java-parser

What is java-parser?

The java-parser npm package is a tool for parsing Java source code into an Abstract Syntax Tree (AST). This allows developers to analyze, transform, and manipulate Java code programmatically.

What are java-parser's main functionalities?

Parsing Java Code

This feature allows you to parse Java source code into an AST. The code sample demonstrates how to parse a simple Java class and print the resulting AST.

const javaParser = require('java-parser');
const javaCode = 'public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }';
const ast = javaParser.parse(javaCode);
console.log(JSON.stringify(ast, null, 2));

AST Traversal

This feature allows you to traverse the AST generated from Java source code. The code sample demonstrates a simple traversal that prints the type of each node in the AST.

const javaParser = require('java-parser');
const javaCode = 'public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }';
const ast = javaParser.parse(javaCode);
function traverse(node) {
  console.log(node.type);
  if (node.children) {
    node.children.forEach(traverse);
  }
}
traverse(ast);

Code Transformation

This feature allows you to transform the Java code by manipulating the AST. The code sample demonstrates how to rename a class in the parsed AST.

const javaParser = require('java-parser');
const javaCode = 'public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }';
const ast = javaParser.parse(javaCode);
// Example transformation: rename the class
ast.children[0].name = 'HelloUniverse';
console.log(JSON.stringify(ast, null, 2));

Other packages similar to java-parser

esprima

Esprima is a high-performance, standard-compliant ECMAScript parser. It parses JavaScript code into an AST, similar to how java-parser works for Java. Esprima is widely used for JavaScript code analysis and transformation.

antlr4

ANTLR (Another Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. ANTLR can be used to parse Java and many other languages, making it more versatile than java-parser, which is specific to Java.

README

java-parser

A Java Parser implemented in JavaScript using the Chevrotain Parsing ToolKit. It outputs a Concrete Syntax Tree, rather than an Abstract Syntax Tree.

• On the Difference between a CST and an AST

Currently the main focus of this project is to be used in implementing a prettier Java plugin. But it could also be used as the basis for other Java related tools in the JavaScript ecosystem.

Installation

npm install java-parser --save-dev

or

yarn add java-parser --dev

Usage

Parsing

const { parse } = require("java-parser");
const javaText = `
public class HelloWorldExample{
  public static void main(String args[]){
    System.out.println("Hello World !");
  }
}
`;

const cst = parse(javaText);
// explore the CST

Traversing the CST

See relevant Chevrotain documentation on CST Traversal.

const {
  BaseJavaCstVisitor,
  BaseJavaCstVisitorWithDefaults
} = require("java-parser");

// Use "BaseJavaCstVisitor" if you need to implement all the visitor methods yourself.
class LambdaArrowsPositionCollector extends BaseJavaCstVisitorWithDefaults {
  constructor() {
    super();
    this.customResult = [];
    this.validateVisitor();
  }

  lambdaExpression(ctx) {
    // Collects all the starting offsets of lambda arrows in lambdas with short (no parenthesis)
    // single argument lists: e.g:
    // - n -> n*n (will be collected)
    // - (n) -> n*n (not collected)
    if (ctx.lambdaParameters[0].children.Identifier) {
      this.customResult.push(ctx.Arrow[0].startOffset);
    }
  }
}

const lambdaArrowsCollector = new LambdaArrowsPositionCollector();
// The CST result from the previous code snippet
lambdaArrowsCollector.visit(cst);
lambdaArrowsCollector.customResult.forEach(arrowOffset => {
  console.log(arrowOffset);
});