Java 实现 TCP 报文段构造、连接建立和拆除

以下是使用 Java 实现构造 TCP 报文段的代码：\n\njava\nimport java.util.Arrays;\n\npublic class TCPHeader {\n private int sourcePort;\n private int destinationPort;\n private int sequenceNumber;\n private int ackNumber;\n private int dataOffset;\n private boolean synFlag;\n private boolean ackFlag;\n private boolean finFlag;\n\n public TCPHeader(int sourcePort, int destinationPort, int sequenceNumber, int ackNumber, int dataOffset, boolean synFlag, boolean ackFlag, boolean finFlag) {\n this.sourcePort = sourcePort;\n this.destinationPort = destinationPort;\n this.sequenceNumber = sequenceNumber;\n this.ackNumber = ackNumber;\n this.dataOffset = dataOffset;\n this.synFlag = synFlag;\n this.ackFlag = ackFlag;\n this.finFlag = finFlag;\n }\n\n public byte[] getBytes() {\n byte[] bytes = new byte[20];\n bytes[0] = (byte) ((sourcePort >> 8) & 0xFF);\n bytes[1] = (byte) (sourcePort & 0xFF);\n bytes[2] = (byte) ((destinationPort >> 8) & 0xFF);\n bytes[3] = (byte) (destinationPort & 0xFF);\n bytes[4] = (byte) ((sequenceNumber >> 24) & 0xFF);\n bytes[5] = (byte) ((sequenceNumber >> 16) & 0xFF);\n bytes[6] = (byte) ((sequenceNumber >> 8) & 0xFF);\n bytes[7] = (byte) (sequenceNumber & 0xFF);\n bytes[8] = (byte) ((ackNumber >> 24) & 0xFF);\n bytes[9] = (byte) ((ackNumber >> 16) & 0xFF);\n bytes[10] = (byte) ((ackNumber >> 8) & 0xFF);\n bytes[11] = (byte) (ackNumber & 0xFF);\n bytes[12] = (byte) ((dataOffset << 4) & 0xF0);\n bytes[13] = 0;\n bytes[14] = 0;\n bytes[15] = 0;\n bytes[16] = (byte) (synFlag ? 2 : 0);\n bytes[17] = (byte) (ackFlag ? 16 : 0);\n bytes[18] = (byte) (finFlag ? 1 : 0);\n bytes[19] = 0;\n return bytes;\n }\n\n @Override\n public String toString() {\n return "TCPHeader{" +\n "sourcePort=" + sourcePort +\n ", destinationPort=" + destinationPort +\n ", sequenceNumber=" + sequenceNumber +\n ", ackNumber=" + ackNumber +\n ", dataOffset=" + dataOffset +\n ", synFlag=" + synFlag +\n ", ackFlag=" + ackFlag +\n ", finFlag=" + finFlag +\n '}';\n }\n}\n\n\n以下是使用 Java 实现 TCP 连接建立的三次握手过程的代码：\n\njava\nimport java.io.IOException;\nimport java.net.ServerSocket;\nimport java.net.Socket;\n\npublic class TCPThreeWayHandshake {\n public static void main(String[] args) {\n try {\n ServerSocket serverSocket = new ServerSocket(1234);\n System.out.println("Server listening on port 1234...");\n Socket clientSocket = serverSocket.accept();\n System.out.println("Client connected.");\n\n // 第一次握手：客户端发送 SYN 包\n TCPHeader synPacket = new TCPHeader(1234, 5678, 0, 0, 5, true, false, false);\n System.out.println("Client sends SYN packet: " + synPacket);\n\n // 第二次握手：服务端发送 SYN-ACK 包\n TCPHeader synAckPacket = new TCPHeader(5678, 1234, 0, 0, 5, true, true, false);\n System.out.println("Server sends SYN-ACK packet: " + synAckPacket);\n\n // 第三次握手：客户端发送 ACK 包\n TCPHeader ackPacket = new TCPHeader(1234, 5678, 0, 0, 5, false, true, false);\n System.out.println("Client sends ACK packet: " + ackPacket);\n\n clientSocket.close();\n serverSocket.close();\n } catch (IOException e) {\n e.printStackTrace();\n }\n }\n}\n\n\n以下是使用 Java 实现 TCP 连接拆除的过程的代码：\n\njava\nimport java.io.IOException;\nimport java.net.Socket;\n\npublic class TCPCloseConnection {\n public static void main(String[] args) {\n try {\n Socket socket = new Socket("localhost", 1234);\n System.out.println("Client connected to server.");\n\n // 请求关闭连接：客户端发送 FIN 包\n TCPHeader finPacket = new TCPHeader(1234, 5678, 0, 0, 5, false, false, true);\n System.out.println("Client sends FIN packet: " + finPacket);\n\n // 等待关闭连接：服务端发送 ACK 包\n TCPHeader ackPacket = new TCPHeader(5678, 1234, 0, 0, 5, false, true, false);\n System.out.println("Server sends ACK packet: " + ackPacket);\n\n // 关闭连接：服务端发送 FIN 包\n TCPHeader finPacket2 = new TCPHeader(5678, 1234, 0, 0, 5, false, false, true);\n System.out.println("Server sends FIN packet: " + finPacket2);\n\n // 确认关闭连接：客户端发送 ACK 包\n TCPHeader ackPacket2 = new TCPHeader(1234, 5678, 0, 0, 5, false, true, false);\n System.out.println("Client sends ACK packet: " + ackPacket2);\n\n socket.close();\n } catch (IOException e) {\n e.printStackTrace();\n }\n }\n}\n\n\n这些代码可以在 Java 的一个类中运行，可以看到连接建立和拆除过程中的相关信息。