Why is Rapidoid Fluent so sweet?

Map<Integer, String> nums = New.map(1, "one", 2, "two", 3, "three");{"1":"one","2":"two","3":"three"}
 
// Find the even numbers from the map - with Rapidoid Fluent (and Java 8 streams behind the scenes):
Find.allOf(nums).where((k, v) -> k % 2 == 0);{"2":"two"}
 
// That is equivalent to the following code:
Map<Integer, String> even = nums.entrySet().stream()
        .filter(num -> num.getKey() % 2 == 0)
        .collect(Collectors.toMap(Entry::getKey, Entry::getValue));
 
System.out.println(even);{"2":"two"}
 
// Or, we can do the same thing in the old way
Map<Integer, String> even2 = new HashMap<>();
 
for (Entry<Integer, String> num : nums.entrySet()) {
    int k = num.getKey();
    if (k % 2 == 0) {
        even2.put(k, num.getValue());
    }
}
 
System.out.println(even2);{"2":"two"}

Project setup with Maven

To run the example, you need to create a new Java 8 project and configure it properly using Maven:
<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.example</groupId>
    <artifactId>my-example</artifactId>
    <version>1.0.0-SNAPSHOT</version>
 
    <dependencies>
        <dependency>
            <groupId>org.rapidoid</groupId>
            <artifactId>rapidoid-fluent</artifactId>
            <version>5.4.5</version>
        </dependency>
    </dependencies>
 
    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
 
</project>

Building the project with Maven is easy:
mvn package