optional examples (#2537)

guest/core-java-9/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.stackify</groupId>
+  <artifactId>core-java-9</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  
+  <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+        </dependency>
+    </dependencies>
+  
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.6.2</version>
+        <configuration>
+          <source>1.9</source>
+          <target>1.9</target>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

guest/core-java-9/src/main/java/com/stackify/optional/User.java

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+package com.stackify.optional;
+
+public class User {
+    private String email;
+    private String password;
+
+    public User(String email, String password) {
+        super();
+        this.email = email;
+        this.password = password;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+}

guest/core-java-9/src/test/java/com/stackify/optional/OptionalTest.java

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+package com.stackify.optional;
+
+import org.junit.Test;
+import java.util.Optional;
+import java.util.List;
+
+import static org.junit.Assert.*;
+import java.util.stream.Collectors;
+
+public class OptionalTest {
+    
+    private User user;
+    
+    @Test
+    public void whenEmptyOptional_thenGetValueFromOr() {
+        User result = Optional.ofNullable(user)
+                .or( () -> Optional.of(new User("default","1234"))).get();
+                 
+        assertEquals(result.getEmail(), "default");
+    }
+    
+    @Test
+    public void whenIfPresentOrElse_thenOk() {
+        Optional.ofNullable(user)
+              .ifPresentOrElse( u -> System.out.println("User is:" + u.getEmail()), () -> System.out.println("User not found"));
+    }
+
+    @Test
+    public void whenGetStream_thenOk() {
+        User user = new User("john@gmail.com", "1234");
+        List<String> emails = Optional.ofNullable(user)
+                .stream()
+                .filter(u -> u.getEmail() != null && u.getEmail().contains("@"))
+                .map( u -> u.getEmail())
+                .collect(Collectors.toList());
+   
+        assertTrue(emails.size() == 1);
+        assertEquals(emails.get(0), user.getEmail());
+    }
+
+}

guest/core-java/pom.xml

@@ -0,0 +1,36 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.stackify</groupId>
+	<artifactId>core-java</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>4.12</version>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-core</artifactId>
+			<version>${log4j2.version}</version>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<version>3.5</version>
+				<configuration>
+					<source>1.8</source>
+					<target>1.8</target>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+	<properties>
+		<log4j2.version>2.8.2</log4j2.version>
+	</properties>
+</project>

guest/core-java/src/main/java/com/stackify/optional/Address.java

@@ -0,0 +1,40 @@
+package com.stackify.optional;
+
+public class Address {
+    private String addressLine;
+    private String city;
+    private Country country;
+
+    public Address(String addressLine, String city, Country country) {
+        super();
+        this.addressLine = addressLine;
+        this.city = city;
+        this.country = country;
+    }
+
+    public String getAddressLine() {
+        return addressLine;
+    }
+
+    public void setAddressLine(String addressLine) {
+        this.addressLine = addressLine;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public Country getCountry() {
+        return country;
+    }
+
+    public void setCountry(Country country) {
+        this.country = country;
+    }
+
+   
+}

guest/core-java/src/main/java/com/stackify/optional/Country.java

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+package com.stackify.optional;
+
+public class Country {
+    private String name;
+    private String isocode;
+
+    public Country(String name, String isocode) {
+        super();
+        this.name = name;
+        this.isocode = isocode;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getIsocode() {
+        return isocode;
+    }
+
+    public void setIsocode(String isocode) {
+        this.isocode = isocode;
+    }
+
+}

guest/core-java/src/main/java/com/stackify/optional/User.java

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+package com.stackify.optional;
+
+import java.util.Optional;
+
+public class User {
+    private String email;
+    private String password;
+
+    private Address address;
+
+    private String position;
+
+    public User(String email, String password) {
+        super();
+        this.email = email;
+        this.password = password;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public Optional<String> getPosition() {
+        return Optional.ofNullable(position);
+    }
+
+    public void setPosition(String position) {
+        this.position = position;
+    }
+
+}

