1. buffer常规操作 略
2. 只读buffer
/**
* 只读buffer
*/
public class BufferTest01 {
public static void main(String[] args) {
IntBuffer buffer = IntBuffer.allocate(10); for (int i = 0; i < 10; i++) {
buffer.put(i);
} buffer.flip();
// 这个buffer1只能读
IntBuffer buffer1 = buffer.asReadOnlyBuffer(); for (int i = 0; i < 10; i++) {
System.out.println(buffer.get());
} // 如果再往buffer1中put数据,则会报错ReadOnlyBufferException
buffer1.put(10); }
}
3. 映射buffer
/**
* MappedByteBuffer 可以让文件直接在堆外内存中修改,这样操作系统不需要拷贝一次
*/
public class MappedByteBufferTest02 {
public static void main(String[] args) throws Exception {
RandomAccessFile file = new RandomAccessFile("1.txt", "rw");
// 获取对应的文件通道
FileChannel channel = file.getChannel();
/*
*FileChannel.MapMode.READ_WRITE: 表示是读写模式
* 0 : 可以修改的起始位置
* 5 : 我映射到内存的大小(不是索引), 即可以将文件1.txt的5个字节映射到内存, 你映射多少个字节 ,就可以修改多少个字节,
*/
MappedByteBuffer mappedByteBuffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, 5);
mappedByteBuffer.put(0, (byte) 'A');// 将第一个位置改成A
mappedByteBuffer.put(4, (byte) 'B'); //将第五个位置改成B file.close(); }
}
4. 分散与聚合
/**
* scattering : 将数据写入到buffer时,可以采用buffer数组 ,依次写入
* gathering : 从buffer读取数据时,可以采用buffer数组 ,依次读
*/
public class ScatteringAndGatheringTest {
public static void main(String[] args) throws Exception { // 使用ServerSocketChannel和SocketChannel
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
InetSocketAddress socketAddress = new InetSocketAddress(8888);
// 绑定端口到socket上,并启动socket服务
serverSocketChannel.socket().bind(socketAddress); ByteBuffer[] buffers = new ByteBuffer[2];
buffers[0] = ByteBuffer.allocate(5);
buffers[1] = ByteBuffer.allocate(3);
int total = 8;
// 等待客户端的连接
System.out.println("等待连接。。。。。");
SocketChannel socketChannel = serverSocketChannel.accept(); // 循环读取数据
while (true) {
int byteRead = 0;
while (byteRead < 8) {
long read = socketChannel.read(buffers);
byteRead += read;
System.out.println("已读取:" + byteRead);
// 流打印, 看看当前buffer的position和limit
Arrays.asList(buffers).stream().map(x -> "position=" + x.position() + ", limit = " + x.limit()).forEach(System.out::println);
} // 切换
Arrays.asList(buffers).forEach(x -> x.flip());
// 将读取出来的数据显示到客户端
long byteWrite = 0;
while (byteRead < total) {
long l = socketChannel.write(buffers);
byteWrite += l;
} // 复位操作 Arrays.asList(buffers).stream().map(x -> x.clear()); System.out.println("byteRead = " + byteRead + ", byteWrite = " + byteWrite + ", total =" + total); }
}
}