I am working on an API in Java that allows users to write scripts and access a specific set of methods that are passed in (in the form of an API object) by the Nashorn script engine.
I want to, in the JavaScript, call a function getDate(), which will return some arbitrary date (as a native JavaScript date) that's provided from the Java side.
I have tried simply putting an org.java.util.Date on the API object, but that won't behave like a JS date. The goal is to make this as simple as possible for end-users who are experienced with JS.
Java Example:
public class MyAPI {
public void log(String text){
System.out.println(text);
}
public Date getDate(){
// Return something that converts to a native-JS date
}
public static void main(){
// MyClassFilter implements Nashorn's ClassFilter
ScriptEngine engine = new NashornScriptEngineFactory().getScriptEngine(new MyClassFilter());
((Invokable) engine).invokeFunction("entryPoint", new MyAPI());
}
JavaScript example
function entryPoint(myApi){
var date = myApi.getDate();
myApi.log(date.getMinutes());
}
jdk.nashorn.internal.* packages are nashorn internal implementation classes. There is no guarantee that these won't be changed or be removed between JDK versions. Besides with a security manager around, accessing these packages from java code directly would result in SecurityException being thrown! With jdk9 modular jdk, these packages are not exported packages from nashorn module and so javac won't even compile your code in jdk9!
I'd recommend using JS wrapper (solution 1) in the answer by user "ug_". If you do have to call from Java, you can use API exported from jdk.nashorn.api.scripting package.
If "engine" is your javax.script.ScriptEngine of nashorn, then you can do something like the following:
import jdk.nashorn.api.scripting.*;
..
public Object getDate() {
// get JS Date constructor object - you can get once and store
// as well/
JSObject dateConstructor = (JSObject) engine.eval("Date");
// now do "new" on it
return dateConstructor.newObject();
}
With that, your JS script can call "getDate()" on your API object and get a JS
Date object. Note that you can also pass constructor arguments to newObject
method call (it is a Java variadic method).
The Nashorn engine has objects it uses internally which represent the Javascript objects. As you have guessed the java.util.Date != new Date() (in javascript). The engine uses a class called jdk.nashorn.internal.objects.NativeDate to represent its JS date.
If I were building this out I would not have the NativeDate constructed in the Java but instead have a wrapper in Javascript for the MyApi object which would contain a few other native JS methods, such as getDate().
var MYAPI_JAVASCRIPT = {
log: function() {
print(arguments);
},
getDate: function() {
return new Date();
}
}
You could then pass that object as the method parameter.
However if your really set on using the NativeDate in your Java code then you can construct one like so:
public NativeDate getDate() {
return (NativeDate) NativeDate.construct(true, null);
}
Related
I have been testing the jint library and hit a snag. Given this class in C#:
public class Foo
{
public string Name { get; } = "Bar";
}
And this code:
Engine engine = new Engine(x => x.AllowClr());
object rc = _engine
.SetValue("foo", new Foo())
.Execute("foo.Name.startsWith('B')")
.GetCompletionValue()
.ToObject();
I get the error: 'Jint.Runtime.JavaScriptException: 'Object has no method 'startsWith'''
This works, however:
"foo.Name == 'Bar'"
So can I get the former to work?
Support for extension methods is added here. But can't get it to work with the .NET string extension methods directly, it does work with an intermediate extensions class.
Update: The string methods like StartsWith aren't real extension methods indeed.
Looks like startsWith is already supported natively now. Replaced GetCompletionValue with the suggested Evaluate
// Works natively with Jint 3.0.0-beta-2032
Engine engine = new Engine();
bool result = engine
.SetValue("foo", new Foo())
.Evaluate("foo.Name.startsWith('B')")
.AsBoolean();
I've tried to add the string extension methods, but that doesn't seem to work. But using your own class for the extension methods and use it that way does work.
public static class CustomStringExtensions
{
public static bool StartsWith(this string value, string value2) =>
value.StartsWith(value2);
}
Engine engine = new Engine(options =>
{
options.AddExtensionMethods(typeof(CustomStringExtensions));
});
bool result = engine
.SetValue("foo", new Foo())
.Evaluate("foo.Name.StartsWith('B')")
.AsBoolean();
I've asked about the native extension methods support here, as I'm curious if and how it is supposed to work.
