Java Interop

,BoxLang is compiled to Java bytecode and runs on the JVM. This gives BoxLang a unique advantage that not only can you write BoxLang but you can also integrate with the running JDK libraries or any Java library you tell the engine to use. This is great, because if there is something already written in Java, just drop it in and use it, well most of the time :) Unless Jar loading hell occurs.

CommandBox even allows you to install jar's from any endpoint into your projects: https://commandbox.ortusbooks.com/package-management/code-endpoints/jar-via-http

install "jar:https://github.com/coldbox-modules/cbox-bcrypt/blob/master/modules/bcrypt/models/lib/jbcrypt.jar?raw=true"

Java Interop | BoxLang : A Modern Dynamic JVM Language

Creating Java Objects

The easiest way to integrate with Java is to be able to instantiate Java objects or call Java static methods on objects. You will do this via the createObject() or the new operator approach. Here is the signatures for both approaches:

createObject( "java", "java.class.path" )

Examples:

// Create a Java JDK Object
var buffer = createObject( "java", "java.lang.StringBuilder" );

// Using a constructor
currentFile = createObject( "java", "java.io.File" ).init( getCurrentTemplatePath() );
writeOutput( currentFile.lastModified() );

// Invoking a static method
javaSystem = new java( "java.lang.System" );
currentTime = javaSystem.currentTimeMillis();
writeOutput( currentTime );

Java Casting

You must remember that Java is a static and typed language. BoxLang is not! If you need to pass in arguments to Java functions that require native types you will have to cast them. We will use the fancy JavaCast() function built-in to the language.

integerObject = createObject( "java", "java.lang.Integer" );
maxInt = integerObject.max( javaCast( "int", 5 ), javaCast( "int", 6 ) );

The javaCast() method takes in two arguments:

• type : The type of casting

• variable : The value to cast

The available casting types are:

• boolean

• double

• float

• int

• long

• string

• null

• byte

• bigdecimal

• char

• short

If you need to cast the type but as an array then you can use the [] in the casting construct. Let's create a stream from an incoming list of values and cast them to an array of objects in Java.

createObject( "java", "java.util.Arrays" )
    .stream(
        javaCast( "java.lang.Object[]", listToArray( arguments.target, "" ) )
    );

Java Nulls

Ohh the dreaded day nulls where created. The variable that means that nothing exists. If you need to pass null into Java object calls then you have two approaches to create them:

javaCast( "null", "" );

nullValue();

Loading Custom Jars/Libraries

The createObject( "java" ) method will look into the BoxLang engine's class loader to discover the class you request. If the class is not located an exception is thrown that the class could not be found. If you want to integrate with third-party Jar's and libraries then you will need to tell the engine where to look for those classes. There are essentially three ways to add custom libraries to the BoxLang engine:

1. Add the jars/libs to the BoxLang Lib paths.

2. The Application.bx allows you to declare a this.javaSettings struct where you can declare an array of locations of the libraries to load upon application startup with some nice modifiers. This will allow you to store and even leverage CommandBox for the management of such jars.

3. The createObject( "java" ) construct allows you to pass in a third argument which can be a location or an array of locations of libraries to class load. This is also great for custom classes, task runners, or isolated class loading.

this.javaSettings

This Application.bx structure takes in 3 keys that will allow you to class load any jar/.class libraries into the running BoxLang application:

Key	Description
loadPaths	An array of paths to the directories that contain Java classes or JAR files.You can also provide the path to a JAR or a class. If the paths are not resolved, an error occurs.
loadBoxLangClassPath	Indicates whether to load the classes from the BoxLang lib directory. The default value is false.
reloadOnChange	Indicates whether to reload the updated classes and JARs dynamically, without restarting BoxLang. The default value is false.
watchInterval	Specifies the time interval in seconds after which to verify any change in the class files or JAR files. This attribute is applicable only if the reloadOnChange attribute is set to true. The default value is 60 seconds.
watchExtensions	Specifies the extensions of the files to monitor for changes. By default, only .class and .jar files are monitored.

Application.bx

class{

    this.javaSettings = {
        loadPaths = [ "./lib", "./config/java/myjar.jar" ],
        reloadOnChange = false
    }

}

Once that is declared in your Application.bx and you execute a createobject() with a class from those libraries, BoxLang will know about them and create them.

createObject() Class Loading

The other approach is to leverage the createObject() call to do class loading.

// Reference
createObject( "java", "path", array or jar location )

// Example
variables.LIB_PATH = expandPath( "/mylib/apache.jar" );
createObject( "java", "org.apache.pdfbox.pdmodel.PDDocument", variables.LIB_PATH );

Dynamic Proxies

BoxLang also allows you to create dynamic proxies from existing BoxLang Classes (.bx). What this means is that a Dynamic proxy lets you pass BoxLang classes to Java objects. Java objects can work with the BoxLang classes seamlessly as if they are native Java objects by implementing the appropriate Java interfaces. You can even use them to simulate Java lambdas as BoxLang classes.

createDynamicProxy( bx, interfaces )

If you want to leverage a Java library that requires a certain type of Java object as an argument and instead of you creating that object in Java, you can see if that argument adheres to a certain interface and BoxLang will create a dynamic proxy that binds it.

createDynamicProxy(
    new proxies.Consumer( arguments.consumer ), // create a Consumer Class
    [ "java.util.function.Consumer" ] // match it to this interface
)

// Here is the Consumer Class

/**
 * Functional Interface that maps to java.util.function.Consumer
 * See https://docs.oracle.com/javase/8/docs/api/java/util/function/Consumer.html
 */
class extends="BaseProxy"{

    /**
     * Constructor
     *
     * @f The lambda or closure to be used in the <code>accept()</code> method
     */
    function init( required f ){
        super.init( arguments.f );
        return this;
    }

    /**
     * Performs this operation on the given argument.
     */
    void function accept( t ){
		loadContext();
        variables.target( t );
    }

    function andThen( after ){}

}

Basically, your class must implement the appropriate methods the interface(s) tell you that it needs. After that, your class will be Java-fide, and it can be used like a native Java interface implementing objects! Enjoy!

Passing Function References / Higher Order Functions

Java methods can be referenced and passed around as a variable and invoked later like UDFs allow.