79 lines
2.1 KiB
Markdown
79 lines
2.1 KiB
Markdown
[](https://www.npmjs.com/package/java-parser)
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# java-parser
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A Java Parser implemented in JavaScript using the [Chevrotain Parsing ToolKit](https://github.com/Chevrotain/chevrotain).
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It outputs a **C**oncrete **S**yntax **T**ree, rather than an **A**bstract **S**yntax **T**ree.
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- [On the Difference between a CST and an AST](https://stackoverflow.com/questions/1888854/what-is-the-difference-between-an-abstract-syntax-tree-and-a-concrete-syntax-tre)
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Currently the main focus of this project is to be used in implementing a prettier Java plugin.
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But it could also be used as the basis for other Java related tools in the JavaScript ecosystem.
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## Installation
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```sh
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npm install java-parser --save-dev
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```
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or
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```sh
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yarn add java-parser --dev
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```
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## Usage
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### Parsing
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```javascript
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const { parse } = require("java-parser");
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const javaText = `
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public class HelloWorldExample{
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public static void main(String args[]){
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System.out.println("Hello World !");
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}
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}
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`;
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const cst = parse(javaText);
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// explore the CST
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```
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### Traversing the CST
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See relevant [Chevrotain documentation on CST Traversal](http://chevrotain.io/docs/guide/concrete_syntax_tree.html#traversing).
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```javascript
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const {
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BaseJavaCstVisitor,
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BaseJavaCstVisitorWithDefaults
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} = require("java-parser");
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// Use "BaseJavaCstVisitor" if you need to implement all the visitor methods yourself.
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class LambdaArrowsPositionCollector extends BaseJavaCstVisitorWithDefaults {
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constructor() {
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super();
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this.customResult = [];
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this.validateVisitor();
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}
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lambdaExpression(ctx) {
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// Collects all the starting offsets of lambda arrows in lambdas with short (no parenthesis)
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// single argument lists: e.g:
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// - n -> n*n (will be collected)
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// - (n) -> n*n (not collected)
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if (ctx.lambdaParameters[0].children.Identifier) {
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this.customResult.push(ctx.Arrow[0].startOffset);
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}
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}
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}
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const lambdaArrowsCollector = new LambdaArrowsPositionCollector();
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// The CST result from the previous code snippet
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lambdaArrowsCollector.visit(cst);
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lambdaArrowsCollector.customResult.forEach(arrowOffset => {
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console.log(arrowOffset);
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});
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```
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