java-class-rs

A Java .class file parser written in Rust, based on the JVM Specification §4.

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Features

• Full constant pool — all 17 entry types including MethodHandle, InvokeDynamic, Module, Package
• Access flags — class, field, and method level
• 20+ specialized attributes — Code, StackMapTable, Exceptions, BootstrapMethods, InnerClasses, Annotations (runtime/parameter/type), NestHost/Members, Record, PermittedSubclasses, and more
• Modified UTF-8 — CESU-8 decoding via the cesu8 crate
• Serde support — optional serde feature for JSON/serialization
• No unsafe — pure safe Rust

Quick Start

# Cargo.toml
[dependencies]
java-class-rs = "0.1"

use java_class_rs::parse_classfile;

let data = std::fs::read("MyClass.class").unwrap();
let (_, class_file) = parse_classfile(&data).unwrap();

println!("Class: {:?}", class_file.this_class_name());
println!("Super: {:?}", class_file.super_class_name());
println!("Java {}.{}", class_file.major_version, class_file.minor_version);

Examples

Iterate methods and fields

for method in &class_file.methods {
    let name = class_file.method_name(method).unwrap_or("<unknown>");
    let desc = class_file.method_descriptor(method).unwrap_or("");
    println!("{} {}", name, desc);
}

Parse specialized attributes

Raw attributes are stored as AttributeInfo (name index + bytes). Use parse_specialized_attribute to decode them:

use java_class_rs::{get_utf8, parse_specialized_attribute, ParsedAttribute};

for attr in &class_file.methods[0].attributes {
    if get_utf8(&class_file.constant_pool, attr.attribute_name_index) == Some("Code") {
        if let ParsedAttribute::Code(code) = parse_specialized_attribute(attr, &class_file.constant_pool) {
            println!("max_stack={}, max_locals={}, bytecode={} bytes",
                code.max_stack, code.max_locals, code.code.len());
        }
    }
}

Serde support

[dependencies]
java-class-rs = { version = "0.1", features = ["serde"] }

let json = serde_json::to_string_pretty(&class_file).unwrap();
println!("{}", json);

Constant pool helpers

use java_class_rs::{get_entry, get_utf8, ConstantPoolEntry};

for (i, entry) in class_file.constant_pool.iter().enumerate() {
    match entry {
        ConstantPoolEntry::Methodref(m) => {
            let class = get_utf8(&class_file.constant_pool, m.class_index).unwrap_or("?");
            println!("#{} Methodref -> {}", i + 1, class);
        }
        _ => {}
    }
}

Supported Attributes

MSRV

Minimum Supported Rust Version: 1.71

License

MIT