[ Java 常見問題 ] Convert List of Bytes to array of bytes

Source From Here 
Question: 
Trying to solve what should be a simple problem. Got a list of Bytes, want to convert it at the end of a function to an array of bytes. 

How-To 
What you can do is use commons-lang's ArrayUtils.toPrimitive(wrapperCollection): 

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1. Byte[] bytes = pdu.toArray(new Byte[pdu.size()]);  
2. return ArrayUtils.toPrimitive(bytes);  

If you can't use commons-lang, simply loop through the array and fill another array of type byte[] with the values (they will be automatically unboxed)