Java之NIO传输数据
NIO可谓陈词旧调,不值一提. 但之前都是泛泛而谈, 现在深入应用才知道秘诀所在. 对于SocketChannel有read()与write(),但由于"非阻塞IO"本质, 这二个方法的返回值提示其字符数目. 说白点, 就是你得有个措施解决可能一次不能完成的操作. 否则, 你在服务端的数据会莫名其妙地乱码, 莫名其妙地不见...
还有另一个关键之处就是Buffer的应用, 重用Buffer的时候务必注意, position, limit的标点. 下面是实质源码:
private void onAccept(SelectionKey key) {
logger.debug("处理Accept事件");
SocketChannel sc = null;
try {
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
sc = ssc.accept();
/* 判断其是否可以连接 */
String client = ((InetSocketAddress) sc.socket().getRemoteSocketAddress()).getAddress().getHostAddress();
if (config.senders.containsKey(client)) {
/* 前缀格式<系统>+<服务器IP>+ */
String prefix = config.senders.getProperty(client);
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ, new AttachObject(encoder.encode(prefix.toString(), config.charset)));
logger.info(String.format("发送者%s连接成功, 记录前缀:%s", client, prefix));
} else {
logger.info(String.format("发送者%s连接拒绝", client));
sc.close();
}
} catch (Exception e) {
logger.error("处理Accept事件错误!", e);
if (sc != null) {
try {
sc.close();
} catch (IOException e1) {
logger.error("关闭异常Socket错误!", e1);
}
}
}
}
使用InetAddress.getHostAddress()才能获取实际意义上的IP.
private void onRead(SelectionKey key) {
/* 必须注意NIO可能无法一次接收完全部数据 */
logger.debug("处理Read事件");
int ret = 0;
int size = 0;
SocketChannel sc = null;
try {
sc = (SocketChannel) key.channel();
AttachObject attach = (AttachObject) key.attachment();
if (attach.idx < 4) {
ret = sc.read(attach.sizeBuf);
if (ret == -1) {
logger.debug("客户端输入流已关闭!");
sc.close();
sc = null;
return;
} else {
attach.idx += ret;
}
}
if (attach.idx == 4) {
attach.sizeBuf.flip();
size = attach.sizeBuf.getInt();
attach.tot = 4 + size;
if (attach.dataBuf.capacity() < size) {
attach.dataBuf = ByteBuffer.allocate(size);
}else {
attach.dataBuf.limit(size);/* 必须限制可读字节数,否则可能读多 */
}
}
if (attach.idx >= 4 && attach.idx < attach.tot) {
ret = sc.read(attach.dataBuf);
if (ret == -1) {
logger.debug("客户端输入流已关闭!");
sc.close();
sc = null;
return;
} else {
attach.idx += ret;
}
}
if (attach.idx == attach.tot) {
attach.dataBuf.flip();
cache.put((byte[]) attach.attach, attach.dataBuf.array(), 0, attach.dataBuf.limit());
attach.reset();
}
} catch (Exception e) {
logger.error("处理Read事件错误!", e);
if (sc != null) {
try {
sc.close();
} catch (IOException e1) {
logger.error("关闭异常Socket错误!", e1);
}
}
}
}
每个Key要有独享的Attachment来保存中间信息, 使用Buffer读取或写入字节务必注意其返回值. 必须在字节数完全读完才能去解码.
public void run() {
ByteBuffer sizeBuf = ByteBuffer.allocate(4);
int idx = 0;
int tot = 0;
LinkedList<byte[]> batch = new LinkedList<byte[]>();
try {
SocketChannel sc = SocketChannel.open();
sc.connect(new InetSocketAddress(outer.config.receiverHost, outer.config.receiverPort));
outer.scList.add(sc);
while (!Thread.currentThread().isInterrupted()) {
batch.clear();
if (outer.cache.get(batch, outer.config.senderBatchSize, true) > 0) {
for (byte[] data : batch) {
/* 必须注意,NIO有可能不会一次写完Buffer的字节 */
idx = 0;
tot = 4 + data.length;
sizeBuf.clear();
sizeBuf.putInt(data.length);
sizeBuf.flip();
do {
idx += sc.write(sizeBuf);
} while (idx < 4);
ByteBuffer dataBuf = ByteBuffer.wrap(data);
do {
idx += sc.write(dataBuf);
} while (idx < tot);
}
}
}
} catch (IOException e) {
throw new RuntimeException(e);
}
}
使用Buffer写字节数据也必须注意其返回值, 在未达到预期时, 使用循环继续.
以上三个方法是Socket NIO的关键所在. 当你接收到的数据乱码的时候,你会想起这些...
