Given this table in Oracle

create table test (bytes raw(100), chset varchar2(50))
insert into test (bytes, chset) values (hextoraw('454647'), 'iso-8859-1')

or in MSSQL

create table test (bytes varbinary(100), chset nvarchar(50))
insert into test (bytes, chset) values (0x454647, 'iso-8859-1')

I'm looking for a comprehensive example of how to create a UDF for Oracle in Java that makes use of Java's text encoding support.

In MSSQL I would create this .Net assembly:

using System.Text;
using Microsoft.SqlServer.Server;

namespace Whatever
{
    public class Common
    {
        [SqlFunction]
        public static string Decode(byte[] Bytes, string EncodingName)
        {
            return Encoding.GetEncoding(EncodingName).GetString(Bytes);
        }
    }
}

and use these commands to register the assembly and define the udf:

create assembly MyAssembly from '...\MyAssembly.dll'

create function decode(@bytes varbinary(max), @chset nvarchar(100))
returns nvarchar(max) as external name MyAssembly.[Whatever.Common].Decode

and use it in a query like this:

> select *, dbo.decode(bytes, chset) decoded from test

bytes      chset       decoded
0x454647   iso-8859-1  EFG

update

so far I've created this Java class:

import java.nio.*;
import java.nio.charset.*;

public class Common
{
    public static String Decode(byte[] Bytes, String CharsetName)
    {
        return Charset.forName(CharsetName).decode(ByteBuffer.wrap(Bytes)).toString();
    }
}

and used these commands to create the UDF:

create directory jdir as 'C:\...';
create java class using bfile (jdir, 'Common.class');

create function jdecode(bytes raw, chset varchar2) return nvarchar2 as language java
name 'Common.Decode(java.lang.byte[], java.lang.String) return java.lang.String';

but when I try to use it I get this error:

> select jdecode(hextoraw('454647'), 'iso-8859-1') from dual

ORA-29531: no method Decode in class Common

update 2

turns out java.lang.byte[] isn't a thing, changing it to just byte[] got things working. Thanks Tim!

create function jdecode(bytes raw, chset varchar2) return nvarchar2 as language java
name 'Common.Decode(byte[], java.lang.String) return java.lang.String';

there's a handy table here: http://download.oracle.com/docs/cd/B19306_01/java.102/b14187/chsix.htm#BABJIJEB