The short answer is: use 'c'
Under the hood, jython is doing the work of converting data types for you.
You can verify with some tests. There is a class java.nio.CharBuffer with a method wrap() that takes a char[] array. Observe that jython array type 'c' works, while everything else fails:
>>> import array
>>> from java.nio import CharBuffer
>>> array.array('c', 'Hello World')
array('c', 'Hello World')
>>> CharBuffer.wrap( array.array('c', 'Hello World') )
Hello World
>>> array.array('b','Hello World')
array('b', [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100])
>>> CharBuffer.wrap( array.array('b', 'Hello World') )
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: wrap(): 1st arg can't be coerced to char[], java.lang.CharSequence
>>> array.array('u', u'Hello World')
array('u', u'Hello World')
>>> CharBuffer.wrap( array.array('u', u'Hello World') )
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: wrap(): 1st arg can't be coerced to char[], java.lang.CharSequence