java

Bridge API to connect with existing Java APIs.

Google Groups Discussion Forum

Other projects that might be helpful

• node-java-maven - manages your node-java classpath by using maven dependency management.

Installation

$ npm install java

Notes:

• node-gyp requires python 2.x not python 3.x. See https://github.com/TooTallNate/node-gyp/issues/155 for more details.
• If you see an error such as "Call to 'node findJavaHome.js' returned exit status 1" Try running node findJavaHome.js in the node-java directory to see the full failure message.
• If you are having problems finding 'jni.h'. Make sure you have the JDK installed not just the JRE. If you are using OpenJDK you want the openjdk-7-jdk package, not openjdk-7-jre. Mavericks users see Issue #86 if you run into this.

Installation OSX

• If you run into strange runtime issues, it could be because the Oracle JDK does not advertise itself as available for JNI. See Issue 90 for more details and manual workarounds. If this does occur for you, please update the issue.

Installation Windows

For 64 bit installs with 32 bit node:

• you need the 32 bit JDK, with the 64 bit JDK you will see LNK2001 errormessages (http://stackoverflow.com/questions/10309304/what-library-to-link-to-on-windows-7-for-jni-createjavavm).
• when using the windows SDK 7.1 command prompt (64 bits) be sure to setenv.cmd /Release /x86

If you get ENOENT errors looking for <nodepath>\node_modules\node-gyp\.., ensure you have node-gyp installed as a global nodule:

npm install -g node-gyp

If you get D9025 warnings and C1083 errors when looking for .sln or .h files, be sure you've got the node-gyp's dependencies, as explained here.

Alternatively, Windows users can easily install all required tools by running the following command in PowerShell as administrator. For more information see windows-build-tools project page:

npm install --global --production windows-build-tools

Installation ARM (Raspberry Pi)

GYP_DEFINES="armv7=0" CCFLAGS='-march=armv6' CXXFLAGS='-march=armv6' npm install java

Manual compile (Using node-gyp)

./compile-java-code.sh
node-gyp configure build
npm test

NOTE: You will need node-gyp installed using "npm install -g node-gyp"

On Raspian you might need a:

• sudo ln -s /usr/lib/jvm/jdk-7-oracle-arm-vfp-hflt /opt/jdk

Some issues with the OpenSDK7 so take the Oracle version for compiling.

Docker

If you want to play with node-java but don't want to setup the build environment you can run it in docker.

docker run -it joeferner/node-java bash

Then inside the docker container create a directory and run

npm install java

Then create a file called test.js with the following contents

var java = require('java');
var javaLangSystem = java.import('java.lang.System');

javaLangSystem.out.printlnSync('Hello World');

Then run

node test.js

Java 1.8 support

Manual compilation for Java 1.8 support requires additional steps:

./compile-java-code.sh
./compile-java8-code.sh
node-gyp configure build
npm test

Java 1.8 language features can be used in Java classes only if a Java 1.8 JRE is available. The script compile-java8-code.sh is used only to compile java classes used in the 'test8' unit tests, but these classes are checked into the test8/ directory. Note that unit tests in the test8/ directory will pass (by design) if run against a Java 1.7 JRE, provided that a java.lang.UnsupportedClassVersionError is caught with the message 'Unsupported major.minor version 52.0' (the expected behavior when Java 1.8 language features are used in an older JRE).

Installation node-webkit

npm install -g nw-gyp
npm install java
cd node_modules/java
nw-gyp configure --target=0.10.5
nw-gyp build

See testIntegration/webkit for a working example

Using node-java in existing maven projects

When using node-java in existing maven projects, all the dependencies and the class files of the project have to be pushed to the classpath.

