#parser #class #decompile #index #attributes #info #parse #acc

bin+lib classy

Classy: A Rust Library for Parsing Java Class Files

5 unstable releases

0.3.0 Jul 21, 2023
0.2.0 Jun 3, 2023
0.1.2 May 18, 2023
0.1.1 May 18, 2023
0.1.0 May 18, 2023


674 lines

Contains (JAR file, 23KB) testdata/test.jar

Classy: A Rust Library for Parsing Java Class Files


Classy is a Rust library for reading Java class files, based on The Java Virtual Machine Specification, Java SE 17 Edition.


Example Usage:

let f = File::open("MyClass.class")?;
let class: ClassFile = read_class(f)?;
println!("Class JVM version: {}.{}", class.major_version, class.minor_version);
println!("Class has {} fields and {} methods", class.field_info.len(), class.method_info.len());

The ClassFile struct contains complete information about a class file:

pub struct ClassFile {
    minor_version: u16,
    major_version: u16,
    constant_pool: Vec<Constant>,
    access_flags: u16,
    this_class: u16,
    super_class: u16,
    interfaces: Vec<u16>,
    field_info: Vec<FieldInfo>,
    method_info: Vec<MethodInfo>,
    attributes: Vec<Attribute>,


A command-line tool is included, which provides examples of using the library.


  • Search for a class in a directory full of Jar files using a regular expression.
  • Partially decompile all classes in a Jar file (similar to javap functionality). Note that this is not a full decompiler. It only shows field and method signatures, not implementation code.


I built this for personal use to help me with a specific task. I am not sure if I will develop it further.


~175K SLoC