Hi Sundar, Yes indeed that helps and it really gets close to my needs, I notice however, if I do that, then:
var ia = new Int8Array(ab) ia.length will never have a valid value, it will be zero regardless of the underlying ArrayBuffer, since the property is read only I cannot assign it myself (since I know the size at construction time) either. Trying to specify the size: var bb = java.nio.ByteBuffer.allocateDirect(12) var ab = new ArrayBuffer(bb) var ia = new Int8Array(ab, 0, 12) it's all 8 bit ints so (bytes) fails with: java.lang.RuntimeException: byteOffset + byteLength out of range, byteOffset=0, elementLength=12, bytesPerElement=1 Is this expected? Or can I specify the length somewhere? Also ab.byteLength prints 0 instead of 12... On Fri, 2018-10-12 at 17:34 +0530, Sundararajan Athijegannathan wrote: > Hi Paulo Lopes, > > ArrayBuffer can be created using a nio ByteBuffer. > > // you could create a ByteBuffer in Java & pass > var bb = java.nio.ByteBuffer.allocateDirect(100) > > // create JS ArrayBuffer backed by Java ByteBuffer instance > var ab = new ArrayBuffer(bb) > > var ia = new Int8Array(ab) > ia[0] = 10 > print(bb.get(0)) > > Hope this helps, > -Sundar > > On 12/10/18, 5:04 PM, Paulo Lopes wrote: > > Hi Hannes, > > > > Thanks for the tip, knowing that the convention isn't possible as > > is, are there any alternatives to get the JVM buffer that backs a > > typed array? > > > > I wanted to perform some work on a given buffer and then pass it to > > the JVM for further processing. Having to copy the buffer byte by > > byte will introduce a penalty that kind of defeats the whole > > purpose of using typed arrays to start with. > > > > > > Paulo Lopes > > Principal Software Engineer > > > > > > Original Message > > From: hannes.wallnoe...@oracle.com > > Sent: October 12, 2018 10:10 AM > > To: pmart...@redhat.com > > Cc: nashorn-dev@openjdk.java.net > > Subject: Re: casting typed array to java byte[] is it possible? > > > > Hi Paulo, > > > > Java.to() would be the way to go, but as you found out it does not > > support typed arrays. > > > > What works is to convert the typed array to an ordinary JS array > > and convert to byte[] from there: > > > > Java.to(Array.prototype.slice.call(arr), 'byte[]‘); > > > > That’s obviously not very elegant nor efficient, but it’s the only > > workaround I can think of. > > > > Hannes > > > > > > > Am 11.10.2018 um 20:21 schrieb Paulo Lopes<pmart...@redhat.com>: > > > > > > Hi, > > > > > > I'm trying to handle a case where a Uint8Array is being passed to > > > a > > > method, that has the signature: > > > > > > String encode(byte[]); > > > > > > Sadly nashorn fails with: > > > > > > java.lang.ClassCastException: Cannot cast > > > jdk.nashorn.internal.objects.NativeUint8Array to [B > > > > > > And trying to help the cast with: > > > > > > javaObj.encode(Java.to(arr, 'byte[]')); > > > > > > Does not help either. The documentation on typed arrays is quite > > > scarce > > > so I cannot see how to handle this, does anyone have a clue? > > > > > > Thanks! > > > Paulo > > >
