Java TCP简单通信带来了意想不到的结果

Question

I`m trying to send some simple data over TCP in my java program:

         String data = "70798090999a9b9c9d9e9fa0a1a2";
             ServerSocket srvr = new ServerSocket(1234);
             Socket skt = srvr.accept();
             OutputStream out = skt.getOutputStream();
             out.write(hexStringToByteArray(data));
             out.close();
             skt.close();
             srvr.close();

With function:

public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

And receive the data as:

     Socket skt = new Socket("localhost", 1234);
     BufferedReader in = new BufferedReader(new
        InputStreamReader(skt.getInputStream()));

     while (!in.ready()) {}
     while (in.ready()) {
     System.out.println(in.read()); // Read one line and output it
     }

But instead of receiving a list of numbers that increment themselves normally, I get something that increases and decreases at whim:

121
196
234
244
246
245
250
249
251
252
8224
176
162

Where am I doing something wrong?

Answer 1

You are sending byte array and reading one byte only.

You have to read using loop like the following:

byte[] arr = new byte[1024];
while (in.read(arr) >= 0) {
    // do something with the data.
}

This will work but still it is not what you really need. Really, you operate with strings but then transform string to byte array manually and then read bytes in order to manually transform them to String again?

Instead you should use PrintWriter to write strings:

PrintWriter writer = new PrintWriter(new OutputStreamWriter(out));
writer.write(str);

and then use BufferedReader when you are reading the data.

BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String line = reader.readLine();

Answer 2

If you want to send bytes, I suggest you read bytes, If you want to send text I suggest you read text. You shouldn't try to mix and match or you are likely to get yourself confused.

byte[] bytes = new BigInteger("70798090999a9b9c9d9e9fa0a1a2", 16).toByteArray();

ServerSocket ss = new ServerSocket(1234);
Socket c = new Socket("localhost", 1234);
Socket s = ss.accept();
final OutputStream out = s.getOutputStream();
out.write(bytes.length);
out.write(bytes);

final DataInputStream in = new DataInputStream(c.getInputStream());
int length = in.read();
byte[] bytes2 = new byte[length];
in.readFully(bytes2);

System.out.println(new BigInteger(1, bytes2).toString(16));
c.close();
s.close();
ss.close();

prints

70798090999a9b9c9d9e9fa0a1a2

Answer 3

Get rid of all the ready() tests. The reads will block until data arrives, so calling ready() is at heat literally a waste of time, and risks missing data.