Someone told me that we use serialization only to convert object to binary? How far is that correct?
It is correct 😁
Class to be serialized needs to implement Serializable or Externalizable
You may then use ObjectOutputStream to serialize and ObjectInputStream to deserialize. As these are IO streams they could be abstractions over a file, socket etc.
I don't think the point is converting an object to binary. The only reason why anyone uses serialization is object storage - either in a file or in a database. The object can then be unserialized for later usage.
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I want objects of a same serializable class to serialize in the same file. I have tried to do it by putting everything in an array and then serialize by I want the objects to be serialized individually and saved into the same file
If you want to serialize multiple objects, why not serialize a collection of those objects? When you deserialize the collection you can access the objects again by iterating. Or if you have some unique identifer for the object you can put them in a map instead and serialize that.
Worth mentioning is that Java serialization will be going away in future with the newer versions. You are better off using a JSON serializer / de-serializer in my opinion, unless you of course are trying to hide the contents somehow. I use FasterXML myself and it works really great with POJOs.
Have you already tried this?
FileOutputStream fout = new FileOutputStream("YourPath", true);
The true value as the second parameter allows you to write in this file in append mode.
So you can serialize them individually and they will be serialized in the same file.
This question already has answers here:
How to send a Java Object in binary format and receive in C server?
(3 answers)
Closed 6 years ago.
I have a java object which I want to send from Java Client(written in Java) using serialization or any other techniques and want to deserialize the same object in Server (written in C) ?
I tried to read the message received in C, but it is some hexadecimal values.
How can I print the same object parameters value in my server written in C.
Thanks in Advance
I would probably serialise the object to JSON; this has the advantage that the serialised object is human-readable. See this answer for a guide on how to serialise to JSON, and this for help on deserialising the result in C.
It depends how are you serialize your java objects. If you're using standard Java serialization mechanism this is could be painful to deserialize it into same object in C. At least you will have two parallel hierarchy of objects in C and Java to support.
I would recommend to take a look into external serialization libraries with code generation which supports both languages, C and Java:
For example:
Apache Thrift
ProtoBuf
I have a java object which I want to send from Java Client(written in Java) using serialization or any other techniques and want to deserialize the same object in Server (written in C) ?
You can't.
C does not even know about objects and when thinking of C++ as another OO language: this has a completly different concept of objects.
So you cant "recreate" a Java object outside a JVM.
But what you most likely want is to tranfer the data your Java object holds to the C-program.
In order to do this you have to specify a protocoll that both, the Java program and the C-program understand. One possibility has been proposed by #Halmackenreuter. Others are XML or CSV. The consensus of all three is: whe convert the data into a plain text file and transfer this to the other end who knows how to read (parse) it. This process is called marshalling/unmarshalling.
there is requirement in which I don't have to use Json. And looking for some binary representation of data. The object needs to be converted into binary format and then have to send across the network and retrieve the same in Server (written in c – Ajay Yadav
Then you have to specify (or know) this binary format and create the stream of bytes to sent over the network.
somebody suggested to use ByteBuffer it to the same. But still struggling on how to use the same. – Ajay Yadav
This still means you cannot send "the java object". You have to put the objects data into the ByteBuffer in the order the protocoll expects them to be.
I need to parse untrusted Java serialized objects. The data is given to me as a byte array (written at some point by ObjectOutputStream).
I do not want to simply call ObjectInputStream.readObject() and/or load the actual object. I am looking for a way to safely parse the bytes and grab field names & values.
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Here's a little summary of my attempt so far, after taking a look at the ObjectInputStream procedure for deserializing objects.
I have tried to extract field types/names (as unicode strings) recursively based on expected stream constants. I end up with a list of field names whose values should appear in the byte array in order. I am uneasy about this approach because it is probably buggy. Especially accommodating for what seems to be individual serialization protocols followed by HashMap, ArrayList, etc. But it might work, if I can figure out a way to read the bytes that represent field values:
I can try to read and store primitives based on size/offset, but when I encounter my first object, it gets a bit more complicated -- there is no clear way to distinguish between which bytes are associated with which values anymore (without actually loading the object in the way that ObjectInputStream probably does?).
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Can anyone suggest either a potential solution that I'm obviously looking past, or a trusted library that can help parse the serialized data without loading objects?
Thank you for reading, and for all comments/suggestions!!! I apologize if something is unclear and I would be happy to clarify if you bear with me.
You can't do this in principle. Any Java class can take over its own Serialization and write arbitrary data to the stream that only it knows how to parse and reconstruct, via code that is only invoked during deserialization.
I have an Array of Objects called "person" and i need to save that data, Is there a way to output an array and then input it back into the program. I have tried simply outputting the raw String and int data that makes up each "person" and the program never writes that data to the specified txt file. Is there a method or function that can write raw object data and then retrieve it?
You should have a look to ObjectOutputStream and ObjectOutputStream and the Serializable interface. What you are trying to do is to serialize your data to a file and load (deserialize) it back again.
You can use standard Java serialisation. Another trivial solution is to use XStream, which will serialise your objects into/from XML. You don't need to implement specific interfaces or annotate your objects (by default) and you'll get a readable (in XML terms) serialisation, which can be useful.
One approach would be to use Serialization provided by Java. You need to implement the java.io.Serializable interface and write and read to and from the ObjectOutputStream and ObjectInputStream classes to store and retrieve data respectively.
You need serialization. Read this.
What are methods to convert data (ints, strings) to bytes in Java? I am looking for methods other than using the Serializable class. I researched and found things like ByteOutputStream.
Can I just parse strings and ints to a byte data type?
Any suggestions?
Have a look at DataInputStream and DataOutputStream, they convert all Java data types to bytes and read/write to an underlying Input/OutputStream.
If you need to read or write ints, longs etc.. to a file, then these are the classes for you.
If instead you are just interested in how to convert then to bytes for other purposes, have a look at the source code of those classes, they convert to big-endian.
Classes supporting the DataOutput interface will do what you want. Use DataInput to read the stream back to data.
The standard encoding method used by Java when serializing is, just as your own thoughts, a simple translation of the fields into a byte stream.
Primitives as well as non-transient, non-static referenced objects are encoded into the stream. Each object that is referenced by the serialized object and must also be serialized.
Other languages, such as PHP for example, serializes to a pretty much human readable format and some implementations serialize to JSON or XML.
In my own mind though, true serialization should be binary byte-per-byte representation of the data. That way it's possible to quickly read all the data up into memory again and it can be executed as is.