Modern Java Development

©2016 IKERLAN. All rights reserved©2016 IKERLAN. All rights reserved
Ikerlan – Java 8
Ángel Conde– [DevOps & Data Engineer]
2016/4/6

©2016 IKERLAN. All rights reserved 2
Outline
1. Maven – Solving the Dependency Hell
2. Java 8 – What's new
3. Logging – Understanding the JVM logging system
4. Useful libraries – do not reinvent the wheel
5. Testing – Mocks Everywhere

Automatize your builds
Tasks called phases.
Dependency management via repositories.
XML configuration, quite verbose.
Plugin support.
1. validate
2. generate-sources
3. process-sources
4. generate-resources
5. process-resources
6. compile
mvn compile

<project xmlns=http://maven.apache.org/POM/4.0.0 …. ">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>es.ikerlan.ulma</groupId>
<artifactId>ulma-supervisor</artifactId>
<version>1.0</version>
</parent>
<artifactId>compactor</artifactId>
<packaging>jar</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
<name>compactor</name>
<repositories> </repositories>
<dependencies> </dependencies>
<build>
<plugins> </plugins>
</build>
</project>
– A “pom” to rule them all

– Dependencies
<dependencies>
<dependency>
<groupId>group-a</groupId>
<artifactId>artifact-a</artifactId>
<exclusions>
<exclusion>
<groupId>group-c</groupId>
<artifactId>excluded-artifact</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>group-a</groupId>
<artifactId>artifact-b</artifactId>
<type>bar</type>
<scope>runtime</scope>
</dependency>
</dependencies>
Transitive dependency support & Scope Limit.

– Useful plugins
1. maven-shade-plugin: Uber Jar generation.
2. findbugs-maven-plugin: static code analysis.
3. maven-surefire-plugin: automates JUnit tests.
4. maven-enforcer-plugin: enforces configuration.
5. docker-maven-plugin: generates Docker images.
6. exec-maven-plugin: provides execution capabilities.

– The Future?
Google’s Maven “successor”
Groovy-based DSL instead of XML.
DAG in order to solve tasks ordering.
Dependency solver.
Multi-language support.

Outline

Java 8 – Default Methods
Allows developer to add new methods to old interfaces.
Used to add Lambdas and Streams support to the JDK8.
public interface oldInterface {
public void existingMethod();
default public void newDefaultMethod() {
System.out.println("New default method" " is added
in interface");
}
}

Java 8 – Functional Interfaces
Interfaces with only one method.
Used for providing lambda support to the JDK.
@FunctionalInterface
public interface Predicate<T>{
boolean test(T t);
}
public static <T> List<T> filter(List<T> list, Predicate<T> p) {
List<T> results = new ArrayList<>();
for(T s: list){
if(p.test(s)){
results.add(s);
}
}
return results;
}

Java 8 – Method References
Class::Method  meaning “use this method as a value”
File[] hiddenFiles = new File(".").listFiles(File::isHidden);
File[] hiddenFiles = new File(".").listFiles(new FileFilter()
{
public boolean accept(File file) {
return file.isHidden();
}
});
Vanilla Java
Java 8

Java 8 – Anonymous Functions (Lambdas)
public static boolean isGreenApple(Apple apple) {
return "green".equals(apple.getColor());
}
Java 7
filterApples(inventory, (Apple a) -> a.getWeight() > 150 );
Java 8
1.(int x, int y) -> x + y
2.(x, y) -> x - y
3.() -> 42
4.(String s) -> System.out.println(s)
5.x -> 2 * x
Introduce the idea of functions into the language.
Kind of anonymous method with compact syntax.

Java 8 – Streams
Lazy Immutable evaluated collections.
Partially evaluated —elements remain to be generated.
Exhausted — when its elements are used up.
An array, a collection, a generator function, or an IO channel.
Two types of operations: intermediate and terminal.
A partially evaluated stream may have infinitely elements.
IntStream.iterate(0, i -> i + 2)
.limit(100)
.forEach(System.out::println);
Stream.generate(Math::random)
.limit(5)
.forEach(System.out::println);

Java 8 – Streams (II)

Java 8 – Streams (III)
List<String> title = Arrays.asList("Java8", “Rules");
Stream<String> s = title.stream();
s.forEach(System.out::println);
s.forEach(System.out::println);
s.stream()
.map(w -> w.split(""))
.flatMap(Arrays::stream)
.distinct()
.collect(Collectors.toList());
s.stream()
.map(word -> word.split(""))
.map(Arrays::stream)
.distinct()
.collect(toList());
List<Integer> result = numbers.stream()
.peek(x -> System.out.println("from stream: " + x))
.map(x -> x + 17)
.collect(toList());
ERROR!! Stream already closed
ERROR!! Nested Stream….

