use Custom Functions errors

I define a function like change encoding from UTF8 to GBK。
when I put it classes and source code into 3rdparty, and use it in query sql like this :
"SELECT encode_translate(columns[0],'UTF-8','GBK') as aaa FROM dfs.`d:/drill_test.csv` LIMIT 20"
it return a error info:
Query Failed: An Error Occurred
org.apache.drill.common.exceptions.UserRemoteException: SYSTEM ERROR: CompileException: Line 92, Column 42: Cannot determine simple type name "UnsupportedEncodingException" Fragment 0:0 [Error Id: 599d0e39-f05a-4ecd-a539-b5338239d63b on XXX.XXXX.com:31010]。

this is resource code of evel :

public void eval() {
// get the value and replace with
String stringValue = org.apache.drill.exec.expr.fn.impl.StringFunctionHelpers.toStringFromUTF8(input.start, input.end, input.buffer);
String fromEncodeValue = org.apache.drill.exec.expr.fn.impl.StringFunctionHelpers.getStringFromVarCharHolder(fromEncode);
String toEncodeValue = org.apache.drill.exec.expr.fn.impl.StringFunctionHelpers.getStringFromVarCharHolder(toEncode);

try

{ String toEncodeStringValue = new String(stringValue.getBytes(fromEncodeValue),toEncodeValue); out.buffer = buffer; out.start = 0; out.end = toEncodeStringValue.getBytes().length; buffer.setBytes(0, toEncodeStringValue.getBytes()); }

catch (UnsupportedEncodingException e) {

}
}

please help me,thank your.