java-bridge-fork
v2.4.10
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A bridge between Node.js and Java APIs
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node-java
A bridge between Node.js programs and Java APIs written in Rust using napi-rs to provide a fast and memory-safe interface between the two languages.
The pre-compiled binaries will be provided with the package, the only thing
you need to do on your machine is install a Java Runtime Environment (JRE)
for this package to use. In contrast to other node.js <-> java
interfaces,
the binary is not hard linked to the JDK it has been compiled with but rather
loads the jvm native library dynamically when the program first starts up.
The full documentation of this package is available here.
NOTE: As of version 2.1.0
, this package has been renamed from @markusjx/java
to java-bridge
.
Installation
npm i java-bridge
Note: In order to use this package on windows, you'll need to install the Visual C++ Redistributable for Visual Studio 2015.
Command line interface
This module also provides a command line interface that allows you to generate typescript definitions for your java classes.
The command line interface is called java-ts-definition-generator
and can be installed using npm install -g java-ts-definition-generator
.
The full documentation can be found here.
Build instructions
This is only required for development purposes. When installing the package using npm i
, you can skip this.
In order to build this project, you should install
- Node.js
- npm
- rustc, the rust compiler
- cargo
- Java JDK 8+
- clang
Then, to build the project, run:
npm install
npm run build
Support Matrix
✅ = Pre-compiled binaries are available
-
= Pre-compiled binaries are not available
| Operating System | i686 | x64 | arm | arm64 | | ---------------- | :--: | :-: | :-: | :---: | | Linux | - | ✅ | - | ✅ | | Windows | ✅ | ✅ | - | - | | macOS | - | ✅ | - | ✅ |
Known working linux distros
| Distro | Version |
| :----: | :-----------: |
| Ubuntu | >= 20.04
|
| Debian | >= bullseye
|
Usage
Example: Hello world from Java
import { importClass } from './java-bridge';
const System = importClass('java.lang.System');
System.out.println('Hello world!');
Create the JVM
Create a new Java VM using the ensureJvm
method.
Calling this after the jvm has already been created will do nothing.
Destroying the jvm manually is not (yet) supported.
Create the JVM with no extra options
This will first search for a suitable jvm
native library on the system and then
start the jvm with no extra options. This is also called when any call to the jvm is made
but the jvm is not yet started.
import { ensureJvm } from 'java-bridge';
ensureJvm();
Create the JVM with extra options
You can pass extra options to the jvm when creating it, for example requesting a specific jvm version, specifying the location of the jvm native library or passing additional arguments to the jvm.
import { ensureJvm, JavaVersion } from 'java-bridge';
ensureJvm({
libPath: 'path/to/jvm.dll',
version: JavaVersion.VER_9,
opts: ['-Xms512m', '-Xmx512m'],
});
All threads will be attached as daemon threads, allowing the jvm to exit when the main thread exits. This behaviour can not be changed, as it may introduce undefined behaviour.
Important note on jvm options: Different arguments must be parsed as separate strings in the opts
array.
Otherwise, the jvm will not be able to parse the arguments correctly.
Notes on electron
When using this package in a packaged electron application, you should unpack this package and
the appropriate binaries for your platform into the app.asar.unpacked
folder. When using
electron-builder, you can do this by adding the following to your package.json
:
{
"build": {
"asarUnpack": [
"node_modules/java-bridge/**",
"node_modules/java-bridge-*/**"
]
}
}
Additionally, you should set the isPackagedElectron
option to true
when creating the jvm:
ensureJvm({
isPackagedElectron: true,
});
This option should not have any effect when not using electron or not having the application packaged.
Inject a JAR into the class path
In order to import your own classes into the node environment, you need
to add the JAR file to the class path. You can do that with the
appendClasspath
or classpath.append
methods. After loading a JAR, you can import classes from it like any other class
from the JVM using importClass
or importClassAsync
.
import { appendClasspath } from 'java-bridge';
// Append a single jar to the class path
appendClasspath('/path/to/jar.jar');
// Append multiple jars to the class path
appendClasspath(['/path/to/jar1.jar', '/path/to/jar2.jar']);
or
import { classpath } from 'java-bridge';
// Append a single jar to the class path
classpath.append('/path/to/jar.jar');
Synchronous calls
If you want to use Java APIs in a synchronous way, you can use the synchronous API of this module. Any call to the Java API will be executed in the same thread as your node process so this may cause your program to hang until the execution is finished. But - in contrast to the asynchronous API - these calls are a lot faster as no extra threads need to be created/attached to the JVM.
