* Given a name of a Java type, returns an object representing that type in Nashorn. The Java class of the objects * used to represent Java types in Nashorn is not {@link java.lang.Class} but rather {@link StaticClass}. They are * the objects that you can use with the {@code new} operator to create new instances of the class as well as to * access static members of the class. In Nashorn, {@code Class} objects are just regular Java objects that aren't * treated specially. Instead of them, {@link StaticClass} instances - which we sometimes refer to as "Java type * objects" are used as constructors with the {@code new} operator, and they expose static fields, properties, and * methods. While this might seem confusing at first, it actually closely matches the Java language: you use a * different expression (e.g. {@code java.io.File}) as an argument in "new" and to address statics, and it is * distinct from the {@code Class} object (e.g. {@code java.io.File.class}). Below we cover in details the * properties of the type objects. *
*Constructing Java objects
* Examples: *
* var arrayListType = Java.type("java.util.ArrayList")
* var intType = Java.type("int")
* var stringArrayType = Java.type("java.lang.String[]")
* var int2DArrayType = Java.type("int[][]")
*
* Note that the name of the type is always a string for a fully qualified name. You can use any of these types to
* create new instances, e.g.:
*
* var anArrayList = new Java.type("java.util.ArrayList")
*
* or
*
* var ArrayList = Java.type("java.util.ArrayList")
* var anArrayList = new ArrayList
* var anArrayListWithSize = new ArrayList(16)
*
* In the special case of inner classes, you can either use the JVM fully qualified name, meaning using {@code $}
* sign in the class name, or you can use the dot:
*
* var ftype = Java.type("java.awt.geom.Arc2D$Float")
*
* and
*
* var ftype = Java.type("java.awt.geom.Arc2D.Float")
*
* both work. Note however that using the dollar sign is faster, as Java.type first tries to resolve the class name
* as it is originally specified, and the internal JVM names for inner classes use the dollar sign. If you use the
* dot, Java.type will internally get a ClassNotFoundException and subsequently retry by changing the last dot to
* dollar sign. As a matter of fact, it'll keep replacing dots with dollar signs until it either successfully loads
* the class or runs out of all dots in the name. This way it can correctly resolve and load even multiply nested
* inner classes with the dot notation. Again, this will be slower than using the dollar signs in the name. An
* alternative way to access the inner class is as a property of the outer class:
*
* var arctype = Java.type("java.awt.geom.Arc2D")
* var ftype = arctype.Float
*
* * You can access both static and non-static inner classes. If you want to create an instance of a non-static * inner class, remember to pass an instance of its outer class as the first argument to the constructor. *
** If the type is abstract, you can instantiate an anonymous subclass of it using an argument list that is * applicable to any of its public or protected constructors, but inserting a JavaScript object with functions * properties that provide JavaScript implementations of the abstract methods. If method names are overloaded, the * JavaScript function will provide implementation for all overloads. E.g.: *
*
* var TimerTask = Java.type("java.util.TimerTask")
* var task = new TimerTask({ run: function() { print("Hello World!") } })
*
* * Nashorn supports a syntactic extension where a "new" expression followed by an argument is identical to * invoking the constructor and passing the argument to it, so you can write the above example also as: *
*
* var task = new TimerTask {
* run: function() {
* print("Hello World!")
* }
* }
*
* * which is very similar to Java anonymous inner class definition. On the other hand, if the type is an abstract * type with a single abstract method (commonly referred to as a "SAM type") or all abstract methods it has share * the same overloaded name), then instead of an object, you can just pass a function, so the above example can * become even more simplified to: *
*
* var task = new TimerTask(function() { print("Hello World!") })
*
* * Note that in every one of these cases if you are trying to instantiate an abstract class that has constructors * that take some arguments, you can invoke those simply by specifying the arguments after the initial * implementation object or function. *
*The use of functions can be taken even further; if you are invoking a Java method that takes a SAM type, * you can just pass in a function object, and Nashorn will know what you meant: *
*
* var timer = new Java.type("java.util.Timer")
* timer.schedule(function() { print("Hello World!") })
*
* * Here, {@code Timer.schedule()} expects a {@code TimerTask} as its argument, so Nashorn creates an instance of a * {@code TimerTask} subclass and uses the passed function to implement its only abstract method, {@code run()}. In * this usage though, you can't use non-default constructors; the type must be either an interface, or must have a * protected or public no-arg constructor. *
** You can also subclass non-abstract classes; for that you will need to use the {@link #extend(Object, Object...)} * method. *
*Accessing static members
* Examples: *
* var File = Java.type("java.io.File")
* var pathSep = File.pathSeparator
* var tmpFile1 = File.createTempFile("abcdefg", ".tmp")
* var tmpFile2 = File.createTempFile("abcdefg", ".tmp", new File("/tmp"))
*
* Actually, you can even assign static methods to variables, so the above example can be rewritten as:
*
* var File = Java.type("java.io.File")
* var createTempFile = File.createTempFile
* var tmpFile1 = createTempFile("abcdefg", ".tmp")
* var tmpFile2 = createTempFile("abcdefg", ".tmp", new File("/tmp"))
*
* If you need to access the actual {@code java.lang.Class} object for the type, you can use the {@code class}
* property on the object representing the type:
*
* var File = Java.type("java.io.File")
* var someFile = new File("blah")
* print(File.class === someFile.getClass()) // prints true
*
* Of course, you can also use the {@code getClass()} method or its equivalent {@code class} property on any
* instance of the class. Other way round, you can use the synthetic {@code static} property on any
* {@code java.lang.Class} object to retrieve its type-representing object:
*
* var File = Java.type("java.io.File")
* print(File.class.static === File) // prints true
*
* {@code instanceof} operator
* The standard ECMAScript {@code instanceof} operator is extended to recognize Java objects and their type objects: *
* var File = Java.type("java.io.File")
* var aFile = new File("foo")
* print(aFile instanceof File) // prints true
* print(aFile instanceof File.class) // prints false - Class objects aren't type objects.
