cheerpjRunLibrary

Load a Java Library

Allows to load a Java Library into JavaScript.

async function cheerpjRunLibrary(classPath: string): Promise<CJ3Library>;

Parameters

classPath (string) - The path to the library’s jar file in the virtual filesystem. Pass an empty string to load the standard library only.

Returns

cheerpjRunLibrary returns a Promise which resolves to a CJ3Library object.

CJ3Library

This object can be used to access the classes and methods of the loaded library through property access:

To load a class, access it and await it.
To call a static method, call it as a method on a loaded class and await it.
To construct a class into an instance, use await new.
To call an instance method, call it as a method on an instance of a loaded class and await it.

Array interoperability is supported:

Passing JS arrays to Java arrays via copying.
Passing JS arrays to Java JSObject.
Passing Java object arrays to JavaScript by reference.
Passing Java primitive arrays to JavaScript
Public Java fields can now be both read/written from JS with appropriate type conversion.
Classes in JS supports instanceof.

Parameters and return values of method calls are automatically converted between JavaScript and Java types.

Examples

Using the standard library

await cheerpjInit();
const lib = await cheerpjRunLibrary("");

const System = await lib.java.lang.System;
await System.out.println("Hello from Java");

Using a custom library

Let’s say we had a library called example.jar compiled from the following class:

package com.example;

public class Example {
  public String[] greetings = {"Hello", "Bye"};
  public void hello() {
    System.out.println("Example says hello!");
  }
}

With example.jar being available on the web server at /example.jar, we could use it like so:

await cheerpjInit();
const lib = await cheerpjRunLibrary("/app/example.jar");

const Example = await lib.com.example.Example;
const example = await new Example();
await example.hello(); // Example says hello!

Access to object property/attribute

From the example above:

const greetingsArray = example["greetings"];

const greetingsArray = example.greetings;

Exception handling

await cheerpjInit();
const lib = await cheerpjRunLibrary("");

try {
  // Attempt to load a class that doesn't exist
  await lib.java.lang.DoesntExist;
} catch (e) {
  await e.printStackTrace(); // java.lang.ClassNotFoundException: java.lang.DoesntExist
}