Convert a .json file to a JSONArray

Question

I used cURL to get some twitter feeds in the form of a json file ("twitter-feed.json"). I want to convert this json file to a JSONArray object. How do I do it?

I am new to Java and json. Your suggestions are most welcome.

FileInputStream infile = new FileInputStream("input/twitter-feed.json");

// parse JSON JSONArray jsonArray = new JSONArray(string);

    // use
    for (int i = 0; i < jsonArray.length(); i++) {
        JSONObject jsonObject = jsonArray.getJSONObject(i);

        System.out.println(jsonObject.getString("id"));
        System.out.println(jsonObject.getString("text"));               
        System.out.println(jsonObject.getString("created_at"));     
    }

Thanks, PD.

Answer 1

You need to read the file first, convert it to String then feed it to the JSONArray (I am assuming that you are using the JSON-Java Project. The code below illustrates how to read the file and set it to JSONArray

// read the source file, source comes from streaming API delimited by newline
// done by curl https://stream.twitter.com/1/statuses/sample.json?delimited=newline -utwitterUsername:twitterPasswd 
// > /Projects/StackOverflow/src/so7655570/twitter.json
FileReader f = new FileReader("/Projects/StackOverflow/src/so7655570/twitter.json");
BufferedReader br = new BufferedReader(f);

ArrayList jsonObjectArray = new ArrayList();
String currentJSONString  = "";

// read the file, since I ask for newline separation, it's easier for BufferedReader
// to separate each String
while( (currentJSONString = br.readLine()) != null ) {
    // create new JSONObject
    JSONObject currentObject = new JSONObject(currentJSONString);

    // there are more than one way to do this, right now  what I am doing is adding
    // each JSONObject to an ArrayList
    jsonObjectArray.add(currentObject);
}

for (int i = 0; i < jsonObjectArray.size(); i++) {
    JSONObject jsonObject = jsonObjectArray.get(i);

    // check if it has valid ID as delete won't have one
    // sample of JSON for delete : 
    // {"delete":{"status":{"user_id_str":"50269460","id_str":"121202089660661760","id":121202089660661760,"user_id":50269460}}}

    if(jsonObject.has("id")) {
        System.out.println(jsonObject.getInt("id"));
        System.out.println(jsonObject.getString("text"));               
        System.out.println(jsonObject.getString("created_at") + "\n");    
    }
}

Steps explanation :

• Stream API does not provide valid JSON as a whole but rather a valid one specified by the delimited field. Which is why, you can't just parse the entire result as is.
• In order to parse the JSON, I use the delimited to use newline since BufferedReader has a method readLine that we could directly use to get each JSONObject
• Once I get each valid JSON from each line, I create JSONObject and add it to the ArrayList
• I then iterate each JSONObject in the ArrayList and print out the result. Note that if you want to use the result immediately and don't have the need to use it later, you can do the processing itself in while loop without storing them in the ArrayList which change the code to:

// read the source file, source comes from streaming API
// done by curl https://stream.twitter.com/1/statuses/sample.json?delimited=newline -utwitterUsername:twitterPasswd 
// > /Projects/StackOverflow/src/so7655570/twitter.json
FileReader f = new FileReader("/Projects/StackOverflow/src/so7655570/twitter.json");
BufferedReader br = new BufferedReader(f);

String currentJSONString  = "";

// read the file, since I ask for newline separation, it's easier for BufferedReader
// to separate each String
while( (currentJSONString = br.readLine()) != null ) {
    // create new JSONObject
    JSONObject currentObject = new JSONObject(currentJSONString);

    // check if it has valid ID as delete status won't have one
    if(currentObject.has("id")) {
        System.out.println(currentObject.getInt("id"));
        System.out.println(currentObject.getString("text"));               
        System.out.println(currentObject.getString("created_at") + "\n");    
    }
}

Answer 2

Use ObjectMapper Class from jackson library like this :

//JSON from file to Object
Staff obj = mapper.readValue(new File("c:\\file.json"), Staff.class);

//JSON from URL to Object
Staff obj = mapper.readValue(new URL("http://mkyong.com/api/staff.json"), Staff.class);

//JSON from String to Object
Staff obj = mapper.readValue(jsonInString, Staff.class);

Answer 3

You may try Gson:

For just arrays you can use:

Gson gson = new Gson();

//(Deserialization)
int[] ints2 = gson.fromJson("[1,2,3,4,5]", int[].class);

To deserialize an array of objects, you can just do:

Container container = new Gson().fromJson(json, Container.class);

As shown here