通过java套接字发送数据的编码问题？

Question

我有以下代码。我可以很好地完成读取并将数据转换为十六进制。问题是当我发回String replyMessage = "7E81";时，设备收到它作为"3745"。哪里不对？这是由于我的编码，还是我需要做一些转换之前，我发回？

w = new BufferedWriter(new OutputStreamWriter(receivedSocketConn1.getOutputStream(),"ISO-8859-15")); // 
r = new BufferedReader(new InputStreamReader(receivedSocketConn1.getInputStream(),"ISO-8859-15")); 
int nextChar=0; 
while ((nextChar=r.read()) != -1) {    
    StringBuilder sb = new StringBuilder(); 
    sb.append(Integer.toHexString(nextChar)); 
    if (sb.length() < 2) { 
     sb.insert(0, '0'); // pad with leading zero if needed 
    } 
    String hexChar = sb.toString(); 
    System.out.println("\n\n hex value is "+Integer.toHexString(nextChar).toUpperCase()+" "+"Int value is:"+nextChar);   
    message = message+hexChar; 
    String messageID=message.substring(2,6); 
    System.out.println("messageId is :"+messageID); 
    if(messageID.equals("0100")){ 
     String replyMessage = "7E81"; 
     w.write(replyMessage+"\r\n"); 
     w.flush(); 
    } 
} 

Answer 1

基于在聊天评论：

文档说

起始字节（1个字节）7E
消息ID（2字节）01 00
消息正文自然（2字节）00 19
电话号码的设备（6字节）09 40 27 84 94 70
消息序列号（2字节）00 01
消息正文（N字节）00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 09 40 27 84 94 70 00
校验码（1字节）19
结束字节（1字节）7E

所以一开始和终止是7E

传出

起始字节（1个字节）7E
消息ID（2字节）81 00
留言身体性质（2字节）00 13
电话号码（6字节）09 40 27 84 94 70
消息序列号（2字节）00 01
消息正文（N字节）00 01 00 32 30 31 31 31 31 30 38 31 31 33 33 32 31 39 36
校验码（1字节）9A
结束字节（1字节）7E

这意味着有问题的协议是一个二进制协议，不发送十六进制的字符串，像你以为的文本协议。因此，您对OutputStreamWriter,InputStreamReader,StringBuilder,toHexString()等的使用全都是对此协议完全错误的。

接收到的每个消息和发送开始与固定13字节的标题，随后的可变长度体（标题指定体长度），并且通过一个固定的2个字节的注脚终止。

考虑到这一点，尝试一些更喜欢这个：

final protected static char[] hexArray = "ABCDEF".toCharArray(); 
public static String bytesToHex(byte[] bytes) { 
    char[] hexChars = new char[bytes.length * 2]; 
    for (int j = 0; j < bytes.length; j++) { 
     int v = bytes[j] & 0xFF; 
     hexChars[j * 2] = hexArray[v >>> 4]; 
     hexChars[j * 2 + 1] = hexArray[v & 0x0F]; 
    } 
    return new String(hexChars); 
} 

... 

w = new DataOutputStream(new BufferedOutputStream(receivedSocketConn1.getOutputStream())); 
r = new DataInputStream(new BufferedInputStream(receivedSocketConn1.getInputStream())); 

... 

if (r.readByte() != 0x7E) // start byte 
{ 
    // ah oh, something went wrong!! 
    receivedSocketConn1.close(); 
    return; 
} 

int messageID = r.readUnsignedShort();  // message ID 
int bodyLen = r.readUnsignedShort();  // message body nature (body length) 
byte[] phoneNum = new byte[6]; 
r.readFully(phoneNum);      // device phone number 
int serialNum = r.readUnsignedShort();  // message serial number 
byte[] messageBody = new byte[bodyLen]; // message body 
r.readFully(messageBody); 
byte checkCode = r.readByte();    // check code 

if (r.readByte() != 0x7E) // end byte 
{ 
    // ah oh, something went wrong!! 
    receivedSocketConn1.close(); 
    return; 
} 

// TODO: validate checkCode if needed... 

System.out.println("messageId is : 0x" + Integer.toHexString(messageID)); 
System.out.println("phoneNum is : " + bytesToHex(phoneNum)); 
System.out.println("serialNum is : 0x" + Integer.toHexString(serialNum)); 
System.out.println("messageBody is : " + bytesToHex(messageBody)); 

// process message data as needed... 

switch (messageID) 
{ 
    case 0x100: 
    { 
     // ... 

     byte[] replyBody = new byte[19]; 
     replyBody[0] = 0x00; 
     replyBody[1] = 0x01; 
     replyBody[2] = 0x00; 
     replyBody[3] = 0x32; 
     // and so on... 

     checkCode = 0x9A; // calculate as needed... 

     w.writeByte(0x7e);    // start byte 
     w.writeShort(0x8100);   // message ID 
     w.writeShort(replyBody.length); // message body nature (body length) 
     w.write(phoneNum);    // device phone number 
     w.writeShort(0x0001);   // message serial number 
     w.write(replyBody);    // message body 
     w.writeByte(checkCode);   // check code 
     w.writeByte(0x7e);    // end byte 

     break; 
    } 

    // other message IDs as needed... 
} 

w.flush();