Java 8 – Streams (IV)
List<String> names = menu.stream()
.filter(d -> d.getCalories() > 300)
.map(Dish::getName)
.limit(3)
.collect(toList());
String traderStr = transactions.stream()
.map(transaction -> transaction.getTrader().getName())
.distinct()
.sorted()
.reduce("", (n1, n2) -> n1 + n2);
.distinct()
.sorted()
.collect(joining());
The second is faster because it avoids String duplication with StringBuilder

Java 8 – Streams (V)
.distinct()
.sorted()
.collect(joining());
Map<Dish.Type, List<Dish>>
dishesByType = menu.stream()
collect(groupingBy(Dish::getType));
The Collector Interface
Implement various useful reduction operations.

Java 8 – Streams (VI)
Immutable parallelism: fork / join pools

Java 8 – Streams (VII)
public static long rangedSum(long n) {
return LongStream.rangeClosed(1, n)
.parallel()
.reduce(0L, Long::sum);
}
public static long parallelSum(long n) {
return Stream.iterate(1L, i -> i + 1)
.limit(n)
.parallel()
.reduce(0L, Long::sum);
}
Avoid this, very slow!! (iterate is not parallel friendly)
Very fast because LongStream provide longs NOT Longs

Java 8 – Streams (VII)
public static long sideEffectSum(long n) {
Accumulator accumulator = new Accumulator();
LongStream.rangeClosed(1,n).
forEach(accumulator::add);
return accumulator.total;
}
public class Accumulator {
public long total = 0;
public void add(long value) {
total += value; }
}
stream.parallel()
.filter(...)
.sequential()
.map(...)
.parallel()
.reduce();
Fine-Grained control?
AVOID MUTABLE STRUCTURES!!!!

Java 8 – More Features
Data & Time API (based on Joda-Time library).
CompletableFuture, futures the functional way.
Optionals for avoiding null checking.
LocalDate today = LocalDate.now();
LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
public void renderPage(CharSequence source) {
List<ImageInfo> info = scanForImageInfo(source);
info.forEach(imageInfo -> CompletableFuture
.supplyAsync(imageInfo::downloadImage)
.thenAccept(this::renderImage));
renderText(source); }
String name = computer.flatMap(Computer::getSoundcard)
.flatMap(Soundcard::getUSB) .map(USB::getVersion)
.orElse("UNKNOWN");

Outline

Logging Systems
In Java world different implementations.
1. Interface.
2. Underlying implementation.
3. Configuration.
private final Logger log = LoggerFactory.getLogger(LogExample.class);
public static void main(String... args) {
log.error("Something's wrong here");
}
static

Slf4j

Slf4j with Logback
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<appender name="STDOUT“ class="c...core.ConsoleAppender">
<encoder class="c...encoder.PatternLayoutEncoder">
<Pattern>
%d{HH:mm:ss} [%thread] %-5level %logger{36} %msg%n
</Pattern>
</encoder>
</appender>
<logger name="es.ikerlan.ulma" level="warn"/>
<logger name="org.apache.hadoop" level="error"/>
<logger name="parquet.hadoop" level="error"/>
<root level="debug">
<appender-ref ref="STDOUT" />
</root>
</configuration>
Logback.xml

Outline

Useful Libraries – lombok
https://projectlombok.org/ – useful decorators.
- @Data: adds setters/getters, constructor.
- @Slf4j: adds logging via SLF4J.
@Data
public class DataExample {
private final String name;
private double score;
}
lombok
@Data
public class DataExample {
private final String name;
private double score;
public String getName(){
return name;
}
public double getScore(){
return score;
}
……
}
vanilla Java

Useful Libraries
http://www.jcabi.com/ – more decorators and utilities (Amazon,
Json, XML….)
https://github.com/google/guava – Google Java core libraries, from
caches, parsers, optionals, collections, etc.
https://commons.apache.org/ – apache hosted libraries.

Outline

– Testing
The facto standard unit testing library for Java.
Best tool for Test Driven development.
@Test : methods to be executed on testing
@Before: executed before each test
@After: executed before each test
@BeforeClass: runs once before the test fixture.
@AfterClass: runs once before the entire test fixture.

– Testing
@Test
public void multiplicationOfZeroIntegersShouldReturnZero()
{
// MyClass is tested
MyClass tester = new MyClass();
// assert statements
assertEquals("10 x 0 must be 0", 0, tester.multiply(10, 0));
}
An example:

– Mocks everywhere
mock()/@Mock: create mock from an object.
when()/given() : to specify how a mock should behave
spy()/@Spy: partial mocking, methods are invoked but still can be verified and stubbed
@InjectMocks: automatically inject mocks/spies fields annotated with @Spy or @Mock
verify(): to check methods were called with given arguments
Mock Object library for testing.

– Mocks everywhere (II)
@Spy
private LocationService locationService;
@Test
public final void spyTest() {
//mock the object
Location loc = new Location();
//we mock the locationService.getLocation method from the real
object using mockito
doReturn(loc).when(locationService).getLocation("test");
Location found = locationService.getLocation("test");
assertEquals(loc, found);
}
An example with @Spy:

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Fax: 943 79 69 44
Questions?
Email: aconde@ikerlan.es
Thanks for your attention:

Modern Java Development

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