JSR-223 Scripting

Java scripting with BoxLang

JSR 223 - Java Scripting

JSR 223, also known as "Scripting for the Java Platform," is a specification that allows Java applications to integrate with scripting languages such as BoxLang, JavaScript, Groovy, Python, and others. It provides a standard API for accessing and embedding these scripting languages within Java code, enabling developers to mix and match Java and scripting languages seamlessly. This flexibility can enhance productivity and facilitate the rapid development of applications that require dynamic scripting capabilities.

BoxLang offers the JSR-233 runtime to integrate with BoxLang from any JVM language.

Scripting Classes

The BoxLang scripting package can be found here: ortus.boxlang.runtime.scripting. The classes that will assist you are:

BoxCompiledScript - Implements the JSR CompiledScript interface (https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/CompiledScript.html)
BoxScopeBindings - Implements the JSR Bindings interface (https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/Bindings.html)
BoxScriptingContext - Implements the JSR ScriptContext interface (https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/ScriptContext.html)
BoxScriptingEngine - Implements the JSR ScriptEngine and Compilable https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/ScriptEngine.html https://docs.oracle.com/en/java/javase/17/docs/api//java.scripting/javax/script/Compilable.html
BoxScriptingFactory - implements the JSR ScriptEngineFactory https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/ScriptEngineFactory.html

Definitions

Script Factory - creates scripting engines and gets metadata about scripting engines.
Script Engine - provides a way to create bindings, scripts, and run statements.
Invocable - Our BoxLang engine also implements the scripting Invocable interface so you can declare functions and classes (coming soon) and then execute them from the calling language.
Bindings - these are like scopes to BoxLang. The bridge between Java and BoxLang
Scripting Context - Like the BoxLang context object, it provides scope lookups and access to bindings.

Bindings

Bindings are under the hood HashMaps. They are used to bind your Java code to the BoxLang code. By default, in BoxLang, we provide three scopes you can bind bindings to:

Engine Scope - The default scope which maps to the BoxLang variables scope
Request Scope - The JSR request scope maps to the BoxLang request scope
Global Scope - The JSR global scope maps to the BoxLang server scope

Discovering Engines

To find out what engines are available in your platform you can run the following:

ScriptEngineManager mgr = new ScriptEngineManager();
List<ScriptEngineFactory> factories = mgr.getEngineFactories();

BoxLang ScriptEngine

To get started, you need to get an instance of the BoxLang Scripting Engine. You can do so by using the Java ScriptEngineManager() class or importing our BoxScriptingEngine class.

import javax.script.*;

ScriptEngine engine = new ScriptEngineManager().getEngineByName( "BoxLang" );

// Or directly via our BoxScriptingFactory class

import ortus.boxlang.runtime.scripting.BoxScriptingFactory;

ScriptEngine engine = new BoxScriptingFactory().getScriptEngine();

You can also cast it to our class to get enhanced methods and functionality

BoxScriptingEngine engine = (BoxScriptingEngine) new BoxScriptingFactory().getScriptEngine();

Debug Mode

If you ever need to send debugging information to the console from the BoxRuntime in the scripting engine, you can create a new script engine and pass the debug flag to it.

import ortus.boxlang.runtime.scripting.BoxScriptingFactory;

ScriptEngine engine = new BoxScriptingFactory().getScriptEngine( true );

This will start up the BoxRuntime in debug mode.

Eval() BoxLang Code

Once you access the script engine, you can use the plethora of eval() methods to execute the BoxLang source and bind with specific dynamic bindings. You can execute scripts from strings or reader objects. You can also compile a script/class into a CompiledScript and then execute it at a later point in time via the compile() methods.

boxlang.eval( "println( 'hello world' )" )

You can use eval with the following signatures

/**
 * Evaluate a script in the context of the ScriptContext
 *
 * @param script  The script to evaluate
 * @param context The context to evaluate the script in
 *
 * @return The result of the script evaluation
 */
public Object eval( String script, ScriptContext context ) throws ScriptException

/**
 * Evaluate a script in the context of the ScriptContext
 *
 * @param reader  The reader to read the script from
 * @param context The context to evaluate the script in
 *
 * @return The result of the script evaluation
 */
public Object eval( Reader reader, ScriptContext context ) throws ScriptException

/**
 * Evaluate a script bound only to the top-level BoxRuntime context
 *
 * @param reader The reader to read the script from
 *
 * @return The result of the script evaluation
 */
public Object eval( Reader reader ) throws ScriptException

/**
 * Evaluate a script using the given Bindings
 *
 * @param script The script to evaluate
 * @param n      The Bindings to use
 *
 * @return The result of the script evaluation
 */
@Override
public Object eval( String script, Bindings n ) throws ScriptException 

@Override
public Object eval( Reader reader, Bindings n ) throws ScriptException 

/**
 * Evaluate a script bound only to the top-level BoxRuntime context
 *
 * @param script The script to evaluate
 *
 * @return The result of the script evaluation
 */
public Object eval( String script ) throws ScriptException

Bindings - Passing Data to the Scripts

Data can be passed into the engine by defining a Bindings object and passing it as a second parameter to the eval function. You will do so by using the createBindings() method. If you casted the engine to our BoxScriptingEngine class, you will also get a createBindings( Map m ) so you can quickly create bindings from a map of data.

