BoxLang Java Integration

Overview

BoxLang compiles to Java bytecode and runs on JRE 21+. It has 100% Java interoperability — any Java library, class, or framework can be used directly from BoxLang code. Type conversion between BoxLang and Java types is automatic in most cases.

Creating Java Objects

Prefer new java:fully.qualified.ClassName() over createObject(). Both work, but the new java: syntax is more concise and idiomatic BoxLang.

// PREFERRED — new java: syntax
var list = new java:java.util.ArrayList()
var map  = new java:java.util.HashMap()
var sb   = new java:java.lang.StringBuilder()

// Also valid — createObject (verbose, legacy style)
var list = createObject( "java", "java.util.ArrayList" ).init()
var map  = createObject( "java", "java.util.HashMap" ).init()

// With constructor args
var list = new java:java.util.ArrayList( 100 )  // initialCapacity
var sb   = new java:java.lang.StringBuilder( "Hello" )

Tip: When you need a class frequently in a file, use import java: at the top (see below) so you can refer to it by short name.

Static Methods and Fields

Best practice: import the class, then call statics directly. Avoid repeating createObject() on every call — it creates a new wrapper each time.

// PREFERRED — import once, call freely
import java:java.util.UUID
import java:java.lang.Math
import java:java.lang.System

var id       = UUID.randomUUID().toString()
var pi       = Math.PI
var sqrt2    = Math.sqrt( 2 )
var abs      = Math.abs( -42 )
var sysProps = System.getProperties()

// AVOID — verbose, allocates a wrapper on every call
var id = createObject( "java", "java.util.UUID" ).randomUUID()
var pi = createObject( "java", "java.lang.Math" ).PI

Named Arguments Are NOT Supported on Java Objects

CRITICAL: BoxLang cannot call Java methods with named arguments. Always use positional arguments when calling Java methods:

// WRONG — will throw "Methods on Java objects cannot be called with named arguments"
emitter.send( data="hello", event="msg" )

// CORRECT — positional only
emitter.send( "hello", "msg" )

Importing Java Classes

Import at the top of a class, template, or script — then reference the class directly by its short name. This is the preferred approach for static calls and repeated instantiation.

// Standard library classes
import java:java.util.ArrayList
import java:java.util.HashMap
import java:java.util.concurrent.ConcurrentHashMap
import java:java.time.LocalDateTime
import java:java.time.format.DateTimeFormatter

// After import, use the short class name directly
var list = new ArrayList()
var map  = new ConcurrentHashMap()
var now  = LocalDateTime.now()            // static method call
var fmt  = DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm:ss" )
var str  = now.format( fmt )

Module-Scoped Classes (@moduleAlias)

When a class lives inside a BoxLang module's classloader (not the system classloader), append @moduleAlias to route through the correct loader:

// Import a class from the "bxinsights" module classloader
import java:ortus.boxlang.insights.InsightsStorage@bxinsights
import java:ortus.boxlang.insights.InsightsContext@bxinsights

// Now use the short name directly — no createObject needed
var storage = InsightsStorage.getInstance()
var events  = InsightsContext.drainSince( lastId )

Without @moduleAlias the runtime would search the system classloader and fail to find module-private classes.

Old Style (still valid, but avoid for repeated use)

// Verbose — ok for a single one-off call
var props = createObject( "java", "java.lang.System" ).getProperties()

Working with Java Objects

// ArrayList
var list = new java.util.ArrayList()
list.add( "apple" )
list.add( "banana" )
list.add( "cherry" )
list.size()           // 3
list.get( 0 )         // "apple"
list.contains( "banana" )  // true
list.remove( 0 )
list.toArray()        // returns Java Object[]

// HashMap
var map = new java.util.HashMap()
map.put( "name",  "Ada Lovelace" )
map.put( "email", "[email protected]" )
map.get( "name" )       // "Ada Lovelace"
map.containsKey( "age" )  // false
map.keySet()            // Java Set of keys

// StringBuilder
var sb = new java.lang.StringBuilder()
sb.append( "Hello" )
sb.append( ", " )
sb.append( "World!" )
sb.toString()   // "Hello, World!"