*
* @param self not used
* @param objTypeName the object whose JS string value represents the type name. You can use names of primitive Java
* types to obtain representations of them, and you can use trailing square brackets to represent Java array types.
* @return the object representing the named type
* @throws ClassNotFoundException if the class is not found
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR)
public static Object type(final Object self, final Object objTypeName) throws ClassNotFoundException {
return type(objTypeName);
}
private static StaticClass type(final Object objTypeName) throws ClassNotFoundException {
return StaticClass.forClass(type(JSType.toString(objTypeName)));
}
private static Class type(final String typeName) throws ClassNotFoundException {
if (typeName.endsWith("[]")) {
return arrayType(typeName);
}
return simpleType(typeName);
}
/**
* Returns name of a java type {@link StaticClass}.
* @param self not used
* @param type the type whose name is returned
* @return name of the given type
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR)
public static Object typeName(final Object self, final Object type) {
if (type instanceof StaticClass) {
return ((StaticClass)type).getRepresentedClass().getName();
} else if (type instanceof Class) {
return ((Class)type).getName();
} else {
return UNDEFINED;
}
}
/**
* Given a script object and a Java type, converts the script object into the desired Java type. Currently it
* performs shallow creation of Java arrays, as well as wrapping of objects in Lists, Dequeues, Queues,
* and Collections. Example:
*
* var anArray = [1, "13", false]
* var javaIntArray = Java.to(anArray, "int[]")
* print(javaIntArray[0]) // prints 1
* print(javaIntArray[1]) // prints 13, as string "13" was converted to number 13 as per ECMAScript ToNumber conversion
* print(javaIntArray[2]) // prints 0, as boolean false was converted to number 0 as per ECMAScript ToNumber conversion
*
* @param self not used
* @param obj the script object. Can be null.
* @param objType either a {@link #type(Object, Object) type object} or a String describing the type of the Java
* object to create. Can not be null. If undefined, a "default" conversion is presumed (allowing the argument to be
* omitted).
* @return a Java object whose value corresponds to the original script object's value. Specifically, for array
* target types, returns a Java array of the same type with contents converted to the array's component type.
* Converts recursively when the target type is multidimensional array. For {@link List}, {@link Deque},
* {@link Queue}, or {@link Collection}, returns a live wrapper around the object, see {@link ListAdapter} for
* details. Returns null if obj is null.
* @throws ClassNotFoundException if the class described by objType is not found
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR)
public static Object to(final Object self, final Object obj, final Object objType) throws ClassNotFoundException {
if (obj == null) {
return null;
}
if (!(obj instanceof ScriptObject) && !(obj instanceof JSObject)) {
throw typeError("not.an.object", ScriptRuntime.safeToString(obj));
}
final Class targetClass;
if(objType == UNDEFINED) {
targetClass = Object[].class;
} else {
final StaticClass targetType;
if(objType instanceof StaticClass) {
targetType = (StaticClass)objType;
} else {
targetType = type(objType);
}
targetClass = targetType.getRepresentedClass();
}
if(targetClass.isArray()) {
return JSType.toJavaArray(obj, targetClass.getComponentType());
}
if (targetClass == List.class || targetClass == Deque.class || targetClass == Queue.class || targetClass == Collection.class) {
return ListAdapter.create(obj);
}
throw typeError("unsupported.java.to.type", targetClass.getName());
}
/**
* Given a Java array or {@link Collection}, returns a JavaScript array with a shallow copy of its contents. Note
* that in most cases, you can use Java arrays and lists natively in Nashorn; in cases where for some reason you
* need to have an actual JavaScript native array (e.g. to work with the array comprehensions functions), you will
* want to use this method. Example:
*
* var File = Java.type("java.io.File")
* var listHomeDir = new File("~").listFiles()
* var jsListHome = Java.from(listHomeDir)
* var jpegModifiedDates = jsListHome
* .filter(function(val) { return val.getName().endsWith(".jpg") })
* .map(function(val) { return val.lastModified() })
*
* @param self not used
* @param objArray the java array or collection. Can be null.
