使用JSONObject和JSONArray创建json字符串

Question

I have data like this:

NewsItem :

• id
• title
• date
• txt

There may be many NewsItems say 10. I have to send them to jquery.

I am doing this:

JSONObject obj = new JSONObject();
JSONArray arr = new JSONArray();

for(int i = 0 ; i< list.size() ; i++){
    p = list.get(i);
    arr.put(p.getId());
    arr.put(p.getTitle());
    arr.put(new MyDateFormatter().getStringFromDateDifference(p.getCreationDate()));
    arr.put(getTrimmedText(p.getText()));
    obj.put(""+i,arr);
    arr = new JSONArray();
}

This will create a JSON string like this : {"1":["id","title","date","txt"],"2":[......and so on...

Is that correct way of doing this?

How can I parse this string so that I can get each news item object in jQuery so that I can access attr.

Like this:

obj.id,
obj.title

Or if this is wrong way of creating JSON string, please suggest some better way with example of parsing in jQuery.

Answer 1

I believe that you're organizing your data backwards. It seems that you want to use an array of NewsItems , and if so, then your java JSON generation code should look like this:

JSONObject obj = new JSONObject();
JSONArray arr = new JSONArray();

for(int i = 0 ; i< list.size() ; i++)
{
    p = list.get(i);

    obj.put("id", p.getId());
    obj.put("title", p.getTitle());
    obj.put("date". new MyDateFormatter().getStringFromDateDifference(p.getCreationDate()));
    obj.put("txt", getTrimmedText(p.getText()));

    arr.put(obj);

    obj = new JSONObject();
}

Now your JSON string will look something like this:

[{"id": "someId", "title": "someTitle", "date": "dateString", "txt": "someTxt"},
 {"id": "someOtherId", "title": "someOtherTitle", "date": "anotherDateString", "txt": "someOtherTxt"},
 ...]

Assuming that your NewsItem gettors return Strings . The JSONObject method put is overloaded to take primitive types also, so if, eg your getId returns an int , then it will be added as a bare JSON int . I'll assume that JSONObject.put(String, Object) calls toString on the value, but I can't verify this.

Now in javascript, you can use such a string directly:

var arr =
    [{"id": "someId", "title": "someTitle", "date": "dateString", "txt": "someTxt"},
     {"id": "someOtherId", "title": "someOtherTitle", "date": "anotherDateString", "txt": "someOtherTxt"}];

for (i = 0; i < arr.length; i++)
    alert(arr[i].title); // should show you an alert box with each first title

Answer 2

The idea of the json object is the same as a dictionary/map where you have keys and values assigned to those keys, so what you want to construct would be something like this:

{"1": {"title": "my title", "date": "17-12-2011", "text": "HELLO!"}, "2": ....}

where the "1" is the id and the contents is another dictionary/map with the info.

lets say you assigned the object to a variable named my_map , now you will be able to handle it as:

 my_map.1.title
 my_map.3.text
 ...

to iterate over it just use:

for (info in my_map){
    data = my_map[info];
    //do what you need
}

Answer 3

For converting JSON object to JSON string use

JSON.stringify(json_object)

For reverse use:

JSON.parse(json_string)

Answer 4

This is the correct way -

final JSONArray arr = new JSONArray();

for(int i = 0 ; i< list.size() ; i++) {
    final JSONObject obj = new JSONObject();
    p = list.get(i);
    obj.add("id", p.getId());
    obj.add("title", p.getTitle());
    obj.add("date", new MyDateFormatter().getStringFromDateDifference(p.getCreationDate()));
    obj.add("txt", getTrimmedText(p.getText()));
    arr.add(obj);
}

This will generate

[{"id": 1, "date": 222, "title": "abc", "txt": "some text"}, {...}]

Now, when you parse the json at client end, you can iterate over the array and for each json object you can access as -

obj.id or obj["id"]