I have loaded a webpage using WebView component and added a JavascriptInterface. Please check the code below,
val webview = WebView(this)
setContentView(webview)
webview.settings.javaScriptEnabled = true
webview.loadUrl(HOME_PAGE_URL)
webview.addJavascriptInterface(JavascriptInterface(),”javascript_bridge”)
And when I call the invoke from Javascript using window.javascript_bridge.showToast(“Information Saved”);
private inner class JavascriptInterface
{
#android.webkit.JavascriptInterface
fun showToast(text: String?)
{
Log.d("WEBVIEW", text);
}
}
I am able to call the method from Javascript to Kotlin without any trouble.
But now I want to pass an Object from Javascript to Kotlin like below,
var info = {
message: “Information Saved”,
ID: 123456
}
And when I call the invoke from Javascript using window.javascript_bridge.showToast(info);
I tried to change to the data type to Any, but the value passed from Javascript is null
private inner class JavascriptInterface
{
#android.webkit.JavascriptInterface
fun showToast(text: Any?)
{
Log.d("WEBVIEW", text.toString());
}
}
As far as i know, the javaScript interface methods only accepts primitive types of data as parameters (as discussed on this question).
If you still want to achieve that, you may serialize the object (to JSON format, for instance) in the javaScript and then Deserialize it in Java.
Hope it helps :)
I'm trying to understand how to properly pass options from the js side of react-native to the java side.
The react-native bridge uses ReadableMap to convert but as a Java noob I'm failing to understand how this works.
More specifically I don't understand:
how the actual conversion works?
how to tell what type/format the downstream Java code wants?
how to properly use ReadableMap to do this?
Generally I would like to know how this works but I'll give the specific example I'm looking at to give some context.
A react-native package exposes a datetime picker.
The JS side has a showTimePicker method:
showTimePicker(date, callback) {
date = date || new Date();
console.log(this.props);
debugger
var options = {
...this.props,
hour:date.getHours(),
minute:date.getMinutes()
};
RCTDateTimePicker.showTimePicker(options, function (hour, minute) {
date.setHours(hour);
date.setMinutes(minute);
callback(date);
});
}
RCTDateTimePicker.showTimePicker is bridged to a Java method on the native side:
#ReactMethod
public void showTimePicker(ReadableMap options, Callback callback) {
DialogFragment timePicker = new TimePicker(options, callback);
timePicker.show(activity.getFragmentManager(), "timePicker");
}
which calls
public TimePicker(ReadableMap options, Callback callback) {
final Calendar c = Calendar.getInstance();
this.callback = callback;
hour = options.hasKey("hour") ? options.getInt("hour") : c.get(Calendar.HOUR_OF_DAY);
minute = options.hasKey("minute") ? options.getInt("minute") : c.get(Calendar.MINUTE);
}
which creates and instance of an Android TimePicker. My goal is to change the style of the Timepicker from watch to spinner.
There is a settable XML attribute android:timePickerMode="spinner" but I don't think I can pass an XML attribute through react-native can I?
I also found a suggestion in comments to pass defStyleAttr to do this, but I don't understand how.
First, see the list of Argument Types from the React Native document for Android Native Modules.
Argument Types
The following argument types are supported for methods
annotated with #ReactMethod and they directly map to their JavaScript
equivalents
Boolean -> Bool
Integer -> Number
Double -> Number
Float -> Number
String -> String
Callback -> function
ReadableMap -> Object
ReadableArray -> Array
So, you can pass the extra field for timePickerMode as a String by updating the options that the JS side passes to include it.
var options = {
...this.props,
hour:date.getHours(),
minute:date.getMinutes(),
timePickerMode:"spinner"
};
And then get that value from the ReadableMap in your custom TimePicker constructor.