One possible solution would be:

Issue the command:

mvn dependency:copy-dependencies

Then create the following module javaInit:

"use strict";
var fs = require("fs");
var java = require("java");
var baseDir = "./target/dependency";
var dependencies = fs.readdirSync(baseDir);
 
dependencies.forEach(function(dependency){
    java.classpath.push(baseDir + "/" + dependency);
})
 
java.classpath.push("./target/classes");
java.classpath.push("./target/test-classes");
 
exports.getJavaInstance = function() {
    return java;
}

and then in the consuming class write:

 
var javaInit = require('./javaInit');
var java = javaInit.getJavaInstance();
 
//your code goes here

Quick Examples

var java = require("java");
java.classpath.push("commons-lang3-3.1.jar");
java.classpath.push("commons-io.jar");
 
var list1 = java.newInstanceSync("java.util.ArrayList");
console.log(list1.sizeSync()); // 0
list1.addSync('item1');
console.log(list1.sizeSync()); // 1
 
java.newInstance("java.util.ArrayList", function(err, list2) {
  list2.addSync("item1");
  list2.addSync("item2");
  console.log(list2.toStringSync()); // [item1, item2]
});
 
var ArrayList = java.import('java.util.ArrayList');
var list3 = new ArrayList();
list3.addSync('item1');
list3.equalsSync(list1); // true

Create a char array

var charArray = java.newArray("char", "hello world\n".split(''));

Create a byte array

var byteArray = java.newArray(
  "byte",
  "hello world\n"
    .split('')
    .map(function(c) { return java.newByte(String.prototype.charCodeAt(c)); }));

Using java.lang.Long and long

JavaScript only supports 32-bit integers. Because of this java longs must be treated specially. When getting a long result the value may be truncated. If you need the original value there is a property off of the result called "longValue" which contains the un-truncated value as a string. If you are calling a method that takes a long you must create it using java.newInstance.

var javaLong = java.newInstanceSync("java.lang.Long", 5);
console.log('Possibly truncated long value: ' + javaLong);
console.log('Original long value (as a string): ' + javaLong.longValue);
java.callStaticMethodSync("Test", "staticMethodThatTakesALong", javaLong);

Exceptions

Exceptions from calling methods either caught using JavaScript try/catch block or passed to a callback as the first parameter may have a property named "cause" which has a reference to the Java Exception object which caused the error.

try {
  java.methodThatThrowsExceptionSync();
} catch(ex) {
  console.log(ex.cause.getMessageSync());
}

AsyncOptions: control over the generation of sync, async & promise method variants.

As of release 0.4.5 it became possible to create async methods that return promises by setting the asyncOptions property of the java object. With release 0.4.7 this feature is extended to allow changing the suffix assigned for sync and async method variants, and to further configure this module to optionally omit generation of any of these variants.

Example:

var java = require("java");
java.asyncOptions = {
  asyncSuffix: undefined,     // Don't generate node-style methods taking callbacks
  syncSuffix: "",              // Sync methods use the base name(!!)
  promiseSuffix: "Promise",   // Generate methods returning promises, using the suffix Promise.
  promisify: require('util').promisify // Needs Node.js version 8 or greater, see comment below
};
java.classpath.push("commons-lang3-3.1.jar");
java.classpath.push("commons-io.jar");
 
java.import("java.util.ArrayList"); // see NOTE below
 
java.newInstancePromise("java.util.ArrayList")
    .then(function(list) { return list.addPromise("item1"); })
    .then(function(list) { return list.addPromise("item2"); })
    .catch(function(err) { /* handle error */ });

NOTES:

