How can i convert java.lang.Object to byte[]

[Neena]

Hi,

How can i convert java.lang.Object to byte[].
cant cast directly. throws ClassCastException.

Regards

Neena

 

[Andrew Thompson]

How can i convert java.lang.Object to byte[].

Serialise it.

 

[megagurka]

Neena skrev:

How can i convert java.lang.Object to byte[].
cant cast directly. throws ClassCastException.

First of all, why do you want to convert an object into a byte[]?
Second, there are an infinite number of formats for storing an object
in a byte[]. Which format do you want? If you don't care, you can
probably use the Java serialization mechanism, see
java.io.Serializable, java.ibjectOutputStream and
java.io.ByteArrayOutputStream for more information.

/JN

 

[Roedy Green]

How can i convert java.lang.Object to byte[].
cant cast directly. throws ClassCastException.

If the backing object is not REALLY a byte[] already then it is
impossible. An Object just has a few fields. You are asking the
machine to create a silk purse out of a sow's ear.

See http://mindprod.com/gotchas.html#ARRAY

 

[Roedy Green]

How can i convert java.lang.Object to byte[].
cant cast directly. throws ClassCastException.

If what you are trying to do is flatten an object for transport, then
you need to serialise it. See http://mindprod.com/applets/fileio.html
for how to write a serialized object into a byte array.

See http://mindprod.com/jgloss/serialization.html

Could we see your surrounding code to understand the context of your
question?

 

[Roedy Green]

How can i convert java.lang.Object to byte[].
cant cast directly. throws ClassCastException.

there is yet another way to interpret your question, how do I write
the fields of a Object (subclass of object really) in binary to a byte
array. For that you can use a DataOutputStream and a ByteArrayStream.
See http://mindprod.com/applets/fileio.html for how to hook them up.

 

[Neena]

I just wanted to pass abytearray to my JNI native code. i will have a
long, string or Calendar objects.
used the following method to create byte[]:

ByteArrayOutputStream bStream = new ByteArrayOutputStream();
ObjectOutputStream oStream = new ObjectOutputStream( bStream );
oStream.writeObject ( obj );
byte[] byteVal = bStream. toByteArray();

thanks alot...

 

[Roedy Green]

I just wanted to pass abytearray to my JNI native code. i will have a
long, string or Calendar objects.
used the following method to create byte[]:

Perhaps you are trying to create something that looks like a C struct
in memory. Then once C has the address of it, it can go to town
without fooling around with JNI field by field access?

If that is true, if you are on a little-endian machine you can use
LEDatastream see http://mindprod.com/products1.html#LEDATASTREAM

Write to a byte array by combining it with a ByteArrayOutputStream.
See http://mindprod.com/applets/fileio.html for details. Tell it you
have little-endian binary data and want to write to a byte array.
For character data, write native platform-encoded bytes, null
terminated in fixed length fields.

If you don't have to worry about compatibility with older JVMs, you
can use nio instead of LEDataStream.

If your machine is big-endian, just tell the file i/o amanuensis you
have big endian binary data instead.

Similarly when you return, you can take the C struct apart again to
get the value in the fields using LEDataInputStream.

This technique should be very fast on the C side, with a fairly heavy
set up cost. The slightly ugly thing about it is if you implement it
on a variety of platforms, on the Java side you need a big and little
endian version, and if there are padding/alignment bytes in the C
struct, they too may be platform dependent. With normal JNI the Java
side is identical for all platforms. Only the C side changes.

 

[Neena]

thanks alot..
i am going to give it a try...)

 

[vakhouri]

Thanks For the reply Neena, it was of great help..