Json/string/byte conversion operations (sending bytes to socket)

Question

I have a problem with converting JSON object to bytes. I need something like:

aJsonObject = new JSONObject();
// ...put somethin
string msg;

msg = aJsonObject.toString();
count = msg.countBytes(); //calculate how many bytes will string `msg` take

THEN I need to convert count to 2-element byte array (actually I need to send 16bit int to socket), convert msg to count-element byte array, link them together and send to TCP socket.

The most compliacted for me is to make count placed on exactly 16 bits.

Exactly same thing I need to do in reverse. Take 2 bytes, make them int, then read int-bytes from socket and eventually convert them to json.

I will be grateful for any help. Thanks in advance.

Remy Lebeau · Accepted Answer · 2018-01-20 07:18:51Z

2

A Java String uses UTF-16 encoding. To convert a String to a byte array, simply call the String.getBytes() method, specifying the desired byte encoding, such as UTF-8. Then read the array's length.

aJsonObject = new JSONObject();
// fill JSON as needed...
String msg = aJsonObject.toString();
byte[] bytes = msg.toBytes(StandardCharsets.UTF_8);
int count = bytes.length;
// use length and bytes as needed...

To reverse the process, simply pass the bytes to the String constructor, specifying the same byte encoding:

bytes[] bytes = ...;
String msg = new String(bytes, StandardCharsets.UTF_8);
// use msg as needed...

edited Jan 20, 2018 at 7:18

answered Jan 20, 2018 at 7:11

Remy Lebeau

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6 Comments

Pandita Over a year ago

Thanks for your answer! Problem with string conversion solved. What about making int count to be placed on exactly 2 bytes?

Remy Lebeau Over a year ago

@Pandita assuming the byte count is always <= 65535, simply typecast the int to short, or for transmission purposes, use DataOutputStream.writeShort().

Pandita Over a year ago

I don't think it is that simple. I mean I need to make int count to be uint16 (unsigned integer that is 16 bits large).

Remy Lebeau Over a year ago

@Pandita I know what you want. What I said will work for that

Pandita Over a year ago

Casting to short didn't work, but I found solution: int count = bytes.length; byte[] data = new byte[2]; data[0] = (byte) (count & 0xFF); data[1] = (byte) ((count >> 8) & 0xFF); Then I send it to ByteArrayOutputStream, concatenate it with msg bytes and use DataOutputStream.write(bytearray) to send whole byte array. Thank you very much!

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