java

Bridge API to connect with existing Java APIs.

java

Bridge API to connect with existing Java APIs.

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###Other projects that might be helpful

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

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.

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"

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
npm test8

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

Quick Examples

var java = require("java");
java.classpath.push("commons-lang3-3.1.jar");
java.classpath.push("commons-io.jar");
 
var list = java.newInstanceSync("java.util.ArrayList");
 
java.newInstance("java.util.ArrayList", function(err, list) {
  list.addSync("item1");
  list.addSync("item2");
});
 
var ArrayList = java.import('java.util.ArrayList');
var list = new ArrayList();
list.addSync('item1');

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(str.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());
}

Promises

As of release 0.4.5 it is possible to create async methods that return promises by setting the asyncOptions property of the java object.

Example:

var java = require("java");
java.asyncOptions = {
  promiseSuffix: "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 */ });

• If you don't want promise-returning methods, simply leave java.asyncOptions unset.
• Sync and standard async methods are still generated as in previous releases. In the future we may provide the option to disable generation of standard async methods.
• asyncOptions.promisify must be a function that given a node.js style async function as input returns a function that returns a promise that is resolved (or rejected) when the async function has completed. Several Promises/A+ libraries provide such functions, but it may be necessary to provide a wrapper function. See testHelpers.js for an example.
• You are free to choose whatever non-empty promiseSuffix you want for the promise-returning methods, but you must specify a value.
• We've tested 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 some other java method is called. You may need to call some other java method such as java.import() to finalize java initialization.

Release Notes

v0.2.0

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

Index

java

• classpath
• options
• import
• newInstance
• instanceOf
• callStaticMethod
• callMethod
• getStaticFieldValue
• setStaticFieldValue
• newArray
• newByte
• newShort
• newLong
• newChar
• newDouble
• newFloat
• newProxy

java objects

• Call Method
• Get/Set Field

API Documentation

java

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.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

• className - The name of the class to create. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)

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

• className - The name of the class to create. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• callback(err, item) - Callback to be called when the class is created.

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

• javaObject - Instance of a java object returned from a method or from newInstance.
• className - A string class name.

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

• className - The name of the class to call the method on. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• 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
});

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

• 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
});

java.getStaticFieldValue(className, fieldName)

Gets a static field value from the specified class.

Arguments

• className - The name of the class to get the value from. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• fieldName - The name of the field to get the value from.

Example

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

java.setStaticFieldValue(className, fieldName, newValue)

Sets a static field value on the specified class.

Arguments

• className - The name of the class to set the value on. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• fieldName - The name of the field to set the value on.
• newValue - The new value to assign to the field.

Example

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

java.newArray(className, values[])

Creates a new java array of type class.

Arguments

• className - The name of the type of array elements. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• values - A javascript array of values to assign to the java array.

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

• val - The value of the java byte.

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

• val - The value of the java short.

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

• val - The value of the java long.

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

• val - The value of the java char.

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

• val - The value of the java double.

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

• val - The value of the java float.

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

• interfaceName - The name of the interface to proxy. For subclasses seperate using a '$' (eg. com.nearinfinty.MyClass$SubClass)
• functions - A hash of functions matching the function in the interface.

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 object

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

• args - The arguments to pass to the method.
• callback(err, item) - Callback to be called when the method has completed.

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.

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.

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.

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.