Bindings bindings = boxlang.createBindings();
bindings.put( "count", 3 );
bindings.put( "name", "luis" );
bindings.put( "age", 1 );

// Or if you have already a map of data
Bindings bindings = boxlang.createBindings( myMap );

// Script and evaluate the last result
result = engine.eval( """
  println( 'Hello, ' & name & '!' )
  newAge = age + 1
  totalAge = newAge + 1
  request.nameTest = name
  server.nameTest = name
""", bindings );

// We cannot use the same bindings, these are just to send
// We need to get the bounded bindings now via the `getBindings()` method
Bindings resultBindings = engine.getBindings();
// The result of the script is the last expression
assertThat( result ).isEqualTo( "World" );
// Test the bindings
assertThat( resultBindings.get( "newAge" ) ).isEqualTo( 2 );
assertThat( engine.getRequestBindings().get( "nameTest" ) ).isEqualTo( "World" );
assertThat( engine.getServerBindings().get( "nameTest" ) ).isEqualTo( "World" );

Once you bind the engine with bindings before execution, you must get the modified bindings via the engine.getBindings() method. If you don't do this, you will only have access to the simple hashmap to bind the engine.

Calling Functions From Java to BoxLang

You can also use the eval() method to define functions, closures, or lambdas in BoxLang and execute them in your host language. We do so by evaluating the script, casting the engine to Invocable, and using the invokeFunction() method.

engine.eval( """
    function sayHello( name ) { 
        return 'Hello, ' & name & '!'
    }
""");

Invocable	invocable	= ( Invocable ) engine;
Object		result		= invocable.invokeFunction( "sayHello", "World" );
assertThat( result ).isEqualTo( "Hello, World!" );

Objects, Functions, Closures, Lambdas, Member Methods, Oh My!

You can also use the invokeMethod( object, name, args ) function, which allows you to target a specific object, such as a BoxLang class, member method, struct, lambda, closure or collection of functions.

// Create a struct
engine.eval( "myStr = { foo : 'bar' }" );
// Make it invocable
Invocable invocable = ( Invocable ) engine;
// Invoke the struct's count() member method
Object result = invocable.invokeMethod( engine.get( "myStr" ), "count" );
assertThat( result ).isEqualTo( 1 );

This is indeed truly powerful as you can not only invoke functions on objects, but also member methods in any valid BoxLang type.

Compiling Scripts

Apart from executing strings, you can also compile BoxLang scripts and evaluate them using the compileScript( String ) or compileScript( Reader ) methods. You will get a Box CompiledScript class, which you can then use the eval() methods and binding methods at a later point in time.

CompiledScript script = engine
		    .compile( """
			import ortus.boxlang.runtime.scopes.Key;

			name = [ 'John', 'Doe',  Key.of( 'test' ) ]
			name.reverse()
		    """ );

// Execute it
Object results	= script.eval();
assertThat( ( Array ) results ).containsExactly( Key.of( "test" ), "Doe", "John" );

Dynamic Interfaces

JSR223 also allows you to dynamically create interface proxies for any functions or classes you map in the dynamic language. Let's say you want to create a nice BoxLang function that maps to a Java Runnable. In our example, we will create the run function and then map that via JSR223 to the Runnable interface so we can execute it as a runnable object.

engine.eval("""
	function run() {
		print('Hello, world! I am running from a thread.');
	}
""");

Invocable invocable = ( Invocable ) engine;
// Map our function to a Runnable class
Runnable runnable = invocable.getInterface( Runnable.class );
runnable.run();

As you can see from the sample above, you can use the getInterface( class<?> ) method to map the evaluated code to any interface of your choosing. Here are the two methods you can use for interfaces:

getInterface( Class<T> ) - Build a dynamic proxy from the evaluated function and the passed in class
getInterface( Object, Class<T> ) - Build a dynamic proxy from the passed in Object and the passed in class.

Let's finish this section with another example. Using a struct and anonymous functions, let's build a BoxLang virtual object and treat it as a Runnable interface.

// Define a BoxLang struct with a `run` key that points to an
// anonymous function
engine.eval("""
  methods = {
    run : function() {
	print('Hello, world!');
    }
  }
""");
// cast it to invocable
Invocable invocable = ( Invocable ) engine;
// Get the interface from that object that map to a Runnable
Runnable runnable = invocable.getInterface( engine.get( "methods" ), Runnable.class );
// Run Forest Run!
runnable.run();

Capturing Output

We have also added the capability for your host language to seed your own String Writers into the engine so you can capture output. BoxLang can produce two types of output

System output - Bifs and components that send output to the System.out
Buffer output - A BoxLang request has an output String buffer that can be used to produce output which can be sent to console, web, etc.

Writer oldWriter = engine.getContext().getWriter();
// Create my own writer
StringWriter	stringWriter	= new StringWriter();
// Talk to the engine's context and seed in the new writer
engine.getContext().setWriter( stringWriter );

// Execute some code that outputs to the system out
engine.eval("""
  println('Hello, world!')
""");

// Now let's get that output!
assertThat( stringWriter.toString().trim() ).isEqualTo( "Hello, world!" );

// Replace the old writer back!
engine.getContext().setWriter( oldWriter );

Runtime Source Code

The runtime source code can be found here: https://github.com/ortus-boxlang/BoxLang/tree/development/src/main/java/ortus/boxlang/runtime/scripting

We welcome any pull requests, testing, docs, etc.

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Last updated 4 months ago