Cleaner code with Guava @alexsimonescu 

http://bit.ly/204MhVV 

Alexandru Simonescu http://blog.alexsimo.com http://alexsimo.com @alexsimonescu [email protected] “Do what you love. Love what you do.” - Ray Bradbury 

No content

Our mission - Write cleaner code - Be more productive - Open mind to new workflows - Discover new types 

What is Guava? 

What is Guava? - Google’s core Java library - Utilities classes and methods - Used in Google and Netflix 

Guava components hashing event bus math reflection networking annotations basic utilities collections concurrency comparison strings primitives ranges functional I/O cache 

Guava components hashing event bus math reflection networking annotations basic utilities collections concurrency ordering strings primitives ranges functional I/O cache 

Basic 

We all love null 

But what “null” really means? 

Failure? Success? Absence? 

Domain problems in Domain Driven Design 

Null use cases - None - Represent some sort of absence - Value not found - Something went wrong :( 

Your task 2. Find better alternative 1. Identify what really means enums constants builders 

Optional 

Optional - may contain non null value (reference is present) - may contain nothing (reference is absent) 

Optional name = Optional.of("Alex");
 Optional age = Optional.absent();
 Optional car = Optional.fromNullable(null);
 
 
 System.out.println(String.format("Name exists: %s", name.isPresent())); System.out.println(String.format("Age or default: %s", age.or(0))); 
 System.out.println(String.format("Car: %s", car.toString())); 

Optional goodness - Increases readability - Makes you analyze absent case - Never forget if a value can be null - Forces you to unwrap Optional 

Strings 

Strings goodness - Join and split strings easily - Characters matching helpers - Safe charsets 

List fruits = Arrays.asList(
 null, "banana", null, "blackberry", null, "guava");
 String joined = Joiner.on(", ").skipNulls().join(fruits);
 
 // banana, blackberry, guava String contacts = "alex:123;bob:321;ana:333;daniel:890;victor: 456";
 
 Splitter.MapSplitter mapSplitter = Splitter.on(";").withKeyValueSeparator(":");
 Map descompose = mapSplitter.split(contacts);
 for (Map.Entry f : descompose.entrySet()) {
 println(String.format("%s -> %s", f.getKey(), f.getValue()));
 } // alex -> 123 // bob -> 321 // ana -> 333 

Person person = persons.get(ONE);
 StringBuffer sb = new StringBuffer();
 sb.append(person.getSuffix());
 sb.append(" --- ");
 sb.append(person.getName());
 sb.append(" --- ");
 sb.append(person.getPhoneNumber());
 String phone = CharMatcher.DIGIT.retainFrom(sb);
 

Objects 

Objects goodness - Easy toString(), hashCode() and equals() - Cleaner compareTo() - Objects comparator 

@Override
 public boolean equals(Object o) {
 if (this == o) return true;
 if (o == null || getClass() != o.getClass()) return false;
 
 Person person = (Person) o;
 
 if (firstName != null ? !firstName.equals(person.firstName) : person.firstName != null) return false;
 if (lastName != null ? !lastName.equals(person.lastName) : person.lastName != null) return false;
 if (name != null ? !name.equals(person.name) : person.name != null) return false;
 if (suffix != null ? !suffix.equals(person.suffix) : person.suffix != null) return false;
 if (phoneNumber != null ? !phoneNumber.equals(person.phoneNumber) : person.phoneNumber != null) return false;
 if (email != null ? !email.equals(person.email) : person.email != null) return false;
 if (website != null ? !website.equals(person.website) : person.website != null) return false;
 if (address != null ? !address.equals(person.address) : person.address != null) return false;
 return car != null ? car.equals(person.car) : person.car == null;
 
 }
 
 @Override
 public int hashCode() {
 int result = firstName != null ? firstName.hashCode() : 0;
 result = 31 * result + (lastName != null ? lastName.hashCode() : 0);
 result = 31 * result + (name != null ? name.hashCode() : 0);
 result = 31 * result + (suffix != null ? suffix.hashCode() : 0);
 result = 31 * result + (phoneNumber != null ? phoneNumber.hashCode() : 0);
 result = 31 * result + (email != null ? email.hashCode() : 0);
 result = 31 * result + (website != null ? website.hashCode() : 0);
 result = 31 * result + (address != null ? address.hashCode() : 0);
 result = 31 * result + (car != null ? car.hashCode() : 0);
 return result;
 } 

No content

@Override
 public boolean equals(Object o) {
 if (this == o) return true;
 if (o == null || getClass() != o.getClass()) return false;
 
 Person person = (Person) o;
 
 if (firstName != null ? !firstName.equals(person.firstName) : person.firstName != null) return false;
 if (lastName != null ? !lastName.equals(person.lastName) : person.lastName != null) return false;
 if (name != null ? !name.equals(person.name) : person.name != null) return false;
 if (suffix != null ? !suffix.equals(person.suffix) : person.suffix != null) return false;
 if (phoneNumber != null ? !phoneNumber.equals(person.phoneNumber) : person.phoneNumber != null) return false;
 if (email != null ? !email.equals(person.email) : person.email != null) return false;
 if (website != null ? !website.equals(person.website) : person.website != null) return false;
 if (address != null ? !address.equals(person.address) : person.address != null) return false;
 return car != null ? car.equals(person.car) : person.car == null;
 
