messageBuf) {
            System.out.println(buf.toString(StandardCharsets.UTF_8));
        }

        /**
         * 结果如下：
         * headBuf 可读字节数： 11
         * BodyBuf 可读字节数： 11
         * messgeBuf可读字节数：  0
         * remove head before -------------
         * array: []
         * length: 0
         * head buffer
         * body buffer
         * remove head after-------------
         * array: []
         * length: 0
         * body buffer
         */
    }

}

待完善