guest/core-java/src/main/java/com/stackify/optional/chaining/Address.java

@@ -0,0 +1,38 @@
+package com.stackify.optional.chaining;
+
+import java.util.Optional;
+
+public class Address {
+    private String addressLine;
+    private String city;
+    private Country country;
+
+    public Address(String addressLine, String city) {
+        this.addressLine = addressLine;
+        this.city = city;
+    }
+
+    public String getAddressLine() {
+        return addressLine;
+    }
+
+    public void setAddressLine(String addressLine) {
+        this.addressLine = addressLine;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public Optional<Country> getCountry() {
+        return Optional.ofNullable(country);
+    }
+
+    public void setCountry(Country country) {
+        this.country = country;
+    }   
+}

guest/core-java/src/main/java/com/stackify/optional/chaining/Country.java

@@ -0,0 +1,28 @@
+package com.stackify.optional.chaining;
+
+public class Country {
+    private String name;
+    private String isocode;
+
+    public Country(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getIsocode() {
+        return isocode;
+    }
+
+    public void setIsocode(String isocode) {
+        this.isocode = isocode;
+    }
+
+   
+}

guest/core-java/src/main/java/com/stackify/optional/chaining/User.java

@@ -0,0 +1,50 @@
+package com.stackify.optional.chaining;
+
+import java.util.Optional;
+
+public class User {
+    private String email;
+    private String password;
+
+    private Address address;
+
+    private String position;
+
+    public User(String email, String password) {
+        this.email = email;
+        this.password = password;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+
+    public Optional<Address> getAddress() {
+        return Optional.ofNullable(address);
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public Optional<String> getPosition() {
+        return Optional.ofNullable(position);
+    }
+
+    public void setPosition(String position) {
+        this.position = position;
+    }
+
+}

guest/core-java/src/main/resources/log4j2.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Configuration status="WARN">
+	<Appenders>
+		  <Console name="Console" target="SYSTEM_OUT">
+            <PatternLayout pattern="%msg%n" />
+        </Console>
+	</Appenders>
+	<Loggers>
+		<Root level="info">
+			<AppenderRef ref="Console" />
+		</Root>
+	</Loggers>
+</Configuration>

