Url encode an HTTP GET Solr request and parse json using gson java library

Make a request to the SOLR webserver and parse the json string to Java classes using the code snippets below.
The JSON to be parsed-

	{
	"responseHeader": {
	"status": 0,
	"QTime": 1,
	"params": {
	"q": "searchterm1 OR searchterm2",
	"q.op": "AND",
	"wt": "json",
	"rows": "10000",
	"version": "2.2"
	}
	},
	"response": {
	"numFound": 2,
	"start": 0,
	"docs": [
	{
	"name": "searchterm1",
	"id": "1"
	},
	{
	"name": "searchterm2",
	"id": "2"
	}
	]
	}
	}

view raw Solr.json hosted with ❤ by GitHub

The corresponding Java classes-

	public class Documents {
	private String name;
	private String id;
	@Override
	public String toString() {
	return id+":"+name;
	}
	public String getName() {
	return name;
	}
	public String getID() {
	return id;
	}
	}
	public class Results {
	private String numFound;
	private ArrayList<Documents> docs;
	@Override
	public String toString() {
	return numFound +" - " + docs.toString();
	}
	public ArrayList<Documents> getDocs(){
	return docs;
	}
	public String getNumFound() {
	return numFound;
	}
	}
	public class Response {
	private Results response;
	@Override
	public String toString() {
	return response.toString();
	}
	}

view raw Classes.java hosted with ❤ by GitHub

Code snippet to make a web server call and parse using gson-

	String REQUEST_URL = "properties/select/?q=" + criteria
	+ "&q.op=AND&rows=10&version=2.2&wt=json";
	try {
	URL url = new URL(webServer + "properties/select/?q="
	+ URLEncoder.encode(criteria, "UTF-8")
	+ "&q.op=AND&rows=10&version=2.2&wt=json");
	BufferedReader in = new BufferedReader(
	new InputStreamReader(url.openStream()));
	String inputLine;
	while ((inputLine = in.readLine()) != null) {
	jsonString = inputLine;
	}
	in.close();
	//Create gson
	Gson gson = new GsonBuilder().create();
	Response r = gson.fromJson(jsonString, Response.class);
	LOG.info("MyGSON:" + r.toString());
	} catch (IOException e) {
	e.getMessage();
	e.printStackTrace();
	} catch (Exception e) {
	e.getMessage();
	e.printStackTrace();
	}

view raw ParseGson.java hosted with ❤ by GitHub

The Java classes must have the same variable names as the Json's keys. Notice how nested Json elements are handled.

JSON

JSON is an acronym for JavaScript Object Notation. It is a means of transferring serialized JavaScript objects so that a JavaScript application can evaluate them and transform them into JavaScript objects which, the application can utilize to perform its operations. In short, JSON is a data interchange format. It is easy to parse and generate in almost any language.

A sample JSON:-

{"continents": {
             "asia":[{"country": "india",
                      "code": "101"
                     },
                     {"country": "japan",
                      "code": "102"
                     }],
             "europe":[{"country": "france",
                        "code": "401"
                     }]
                  }
}

The most notable features of JSON are:-

1. It is basically a collection of name-value pairs ("key": "value") separated by a colon.
2. It is not only easy to read for humans but also easy to parse by the machines.
3. Values can be a string, an integer, an object or an array.
    Standard literals like True, False, null are also acceptable.
4. Each object is placed between {...}.
5. Arrays are place between [...] and are comma separated.
6. It can be passed using httpWebRequest.
7. Reserved keywords from JavaScript are not allowed in JSON.
8. JSON can be parsed using the eval() method in JavaScript.
9. It uses Unicode.


Common errors like the "missing } after property list" can be corrected
using a JSON validator like www.jsonlint.com