Decode and encode BCEL class

main.java

package main;

import java.io.*;
import java.nio.*;
import java.nio.file.*;
import org.apache.bcel.classfile.Utility;

public class Main {
    public static void help() {
        System.out.println(
            "Usage:\n" + 
            "  java -jar bcelClassUtil -d $$BCEL$$...\n" +
            "  java -jar bcelClassUtil -e XX.class\n"
        );
        System.exit(0);
    }

    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            help();
        }

        if (args[0].equals("-d")) {
            decode(args[1]);
        } else if (args[0].equals("-e")) {
            encode(args[1]);
        } else {
            help();
        }
    }

    public static void decode(String input) throws Exception {
        System.out.println("Saving foo.class");

        if (input.startsWith("$$BCEL$$")){
            input = input.substring(8);
        } else {
            throw new Exception("invalid BECL class bytecode");
        }

        byte[] data = Utility.decode(input, true);
        Files.write(Paths.get("foo.class"), data);
    }

    public static void encode(String filename) throws Exception {
        byte[] data = Files.readAllBytes(Paths.get(filename));
        System.out.println("$$BCEL$$" + Utility.encode(data, true));
    }
}