• If you want the defacto standard behavior, simply don't set java.asyncOptions.
• If you do provide asyncOptions, be aware that this module will not generate method variants of a given flavor if you don't provide a string value for the corresponding suffix (asyncSuffix, syncSuffix, promiseSuffix). In the example above, the application is configured to omit the method variants using node-style async callback functions.
• If you provide asyncOptions.promiseSuffix then you must also set asyncOptions.promisify to a function that promisifies a node-style async function. I.e. the provided function must take as input a function whose last argument is a node callback function, and it must return an equivalent promise-returning function. Several Promises/A+ libraries provide such functions, but it may be necessary to provide a wrapper function. See testHelpers.js for an example.
• For promisify implementation, if you are using Node.js version 8.0.0 or newer then promisify: require('util').promisify will work out of the box. If you need to support and older Node.js version then an implementation needs to be provided, for example, promisify: require("when/node").lift
• If you provide asyncOptions.promisify then you must provide a non-empty string for asyncOptions.promiseSuffix.
• Either (but not both) asyncSuffix or syncSuffix can be the empty string. If you want the defacto standard behavior for no suffix on async methods, you must provide an empty string for asyncSuffix.
• We've tested promises with five Promises/A+ implementations. See testHelpers.js for more information.
• NOTE: Due to specifics of initialization order, the methods java.newInstancePromise, java.callMethodPromise, and java.callStaticMethodPromise are not available until the JVM has been created. You may need to call some other java method such as java.import() to finalize java initialization, or even better, the function java.ensureJvm().

Special note about the exported module functions newInstance, callMethod, and callStaticMethod.

These methods come in both async and sync variants. If you provide the promisify and promiseSuffix attributes in asyncOptions then you'll also get the Promises/A+ variant for these three functions. However, if you change the defacto conventions for the syncSuffix (i.e. 'Sync') and/or asyncSuffix (i.e. '') it will not affect the naming for these three functions. I.e. no matter what you specify in asyncOptions, the async variants are named newInstance, callMethod, and callStaticMethod, and the sync variants are named newInstanceSync, callMethodSync, and callStaticMethodSync.

Varargs support

With v0.5.0 node-java now supports methods with variadic arguments (varargs). Prior to v0.5.0, a JavaScript call to a Java varargs method had to construct an array of the variadic arguments using java.newArray(). With v0.5.0 JavaScript applications can simply use the variadic style.

In most cases it is still acceptable to use java.newArray(). But it is now possible to pass a plain JavaScript array, or use the variadic style. For example, consider these snippets from the unit test file test/varargs-test.js:

    test.equal(Test.staticVarargsSync(5, 'a', 'b', 'c'), '5abc');
    test.equal(Test.staticVarargsSync(5, ['a', 'b', 'c']), '5abc');
    test.equal(Test.staticVarargsSync(5, java.newArray('java.lang.String', ['a', 'b', 'c'])), '5abc');

Note that when passing a JavaScript array (e.g. ['a', 'b', 'c']) for a varargs parameter, node-java must infer the Java type of the array. If all of the elements are of the same JavaScript primitive type (string in this example) then node-java will create a Java array of the corresponding type (e.g. java.lang.String). The Java types that node-java can infer are: java.lang.String, java.lang.Boolean, java.lang.Integer, java.lang.Long, and java.lang.Double. If an array has a mix of Integer, Long, and Double, then the inferred type will be java.lang.Number. Any other mix will result in an inferred type of java.lang.Object.

Methods accepting varargs of a generic type are also problematic. You will need to fall back to using java.newArray(). See Issue #285.

JVM Creation

With v0.5.1 a new API is available to make it easier for a complex application to have full control over JVM creation. In particular, it is now easier to compose an application from several modules, each of which must add to the Java classpath and possibly do other operations just before or just after the JVM has been created. See the methods ensureJvm and registerClient. See also several of the tests in the testAsyncOptions directory.

Release Notes

v0.5.0

• Support for varargs. This change is not 100% backwards compatible, but the fix is generally easy and results in more natural code.

v0.2.0

• java.lang.Long and long primitives are handled better. See (Issue #37) and (Issue #40).

Index

java

• classpath
• options
• asyncOptions
• import
• newInstance
• instanceOf
• callStaticMethod
• callMethod
• getStaticFieldValue
• setStaticFieldValue
• newArray
• newByte
• newShort
• newLong
• newChar
• newDouble
• newFloat
• newProxy
• isJvmCreated
• registerClient
• registerClientP
• ensureJvm

java objects

• Call Method
• Get/Set Field

API Documentation

java

classpath

java.classpath*

Array of paths or jars to pass to the creation of the JVM.

