Bridge API to connect with existing Java APIs.
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###Other projects that might be helpful
$ 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"
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');
var charArray = java.newArray("char", "hello world\n".split(''));
var byteArray = java.newArray(
"byte",
"hello world\n"
.split('')
.map(function(c) { return java.newByte(str.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());
}
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');
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');
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.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
});
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.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.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
});
Gets a static field value from the specified class.
Arguments
Example
var data = java.getStaticFieldValue("com.nearinfinty.MyClass", "data");
Sets a static field value on the specified class.
Arguments
Example
java.setStaticFieldValue("com.nearinfinty.MyClass", "data", "Hello World");
Creates a new java array of type class.
Arguments
Example
var newArray = java.newArray("java.lang.String", ["item1", "item2", "item3"]);
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);
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);
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);
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');
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);
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);
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();
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; }
});
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;
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 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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