Polyglot programming on the JVM

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Combining JavaScript and Java  Polyglot programming on the JVM Ben Ripkens 30 June 2014

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@BenRipkens • Consulting • Software Development • Trainings

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Agenda • How not to "share" code • Possible alternatives • Nashorn and JS engine primer • complete Nashorn example • Other ecosystems • Summary

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  What happens today

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Web App Mobile App Server Java JavaScript Objective-C Swift

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Web App Server Java JavaScript

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That would be great!

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******** Password Strength weak

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******** Password Strength great

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No content

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Web App Server Java JavaScript function getPwStrength(s) { return 'weak'; } Strength getPwStrength(String s) { return Strength.WEAK; }

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No content

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function getPwStrength(s) { return 'weak'; } Strength getPwStrength(String s) { return Strength.WEAK; } SonarQube is happy! Duplications 2.4% 520 lines 28 blocks 20 files

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  Let's improve on that

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Possibility 1:  Logic only on the server-side Web App Server Java JavaScript function getPwStrength(s) { var url = '/pwstrength?pw=' + encodeURIComponent(s); return $.get(url); } @GET @Path("/pwstrength") @Produces("application/json") Strength getPwStrength( @QueryParam("pw") String pw) { return Strength.WEAK; }

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Possibility 2:  Domain Speciﬁc Languages must contain /a-z/ must contain /A-Z/ must contain /0-9/ should be longer than 6

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Possibility 3:  Share code via GWT Java JavaScript

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Possibility 4:  JavaScript on the Server Web App Server Java JavaScript function getPwStrength(s) { return 'weak'; } JavaScript

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How is this better than GWT? • Java is not a native language of the web • GWT compiles Java to another language • GWT needs to include many standard libraries in order to make the magic work • GWT needs complex build steps

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“GWT is a reasonable implementation of a poor architectural choice. [...] First, in many ways, JavaScript is more powerful and expressive than Java, so we suspect that the generation is going in the wrong direction. [...]” ! ThoughtWorks Technology Radar July 2011 http://www.thoughtworks.com/radar/#/platforms/gwt

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https://twitter.com/stilkov/status/313740729577000960

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  Nashorn Primer

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Nashorn in a nutshell • JavaScript engine (ECMAScript 5) • part of JDK 8 • JavaScript is compiled to bytecode in memory • replaces Mozilla's Rhino engine

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Hello World ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("nashorn"); String js = "print('Hello World!');" engine.eval(js); Unfortunately there is a small issue...

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Syntax and Semantic Event Loop setTimeout Call Stack Task Queue setInterval XMLHttpRequest Math / Date

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HTML 5 Specification (section 6) ECMAScript XMLHttpRequest Specification Syntax and Semantic Event Loop setTimeout Call Stack Task Queue setInterval XMLHttpRequest Math / Date

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JavaScript Engine Syntax and Semantic Call Stack Math / Date Memory Management

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JavaScript Engine Syntax and Semantic Call Stack Math / Date Memory Management

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• It is possible to import and use Java classes • this provides the ability to build your own event loop • some awesome people have already done this, but it needs to be improved: ! • if you only need the event loop: Simulating Browser APIs https://gist.github.com/bripkens/8597903 https://bugs.openjdk.java.net/browse/JDK-8006183

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  Example  PW strength check logic

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http://xkcd.com/936/ Step 1:  Our PW check shouldn't suck

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Step 1 (contd.):  Our PW check shouldn't suck https://tech.dropbox.com/2012/04/zxcvbn-realistic-password-strength-estimation/

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Step 1 (contd.):  Our PW check shouldn't suck bower install --save dropbox/zxcvbn#v1.0 Remember this dependency Install from GitHub dropbox/zxcvbn repository the tag v1.0 Save dependency to local disc

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Step 2  Make it work on the server var result = zxcvbn('myPasswordIsRatherLong'); expect(result.score).toBe(2);

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assertThat(result.get("score"), is(2)); Step 2 (contd.):  Make it work on the server ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("nashorn"); Bindings globalScope = engine.getBindings(ScriptContext.ENGINE_SCOPE); globalScope.put("window", globalScope); engine.eval(slurp("/bower_components/zxcvbn/zxcvbn.js")); String js = "zxcvbn('myPasswordIsRatherLong');";  Map result = (Map) engine.eval(js);

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  Moving beyond validation

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• Generate hints for the user based on data that has been loaded • use the same template engine on client and server • compile LESS CSS on the server What you might want to do

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• basically Node.js on the JVM with the help of Nashorn • enables you to do require('events') and more • uses libuv to support Node.js APIs • unfortunately still very young and not well documented Avatar.js to the rescue

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Node.js modules Run with Avatar.js on the JVM Transpile with browserify Run in the browser [ browser ] [ JVM ] Run on Node.js [ Node.js ]

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What about the simpliﬁcation?

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Web App Server Java JavaScript

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Web App Mobile App Server Java JavaScript Objective-C Objective-C

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Objective-C #import ! NSString* js = @"Math.max(2, 3);"; JSContext* context = [[JSContext alloc] init]; JSValue* value = [context evaluateScript:js]; NSLog(@"Max = %d", [value toInt32]);

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Summary

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JavaScript is ubiquitous Avatar.js

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• Share not only business, but also UI logic • Oﬄine-ﬁrst becomes more and more viable • run Node.js modules as part of your Maven based build process • we will probably come up with some very interesting use cases Summary

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THANKS! @BenRipkens github.com/bripkens/java-with-javascript  [email protected]  http://codecentric.de

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• On password strength estimation • http://xkcd.com/936/ • https://tech.dropbox.com/2012/04/zxcvbn-realistic-password-strength- estimation/ • http://www.troyhunt.com/2014/05/the-ebay-breach-answers-to-questions.html • Specifications • http://www.ecma-international.org/ecma-262/5.1/ • http://www.w3.org/TR/html5/webappapis.html#timers • http://www.w3.org/TR/XMLHttpRequest/ • Misc • https://avatar-js.java.net/ • http://alistapart.com/article/offline-first References