* @return a JavaScript array with the copy of Java array's or collection's contents. Returns null if objArray is
* null.
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR)
public static NativeArray from(final Object self, final Object objArray) {
if (objArray == null) {
return null;
} else if (objArray instanceof Collection) {
return new NativeArray(((Collection)objArray).toArray());
} else if (objArray instanceof Object[]) {
return new NativeArray(((Object[])objArray).clone());
} else if (objArray instanceof int[]) {
return new NativeArray(((int[])objArray).clone());
} else if (objArray instanceof double[]) {
return new NativeArray(((double[])objArray).clone());
} else if (objArray instanceof long[]) {
return new NativeArray(((long[])objArray).clone());
} else if (objArray instanceof byte[]) {
return new NativeArray(copyArray((byte[])objArray));
} else if (objArray instanceof short[]) {
return new NativeArray(copyArray((short[])objArray));
} else if (objArray instanceof char[]) {
return new NativeArray(copyArray((char[])objArray));
} else if (objArray instanceof float[]) {
return new NativeArray(copyArray((float[])objArray));
} else if (objArray instanceof boolean[]) {
return new NativeArray(copyArray((boolean[])objArray));
}
throw typeError("cant.convert.to.javascript.array", objArray.getClass().getName());
}
/**
* Return properties of the given object. Properties also include "method names".
* This is meant for source code completion in interactive shells or editors.
*
* @param object the object whose properties are returned.
* @return list of properties
*/
public static List
* var ArrayList = Java.type("java.util.ArrayList")
* var ArrayListExtender = Java.extend(ArrayList)
* var printSizeInvokedArrayList = new ArrayListExtender() {
* size: function() { print("size invoked!"); }
* }
* var printAddInvokedArrayList = new ArrayListExtender() {
* add: function(x, y) {
* if(typeof(y) === "undefined") {
* print("add(e) invoked!");
* } else {
* print("add(i, e) invoked!");
* }
* }
*
* We can see several important concepts in the above example:
*
* var Runnable = Java.type("java.lang.Runnable")
* var R1 = Java.extend(Runnable, {
* run: function() {
* print("R1.run() invoked!")
* }
* })
* var r1 = new R1
* var t = new java.lang.Thread(r1)
* t.start()
* t.join()
*
* As you can see, you don't have to pass any object when you create a new instance of {@code R1} as its
* {@code run()} function was defined already when extending the class. If you also want to add instance-level
* overrides on these objects, you will have to repeatedly use {@code extend()} to subclass the class-level adapter.
* For such adapters, the order of precedence is instance-level method, class-level method, superclass method, or
* {@code UnsupportedOperationException} if the superclass method is abstract. If we continue our previous example:
*
* var R2 = Java.extend(R1);
* var r2 = new R2(function() { print("r2.run() invoked!") })
* r2.run()
*
* We'll see it'll print {@code "r2.run() invoked!"}, thus overriding on instance-level the class-level behavior.
* Note that you must use {@code Java.extend} to explicitly create an instance-override adapter class from a
* class-override adapter class, as the class-override adapter class is no longer abstract.
*
* var cw = new FilterWriterAdapter(sw) {
* write: function(s, off, len) {
* s = capitalize(s, off, len)
* cw_super.write(s, 0, s.length())
* }
* }
* var cw_super = Java.super(cw)
*
* @param self the {@code Java} object itself - not used.
* @param adapter the original Java adapter instance for which the super adapter is created.
* @return a super adapter for the original adapter
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR, name="super")
public static Object _super(final Object self, final Object adapter) {
return Bootstrap.createSuperAdapter(adapter);
}
/**
* Returns an object that is compatible with Java JSON libraries expectations; namely, that if it itself, or any
* object transitively reachable through it is a JavaScript array, then such objects will be exposed as
* {@link JSObject} that also implements the {@link List} interface for exposing the array elements. An explicit
* API is required as otherwise Nashorn exposes all objects externally as {@link JSObject}s that also implement the
* {@link Map} interface instead. By using this method, arrays will be exposed as {@link List}s and all other
* objects as {@link Map}s.
* @param self not used
* @param obj the object to be exposed in a Java JSON library compatible manner.
* @return a wrapper around the object that will enforce Java JSON library compatible exposure.
*/
@Function(attributes = Attribute.NOT_ENUMERABLE, where = Where.CONSTRUCTOR)
public static Object asJSONCompatible(final Object self, final Object obj) {
return ScriptObjectMirror.wrapAsJSONCompatible(obj, Context.getGlobal());
}
}