[Pattern] Class-file parsing with the standard API

[brunoborges]

Category

tooling

Slug

class-file-api

Title

Class-file parsing with the standard API

Difficulty

advanced

Since JDK

24

Summary

Use the standard Class-File API for class-file parsing and transformation.

Old code label

Third-party bytecode parser

Old code

ClassReader reader = new ClassReader(Files.readAllBytes(classFile));
reader.accept(visitor, 0);

Modern code label

Java 24+

Modern code

ClassModel model = ClassFile.of().parse(classFile);
model.methods().forEach(method ->
        System.out.println(method.methodName().stringValue()));

Explanation

The Class-File API, finalized in JDK 24, provides supported models and transformations for JVM class files. It tracks the class-file format with the JDK and removes the need for third-party libraries in many inspection and generation tasks.

Why the modern way wins

🛡 Supported API — Ships and evolves with the JDK class-file format.
📦 Fewer dependencies — Handles common bytecode tasks without an external library.
🧩 Composable models — Parsing, building, and transformation share one API.