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I've read a lot of answers about it, but sometimes they were arrays and some others were objects, here there are both together.

I have more variables of the same object stored in an array. Now i want to convert all of these to a string, so that i can send by HTTP POST request to the server and then PHP must be able to read them with JSON decode.

So that's the code Java in my Android app:

Object Class

class DataMisurati {
    float valori[]=new float[3];
    long tempo;
    DataMisurati() {  }
    DataMisurati(float[] values, long temp) { 
        this.valori[0] = values[0]; 
        this.valori[1] = values[1]; 
        this.valori[2] = values[2]; 
        this.tempo=temp;
    }

  }

And here some of the main code:

DataMisurati[] daticompleti;

//now i fill the array daticompleti

//here must be the code to Json the array of objects and then convert it to string

Then there must be the HTTP post with sending the string.

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2 Answers

up vote 0 down vote accepted

I found Gson to be the easiest to work with custom objects. First download the Gson jar from here: http://code.google.com/p/google-gson/downloads/list

Then, import the jar into your project, this is done slightly differently based on the IDE you're using. Once you have the jar into your project, do an import statement at the top where all the other import statements are:

import com.google.gson.Gson;

Then go from object to string like this:

Gson gson = new Gson();
String jsonString = gson.toJson(daticompleti);

Then, in your http connection you want to set the request entity like this:

request.setEntity(new ByteArrayEntity(jsonString.getBytes("UTF8")));

or however you're doing the connection stuff. The important thing is to use the getBytes because post bodies use raw data.

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as a side note, GSON is very slow. i did a test across GSON, org.json, and Jackson. GSON was 5x slower than org.json, and 10x slower than Jackson. Jackson has object binding just like GSON. –  Jeffrey Blattman Nov 9 '11 at 21:28
 
Many thanx!!! Veri usefull. But there a way to do it with org.json that is already include in Eclipse? –  Lork Nov 10 '11 at 8:09
1  
Kind of, but of course you lose the benefit of using your custom objects as is... I think you have to use the JSONObject or one of a few generic Java types. Then you use put's and get's in a generic way so you'll have to convert your object to a JSONObject and back again. Just seems easier to import a jar. –  Vinnie Nov 10 '11 at 16:39
 
Yes it was! I used GSON and is perfect!!!! Thanx!!! –  Lork Nov 10 '11 at 17:03
up vote 1 down vote

Would definitely agree with Vinnie that GSON is the way to go. Personally I'd suggest you skip the clever object binding stuff and look at the JSONWriter class instead. This is a lot quicker than the Gson.toJson() method (it doesn't do refection magic behind the scenes), uses less memory and scales better. The downside is you need to write a bit more code to encode your JSON, but I think that's a worthy trade-off when working on a constrained mobile platform.

Using JSONWriter also means you only need to import the GSON stream package into your app (14kb) rather than the full GSON package (515kb).

I believe the GSON stream package is essentially what Google have bundled into the latest versions of Android Framework.

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