New features of Java8 how to use jjs tools
This article mainly explains "how to use the new Java8 feature jjs tool". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to use the new Java8 feature jjs tool".
There are mainly two aspects, the jjs tool and the API under the javax.script package:
Jjs is shipped under java_home/bin. As an example, let's create a func.js with the following content:
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Function f () {return 1;}
Print (f () + 1)
Run this file and pass it as an argument to jjs
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Jjs func.js
Output: 2
Another aspect is javax.script, which is also the API left over from the previous Rhino.
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ScriptEngineManager manager = new ScriptEngineManager ()
ScriptEngine engine = manager.getEngineByName ("JavaScript")
System.out.println (engine.getClass () .getName ())
System.out.println ("Result:" + engine.eval ("function f () {return 1;}; f () + 1;"))
The output is as follows:
Jdk.nashorn.api.scripting.NashornScriptEngine
Nashorn VS Rhino
It is nothing new for javascript to run on jvm. Rhino has existed since jdk6, but now the official explanation is that Rhino is so slow compared to other javascript engines (such as google's V8) that it is better to rewrite Rhino than other javascript engines. Since performance is a highlight of Nashorn, let's test the performance comparison. In order to compare the performance between the two, you need to use Esprima, an ECMAScript parsing framework, to parse the uncompressed version of jquery (about 268kb). The core test code is as follows:
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Static void rhino (String parser, String code) {
String source = "speedtest"
Int line = 1
Context context = Context.enter ()
Context.setOptimizationLevel (9)
Try {
Scriptable scope = context.initStandardObjects ()
Context.evaluateString (scope, parser, source, line, null)
ScriptableObject.putProperty (scope, "$code", Context.javaToJS (code, scope))
Object tree = new Object ()
Object tokens = new Object ()
For (int I = 0; I < RUNS; + + I) {
Long start = System.nanoTime ()
Tree = context.evaluateString (scope, "esprima.parse ($code)", source, line, null)
Tokens = context.evaluateString (scope, "esprima.tokenize ($code)", source, line, null)
Long stop = System.nanoTime ()
System.out.println ("Run #" + (I + 1) + ":" + Math.round ((stop-start) / 1e6) + "ms")
}
} finally {
Context.exit ()
System.gc ()
}
}
Static void nashorn (String parser, String code) throws ScriptException,NoSuchMethodException {
ScriptEngineManager factory = new ScriptEngineManager ()
ScriptEngine engine = factory.getEngineByName ("nashorn")
Engine.eval (parser)
Invocable inv = (Invocable) engine
Object esprima = engine.get ("esprima")
Object tree = new Object ()
Object tokens = new Object ()
For (int I = 0; I < RUNS; + + I) {
Long start = System.nanoTime ()
Tree = inv.invokeMethod (esprima, "parse", code)
Tokens = inv.invokeMethod (esprima, "tokenize", code)
Long stop = System.nanoTime ()
System.out.println ("Run #" + (I + 1) + ":" + Math.round ((stop-start) / 1e6) + "ms")
}
/ / System.out.println ("Data is" + tokens.toString () + "and" + tree.toString ())
}
As can be seen from the code, the test program will execute Esprima's parse and tokenize to run the contents of the test file. Rhino and Nashorn will be executed 30 times respectively. At the beginning, Rhino needs 1726 ms and slowly accelerates, and finally stabilizes at around 950ms. Nashorn has another feature: it takes 3682ms to run * times, but it accelerates quickly after warm-up, and finally stabilizes at 175ms each time, as shown in the following figure.
Nashorn first compiles the javascript code to java bytecode, and then runs it on jvm, which is also executed using the invokedynamic command at the bottom, so it runs very fast.
Why use java to implement javascript
This is also what most students are concerned about. I agree with this point of view:
Mature GC
Mature JIT compiler
Multithreading support
Rich standard libraries and third-party libraries
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