All synchronous java methods are proceeded with the postfix Sync
.
This means, all methods of a class (static and non-static) are generated twice,
once as a synchronous call and once as an asynchronous call.
If you are looking for asynchronous calls, take a look at the next section.
In order to import a class synchronously, you can use the importClass
function.
Using this method does not affect your ability to call any method of the class asynchronously.
import { importClass } from 'java-bridge';
// Import a class
const JString = importClass('java.lang.String');
// Create a new instance of the class
const str = new JString('Hello World');
// Call a method on the instance
str.lengthSync(); // 11
// Supported native types will be automatically converted
// to the corresponding type in the other language
str.toStringSync(); // 'Hello World'
Asynchronous calls
If you want to use Java APIs in an asynchronous way, you can use the asynchronous API of this module. Any call to the Java API will be executed in a separate thread and the execution will not block your program. This is in general a lot slower as the synchronous API but allows the program to run more smoothly.
If you want to improve the performance of the asynchronous API, you can force the module to attach any thread as a daemon thread to the JVM. This allows the program to not constantly attach new threads to the JVM as the old ones can be reused and thus improves the performance.
In order to import a class asynchronously, you can use the
importClassAsync
function.
import { importClassAsync } from 'java-bridge';
const JString = await importClassAsync('java.lang.String');
// Create a new instance asynchrnously using 'newInstanceAsync'
const str = await JString.newInstanceAsync('Hello World');
// Call methods asynchronously
await str.length(); // 11
await str.toString(); // 'Hello World'
Implement a Java interface
You can also implement a Java interface in node.js using the
newProxy
method.
Please note that when calling a java method that uses an interface defined by this method,
you must call that method using the interface asynchronously as Node.js is single threaded
and can't wait for the java method to return while calling the proxy method at the same time.
import { newProxy } from 'java-bridge';
const proxy = newProxy('path.to.MyInterface', {
// Define methods...
});
// Do something with the proxy
instance.someMethod(proxy);
// Destroy the proxy
proxy.reset();
Redirect the stdout and stderr from the java process
If you want to redirect the stdout and/or stderr from the java
process to the node.js process, you can use the
enableRedirect
method.
import { stdout } from 'java-bridge';
const guard = stdout.enableRedirect(
(_, data) => {
console.log('Stdout:', data);
},
(_, data) => {
console.error('Stderr:', data);
}
);
Logging
If you want to enable logging for this module, you need to re-compile the module
with the log
feature. Please install the dependencies listed in the
build section and run npm run build:all
to build the module with
all features enabled.
Logged events include:
- Class loading
- Method calls
- Class instance creation
- Method and class lookup
Note: Logging affects the performance of the module. Thus, it is recommended to only enable logging when debugging.
For further information on how to use the logging feature, please take a look at the logging module documentation.
Value conversion rules
- Any basic value such as
string
,number
,boolean
orBigInt
may be passed to methods accepting matching types string
values will always be converted tojava.lang.String
string
values with just one character may be converted tochar
orjava.lang.Char
if required- Thus, in order to pass a
char
to a java method, use astring
containing just one character number
values will be converted toint
,long
,double
,float
,java.lang.Integer
,java.lang.Long
,java.lang.Double
orjava.lang.Float
depending on the type the java function to call requiresboolean
values will be converted to eitherboolean
orjava.lang.Boolean
BigInt
values will be converted to eitherlong
orjava.lang.Long
- Arrays will be converted to java arrays. Java arrays may only contain a single value type, therefore the type of the first element in the array will be chosen as the array type, empty arrays need no conversions.
java.lang.String
values will be converted tostring
int
,double
,float
,java.lang.Integer
,java.lang.Double
orjava.lang.Float
values will be converted tonumber
long
orjava.lang.Long
values will always be converted toBigInt
boolean
orjava.lang.Boolean
values will be converted toboolean
char
orjava.lang.Character
values will be converted tostring
- Java arrays will be converted to javascript arrays, applying the rules mentioned above except
- Byte arrays will be converted to
Buffer
and vice-versa