java - 通过java套接字发送数据的编码问题？

Question

我有以下代码。我可以很好地读取数据并将数据转换为十六进制。问题是，当我发回 StringreplyMessage = "7E81"; 时，设备将其接收为 "3745"。怎么了？是因为我的编码问题，还是需要在发回之前进行一些转换？

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

基于聊天中的评论:

the documentation say

Start Byte (1 Byte) 7e
Message ID (2 Byte) 01 00
Message Body Nature (2 Byte) 00 19
Phone no. of Device (6 Byte) 09 40 27 84 94 70
Message Serial number (2 Byte) 00 01
Message Body (N Byte) 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
Check Code (1Byte) 19
End Byte (1Byte) 7E

so the start and termination is 7E

for outgoing

Start Byte (1 Byte) 7e
Message ID (2 Byte) 81 00
Message Body Nature (2 Byte) 00 13
Phone no. of Device (6 Byte) 09 40 27 84 94 70
Message Serial number (2 Byte) 00 01
Message Body (N Byte) 00 01 00 32 30 31 31 31 31 30 38 31 31 33 33 32 31 39 36
Check Code (1Byte) 9A
End Byte (1Byte) 7e

这意味着所讨论的协议(protocol)是二进制协议(protocol)，而不是像您想象的那样发送十六进制字符串的文本协议(protocol)。因此，您对 OutputStreamWriter、InputStreamReader、StringBuilder、toHexString() 等的使用都是对于这个协议(protocol)来说完全错误。

接收和发送的每条消息都以固定的 13 字节 header 开始，后跟可变长度的正文( header 指定正文长度)，并以固定的 2 字节页脚结束。

考虑到这一点，尝试类似这样的事情:

final protected static char[] hexArray = "0123456789ABCDEF".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();