ClassDefiner

The ClassDefiner is a utility extending ClassLoader which takes in one or more classes as a Map<String, byte[]> and defines them at runtime.

• Keys are the class name format you'd use for Class.forName(String) and thus would look like java.lang.String.
• Values are the raw bytes of the class file.

Usage

String name = "com/example/StringMapper"; // Internal name format
String sourceName = name.replace('/', '.'); // Source name format

// Example code to generate an interface
ClassWriter cw = new ClassWriter(0);
cw.visit(V1_8, ACC_PUBLIC | ACC_INTERFACE, name, "java/lang/Object", null, null);
cw.visitMethod(ACC_PUBLIC, "map", "(Ljava/lang/String;)Ljava/lang/String;", null, null);
cw.visitEnd();
byte[] bytes = cw.toByteArray();

// Definer with a single class
ClassDefiner cd = new ClassDefiner(sourceName, bytes);

// Definer with a map of entries
ClassDefiner cd = new ClassDefiner(Map.of(sourceName, bytes));

// Loading the class
Class<?> cls = definer.findClass(sourceName);