1) Assuming you have the JSON libraries on your path (from www.json.org), it's pretty easy.

import org.json.JSONTokener;
...

URI uri = new URI("http://someserver/data.json");
JSONTokener tokener = new JSONTokener(uri.toURL().openStream());
JSONObject root = new JSONObject(tokener);

From there, you can address the various parts of the JSON object. Take a look at the Javadocs for the specifics. https://developer.android.com/reference/org/json/package-summary.html

The org.json library is easy to use.

Just remember (while casting or using methods like getJSONObject and getJSONArray) that in JSON notation

• [ … ] represents an array, so library will parse it to JSONArray
• { … } represents an object, so library will parse it to JSONObject

Example code below:

import org.json.*;

String jsonString = ... ; //assign your JSON String here
JSONObject obj = new JSONObject(jsonString);
String pageName = obj.getJSONObject("pageInfo").getString("pageName");

JSONArray arr = obj.getJSONArray("posts"); // notice that `"posts": [...]`
for (int i = 0; i < arr.length(); i++)
{
    String post_id = arr.getJSONObject(i).getString("post_id");
    ......
}

You may find more examples from: Parse JSON in Java

Downloadable jar: http://mvnrepository.com/artifact/org.json/json

It so happens i got it before someone else had a chance to help. In case someone else has similar question, i am posting an answer below:

JSONObject o = new JSONObject(s);

JSONArray arrayOfTests = (JSONArray) ((JSONObject) o.get("Groups")).get("Test");

for (int i = 0; i < arrayOfTests.length(); i++) {
    System.out.println(arrayOfTests.get(i));
}