Bridge API to connect with existing Java APIs.
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$ npm install java
Notes:
node findJavaHome.js in the node-java directory to see the full failure message.For 64 bit installs with 32 bit node:
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.
GYP_DEFINES="armv7=0" CCFLAGS='-march=armv6' CXXFLAGS='-march=armv6' npm install java
./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:
Some issues with the OpenSDK7 so take the Oracle version for compiling.
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
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).
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
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
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
var charArray = java.newArray("char", "hello world\n".split(''));
var byteArray = java.newArray(
"byte",
"hello world\n"
.split('')
.map(function(c) { return java.newByte(String.prototype.charCodeAt(c)); }));
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 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());
}
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("when/node").lift
};
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 */ });
asyncSuffix, syncSuffix, promiseSuffix). In the example above, the application is configured to omit the method variants using node-style async callback functions.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.asyncOptions.promisify then you must provide a non-empty string for asyncOptions.promiseSuffix.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.testHelpers.js for more information.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().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.
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.
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.
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');
java.options*
Array of options to pass to the creation of the JVM.
All items must be added to the options before calling any other node-java methods.
Example
java.options.push('-Djava.awt.headless=true');
java.options.push('-Xmx1024m');
java.import(className)*
Loads the class given by className such that it acts and feels like a javascript object.
Arguments
Example
var Test = java.import('Test');
Test.someStaticMethodSync(5);
console.log(Test.someStaticField);
var value1 = Test.NestedEnum.Value1;
var test = new Test();
list.instanceMethodSync('item1');
java.newInstance(className, [args...], callback)*
java.newInstanceSync(className, [args...]) : result
Creates an instance of the specified class. If you are using the sync method an exception will be throw if an error occures, otherwise it will be the first argument in the callback.
Arguments
Example
var list = java.newInstanceSync("java.util.ArrayList");
java.newInstance("java.util.ArrayList", function(err, list) {
if(err) { console.error(err); return; }
// new list
});
java.instanceOf(javaObject, className)*
Determines of a javaObject is an instance of a class.
Arguments
Example
var obj = java.newInstanceSync("my.package.SubClass");
if(java.instanceOf(obj, "my.package.SuperClass")) {
console.log("obj is an instance of SuperClass");
}
java.callStaticMethod(className, methodName, [args...], callback)*
java.callStaticMethodSync(className, methodName, [args...]) : result
Calls a static method on the specified class. If you are using the sync method an exception will be throw if an error occures, otherwise it will be the first argument in the callback.
Arguments
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
});
java.callMethod(instance, methodName, [args...], callback)*
java.callMethodSync(instance, methodName, [args...]) : result
Calls a method on the specified instance. If you are using the sync method an exception will be throw if an error occures, otherwise it will be the first argument in the callback.
Arguments
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
});
java.getStaticFieldValue(className, fieldName)*
Gets a static field value from the specified class.
Arguments
Example
var data = java.getStaticFieldValue("com.nearinfinty.MyClass", "data");
java.setStaticFieldValue(className, fieldName, newValue)*
Sets a static field value on the specified class.
Arguments
Example
java.setStaticFieldValue("com.nearinfinty.MyClass", "data", "Hello World");
java.newArray(className, values[])*
Creates a new java array of type class.
Arguments
Example
var newArray = java.newArray("java.lang.String", ["item1", "item2", "item3"]);
java.newByte(val)*
Creates a new java byte. This is needed because javascript does not have the concept of a byte.
Arguments
Example
var b = java.newByte(12);
java.newShort(val)*
Creates a new java short. This is needed because javascript does not have the concept of a short.
Arguments
Example
var s = java.newShort(12);
java.newLong(val)*
Creates a new java long. This is needed because javascript does not have the concept of a long.
Arguments
Example
var s = java.newLong(12);
java.newChar(val)*
Creates a new java char. This is needed because javascript does not have the concept of a char.
Arguments
Example
var ch = java.newChar('a');
java.newDouble(val)*
Creates a new java double. This is needed to force javascript's number to a double to call some methods.
Arguments
Example
var d = java.newDouble(3.14);
java.newFloat(val)*
Creates a new java float. This is needed to force javascript's number to a float to call some methods.
Arguments
Example
var f = java.newFloat(3.14);
java.newProxy(interfaceName, functions)*
Creates a new java Proxy for the given interface. Functions passed in will run on the v8 main thread and not a new thread.
The returned object has a method unref() which you can use to free the object for garbage collection.
Arguments
Example
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();
java.isJvmCreated()*
Returns true if the JVM has been created. The JVM can only be created once.
java.registerClient(before, after)*
Register that a client wants to be called back immediately before and/or immediately after the JVM is created. If used, this function must be called before the JVM has been created. The before function is typically used to add to the classpath. The function may execute asynchronous operations (such as a async glob function). The after function is sometimes useful for doing one-time initialization that requires the JVM to first be initialized. If either function is unnecessary, use null or undefined. See also registerClientP and ensureJvm. See the unit tests in testAsyncOptions for examples.
java.registerClientP(before, after)*
Like java.registerClient, but before and after are assumed to be functions returning promises.
java.ensureJvm(callback)*
If the JVM has not yet been created, execute the full JVM initialization process, then call callback function when initialization is complete. If the JVM has been created, just call the callback. Note that the full initialization process includes: 1) executing all registered client before hooks, 2) creating the JVM, then 3) executing all registered client after hooks.
obj.methodName([args...], callback)*
obj.methodNameSync([args...]) : result
Once you have a java object either by creating a new instance or as a result of a method call you can then call methods on that object. All public, non-static methods are exposed in synchronous and asynchronous flavors.
Arguments
Example
var list = java.newInstanceSync("java.util.ArrayList");
list.addSync("item1");
list.add("item2", function(err, result) {
if(err) { console.error(err); return; }
});
obj.fieldName = val*
val = obj.fieldName
Once you have a java object either by creating a new instance or as a result of a method call you can get instance field values.
Example
var list = java.newInstanceSync("com.nearinfinty.MyClass");
list.data = "test";
var data = list.data;
Getting the Full Method Signature
Run javap -s -classpath <your-class-path> <your-class-name>. Find the method name you are looking for. For example:
public int methodAmbiguous(java.lang.Double);
Signature: (Ljava/lang/Double;)I
The full method signature would be methodAmbiguous(Ljava/lang/Double;)I.
If you have grep, a shortcut is javap -s -classpath . my.company.MyClass | grep -A1 myMethodName.
The JVM intercepts signals (Ctrl+C, etc.) before node/v8 gets to handle them. To fix this there are a couple options.
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”.
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.");
}
}));
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.
The Javscript 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 simpy 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
Either postInstall.js didn't run or there was a problem detecting java. Try running postInstall.js manually.
npm install
node-gyp build --debug
gdb --args `which node` ./node_modules/.bin/nodeunit test
(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.
FAQs
Bridge API to connect with existing Java APIs.
The npm package java receives a total of 14,780 weekly downloads. As such, java popularity was classified as popular.
We found that java demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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