[Java 8] Optional Example

Scenario

How-To
1. pom.xml

<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>albert</groupId>
    <artifactId>test</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>test</name>
    <url>http://maven.apache.org</url>

    <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>

    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.0</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

2. Create a Person class

package albert.test;

import lombok.Builder;
import lombok.Data;
import lombok.ToString;

@Data
@Builder
@ToString
public class Person {

    private Integer id;
    private String name;
    private String gender;
    
}

3. Create a custom exception

package albert.test;

public class PersonNotFoundException extends Exception {

    public PersonNotFoundException() {
        super();
    }

    public PersonNotFoundException(String message, Throwable cause, boolean enableSuppression,
            boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }

    public PersonNotFoundException(String message, Throwable cause) {
        super(message, cause);
    }

    public PersonNotFoundException(String message) {
        super(message);
    }

    public PersonNotFoundException(Throwable cause) {
        super(cause);
    }

}

4. Create a OptionalTest class

package albert.test;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

public class OptionalTest {

    private Person albert = Person.builder().id(1).name("Albert").gender("Male").build();
    private Person mandy = Person.builder().id(2).name("Mandy").gender("Female").build();
    private Person eric = Person.builder().id(3).name("Graham").gender("Male").build();
    private List<Person> people = Arrays.asList(albert, mandy, eric);

    public Person getByNameByOldWay(String name) throws PersonNotFoundException {
        Person result = null;
        for (Person p : people) {
            if (p.getName().equals(name)) {
                result = p;
                break;
            }
        }
        if (result == null) {
            throw new PersonNotFoundException("Cannot find " + name);
        }
        return result;
    }

    public Person getByNameOrElseThrow(String name) throws PersonNotFoundException {
        Optional<Person> person = people.stream().filter(p -> name.equals(p.getName())).findFirst();
        return person.isPresent() ? person.get()
                : person.orElseThrow(() -> new PersonNotFoundException("Cannot find " + name));
    }

}

Reference
[1] Optional in Java 8 cheat sheet