 }
 
 @Override
 public int hashCode() {
 int result = firstName != null ? firstName.hashCode() : 0;
 result = 31 * result + (lastName != null ? lastName.hashCode() : 0);
 result = 31 * result + (name != null ? name.hashCode() : 0);
 result = 31 * result + (suffix != null ? suffix.hashCode() : 0);
 result = 31 * result + (phoneNumber != null ? phoneNumber.hashCode() : 0);
 result = 31 * result + (email != null ? email.hashCode() : 0);
 result = 31 * result + (website != null ? website.hashCode() : 0);
 result = 31 * result + (address != null ? address.hashCode() : 0);
 result = 31 * result + (car != null ? car.hashCode() : 0);
 return result;
 } 

@Override
 public String toString() {
 return MoreObjects.toStringHelper(this)
 .add("firstName", firstName)
 .add("lastName", lastName)
 .add("name", name)
 .add("suffix", suffix)
 .add("phoneNumber", phoneNumber)
 .add("email", email)
 .add("website", website)
 .add("address", address.toString())
 .toString();
 } 

@Override
 public boolean equals(Object object) {
 
 if (object instanceof Person) {
 Person that = (Person) object;
 return Objects.equal(this.name, that.name)
 && Objects.equal(this.firstName, that.firstName)
 && Objects.equal(this.email, that.email);
 }
 return false;
 }
 
 @Override
 public int hashCode() {
 return Objects.hashCode(name, firstName, email);
 } 

@Override
 public int compareTo(Person o) {
 return ComparisonChain.start()
 .compare(this.name, o.name)
 .compare(this.firstName, o.firstName)
 .compare(this.email, o.email)
 .result();
 } 

Bonus! 

public static void main(String[] args) {
 
 Stopwatch stopwatch = Stopwatch.createStarted();
 
 List pers = PersonRepository.getByLimit(50);
 
 Iterable dtos = from(pers).transform(personToDto);
 
 from(personDtos).forEach(printer);
 
 long nanos = stopwatch.elapsed(TimeUnit.NANOSECONDS);
 } 

Preconditions 

Preconditions goodness - Validate arguments - Check for null - Check elements in Lists, String or Array 

import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 
 public class PreconditionsSample { 
 public static void main(String[] args) { 
 checkState(args.length > 0, "Too less parameters”); 
 checkNotNull(args, "You have to pass some parameters");
 }
 }
 

Ordering 

Ordering goodness - Ordering is a special Comparator instance - Guava’s fluent Comparator class - Chaining methods 

Ordering bySuffix = new Ordering() {
 @Override
 public int compare(Person p1, Person p2) {
 return p1.getSuffix().compareTo(p2.getSuffix());
 }
 };
 Ordering byNameLength = new Ordering() {
 @Override
 public int compare(Person p1, Person p2) {
 return Ints.compare(p1.getName().length(), p2.getName().length());
 }
 };
 
 List persons = PersonRepository.instance().getByLimit(50);
 Collections.sort(persons, byNameLength.compound(bySuffix)); 

Collections 

Collection goodness - New collections not included in JDK - Immutable collections 

Why immutable? - Thread safe: no race conditions - More memory efficient that mutable alternative - Safe for use by untrusted libraries - Guava collection types doesn’t allow nulls 

New collection types - Multiset - Multimap - BiMap - Table - ClassToInstanceMap - RangeSet 

Multiset - Generalization of the notion of Set - Members allowed to appear more than once - Order is irrelevant 

Multimap - Associates keys to arbitrary values - Alternative to Map> or Map> A -> 1 A -> 2 A -> 4 B -> 3 C -> 5 A -> [1, 2, 4] B -> 3 C -> 5 

Bimap - Map values back to keys - Alternative to keep in sync two Map 


 Person p1 = new Person("Alex", "Simonescu");
 Person p2 = new Person("Josh", "Block");
 
 BiMap emailPerson = HashBiMap.create();
 emailPerson.put("[email protected]", p1);
 emailPerson.put("[email protected]", p2);
 
 String p1Email = emailPerson.inverse().get(p1);
 

Table - Really a Table collection. Surprised? - Implementations as: • HashBasedTable, • TreeBasedTable, • ImmutableBasedTable • ArrayTable 

String[] names = {"Bob", "Alice", "Andy", "Carol", "Ben"};
 
 // Table of names
 Table table = HashBasedTable.create();
 
 // First letter is a row key, length is a column key
 for (String name : names) {
 table.put(name.charAt(0), name.length(), name);
 }
 
 // Value corresponding to the given row and column keys
 table.get('A', 5); // -> Alice
 table.get('B', 3); // -> Ben
 
 // Set of column keys that have one or more values in the table
 table.columnKeySet(); // -> [4, 5, 3]
 
