java-class-tools
The structure of the ClassFile object returned by JavaClassFileReader#read and its inner objects matches the Java Virtual Machine Specification, therefore you can use this specification as a guide on how to understand and change a Class file.
Install
npm install java-class-tools
Examples:
- Browser usage example (List all methods and fields of a class file)
- Node usage example (Simple disassembler)
- Try yourself (RunKit: you must login with GitHub to be able to fork it)
Print method names (Node.js):
const { JavaClassFileReader } = require('java-class-tools');
const { TextDecoder } = require('util');
const reader = new JavaClassFileReader();
const classFile = reader.read('./Foo.class');
const textDecoder = new TextDecoder();
classFile.methods.forEach(md => {
/**
* Method name in constant-pool.
*
* Points to a CONSTANT_Utf8_info structure: https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.7
*/
const nameInConstantPool = classFile.constant_pool[md.name_index];
// It is also possible to use the string_decoder builtin module.
const name = textDecoder.decode(new Uint8Array(nameInConstantPool.bytes));
console.log(name);
});Print method names (Node.js):
<script src="https://cdn.jsdelivr.net/npm/java-class-tools@latest/dist/java-class-tools.min.js"></script>
<script>
fetch('https://gist.githubusercontent.com/leonardosnt/69207dd9bcae55c93ff8fe6546c92eef/raw/fa008a94f9bc208cfa593cf568f0c504e3b30413/Class.class')
.then(r => r.arrayBuffer())
.then(printAllMethods);
function printAllMethods(classData) {
const reader = new JavaClassTools.JavaClassFileReader();
const classFile = reader.read(classData);
const textDecoder = new TextDecoder();
classFile.methods.forEach(method => {
/**
* Method name in constant-pool.
*
* Points to a CONSTANT_Utf8_info structure: https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.7
*/
const nameEntry = classFile.constant_pool[method.name_index];
const name = textDecoder.decode(new Uint8Array(nameEntry.bytes));
console.log(name);
});
}
</script>License
Copyright (C) 2017-2020 leonardosnt <[email protected]>
Licensed under the MIT License. See LICENSE file in the project root for full license information.