Add (Syntactic) Sugar To Your Java

Add Sugar to your Java “ how we architected from the ground up for testability, and why” Pascal-Louis Perez – .com Pascal-Louis Perez, kaChing Group Inc. V SYNTACTIC

.com Pascal-Louis Perez, kaChing Group Inc.

our system in 30 seconds Pascal-Louis Perez, kaChing Group Inc.

Overview Components versus Layers Type Driven Development 1:1 principle Family Polymorphism Annotations Meta Information Typing Extensions Object Oriented design replaces Conditionals Delegation State Pattern Declarative Programming Domain Specific Language Factories Pascal-Louis Perez, kaChing Group Inc. τ @ what?

µ-Java Imagine Java deprived of all native types ( boolean , int , …) and all control-flow constructs ( if then else , for , while , …) How do you encode booleans using only objects? What about integers? Is µ-Java Turing-complete? Pascal-Louis Perez, kaChing Group Inc.

µ-Java: boolean if (condition) statement1 else statement2 condition.if(statement1, statement2) Bool class with True and False subclasses in True, if computes statement1 In False, if computes statement2 Statements are instances of Thunk<Void> Pascal-Louis Perez, kaChing Group Inc.

Growing a Language Pascal-Louis Perez, kaChing Group Inc. expressiveness µ-Java 1 Do not take things for granted 2 Think outside the Language

Testable Code Because… It allows quick iterations It makes it easy to scale the team It is more cost effective than debugging It obsoletes the need for functional QA It facilitates continuous refactoring, allowing the code to get better with age It attracts the right kind of engineers Pascal-Louis Perez, kaChing Group Inc.

It’s a lot of fun! Pascal-Louis Perez, kaChing Group Inc.

And it can be very geeky! Pascal-Louis Perez, kaChing Group Inc.

Software is Traditionally Layered Examples Jetty Apache HTTP client Pascal-Louis Perez, kaChing Group Inc. STOP

Think about Components Provides Functionality… given Required Services. Yields reusable software Key to testability Pascal-Louis Perez, kaChing Group Inc.

Wireable Puzzle Pieces What if I want only one thread pool in my whole app server? In Scala ( http://www.scala-lang.org ) new JettyServer with MyThreadPool; new ParallelRpc with MyThreadPool; Pascal-Louis Perez, kaChing Group Inc.

Dependency Injection to the Rescue class UserServiceImpl implements UserService { @Inject UserServiceImpl( HttpClient, … ) { … } Pascal-Louis Perez, kaChing Group Inc. required services functionality τ

Add Retrying Logic class MyExtendedUserServiceImpl implements UserService { @Inject UserServiceImpl( UserServiceImpl ) … User getUser (Id<User> id) { User u = null; for (int i=0; i<5 && u == null; i++) u = delegate . getUser (id); return u; } Pascal-Louis Perez, kaChing Group Inc.

QueryEngine Software platform to build services quickly Unit of work is a Query query constructors define input parameters queries can request dependencies at run-time queries do work and produce a value which is then post-processed (serialized, stored, …) Soon open-sourced http://code.google.com/p/queryengine/ Pascal-Louis Perez, kaChing Group Inc.

Shell’s “everything is a process” Pascal-Louis Perez, kaChing Group Inc. process stdin args stdout stderr return code

Shell is a plumbing language if echo $name | grep –q “Jack”; then Pascal-Louis Perez, kaChing Group Inc. echo $name $name grep -q return code if return code

Queries Pascal-Louis Perez, kaChing Group Inc. query dependencies exception arguments value

Query Constructors Similar to dependency injection, you ask for the arguments you need rather than fetch them from the environment Type safe regardless of input format Pascal-Louis Perez, kaChing Group Inc.

Query Constructors AddToWatchlist(Id<User>, Symbol) AddToGroup(Id<User>, Id<Group>, @Optional boolean) PlaceOrder(Id<User>, Action, Symbol, @Positive int) PostMessage(Id<User>, Id<Wall>, Text<Plain>) Pascal-Louis Perez, kaChing Group Inc. @ τ

HelloWorld Query class HelloWorld extends AbstractQuery<String> { HelloWorld(String name) { … @Inject DateTime now; String process() { return now + “: Hello ” + name; } } Pascal-Louis Perez, kaChing Group Inc.

QueryDriver Pascal-Louis Perez, kaChing Group Inc. @ query monitoring retrying transacting injecting scoping V LazyManager

Adapt Queries Backend servers Frontend server for GWT Command-line tools Tests Pascal-Louis Perez, kaChing Group Inc.

Conditionals Complicate Testing if (a) { if (b) { section 1 } else { section 2 } } else { if (b) { section 3 } else { section 4 } } Branch coverage requires a lot of tests Typically, deep conditionals require a lot of obscure setup in tests Ties more closely the test and the implementation Pascal-Louis Perez, kaChing Group Inc.

Thunk<T> abstract class Thunk<T> { private boolean evaluated = false; private T value; public T get() { if (!evaluated) { value = compute(); evaluated = true; } return value; } abstract protected T compute(); } Pascal-Louis Perez, kaChing Group Inc.

