Question

Good day,

I am having some trouble. I am trying to send a character array over the network to a server.

here is my code:

char[] arr= {3,4};    
public void sendMessage(String message){
    if (out != null && !out.checkError()) {
        out.print(arr);
        out.flush();
    }
}

When I run that, lanshark detects that it recieved a packet with 2 bytes of data. ok good all is well.

Now when i run this:

 char[] arr= {3,160};      // notice 160 *****
public void sendMessage(String message){
    if (out != null && !out.checkError()) {
        out.print(arr);
        out.flush();
    }
}

lanshark says that the packet has 3 bytes of data? the exact data is :

03 c2 a0

Now why is it adding the c2 in there? i understand that it has some thing to do with the fact that my char is bigger than 127. But i need to send this value of 160 .

Please can you help me. Do i need to use another type of data, or send it in a different way? I know you can do this in C. How can i do it in java?

here is the code for my out object:

PrintWriter out;
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);

Thanks

Answer 1

In fact, the program is doing exactly what you told it to do. It is sending two characters; i.e. the unicode codepoints 3 (\u0003) and 160 (\u00a0). These characters are being encoded using your platform’s default character encoding … which appears to be UTF-8. The bytes c2 a0 are the UTF-8 encoding for the \u00a0 character.

But what you are actually trying to do is send 2 bytes.

In Java char is a 16 bit type, not an 8 bit type. If you want to send 8 bit values you need to use the byte type.

The other mistake you are making is that you are trying to send (essentially) binary data using a Writer. The Writer interface is for (16-bit) character oriented data. You should be using the OutputStream API …

Anyhow … here’s a code snippet to illustrate how you should send an array of bytes;

byte[] arr = new byte[]{3, (byte) 160);
OutputStream out = socket.getOutputStream();
out.write(arr);

---

I just changed it to that now, ” out.print(new String(arr).getBytes(Charset.forName(“UTF-8″))); ” and this is the data i get on wireshark: 11 bytes : 5b42403431653230396538 it should still be 2 bytes?

You are making it worse!

Lets take this apart:

• new String(arr) gives you a 2 character String.
• .getBytes(...) will turn that into a 3 byte array containing the bytes 03 c2 a0.
• out.print(...) will attempt to call a print method on the PrintWriter API.

But which one? Well you supplied an argument whose declared type is byte[]. And that will result in you calling print(Object).

But wait a minute … what does PrintWriter.print(Object) do? Well the first thing is that it does is to call toString() on the argument.

And what does that do? Well since the object is a byte[], this calls the default toString() method provided by java.lang.Object. And that gives you a String that looks like B[@xxxxxxxx where [B is the “class name” for a byte array, and the sequence of xs is a hexadecimal representation of the array object’s identity hashcode!

And then you output that that String.

And behold your 2 bytes (actually characters) have turned into 11 bytes.