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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// API class

package org.mozilla.javascript;

/**
 * Embeddings that wish to provide their own custom wrappings for Java
 * objects may extend this class and call
 * {@link Context#setWrapFactory(WrapFactory)}
 * Once an instance of this class or an extension of this class is enabled
 * for a given context (by calling setWrapFactory on that context), Rhino
 * will call the methods of this class whenever it needs to wrap a value
 * resulting from a call to a Java method or an access to a Java field.
 *
 * @see org.mozilla.javascript.Context#setWrapFactory(WrapFactory)
 * @since 1.5 Release 4
 */
public class WrapFactory
{
    /**
     * Wrap the object.
     * 
     * The value returned must be one of
     * 

     * java.lang.Boolean
     * java.lang.String
     * java.lang.Number
     * org.mozilla.javascript.Scriptable objects
     * The value returned by Context.getUndefinedValue()
     * null
     * 
     * @param cx the current Context for this thread
     * @param scope the scope of the executing script
     * @param obj the object to be wrapped. Note it can be null.
     * @param staticType type hint. If security restrictions prevent to wrap
              object based on its class, staticType will be used instead.
     * @return the wrapped value.
     */
    public Object wrap(Context cx, Scriptable scope,
                       Object obj, Class staticType)
    {
        if (obj == null || obj == Undefined.instance
            || obj instanceof Scriptable)
        {
            return obj;
        }
        if (staticType != null && staticType.isPrimitive()) {
            if (staticType == Void.TYPE)
                return Undefined.instance;
            if (staticType == Character.TYPE)
                return Integer.valueOf(((Character) obj).charValue());
            return obj;
        }
        if (!isJavaPrimitiveWrap()) {
            if (obj instanceof String || obj instanceof Number
                || obj instanceof Boolean)
            {
                return obj;
            } else if (obj instanceof Character) {
                return String.valueOf(((Character)obj).charValue());
            }
        }
        Class cls = obj.getClass();
        if (cls.isArray()) {
            return NativeJavaArray.wrap(scope, obj);
        }
        return wrapAsJavaObject(cx, scope, obj, staticType);
    }

    /**
     * Wrap an object newly created by a constructor call.
     * @param cx the current Context for this thread
     * @param scope the scope of the executing script
     * @param obj the object to be wrapped
     * @return the wrapped value.
     */
    public Scriptable wrapNewObject(Context cx, Scriptable scope, Object obj)
    {
        if (obj instanceof Scriptable) {
            return (Scriptable)obj;
        }
        Class cls = obj.getClass();
        if (cls.isArray()) {
            return NativeJavaArray.wrap(scope, obj);
        }
        return wrapAsJavaObject(cx, scope, obj, null);
    }

    /**
     * Wrap Java object as Scriptable instance to allow full access to its
     * methods and fields from JavaScript.
     * 
     * {@link #wrap(Context, Scriptable, Object, Class)} and
     * {@link #wrapNewObject(Context, Scriptable, Object)} call this method
     * when they can not convert javaObject to JavaScript primitive
     * value or JavaScript array.
     * 

     * Subclasses can override the method to provide custom wrappers
     * for Java objects.
     * @param cx the current Context for this thread
     * @param scope the scope of the executing script
     * @param javaObject the object to be wrapped
     * @param staticType type hint. If security restrictions prevent to wrap
                object based on its class, staticType will be used instead.
     * @return the wrapped value which shall not be null
     */
    public Scriptable wrapAsJavaObject(Context cx, Scriptable scope,
                                       Object javaObject, Class staticType)
    {
        return new NativeJavaObject(scope, javaObject, staticType);
    }

    /**
     * Wrap a Java class as Scriptable instance to allow access to its static
     * members and fields and use as constructor from JavaScript.
     * 
     * Subclasses can override this method to provide custom wrappers for
     * Java classes.
     *
     * @param cx the current Context for this thread
     * @param scope the scope of the executing script
     * @param javaClass the class to be wrapped
     * @return the wrapped value which shall not be null
     * @since 1.7R3
     */
    public Scriptable wrapJavaClass(Context cx, Scriptable scope,
                                    Class javaClass)
    {
        return new NativeJavaClass(scope, javaClass);
    }

    /**
     * Return false if result of Java method, which is instance of
     * String, Number, Boolean and
     * Character, should be used directly as JavaScript primitive
     * type.
     * By default the method returns true to indicate that instances of
     * String, Number, Boolean and
     * Character should be wrapped as any other Java object and
     * scripts can access any Java method available in these objects.
     * Use {@link #setJavaPrimitiveWrap(boolean)} to change this.
     */
    public final boolean isJavaPrimitiveWrap()
    {
        return javaPrimitiveWrap;
    }

    /**
     * @see #isJavaPrimitiveWrap()
     */
    public final void setJavaPrimitiveWrap(boolean value)
    {
        Context cx = Context.getCurrentContext();
        if (cx != null && cx.isSealed()) {
            Context.onSealedMutation();
        }
        javaPrimitiveWrap = value;
    }

    private boolean javaPrimitiveWrap = true;

}