Thunk<T> without conditional abstract class Thunk<T> { private Getter value = new Getter<T>() { public T get() { final T v = compute(); value = new Getter<T>() { T get() { return v; } }; return value .get(); } }; public T get() { return value .get(); } Pascal-Louis Perez, kaChing Group Inc.

JsonMarshaller Marshalling library converting Java POJOs into JSON and vice-versa. Annotations and persistence ideas inspired by Hibernate “ kaChing’s proto buffers” http://code.google.com/p/jsonmarshaller/ Pascal-Louis Perez, kaChing Group Inc.

JsonMarshaller @Entity class Googler { @Value List<Cafe> favoriteCafes; } createMarshaller(Googler.class).marshall(…); produces {“favoriteCafes”:[“150”, “Charlie’s”]} Pascal-Louis Perez, kaChing Group Inc.

JsonMarshaller @Value ABC enumAbc; @Value(ordinal = true) ABC enumAbc; dedicated code is wired at creation time (almost) no conditionals at run-time Pascal-Louis Perez, kaChing Group Inc. @

JsonMarshaller Conditionals if(annotation.ordinal) marshallOrdinal() else marshallName() Delegation marshall() Pascal-Louis Perez, kaChing Group Inc.

kaChing’s API REST path parsing REST API with paths such as /users/ :id: /users/ :id: /portfolio/trades/ :tradeId: /communities/everyone/insight HTTP parameters Headers (X-KaChing-ApiKey, X-KaChing-RemoteKey) GET, PUT, POST, DELETE Pascal-Louis Perez, kaChing Group Inc.

Express “ what ” instead of Coding “ how ” path( "users", path( FetchUser.class, path( "watchlist", QuerySpec. of( FetchUser.class, a sList(UserPart.WATCHLIST)), path( immutableMap( PUT, AddToWatchlist.class, DELETE, RemoveFromWatchlist.class)))), Pascal-Louis Perez, kaChing Group Inc. τ /users/ :id: handled by FetchUser.class /users/ :id: /watchlist handled by FetchUser.class with the extra paramater WATCHLIST PUT /users/ :id: /watchlist handled by AddToWatchlist.class what?

I’ll have a big boilerplate for lunch Portfolio p = new Portfolio(…); Stock ko = new Stock(…); p.executeTrade( new BuyStockTrade(ko, …)); p.executeTrade(new Interest(…)); p.executeTrade( new SellStockTrade(ko, …)); Pascal-Louis Perez, kaChing Group Inc.

… or maybe not Pascal-Louis Perez, kaChing Group Inc. portfolio(now, 90) .buyStock(now, "KO", 10, 1) .payInterest(later, fedRateRepository) .sellStock(latest, "KO", 10, 1) .get() what?

Find Managers Pascal-Louis Perez, kaChing Group Inc. order constraint

Constraint, Index, Selector Constraint: search criteria on one dimension e.g. age = 4 Index: search structure can handle only one kind of constraint Selector: constraint template used to find appropriate index e.g. age = ? Pascal-Louis Perez, kaChing Group Inc. dimension 1 dimension 2 … order 1 order 2 …

Practice Safe Programming: Use Types Pascal-Louis Perez, kaChing Group Inc. Selector createIndex : Index Index search( Constraint) Constraint getSelector : Selector

Practice Safe Programming: Use Types Pascal-Louis Perez, kaChing Group Inc. τ Selector <M> createIndex : Index <M> Index <M> search( Constraint <M> ) Constraint <M> getSelector : Selector <M>

Summary of the Examples Pascal-Louis Perez, kaChing Group Inc. τ @ dependency injection query constructors query driver thunk JsonMarshaller API paths parsing builder pattern family polymorphism ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ µ-Java ✓ what?

Key Takeaways Build components instead of providing extension points Apply the 1:1 principle Simplify your life with annotations Use delegation instead of conditionals Languages are conveniences, not barriers Pascal-Louis Perez, kaChing Group Inc.

Further Readings TotT: Too Many Tests http://googletesting.blogspot.com/2008/02/in-movie-amadeus-austrian-emperor.html TotT: The Invisible Branch http://googletesting.blogspot.com/2008/05/tott-invisible-branch.html JsonMarshaller http://code.google.com/p/jsonmarshaller/ Real-World Scala: Dependency Injection http://jonasboner.com/2008/10/06/real-world-scala-dependency-injection-di/ Scalable Component Abstraction http://lamp.epfl.ch/~odersky/papers/ScalableComponent.pdf Unifying Type Parameters in Java http://blog.kaching.com/index.php/2009/01/16/unifying-type-parameters-in-java/ Japex: Micro-Benchmarking https://japex.dev.java.net/ The Testability Explorer, Misko Hevery http://misko.hevery.com Growing a Language, by Guy Steele http://video.google.com/videoplay?docid=-8860158196198824415 Type-Safe Builder Pattern in Scala http://blog.rafaelferreira.net/2008/07/type-safe-builder-pattern-in-scala.html Pascal-Louis Perez, kaChing Group Inc.

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