 // View of all mappings that have the given row key
 table.row('A'); // -> {4=Andy, 5=Alice} 

ClassToInstance - Map types to values of that type - No need of getInstance(Class) and T putInstance(Class, T) 

ClassToInstanceMap numbers = MutableClassToInstanceMap.create();
 
 numbers.putInstance(Integer.class, Integer.valueOf(0));
 numbers.putInstance(Double.class, Double.valueOf(1));
 numbers.putInstance(Float.class, Float.valueOf(3)); double myNum = numbers.getInstance(Double.class); 

No content

Collection Utils 

Collections hierarchy interface Iterable interface Collection interface Set interface List interface Queue 

Static Constructors 
 List list = Lists.newArrayList();
 
 
 Map map = Maps.newLinkedHashMap();
 
 
 Set set = Sets.newHashSet(repo.getByLimit(50));
 
 
 List elements = Lists.newArrayList("alpha", "beta", "gamma"); 

Iterables 
 frequency(Iterable object)
 
 
 concat(Iterable)
 
 
 partition(Iterable)
 
 
 getFirst(Iterable, default) 

Iterables Collections style 
 addAll(Collection addTo, Iterable toAdd)
 
 
 removeAll(Iterable removeFrom, Collection toRemove)
 
 
 contains(Iterable, Object) get(Iterable, int) 
 
 retainAll(Iterable removeFrom, Collection toRetain) 

Sets 
 union(Set, Set) intersection(Set, Set) difference(Set, Set) symmetricDifference(Set, Set) cartesianProduct(List) powerSet() 

Functional 

Functional goodness - Kind of functional style on Java - Still not Scala - Handy filtering and transforming collections 

Functional concepts - Function —> A => B - Predicate —> T => Boolean 

Sometimes imperative version is more readable, concrete and efficient. Functional danger zone 

List states = Lists.newArrayList(
 new State("MT", false),
 new State("ID", false),
 new State("WY", false),
 new State("SD", false),
 new State("NE", false),
 new State("WI", false),
 new State("IN", false),
 new State("TX", false),
 new State("CA", true),
 new State("AZ", true),
 new State("NM", true),
 new State("AR", true),
 new State("IL", true),
 new State("IA", true)); Predicate withI = state -> state.getAbbreviation().startsWith("I");
 Predicate isExpanded = state -> state.isExpanded();
 
 Collection filtered = filter(states, or(withI, not(isExpanded))); 

Function emailToUpper = person -> {
 person.setEmail(person.getEmail().toUpperCase());
 return person;
 };
 
 Function toUsername = person -> {
 String[] chunks = person.getEmail().split("@");
 return chunks[0];
 };
 
 List people = getPeople();
 Collection usernames = transform(people, compose(toUsername, emailToUpper)); 

Predicate isNotNull = Predicates.notNull();
 Predicate isPerson = Predicates.instanceOf(Person.class);
 Predicate startsWithA = person -> person.getName().toLowerCase().startsWith("a");
 Predicate hasCar = person -> person.getCar().isPresent();
 
 Function toCarName = person -> person.getCar().get().getName();
 
 ImmutableList people = ImmutableList.copyOf(getPeople());
 
 List cars = FluentIterable
 .from(people)
 .filter(isNotNull)
 .filter(isPerson)
 .filter(startsWithA)
 .filter(hasCar)
 .transform(toCarName)
 .toList(); 

Concurrency 

Concurrency goodness - Future on steroids - Allows registering callback when finished - Provides more executors 

ExecutorService executorService = Executors.newFixedThreadPool(1);
 ListeningExecutorService executor = MoreExecutors.listeningDecorator(executorService);
 
 ListenableFuture future = executor.submit(() -> {
 Thread.sleep(1000);
 return "Task completed";
 });
 
 future.addListener(() -> runOnCompletion(), executor);
 

ExecutorService executorService = Executors.newCachedThreadPool();
 ListeningExecutorService executor = MoreExecutors.listeningDecorator(executorService);
 
 ListenableFuture future = executor.submit(() -> {
 Thread.sleep(1000);
 return "Task completed";
 });
 
 Futures.addCallback(future, new FutureCallback() {
 @Override
 public void onSuccess(String s) {
 System.out.println("Task succeed: " + s);
 }
 
 @Override
 public void onFailure(Throwable throwable) {
 System.out.println("Task failed");
 }
 }, executor); 

Guava Darkside 

Guava Darkside - Heavy library —> use Proguard or similar - Lot’s of utilities —> extract only needed 

https://github.com/android10/arrow 

https://github.com/alexsimo/toolbelt 

Guava vs Java 8 

Writing clean code is your responsibility 

+ Inspiring people 

Questions? 

Sample project https://github.com/alexsimo/guava-demo 

Links • http://www.tfnico.com/presentations/google-guava • http://gdg-krakow.github.io/google-io-ext-2012-guava/ • http://www.baeldung.com/category/guava/ • https://robinst.github.io/guava-java8-presentation/#/ 

Thanks! @alexsimonescu