String timePickerMode = options.hasKey("timePickerMode") ?
options.getString("timePickerMode") : defaultTimePickerMode;
Now you have the value you wish to set. Unfortunately it does not appear that timePickerMode can be set programmatically. This SO question asks how to do it and #alanv (whose profile indicates they are a Software Engineer at Google) indicates that it is not possible at runtime.
As far as I know we can call C# function from Javascript, that is loaded inside a WebBrowser control, following code shows how I usually do it.
Form1.cs
public partial class Form1 : Form{
private WebBrowser webBrowser1;
public ApplicationWindow(){
InitializeComponent();
WebBrowser webBrowser1 = new WebBrowser();
//some code follows
webBrowser1.ObjectForScripting = new ScriptManager();
this.webBrowser1.Url = new Uri("file:///d:/ui/application.html");
}
}
}
ScriptManager.cs
namespace WindowsFormsApplication10 {
[ComVisible(true)]
public class ScriptManager{
public string GetAllDomains(){
string result=null;
//does something;
return result;
}
}
}
application.html
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
$(document).ready(function () {
var result = window.external.GetAllDomains();
//it works but this is what puzzles me.
});
</script>
The questions that intrigues me are
why we need ComVisible to be true for class whose object we are going to use as objectForScripting?
How Javascript object window.external has the same methods as in objectForScripting?
How they handle cross language type conversion?
I wonder why no one answered for so long. The answer to all your questions is COM - Component Object Model.
Windows is providing ability (using COM) for classes and functions from one program (exe) to be accessible outside the exe.
So
1) why we need ComVisible to be true for class whose object we are going to use as objectForScripting?
-> This tells windows to make the class and its methods visible to the webbrowser.
2) How Javascript object window.external has the same methods as in objectForScripting?
-> The javascript is calling methods of the class made visible in above answer.
3) How they handle cross language type conversion?
-> COM handles the types internally so methods in one programming language can be called from another programming language.
I have seen this for BHO extensions, where the JavaScript can call functions in the C++ BHO. But lets say I am not using a BHO, instead I have a C++ console application that creates an IE COM object like so:
HRESULT hr = CoCreateInstance(
CLSID_InternetExplorer,
NULL,
CLSCTX_LOCAL_SERVER,
IID_IWebBrowser2,
(void**)&_cBrowser);
I also have a class which "owns" the IWebBrowser2 object that comes back from this function.
class BrowserWrapper{
public:
CComPtr<IWebBrowser2> pBrowser;
void SomeFunction(...)
}
Is there a way to call a function like "SomeFunction" in the wrapper class from the JavaScript in the spawned IWebBrowser2 object?
You must implement the IDocHostUIHandler interface and set it to the web browser with a code similar to this (extracted from the doc):
ComPtr<IDispatch> spDocument;
hr = spWebBrowser2->get_Document(&spDocument);
if (SUCCEEDED(hr) && (spDocument != nullptr))
{
// Request default handler from MSHTML client site
ComPtr<IOleObject> spOleObject;
if (SUCCEEDED(spDocument.As(&spOleObject)))
{
ComPtr<IOleClientSite> spClientSite;
hr = spOleObject->GetClientSite(&spClientSite);
if (SUCCEEDED(hr) && spClientSite)
{
// Save pointer for delegation to default
m_spDefaultDocHostUIHandler = spClientSite;
}
}
// Set the new custom IDocHostUIHandler
ComPtr<ICustomDoc> spCustomDoc;
if (SUCCEEDED(spDocument.As(&spCustomDoc)))
{
// NOTE: spHandler is user-defined class
spCustomDoc->SetUIHandler(spHandler.Get());
}
}
You must specifically implement the GetExternal method
Now, in IE's javascript (or vbscript for that matter), you can access your host with a call like this:
var ext = window.external; // this will call your host's IDocHostUIHandler.GetExternal method
ext.SomeFunction(...); // implemented by your object
What you return in GetExternal must be an IDispatch object that you can design the way you want.
You need to implement the IDocHostUIHandler interface. This has a method called GetExternal - which you need to return an object that implements IDispatch.
In the javascript, you can call window.external.something() - which will cause the browser to query for your external implementation - the IDispatch object - and it will then use the IDispatch to execute something.