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.

VSYNTAC

TI C

.com


our system in 30 seconds


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


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?


µ-Java: boolean

• if (condition) statement1else 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>


Growing a Language


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


It’s a lot of fun!


And it can be very geeky!


Software is Traditionally Layered

• Examples– Jetty– Apache HTTP client


STOP

Think about Components

• Provides Functionality…• given Required Services.• Yields reusable software• Key to testability


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;


http://www.scala-lang.org/

Dependency Injection to the Rescue

class UserServiceImpl

implements UserService {

@Inject

UserServiceImpl(HttpClient, …) { …

}


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; }


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/


http://code.google.com/p/queryengine/

Shell’s “everything is a process”

process

stdin args

stdoutstderr return code


Shell is a plumbing language

if echo $name | grep –q “Jack”; then

echo

$name

$name

grep

-q

return code

if

return code


Queries

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


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>)


@τ

HelloWorld Query

class HelloWorld extends AbstractQuery<String> {

HelloWorld(String name) { …

@Inject DateTime now;

String process() {

return now + “: Hello ” + name;

}

}


QueryDriver


query

mon

itorin

g

retr

ying

tran

sact

ing

inje

ctin

g

scop

ing

V

Lazy

Man

ager

@

Adapt Queries

• Backend servers• Frontend server for GWT• Command-line tools• Tests


Conditionals Complicate Testingif (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


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();

}


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(); }


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/


http://code.google.com/p/jsonmarshaller/

JsonMarshaller

@Entityclass Googler {

@ValueList<Cafe> favoriteCafes;

}

createMarshaller(Googler.class).marshall(…);

produces

{“favoriteCafes”:[“150”, “Charlie’s”]}


JsonMarshaller

@Value ABC enumAbc;

@Value(ordinal = true) ABC enumAbc;

• dedicated code is wired at creation time• (almost) no conditionals at run-time


@

JsonMarshaller

Conditionals

if(annotation.ordinal)

marshallOrdinal()

else

marshallName()

Delegation

marshall()


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


Express “what” instead of Coding “how”

path(

"users",

path(

FetchUser.class,

path(

"watchlist",

QuerySpec.of(

FetchUser.class,

asList(UserPart.WATCHLIST)),

path(immutableMap(

PUT, AddToWatchlist.class,

DELETE, RemoveFromWatchlist.class)))),


/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?

τ

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, …));


… or maybe not


portfolio(now, 90) .buyStock(now, "KO", 10, 1) .payInterest(later, fedRateRepository) .sellStock(latest, "KO", 10, 1) .get()

what?

Find Managers


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 = ?


dimension 1

dimension 2

…

orde

r 1

orde

r 2

…

Practice Safe Programming: Use Types


Selector

createIndex : Index

Index

search(Constraint)

Constraint

getSelector : Selector

Practice Safe Programming: Use Types


Selector<M>

createIndex : Index<M>

Index<M>

search(Constraint<M>)

Constraint<M>

getSelector : Selector<M>

τ

Summary of the Examples


τ @what?

dependency injection

query constructors

query driver

thunk

JsonMarshaller

API paths parsing

builder pattern

family polymorphism

✓ ✓✓ ✓

✓ ✓✓ ✓

✓ ✓✓

✓

µ-Java ✓

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


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 Heveryhttp://misko.hevery.com

• Growing a Language, by Guy Steelehttp://video.google.com/videoplay?docid=-8860158196198824415

• Type-Safe Builder Pattern in Scalahttp://blog.rafaelferreira.net/2008/07/type-safe-builder-pattern-in-scala.html


http://googletesting.blogspot.com/2008/02/in-movie-amadeus-austrian-emperor.html

http://googletesting.blogspot.com/2008/05/tott-invisible-branch.html

http://code.google.com/p/jsonmarshaller/

http://jonasboner.com/2008/10/06/real-world-scala-dependency-injection-di/

http://lamp.epfl.ch/~odersky/papers/ScalableComponent.pdf

http://blog.kaching.com/index.php/2009/01/16/unifying-type-parameters-in-java/

https://japex.dev.java.net/

http://misko.hevery.com/

http://video.google.com/videoplay?docid=-8860158196198824415

http://en.wikipedia.org/wiki/State_pattern

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Add (Syntactic) Sugar To Your Java