Put byte array to JSON and vice versa

63

Is it possible to put a byte[] (byte array) to JSON?

if so, how can I do that in java? then read that JSON and convert that field again to byte[]?

This question is tagged with java json bytearray

~ Asked on 2013-12-20 15:21:48

The Best Answer is


72

Here is a good example of base64 encoding byte arrays. It gets more complicated when you throw unicode characters in the mix to send things like PDF documents. After encoding a byte array the encoded string can be used as a JSON property value.

Apache commons offers good utilities:

 byte[] bytes = getByteArr();
 String base64String = Base64.encodeBase64String(bytes);
 byte[] backToBytes = Base64.decodeBase64(base64String);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding

Java server side example:

public String getUnsecureContentBase64(String url)
        throws ClientProtocolException, IOException {

            //getUnsecureContent will generate some byte[]
    byte[] result = getUnsecureContent(url);

            // use apache org.apache.commons.codec.binary.Base64
            // if you're sending back as a http request result you may have to
            // org.apache.commons.httpclient.util.URIUtil.encodeQuery
    return Base64.encodeBase64String(result);
}

JavaScript decode:

//decode URL encoding if encoded before returning result
var uriEncodedString = decodeURIComponent(response);

var byteArr = base64DecToArr(uriEncodedString);

//from mozilla
function b64ToUint6 (nChr) {

  return nChr > 64 && nChr < 91 ?
      nChr - 65
    : nChr > 96 && nChr < 123 ?
      nChr - 71
    : nChr > 47 && nChr < 58 ?
      nChr + 4
    : nChr === 43 ?
      62
    : nChr === 47 ?
      63
    :
      0;

}

function base64DecToArr (sBase64, nBlocksSize) {

  var
    sB64Enc = sBase64.replace(/[^A-Za-z0-9\+\/]/g, ""), nInLen = sB64Enc.length,
    nOutLen = nBlocksSize ? Math.ceil((nInLen * 3 + 1 >> 2) / nBlocksSize) * nBlocksSize : nInLen * 3 + 1 >> 2, taBytes = new Uint8Array(nOutLen);

  for (var nMod3, nMod4, nUint24 = 0, nOutIdx = 0, nInIdx = 0; nInIdx < nInLen; nInIdx++) {
    nMod4 = nInIdx & 3;
    nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << 18 - 6 * nMod4;
    if (nMod4 === 3 || nInLen - nInIdx === 1) {
      for (nMod3 = 0; nMod3 < 3 && nOutIdx < nOutLen; nMod3++, nOutIdx++) {
        taBytes[nOutIdx] = nUint24 >>> (16 >>> nMod3 & 24) & 255;
      }
      nUint24 = 0;

    }
  }

  return taBytes;
}

~ Answered on 2013-12-20 15:33:21


13

The typical way to send binary in json is to base64 encode it.

Java provides different ways to Base64 encode and decode a byte[]. One of these is DatatypeConverter.

Very simply

byte[] originalBytes = new byte[] { 1, 2, 3, 4, 5};
String base64Encoded = DatatypeConverter.printBase64Binary(originalBytes);
byte[] base64Decoded = DatatypeConverter.parseBase64Binary(base64Encoded);

You'll have to make this conversion depending on the json parser/generator library you use.

~ Answered on 2013-12-20 15:26:27


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