Automatic Type Conversion

BoxLang automatically converts between its types and Java types:

// BoxLang array → Java List
var bxArray  = [1, 2, 3]
var javaList = createObject( "java", "java.util.ArrayList" ).init( bxArray )

// Java List → BoxLang array (automatic when assigned)
var backToArray = javaList.toArray()

Passing Closures as Java Functional Interfaces

BoxLang closures are automatically proxied to Java functional interfaces:

import java.util.Arrays
import java.util.Comparator

// Sort a Java list using a BoxLang lambda as Comparator
var names = new java.util.ArrayList()
names.add( "Charlie" )
names.add( "Alice" )
names.add( "Bob" )

names.sort( (a, b) -> a.compareTo( b ) )   // BoxLang lambda → Comparator
names  // ["Alice", "Bob", "Charlie"]

// Runnable
var thread = new java.lang.Thread( () -> {
    println( "Running in Java thread!" )
})
thread.start()
thread.join()

// Java Stream API with BoxLang lambdas
import java.util.stream.Collectors

var nums     = new java.util.ArrayList()
[1,2,3,4,5,6].each( (n) -> nums.add(n) )
var evenNums = nums.stream()
    .filter( (n) -> n % 2 == 0 )
    .map( (n) -> n * n )
    .collect( Collectors.toList() )

Handling Java Exceptions

try {
    var conn = DriverManager.getConnection( url, user, pass )
} catch ( "java.sql.SQLException" e ) {
    writeOutput( "SQL error: #e.message#" )
} catch ( "java.lang.ClassNotFoundException" e ) {
    writeOutput( "Driver not found: #e.message#" )
} catch ( any e ) {
    writeOutput( "Java error: #e.type# — #e.message#" )
}

Including Java Libraries (JARs)

Via Application.bx

class {
    this.javaSettings = {
        loadPaths            : [ "lib/", "lib/vendor.jar" ],
        loadColdFusionClassPath : false,
        reloadOnChange       : false
    }
}

Via Module libs/ Folder

Drop JARs into the module's libs/ directory — they are scoped to that module:

my-module/
├── ModuleConfig.bx
├── libs/
│   ├── my-library-1.2.3.jar
│   └── dependency.jar

Via Maven (Gradle-based modules)

// build.gradle
dependencies {
    implementation "com.example:my-library:1.2.3"
}

Java Time API

import java.time.LocalDate
import java.time.LocalDateTime
import java.time.ZonedDateTime
import java.time.ZoneId
import java.time.format.DateTimeFormatter
import java.time.temporal.ChronoUnit

var now      = LocalDateTime.now()
var today    = LocalDate.now()
var utcNow   = ZonedDateTime.now( ZoneId.of( "UTC" ) )

// Format
var fmt    = DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm:ss" )
var str    = now.format( fmt )

// Parse
var parsed = LocalDate.parse( "2024-01-15" )

// Arithmetic
var nextWeek = now.plus( 7, ChronoUnit.DAYS )
var daysBetween = ChronoUnit.DAYS.between( today, LocalDate.of(2025,1,1) )

JSR-223: BoxLang as a Java Scripting Engine

Use BoxLang from inside a Java application:

// Java code
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

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

engine.put("greeting", "Hello from Java!");
engine.eval("println( greeting )");

Object result = engine.eval("return 1 + 2");
System.out.println(result);  // 3

Reflection and Introspection

// Get Java class from a BoxLang object
var obj   = new java.util.ArrayList()
var clazz = obj.getClass()
var name  = clazz.getName()   // "java.util.ArrayList"

// List methods
var methods = clazz.getMethods()
for ( var method in methods ) {
    writeOutput( method.getName() & "<br>" )
}

// Check instanceof
if ( isInstanceOf( obj, "java.util.List" ) ) {
    // ...
}

Common Java Libraries in BoxLang

// Apache Commons Lang
import org.apache.commons.lang3.StringUtils
StringUtils.isBlank( "  " )    // true
StringUtils.capitalize( "hello" )  // "Hello"

// Google Guava
import com.google.common.collect.ImmutableList
var list = ImmutableList.of( "a", "b", "c" )

// Jackson JSON (if bundled)
import com.fasterxml.jackson.databind.ObjectMapper
var mapper = new ObjectMapper()
var json   = mapper.writeValueAsString( myStruct )
var parsed = mapper.readValue( json, createObject("java","java.util.Map").getClass() )

References

• Java Integration
• JSR-223
• JRE 21 Virtual Threads