Facilite a vida com guava

Facilite a vida com Guava
@programadorfsa
+RomualdoCosta
www.programadorfeirense.com.br

Problema: validação
boolean estaPreenchida = minhaString != null && minhaString.isEmpty();

Problema: ler um arquivo
try(BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append(System.lineSeparator());
line = br.readLine();
}
String everything = sb.toString();
}

Software baseado em componentes
● Don’t repeat youself!
● Faça você mesmo ou pegue pronto.
● Interface bem definida e sem estado.
● Pode ser substituído por outro
componentes

Guava
● https://github.com/google/guava
● Java 1.6 ou maior
● Usadas em projetos Java do Google
● collections, caching, primitives support, concurrency libraries, common
annotations, string processing, I/O ...

Maven
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>19.0</version>
</dependency>

Gradle
dependencies {
compile 'com.google.guava:guava:19.0'
}

Lidando com valores nulos
Integer a=5;
Integer b=null;
//algumas operações
Optional<Integer> possible=Optional.fromNullable(a);
System.out.println(possible.isPresent());//tem algo não nulo?
System.out.println(possible.or(10));//se for nulo, retorna 10 por padrão
System.out.println(MoreObjects.firstNonNull(a, b));//seleciona entre dois
valores
String nome=new String();
System.out.println(Strings.isNullOrEmpty(nome));

Pré condições
import static com.google.common.base.Preconditions.checkElementIndex;
Integer[]arr=new Integer[5];
//algum código
int index=5;
checkElementIndex(index, arr.length, "index");
/*
Exception in thread "main" java.lang.IndexOutOfBoundsException: index (5) must be
less than size (5)
at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:
310)
at br.gdg.fsa.Main.main(Main.java:43)
*/

Pré condições
import static com.google.common.base.Preconditions.checkNotNull;
Integer a=null;
checkNull(a);
/*
Exception in thread "main" java.lang.NullPointerException
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:212)
*/

Pré condições
import static com.google.common.base.Preconditions.checkArgument;
int i=-1;
checkArgument(index >= 0, "Argument was %s but expected nonnegative", index);
/*
Exception in thread "main" java.lang.IllegalArgumentException: Argument was -1 but
expected nonnegative
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:146)
*/

Comparação de objetos
class Person implements Comparable<Person> {
public String lastName;
public String firstName;
public int zipCode;
public int compareTo(Person other) {
int cmp = lastName.compareTo(other.lastName);
if (cmp != 0) {
return cmp;
}
cmp = firstName.compareTo(other.firstName);
if (cmp != 0) {
return cmp;
}
return Integer.compare(zipCode, other.zipCode);
}
}

Comparação de objetos com Guava
class Person implements Comparable<Person> {
public String lastName;
public String firstName;
public int zipCode;
public int compareTo(Person that) {
return ComparisonChain.start()
.compare(this.lastName, that.lastName)
.compare(this.firstName, that.firstName)
.compare(this.zipCode, that.zipCode)
.result();
}
}

Ordenação
Integer[]arr=new Integer[5]; arr[0]=1; arr[1]=10; arr[2]=100; arr[3]
=1000; arr[4]=10000;
List<Integer> list = Lists.newArrayList(arr);
Ordering<Integer> ordering=Ordering.natural().reverse();
System.out.println(ordering.min(list)); //10000

Collections
Set<Type> copySet = Sets.newHashSet(elements);
List<String> theseElements = Lists.newArrayList("alpha", "beta",
"gamma");
List<Type> exactly100 = Lists.newArrayListWithCapacity(100);
List<Type> approx100 = Lists.newArrayListWithExpectedSize
(100);
Set<Type> approx100Set = Sets.newHashSetWithExpectedSize
(100);

Hashing
HashFunction hf = Hashing.md5();// seleciona algoritmo
HashCode hc = hf.newHasher()
.putLong(id)
.putString(name, Charsets.UTF_8)
.putObject(person, personFunnel)
.hash();
Funnel<Person> personFunnel = new Funnel<Person>() {
@Override
public void funnel(Person person, PrimitiveSink into) {
into
.putString(person.firstName, Charsets.UTF_8)
.putString(person.lastName, Charsets.UTF_8)
.putInt(person.zipcode);
}
};

IO
List<String> linhas = Files.readLines(arquivo, Charsets.UTF_8);
Closer closer = Closer.create();
try {
InputStream in = closer.register(openInputStream());
OutputStream out = closer.register(openOutputStream());
// do stuff with in and out
} catch (Throwable e) { // must catch Throwable
throw closer.rethrow(e);
} finally {
closer.close();
}

Ranges
Range<Integer> range=Range.closed(1, 10);
ContiguousSet<Integer> values=ContiguousSet.create(range, DiscreteDomain.
integers());
List<Integer> list = Lists.newArrayList(values);

E muito mais...
● Imuttable Collections
● Novos Collections: BiMap, MultiMap, Table, RangeSet...
● EventBus
● Math
● Strings (split, join, match, charset)
● Caches
● Reflection
● Functional Idioms (Functions, Predicates)
● Primitives

Facilite a vida com guava

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