guest/core-java/src/test/java/com/stackify/optional/OptionalTest.java

@@ -0,0 +1,166 @@
+package com.stackify.optional;
+
+import static org.junit.Assert.*;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.junit.Test;
+
+public class OptionalTest {
+
+    private User user;
+
+    private Logger logger = LogManager.getLogger(OptionalTest.class);
+
+    @Test(expected = NullPointerException.class)
+    public void testNull() {
+        String isocode = user.getAddress().getCountry().getIsocode().toUpperCase();
+    }
+
+    @Test
+    public void test() {
+
+        if (user != null) {
+            Address address = user.getAddress();
+            if (address != null) {
+                Country country = address.getCountry();
+                if (country != null) {
+                    String isocode = country.getIsocode();
+                    if (isocode != null) {
+                        isocode = isocode.toUpperCase();
+                    }
+                }
+            }
+        }
+
+    }
+
+    @Test(expected = NoSuchElementException.class)
+    public void whenCreateEmptyOptional_thenNull() {
+        Optional<User> emptyOpt = Optional.empty();
+        emptyOpt.get();
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void whenCreateOfEmptyOptional_thenNullPointerException() {
+        Optional<User> opt = Optional.of(user);
+    }
+
+    @Test
+    public void whenCreateOfNullableOptional_thenOk() {
+        String name = "John";
+        Optional<String> opt = Optional.ofNullable(name);
+        assertEquals("John", opt.get());
+    }
+
+    @Test
+    public void whenCheckIsPresent_thenOk() {
+        user = new User("john@gmail.com", "1234");
+        Optional<User> opt = Optional.ofNullable(user);
+        assertTrue(opt.isPresent());
+
+        assertEquals(user.getEmail(), opt.get().getEmail());
+    }
+
+    @Test
+    public void whenCheckIfPresent_thenOk() {
+        user = new User("john@gmail.com", "1234");
+        Optional<User> opt = Optional.ofNullable(user);
+        assertTrue(opt.isPresent());
+
+        opt.ifPresent(u -> assertEquals(user.getEmail(), u.getEmail()));
+    }
+
+    @Test
+    public void whenEmptyValue_thenReturnDefault() {
+        User user = null;
+        User user2 = new User("anna@gmail.com", "1234");
+        User result = Optional.ofNullable(user).orElse(user2);
+
+        assertEquals("anna@gmail.com", result.getEmail());
+    }
+
+    @Test
+    public void whenValueNotNull_thenIgnoreDefault() {
+        User user = new User("john@gmail.com", "1234");
+        User user2 = new User("anna@gmail.com", "1234");
+        User result = Optional.ofNullable(user).orElse(user2);
+
+        assertEquals("john@gmail.com", result.getEmail());
+    }
+
+    @Test
+    public void whenSetDefaultOrElseGet_thenOk() {
+        User user = null;
+        User user2 = new User("anna@gmail.com", "1234");
+        User result = Optional.ofNullable(user).orElseGet(() -> user2);
+
+        assertEquals("anna@gmail.com", result.getEmail());
+    }
+
+    @Test
+    public void givenPresentValue_whenCompare_thenOk() {
+        User user = new User("john@gmail.com", "1234");
+        logger.info("Using orElse");
+        User result = Optional.ofNullable(user).orElse(createNewUser());
+        logger.info("Using orElseGet");
+        User result2 = Optional.ofNullable(user).orElseGet(() -> createNewUser());
+    }
+
+    private User createNewUser() {
+        logger.info("Creating New User");
+        return new User("extra@gmail.com", "1234");
+    }
+
+    @Test
+    public void givenEmptyValue_whenCompare_thenOk() {
+        User user = null;
+        logger.info("Using orElse");
+        User result = Optional.ofNullable(user).orElse(createNewUser());
+        logger.info("Using orElseGet");
+        User result2 = Optional.ofNullable(user).orElseGet(() -> createNewUser());
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void whenThrowException_thenOk() {
+        User result = Optional.ofNullable(user).orElseThrow(() -> new IllegalArgumentException());
+    }
+
+    @Test
+    public void whenMap_thenOk() {
+        user = new User("anna@gmail.com", "1234");
+        String email = Optional.ofNullable(user).map(u -> u.getEmail()).orElse("default@gmail.com");
+        assertEquals(email, user.getEmail());
+
+    }
+
+    @Test
+    public void whenFlatMap_thenOk() {
+        user = new User("anna@gmail.com", "1234");
+        user.setPosition("Developer");
+        String position = Optional.ofNullable(user).flatMap(u -> u.getPosition()).orElse("default");
+        assertEquals(position, user.getPosition().get());
+
+    }
+
+    @Test
+    public void whenFilter_thenOk() {
+        user = new User("anna@gmail.com", "1234");
+        Optional<User> result = Optional.ofNullable(user).filter(u -> u.getEmail() != null && u.getEmail().contains("@"));
+
+        assertTrue(result.isPresent());
+    }
+
+    @Test
+    public void whenStream_thenOk() {
+        List<User> users = new ArrayList<>();
+        User user = users.stream().findFirst().orElse(new User("default", "1234"));
+        assertEquals(user.getEmail(), "default");
+    }
+
+}

guest/core-java/src/test/java/com/stackify/optional/chaining/OptionalChainingTest.java

@@ -0,0 +1,36 @@
+package com.stackify.optional.chaining;
+
+import static org.junit.Assert.*;
+
+import java.util.Optional;
+
+import org.junit.Test;
+
+public class OptionalChainingTest {
+
+    @Test
+    public void whenChaining_thenOk() {
+        User user = new User("anna@gmail.com", "1234");
+
+        String result = Optional.ofNullable(user)
+                .flatMap(u -> u.getAddress())
+                .flatMap(a -> a.getCountry())
+                .map(c -> c.getIsocode())
+                .orElse("default");
+
+        assertEquals(result, "default");
+    }
+    
+    @Test
+    public void whenChainingWithMethodReferences_thenOk() {
+        User user = new User("anna@gmail.com", "1234");
+
+        String result = Optional.ofNullable(user)
+                .flatMap(User::getAddress)
+                .flatMap(Address::getCountry)
+                .map(Country::getIsocode)
+                .orElse("default");
+
+        assertEquals(result, "default");
+    }
+}