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I'm new to Java and I'm no sure how to do the following:

A Scala application somewhere converts a String into bytes: 

ByteBuffer.wrap(str.getBytes)

I collect this byte array as a Java String, and I wish to do the inverse of what the Scala code above did, hence get the original String (object str above).

Getting the ByteBuffer as a String to begin with is the only option I have, as I'm reading it from an AWS Kinesis stream (or is it?). The Scala code shouldn't change either.

Example string:

String str = "AAAAAAAAAAGZ7dFR0XmV23BRuufU+eCekJe6TGGUBBu5WSLIse4ERy9............";

How can this be achieved in Java?

EDIT

Okay, so I'll try to elaborate a little more about the process:

  1. A 3rd party Scala application produces CSV rows which I need to consume

  2. Before storing those rows in an AWS Kinesis stream, the application does the following to each row:

    ByteBuffer.wrap(output.getBytes);

  3. I read the data from the stream as a string, and the string could look like the following one:

    String str = "AAAAAAAAAAGZ7dFR0XmV23BRuufU+eCekJe6TGGUBBu5WSLIse4ERy9............";

  4. I need to restore the contents of the string above into its original, readable, form;

I hope I've made it clearer now, sorry for puzzling you all to begin with.

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5
  • Won't something like str.toCharArray.map(_.toByte) work in Java? Commented Sep 16, 2014 at 12:21
  • Possibly, but I'm not sure I unserstand what you did there with the map(_.toByte) part Commented Sep 16, 2014 at 12:34
  • 3
    "I read the data from the stream as a string" -- how? Do you just pass the byte array into a String constructor, or do you use some kind of encoding like base64? Commented Sep 16, 2014 at 13:12
  • 1
    I googled aws kinesis and it seems like they base64 encode the records. Updated my answer. Commented Sep 16, 2014 at 13:25
  • Another lesson learnt from this: GetShardIteratorResult.getShardIterator() returns a string onle, while GetRecordsRequest getRecordsRequest = new GetRecordsRequest(); along with getRecords(getRecordsRequest); gets the desired ByteBuffer type. Commented Sep 17, 2014 at 8:32

5 Answers 5

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3

If you want to go from byte[] to String, try new String(yourBytes).

Both getBytes and the String(byte[]) uses the default character encoding.

From Amazon Kinesis Service API Reference:

The data blob to put into the record, which is Base64-encoded when the blob is serialized.

You need to base64 decode the string. Using Java 8 it would look like:

byte[] bytes = Base64.getDecoder().decode("AAAAAAAAAAGZ7dFR0XmV23BR........");
str = new String(bytes, "utf-8"));

Other options: Base64 Encoding in Java

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8 Comments

I actually tried that, this could have been simpler if my input wasn't a String that is bytes (see above). What you suggest simply treats the string as if it was the content of it in its readable form.
Could you elaborate. I thought you basically wanted the inverse of getBytes?
Sure: I have a string that looks like this: "String str = "AAAAAAAAAAGZ7dFR0XmV23BR". I know that it's been converted to bytes but I get it as a String type. I want to know what's behind those bytes in a readable form
But how was "AAAAAAAAAAGZ7dFR0XmV23BR" produced? You mention getBytes, but that gives byte[] not String.
My apologies, my question was unorganized. what happens is this: 1. A Scala application takes a String, does "getBytes()", wraps it in ByteBuffer. ---> 2. I read this ByteBuffer as a String. ---> I'd like to know what was originally the content of the string. In one code line, this is what's done with the original string: ByteBuffer.wrap(output.getBytes)
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1

I m not sure if I understand the question exactly but do you mean this?

String decoded = new String(bytes);
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0 
public static void main(String[] args){
    String decoded = new String(bytesData);
    String actualString;
    try{
       actualString = new String(bytesData,"UTF-8");
       System.out.printLn("String is" + actualString);
    }catch(UnsupportedEncodingException e){
       e.printstacktrace();
    }
}
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1 Comment

What you suggest simply treats the string as if it were the content of it in its readable form. The original String looks like this: String str = "AAAAAAAAAAGZ7dFR0XmV23BR........"
0

Sorry,wrong answer. Again,ByteBuffer is a java class. SO they may work the same way You need java version..

From kafka ApiUtils:

def writeShortString(buffer:ByteBuffer,string:String){
   if(String == null){
       buffer.putShort(-1)
   }
   else{
     val encodedString = string.getBytes(“utf-8”)
     if(encodedString.length > Short.MaxValue){
         throw YourException(Your Message)
     else{
        buffer.putShort(encodedString.length.asInstanceOf[Short])
        buffer.put(encodedString)
   }
  }

}

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0

For Kinesis data blobs: 

private CharsetDecoder decoder = Charset.forName("UTF-8").newDecoder();
decoder.decode(record.getData()).toString();
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