Custom JSON.net serialization and deserialization

Question

I am writing out data into JSON format to be consumed by another program. I need to serialize the large number of JSON objects into a file. Using JSON.net this is really straight forward to serialize with the following lines of code:

[JsonConverter(typeof(SimpleClassSerializer))]
public class SimpleClass
{
    public string name;
}

SimpleClass obj1 = new SimpleClass { name="exampleObj1" };
string serialised = JsonConvert.SerializeObject(obj1, Formatting.Indented);

Giving the output:

{
  "name": "exampleObj1"
}

I will actually be working with multiple SimpleClass (example class) objects and want to serialize them all (as I receive them).

Using the following example code, this is nice and simple if I have an array or list:

SimpleClass[] arr1 = new SimpleClass[3];

SimpleClass obj1 = new SimpleClass { name="exampleObj1" };
SimpleClass obj2 = new SimpleClass { name = "exampleObj2" };
SimpleClass obj3 = new SimpleClass { name = "exampleObj3" };

arr1[0] = obj1;
arr1[1] = obj2;
arr1[2] = obj3;

string serialised = JsonConvert.SerializeObject(arr1, Formatting.Indented);

Giving me the following output:

[
  {
    "name": "exampleObj1"
  },
  {
    "name": "exampleObj2"
  },
  {
    "name": "exampleObj3"
  }
]

This is easily deserialized into an array.

However, I cannot declare an array up front (for example string[] arr = new string[50000]) because I wont know the number of objects I am dealing with and because of memory constraints (the data in each object is huge). I cannot use a list mainly because of memory constraints as well.

If I do the following:

SimpleClass obj1 = new SimpleClass { name="exampleObj1" };
SimpleClass obj2 = new SimpleClass { name = "exampleObj2" };
SimpleClass obj3 = new SimpleClass { name = "exampleObj3" };

string serialised = JsonConvert.SerializeObject(obj1, Formatting.Indented);
serialised += JsonConvert.SerializeObject(obj2, Formatting.Indented);
serialised += JsonConvert.SerializeObject(obj3, Formatting.Indented);

Giving me this:

{
  "name": "exampleObj1"
}{
  "name": "exampleObj2"
}{
  "name": "exampleObj3"
}

The main thing here is that I have an open file and I am streaming the serialized objects into the file as I receive them. Giving me this format shown above. When attempting to deserialize such an object, I get an error as it is basically expecting it to be an array.

Whats the best approach to achieve continuous serialization in this manner?

Ideally if i could do some custom serialization where I start out writing "[" into the file at the beginning and "]" at the end (and the comma's inbetween each object!), then the consuming app could deserialize into an array. How do I do this?

Json.net has a JsonWriter and JsonSerializer. See this James Newton-King blog post. james.newtonking.com/archive/2009/02/14/… — cgotberg
– cgotberg, Commented Sep 2, 2014 at 20:19

Rob · Accepted Answer · 2014-09-02 20:40:56Z

2

Based on the information given to me by cgotberg (sorry dont seem to be able to mark a comment as the answer! :-s)

Here was the solution:

using (FileStream fs = File.Open(@"c:\temp\a.json", FileMode.Create))
     using (StreamWriter sw = new StreamWriter(fs))
          using (JsonWriter jw = new JsonTextWriter(sw))
               {
                   jw.Formatting = Formatting.Indented;

                   JsonSerializer serializer = new JsonSerializer();
                   sw.Write("[");
                   serializer.Serialize(jw, obj1);
                   sw.Write(",");
                   serializer.Serialize(jw, obj2);
                   sw.Write(",");
                   serializer.Serialize(jw, obj3); 
                   sw.Write("]");
                }

answered Sep 2, 2014 at 20:40

Rob

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