All items must be added to the classpath before calling any other node-java methods.

Example

java.classpath.push('commons.io.jar');
java.classpath.push('src');

options

java.options.push('-Djava.awt.headless=true');
java.options.push('-Xmx1024m');

asyncOptions

java.asyncOptions = {
  asyncSuffix: undefined,     // Don't generate node-style methods taking callbacks
  syncSuffix: "",              // Sync methods use the base name(!!)
  promiseSuffix: "Promise",   // Generate methods returning promises, using the suffix Promise.
  promisify: require('util').promisify // Needs Node.js version 8 or greater, see comment below
  ifReadOnlySuffix: "_alt"
};

• asyncSuffix Suffix for callback-based async method call signatures.
• syncSuffix Suffix for synchronous method call signatures.
• promiseSuffix Suffix for promise-based async method call signatures
• promisify Callback-to-promise transform implementation. From Node.js version 8 one can just use Node.js implementation: promisify: require('util').promisify.
• ifReadOnlySuffix See Static Member Name Conflicts.

See Async Options for details.

import

var Test = java.import('Test');
Test.someStaticMethodSync(5);
console.log(Test.someStaticField);

var value1 = Test.NestedEnum.Value1;

var test = new Test();
list.instanceMethodSync('item1');

newInstance

var list = java.newInstanceSync("java.util.ArrayList");

java.newInstance("java.util.ArrayList", function(err, list) {
  if(err) { console.error(err); return; }
  // new list
});

instanceOf

var obj = java.newInstanceSync("my.package.SubClass");

if(java.instanceOf(obj, "my.package.SuperClass")) {
  console.log("obj is an instance of SuperClass");
}

callStaticMethod

• className - The name of the class to call the method on. Separate nested classes using '$' (eg. com.nearinfinty.MyClass$NestedClass).
• methodName - The name of the method to call. The method name can include the full signature (see Getting the full method signature).
• callback(err, item) - Callback to be called when the class is created.

Example

var result = java.callStaticMethodSync("com.nearinfinty.MyClass", "doSomething", 42, "test");

java.callStaticMethod("com.nearinfinty.MyClass", "doSomething", 42, "test", function(err, results) {
  if(err) { console.error(err); return; }
  // results from doSomething
});

callMethod

• instance - An instance of the class from newInstance.
• methodName - The name of the method to call. The method name can include the full signature (see Getting the full method signature).
• callback(err, item) - Callback to be called when the class is created.

Example

var instance = java.newInstanceSync("com.nearinfinty.MyClass");

var result = java.callMethodSync("com.nearinfinty.MyClass", "doSomething", 42, "test");

java.callMethodSync(instance, "doSomething", 42, "test", function(err, results) {
  if(err) { console.error(err); return; }
  // results from doSomething
});

getStaticFieldValue

var data = java.getStaticFieldValue("com.nearinfinty.MyClass", "data");

setStaticFieldValue

java.setStaticFieldValue("com.nearinfinty.MyClass", "data", "Hello World");

newArray

var newArray = java.newArray("java.lang.String", ["item1", "item2", "item3"]);

newByte

var b = java.newByte(12);

newShort

var s = java.newShort(12);

newLong

var s = java.newLong(12);

newChar

var ch = java.newChar('a');

newDouble

var d = java.newDouble(3.14);

newFloat

var f = java.newFloat(3.14);

newProxy

var myProxy = java.newProxy('java.lang.Runnable', {
  run: function () {
    // This is actually run on the v8 thread and not the new java thread
    console.log("hello from thread");
  }
});

var thread = java.newInstanceSync("java.lang.Thread", myProxy);
thread.start();

isJvmCreated

registerClient

registerClientP

ensureJvm

java object

Call Method

var list = java.newInstanceSync("java.util.ArrayList");
list.addSync("item1");
list.add("item2", function(err, result) {
  if(err) { console.error(err); return; }
});

Field Access

var list = java.newInstanceSync("com.nearinfinty.MyClass");
list.data = "test";
var data = list.data;

Getting the Full Method Signature

public int methodAmbiguous(java.lang.Double);
  Signature: (Ljava/lang/Double;)I

Signal Handling

The JVM intercepts signals (Ctrl+C, etc.) before node/v8 gets to handle them. To fix this there are a couple options.

