CODEWITHSUNDEEP
c#javaandroid.netserialization
ikiw
ikiw

Reputation: 21

Transferring data from C# to Java via serialization

I have a Java application for Android that will have some static data, which will be loaded at start up. This data is generated by a C# app as a bunch of classes with lists and Dictionaries, something like this:

public class DataContainer
{
    public List<A> As = new List<A>();
    public Dictionary<int, B> Bs = new Dictionary<int, B>();
    // ...
}

public class A
{
    public int IdA;
    public int IdSomething;
    public DateTime dt;
    //...
}

public class B
{
    public int IdB;
    public string Name;
    List<C> Cs = new List<C>();
    //...
}

public class C
{
    //...
}

(The DataContainer class is the root class that contains all the data to be transferred. I then have a similar class structure in the Java project into which I want the data to be imported.)

My issue is that I can't seem to find a combination of a .NET and Java tools/libraries that would be able to write and read the same format.

I've tried JSON with DataContractJsonSerializer and then loading with GSON but that doesn't work with Dictionaries/Maps (works fine with Lists but I need the dictionaries). The .NET exporter uses format like

"Bs":[{"Key":1,"Value":{...}}, ...]

while it looks like GSON uses

{key:value,key:value,...}

I've also looked at some XML but since there isn't a standard formatting all the libraries use something different by default and I really don't want to write all the writing/parsing rules by hand. Also, JSON has much less overhead compared to XML.

So, is there some pair of libraries for .NET export and Java import that can handle nested classes with Lists and Dictionaries? The things I've managed to find were either in the other direction or did just simple one class serialization.

BTW: I'm also using Tuples for Dictionary keys, but if nothing can handle that I'll just use nested Dictionaries, that is not a big deal.

EDIT: Since I can't answer my own question due to low rep here is the solution that worked for me:

So, I've tried a few more combinations and serializing using JSon.NET on the C#/.NET side and then loading using GSON on the Java side works great, except Tuples. For example, using Tuple as a key for dictionary will get serialized as:

{ "(False, 3)" : { ... }, "(True, 1)" : { ... }, ... }

So I have to use String keys in Java for now but that is not an issue. Possible solution is to write a custom class for the Tuple in both .NET and Java.

Example code:

        string serializeObject = JsonConvert.SerializeObject(dataContainer, new IsoDateTimeConverter());
        File.WriteAllText("test.json", serializeObject);

and Java:

    InputStream is = getResources().openRawResource(R.raw.test); // open from /res/raw/test.json
    Gson gson = new Gson();
    InputStreamReader r = new InputStreamReader(is);
    DataContainer dc = gson.fromJson(r, DataContainer.class);
    Log.i("jsondebug", dc.Packers.get(0).Something);

Upvotes: 2

Views: 2777

Answers (3)

Andrei Zagorneanu
Andrei Zagorneanu

Reputation: 221

You can have a look at Google Protocol Buffers. Protocol buffers are Google's lingua franca for data. Below is an excerpt from Protocol Buffers Developer Guide:

Protocol buffers are a flexible, efficient, automated mechanism for serializing structured data – think XML, but smaller, faster, and simpler. You define how you want your data to be structured once, then you can use special generated source code to easily write and read your structured data to and from a variety of data streams and using a variety of languages. You can even update your data structure without breaking deployed programs that are compiled against the "old" format.

Protocol buffers have many advantages over XML for serializing structured data. Protocol buffers:

  1. are simpler
  2. are 3 to 10 times smaller
  3. are 20 to 100 times faster
  4. are less ambiguous
  5. generate data access classes that are easier to use programmatically

Upvotes: 2

Eric Levine
Eric Levine

Reputation: 13564

I think you need to approach this from a different perspective. Think first about a JSON or XML format that will work well with both the C# and Java side. Think of that as an API or contract between the C# and Android apps. Instead of using libraries that marshall/unmarshall according to their own formats, make the code on each side read/write to the contract you defined.

Alternatively, you might want to look into using a binary format like Apache Thrift or Protocol Buffers.

Upvotes: 1

duffymo
duffymo

Reputation: 308918

An XML mapping would work just fine. Serialize as XML and send it over. You'll need marshallers and unmarshallers on either end.

Java has its JAXB standard for binding XML to objects. Perhaps you can manage it if you follow that standard.

Upvotes: 1

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