import java.io.IOException;
import java.io.OutputStream;  public interface Framer {  void frameMsg(byte[] message, OutputStream out) throws IOException;  byte[] nextMsg() throws IOException;
}  

import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;  public class DelimFramer implements Framer {  private InputStream in;        // 数据来源  private static final byte DELIMITER = '\n'; // 定界符  public DelimFramer(InputStream in) {  this.in = in;  }  public void frameMsg(byte[] message, OutputStream out) throws IOException {  for (byte b : message) {  if (b == DELIMITER) {  //如果在消息中检查到界定符，则抛出异常  throw new IOException("Message contains delimiter");  }  }  out.write(message);  out.write(DELIMITER);  out.flush();  }  public byte[] nextMsg() throws IOException {  ByteArrayOutputStream messageBuffer = new ByteArrayOutputStream();  int nextByte;  while ((nextByte = in.read()) != DELIMITER) {  //如果流已经结束还没有读取到定界符  if (nextByte == -1) {   //如果读取到的流为空，则返回null  if (messageBuffer.size() == 0) {   return null;  } else {   //如果读取到的流不为空，则抛出异常  throw new EOFException("Non-empty message without delimiter");  }  }  messageBuffer.write(nextByte);   }  return messageBuffer.toByteArray();  }
}  

import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;  public class LengthFramer implements Framer {  public static final int MAXMESSAGELENGTH = 65535;  public static final int BYTEMASK = 0xff;  public static final int SHORTMASK = 0xffff;  public static final int BYTESHIFT = 8;  private DataInputStream in;  public LengthFramer(InputStream in) throws IOException {  this.in = new DataInputStream(in);    //数据来源
  }  //对字节流message添加成帧信息，并输出到指定流   public void frameMsg(byte[] message, OutputStream out) throws IOException {  //消息的长度不能超过65535  if (message.length > MAXMESSAGELENGTH) {  throw new IOException("message too long");  }  out.write((message.length >> BYTESHIFT) & BYTEMASK);  out.write(message.length & BYTEMASK);  out.write(message);  out.flush();  }  public byte[] nextMsg() throws IOException {  int length;  try {   //该方法读取2个字节，将它们作为big-endian整数进行解释，并以int型整数返回它们的值  length = in.readUnsignedShort();   } catch (EOFException e) { // no (or 1 byte) message  return null;  }  // 0 <= length <= 65535  byte[] msg = new byte[length];  //该方法处阻塞等待，直到接收到足够的字节来填满指定的数组
    in.readFully(msg);   return msg;  }
}