Embed node.js application from java project with J2V8 - resolving relative paths in node.js

Question

Having problem while running Node.js application (1) on the JVM using J2V8 from another Java-based application (2). Starting script of application (1) fails on line

fs.readFileSync('./lib/someFile.json') 

because J2V8 provides '.' path to an application (2) root directory but I need '.' to be path to an application (1) root directory.

How can I deal with it only making changes in project (2)?

UPDATE: added Java code which starts node.js application.

public static void main(String[] args) {
        final NodeJS nodeJS = NodeJS.createNodeJS();
        File nodeScript = new File("/media/Projects/Test/start.js");
        nodeJS.exec(nodeScript);
        while(nodeJS.isRunning()) {
            nodeJS.handleMessage();
        }
        nodeJS.release();
}

Answer 1

You can use __dirname to have the path to the directory where your Node script is in.

For example:

fs.readFileSync(__dirname + '/lib/someFile.json');

might do what you need.

Or using path.join:

var path = require('path');
fs.readFileSync(path.join(__dirname, 'lib', 'someFile.json');

with path.join you can do things like:

console.log(path.join(__dirname, '..', 'lib', 'someFile.json'));

to access lib that is one level up from your Node program etc. Also, thanks to path.join you don't have to think about path delimiters on different operating systems (like / on Unix/Linux and \ on Windows).

Making only changes to your Java project you would have to run your Node application with a different working directory. It depends how you run it but what you should do is change directory to the one that you want to have the '.' point to before running the Node application. You have provided no code example of actually running the Node application from your Java application so it's hard to say anything more.

Update

It seems that you're using J2V8. There is an open issue on GitHub related to what you're trying to do: Issue #185: Set the working directory.

You may try to change the working directory before you start your Node program from Java - using whatever is the Java equivalent of the chdir system call.

Alternatively you can copy your Node program into your Java project, so that their '.' directories are the same, so that you could call it with:

File nodeScript = new File("./start.js");

When you can call start.js as ./start.js then the '.' in Node should be the directory where the start.js file is located in.