Using CFML Functions and Components in Java

edit Introduced: 6.0

Using CFML Functions and Components in Java

Many Java libraries accept objects that implement specific interfaces - contracts defining what methods an object must have. Lucee lets you pass CFML components and functions directly to Java code.

Java terms: A Java interface defines method signatures a class must implement (like a blueprint). A lambda is a shorthand for a single-method interface - Java 8+ uses these heavily for callbacks and streaming APIs.

Component to Java Interface

Implement the interface's methods in your component:

// MyString.cfc - implements CharSequence interface
component {
	function init( String str ) {
		variables.str = reverse( arguments.str );
	}

	function length() {
		return str.length();
	}

	// ... implement other CharSequence methods
}

Then pass it to Java methods expecting that interface:

HashUtil = createObject( "java", "lucee.commons.digest.HashUtil" );
cfc = new MyString( "Susi Sorglos" );

// HashUtil.create64BitHashAsString() expects CharSequence - Lucee converts automatically
hash = HashUtil.create64BitHashAsString( cfc );
dump( hash );

Using implementsJava and onMissingMethod

Declare the interface explicitly and handle method calls dynamically:

component implementsJava="java.util.List" {
	function onMissingMethod( name, args ) {
		if ( name == "size" ) return 10;
		throw "method #name# is not supported!";
	}
}

See Java - Explicit Casting of a Component to a Specific Interface for when you need to cast components to specific interfaces.

Functions as Java Lambdas

When a Java method expects a functional interface (an interface with one method), you can pass a CFML function directly. Lucee converts it automatically:

numeric function doubleIt( numeric i ) {
	return i * 2;
}

// Java's IntStream.map() expects IntUnaryOperator (one method: int applyAsInt(int))
import java.util.stream.IntStream;
result = IntStream::of( 1, 2, 3 ).map( doubleIt ).sum();
dump( result ); // 12 (2 + 4 + 6)

See Java in Functions and Closures, function() type='java' for more on Java lambdas and the type="java" function attribute.

See also