What is IllegalArgumentException: Prefix string too short

Check if your code creating temp file using File.createTemFile(prefix,suffic, new File("test") method with prefix <3 characters.="characters." p="p">
File API doc:

public static File createTempFile(String prefix,

                                  String suffix,

                                  File directory)

                           throws IOException

Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name. If this method returns successfully then it is guaranteed that: 

Throws:

IllegalArgumentException - If the prefix argument contains fewer than three characters