Signal Handling Option 1

One option to capture these events is to add the following flag:

java.options.push('-Xrs');

As man java says, the -Xrs flag will “reduce usage of operating-system signals by [the] Java virtual machine (JVM)”, to avoid issues when developing “applications that embed the JVM”.

Signal Handling Option 2

Hook into the runtime shutdown hook.

First create a java wrapper around the Runtime.addShutdownHook method to allow using a proxy object.

public class ShutdownHookHelper {
  public static void setShutdownHook(final Runnable r) {
    Runtime.getRuntime().addShutdownHook(new Thread() {
      @Override
      public void run() {
        r.run();
      }
    });
  }
}

Compile ShutdownHookHelper and then use it as follows.

var java = require('./');
java.classpath.push('.');
var ShutdownHookHelper = java.import('ShutdownHookHelper');
 
ShutdownHookHelper.setShutdownHookSync(java.newProxy('java.lang.Runnable', {
  run: function () {
    console.log("do shutdown stuff here instead.");
  }
}));

Object lifetime

When you call a Java method through node-java, any arguments (V8/JavaScript objects) will be converted to Java objects on the v8 main thread via a call to v8ToJava (found in utils.cpp). The JavaScript object is not held on to and can be garbage collected by v8. If this is an async call, the reference count on the Java objects will be incremented. The Java method will be invoked in a node.js async thread (see uv_queue_work). When the method returns, the resulting object will be returned to the main v8 thread and converted to JavaScript objects via a call to javaToV8 and the Java object's reference count will then be decremented to allow for garbage collection. The resulting v8 object will then be returned to the callers callback function.

Static member name conflicts ('name', 'arguments', 'caller')

The JavaScript object returned by java.import(classname) is a JavaScript constructor Function, implemented such that you can create instances of the Java class. For example:

var Test = java.import('Test');
var test = new Test();
 
Test.someStaticMethod(function(err, result) { ... });
 
var value1 = Test.NestedEnum.Value1;

But JavaScript reserves a few property names of Function objects: name, arguments, and caller. If your class has public static members (either methods or fields) with these names, node-java is unable to create the necessary property to implement the class's API. For example, suppose your class Test implements a static method named caller, or has a NestedEnum with a value name:

public class Test {
    ...
    public static String caller() { return "something"; }
    public enum NestedEnum { foo, name };
}

In JavaScript, you would expect to be able to use those static members like this:

var Test = java.import('Test');
Test.caller(function(err, result) { ... });  // ERROR
var value = Test.NestedEnum.name;  // ERROR

Node-java can't create those properties, so the above code won't work. Instead, node-java appends a suffix to the name. The default suffix is simply an underscore _, but you can change the suffix using asyncOptions:

var java = require('java');
 
java.asyncOptions = {
  asyncSuffix: "",
  syncSuffix: "Sync",
  ifReadOnlySuffix: "_alt"
};
 
var Test = java.import('Test');
Test.caller_alt(function(err, result) { ... });  // OK
var value = Test.NestedEnum.name_alt;  // OK

Troubleshooting

Error: Cannot find module '../build/jvm_dll_path.json'

Either postInstall.js didn't run or there was a problem detecting java. Try running postInstall.js manually.

Debugging

    npm install
    node-gyp build --debug
    gdb --args `which node` ./node_modules/.bin/nodeunit test

License

(The MIT License)

Copyright (c) 2012 Near Infinity Corporation

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.