2. Overall presenta3on
Introduc3on to Domain Specific Languages and
its techniques. As well as showing Fluent
Valida3on Framework concep3on process.
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3. Domain Specific Language (DSL) is a
programming language dedicated to
solve problems of an specific domain
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4. which can be technical
SQL
HQL
CSS
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5. or business related.
Banking
Manufacturing
Logis3cs
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6. A DSL can be internal or external.
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7. External DSLs are self‐contained
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8. while internal DSLs remain on top of
other programming languages.
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9. In other words, internal DSLs are APIs.
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That's why they're also known as Fluent Interfaces!

10. DSLs allow you to express domains clearly.
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11. For example, while a business analyst of
a banking domain would say
Transfer 5.000,00 from Client A's cash account to Client B's savings account.
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12. A common JAVA implementa3on could be
bankService.transfer(5000.00,
clientA.getCashAccount(),
clientB.getSavingsAccount());
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13. An external DSL could express the same as
transfer 5000 from clientA.cashAccount to clientB.savingsAccount
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14. And an internal DSL in JAVA could look like
bankService.execute( new Transfer()
.of(5000)
.from(clientA.cashAccount())
.to(clientB.savingsAccount()));
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15. It’s not about one single method
public Transfer of(double value);
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16. but an en3re meaningful opera3on.
new Transfer()
.of(5000)
.from(clientA.cashAccount())
.to(clientB.savingsAccount())
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17. Some techniques to define internal DSLs
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18. Method Chaining
new Transfer()
.of(5000)
.from(clientA.cashAccount())
.to(clientB.savingsAccount())
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19. Nested Func3on
bankService.transfer(5000,
from(clientA.cashAccount()),
to(clientB.savingsAcount()));
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20. Object Scoping
bankService.execute(
new Transfer(){{
of(5000);
from(clientA.cashAccount());
to(clientB.savingsAccount());
}});
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21. Fluent Valida3on Framework is a lab
project applying Fluent Interfaces to the
domain of code valida3on.
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22. Main idea was changing valida3ons like
if(arg0 == null)
throw new IllegalArgumentException();
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23. to something like
ensure(arg0).isNotNull();
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24. How to change excep3on message?
ensure(arg0).isNotNull().otherwise("arg0 cannot be null");
//doesn't work
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25. Trigger method at the end of the expression
ensure(arg0).isNotNull().now();
ensure(arg0).isNotNull()
.otherwise()
.throwThis(
new IllegalStateException())
.now();
//not cool!
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26. Another op3on was crea3ng two entry points
ensure(arg0).isNotNull();
analyse(arg0).and().throwThis(new IllegalStateException()).ifNull();
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27. Mixing method chaining with nested func3ons
ensure(myObject).is(inValidState());
analyse(systemReport).and(notifyByEmail()).ifIsNot(operatingWell());
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the solu3on became extensible!

28. Today we saw
DSLs are cool!
External DSLs are hard to implement
Fluent Interfaces and Internal DSLs are the same thing
Fluent Interfaces work great for extensively used APIs
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29. That’s all folks!
project hXp://fluval.sourceforge.net
blog hXp://blog.danielgazineu.com
email/gtalk danielgazineu@gmail.com
twiXer @danielgazineu
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