ChannelUtil.java

package proj.zoie.api.impl.util;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;

public class ChannelUtil {
  public static long writeInt(WritableByteChannel channel, int val) throws IOException {
    ByteBuffer buf = ByteBuffer.allocate(4);
    buf.putInt(val);
    buf.rewind();
    return writeByteBuffer(channel, buf, 4);
  }

  public static long writeLong(WritableByteChannel channel, long val) throws IOException {
    ByteBuffer buf = ByteBuffer.allocate(8);
    buf.putLong(val);
    buf.rewind();
    return writeByteBuffer(channel, buf, 8);
  }

  /**
   * Writes bytes from buf to the channel until at least bytesToWrite number of bytes are written.
   * @param channel the destination channel
   * @param buf the source buffer
   * @param t the number of bytes to write
   * @return the number of bytes written
   * @throws IOException
   */
  private static int writeByteBuffer(WritableByteChannel channel, ByteBuffer buf, int bytesToWrite)
      throws IOException {
    int t = bytesToWrite; // remaining bytes to write
    while (t > 0) {
      t -= channel.write(buf);
    }
    return bytesToWrite - t;
  }

  public static long writeString(WritableByteChannel channel, String val) throws IOException {
    int len = val.length();
    int size;
    ByteBuffer buf = ByteBuffer.allocate(size = 4 + 2 * len);
    buf.putInt(len);
    for (int i = 0; i < len; i++) {
      buf.putChar(val.charAt(i));
    }
    buf.rewind();
    return writeByteBuffer(channel, buf, size);
  }

  public static int readInt(ReadableByteChannel channel) throws IOException {
    ByteBuffer buf = ByteBuffer.allocate(4);
    if (fillBuffer(channel, buf, true)) {
      buf.rewind();
      return buf.getInt();
    }
    return -1;
  }

  public static long readLong(ReadableByteChannel channel) throws IOException {
    ByteBuffer buf = ByteBuffer.allocate(8);
    if (fillBuffer(channel, buf, true)) {
      buf.rewind();
      return buf.getLong();
    }
    return -1L;
  }

  public static String readString(ReadableByteChannel channel) throws IOException {
    int nameLen = readInt(channel); // name length
    if (nameLen < 0) return null;

    ByteBuffer buf = ByteBuffer.allocate(nameLen * 2);
    if (fillBuffer(channel, buf, true)) {
      char[] name = new char[nameLen];
      buf.rewind();
      for (int i = 0; i < nameLen; i++) {
        name[i] = buf.getChar();
      }
      return new String(name);
    }
    return null;
  }

  public static boolean fillBuffer(ReadableByteChannel channel, ByteBuffer buf, boolean clear)
      throws IOException {
    if (clear) buf.clear();

    while (true) {
      int cnt = channel.read(buf);
      if (cnt < 0) return false;
      if (buf.position() == buf.capacity()) break;// fill to capacity
    }
    return true;
  }
}