Question

Is it 100% safe (exception / error free) to convert a byte[] that includes random binary data to a String via the constructor:

new String(bytes);
// -- or --
new String(bytes,"UTF-8");  // Or other charset

My concern is whether invalid UTF-8 bytes will cause an exception or other failure instead of just a possibly partially garbled message.

I have tried some known bad byte values, as they appear to work as expected. E.g:

byte[] bytes = new byte[] {'a','b','c',(byte)0xfe,(byte)0xfe,(byte)0xff,(byte)0xff,'d','e','f'};

String test = new String(bytes,"UTF-8");

System.out.println(test);

Prints “abc????def”.

My concern is if certain other combinations can fail in other unexpected ways since I cannot guarantee that I can test every invalid combination.

Answer 1

This is covered in the docs:

This method always replaces malformed-input and unmappable-character sequences with this charset’s default replacement string

One thing that will fail, if you’re not always using UTF-8, is that it can throw UnsupportedEncodingException.