Java Byte Array to String to Byte Array

What I did:

return to clients:

byte[] result = ****encrypted data****;

String str = Base64.encodeBase64String(result);

return str;

receive from clients:

 byte[] bytes = Base64.decodeBase64(str);

your data will be transferred in this format:

OpfyN9paAouZ2Pw+gDgGsDWzjIphmaZbUyFx5oRIN1kkQ1tDbgoi84dRfklf1OZVdpAV7TonlTDHBOr93EXIEBoY1vuQnKXaG+CJyIfrCWbEENJ0gOVBr9W3OlFcGsZW5Cf9uirSmx/JLLxTrejZzbgq3lpToYc3vkyPy5Y/oFWYljy/3OcC/S458uZFOc/FfDqWGtT9pTUdxLDOwQ6EMe0oJBlMXm8J2tGnRja4F/aVHfQddha2nUMi6zlvAm8i9KnsWmQG//ok25EHDbrFBP2Ia/6Bx/SGS4skk/0couKwcPVXtTq8qpNh/aYK1mclg7TBKHfF+DHppwd30VULpA== 

String coolString = "cool string";

byte[] byteArray = coolString.getBytes();

String reconstitutedString = new String(byteArray);

System.out.println(reconstitutedString);

That outputs "cool string" to the console.

It's pretty darn easy.

You can't just take the returned string and construct a string from it... it's not a byte[] data type anymore, it's already a string; you need to parse it. For example :

String response = "[-47, 1, 16, 84, 2, 101, 110, 83, 111, 109, 101, 32, 78, 70, 67, 32, 68, 97, 116, 97]";      // response from the Python script

String[] byteValues = response.substring(1, response.length() - 1).split(",");
byte[] bytes = new byte[byteValues.length];

for (int i=0, len=bytes.length; i<len; i++) {
   bytes[i] = Byte.parseByte(byteValues[i].trim());     
}

String str = new String(bytes);

** EDIT **

You get an hint of your problem in your question, where you say "Whatever I seem to try I end up getting a byte array which looks as follows... [91, 45, ...", because 91 is the byte value for [, so [91, 45, ... is the byte array of the string "[-45, 1, 16, ..." string.

The method Arrays.toString() will return a String representation of the specified array; meaning that the returned value will not be a array anymore. For example :

byte[] b1 = new byte[] {97, 98, 99};

String s1 = Arrays.toString(b1);
String s2 = new String(b1);

System.out.println(s1);        // -> "[97, 98, 99]"
System.out.println(s2);        // -> "abc";

As you can see, s1 holds the string representation of the array b1, while s2 holds the string representation of the bytes contained in b1.

Now, in your problem, your server returns a string similar to s1, therefore to get the array representation back, you need the opposite constructor method. If s2.getBytes() is the opposite of new String(b1), you need to find the opposite of Arrays.toString(b1), thus the code I pasted in the first snippet of this answer.