View
5.195
Download
1
Category
Preview:
Citation preview
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
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) 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>
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”
process
stdin args
stdoutstderr return code
Pascal-Louis Perez, kaChing Group Inc.
Shell is a plumbing language
if echo $name | grep –q “Jack”; then
echo
$name
$name
grep
-q
return code
if
return code
Pascal-Louis Perez, kaChing Group Inc.
Queries
query
dependencies
exception
arguments
value
Pascal-Louis Perez, kaChing Group Inc.
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
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
Pascal-Louis Perez, kaChing Group Inc.
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
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
@Entityclass Googler {
@ValueList<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,
asList(UserPart.WATCHLIST)),
path(immutableMap(
PUT, AddToWatchlist.class,
DELETE, RemoveFromWatchlist.class)))),
Pascal-Louis Perez, kaChing Group Inc.
/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, …));
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
…
orde
r 1
orde
r 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.
Selector<M>
createIndex : Index<M>
Index<M>
search(Constraint<M>)
Constraint<M>
getSelector : Selector<M>
τ
Summary of the Examples
Pascal-Louis Perez, kaChing Group Inc.
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
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 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
Pascal-Louis Perez, kaChing Group Inc.
Recommended