How to parse Json using Java?

Question

I want to parse a json object in java.The json file is {"l1":"1","l2":"0","f1":"0","connected":"0","all":"0"} i am trying to write a java program to print above json as

l1=1
l2=0
f1=0
connected=0
all=0

The number of entries in the json file can be increased, so i have to loop through the json and print all data. This is what i've done so far.

public class main {
    public static void main(String[] args){
        try{
            URL url = new URL("http://localhost/switch.json");
            JSONTokener tokener = new JSONTokener(url.openStream());
            JSONObject root = new JSONObject(tokener);
            JSONArray jsonArray = root.names();
            if (jsonArray != null) { 
               int len = jsonArray.length();
               for (int i=0;i<len;i++){ 
                  System.out.println(jsonArray.get(i).toString());
               } 
            }   
        }catch (Exception e) {
            e.printStackTrace();
            System.out.println("Error Occured");
        }
    }
}

the above program can only print the first item of each array. But i am trying get the result i mentioned in the beginning. Can anybody help ??

Show us an example of such a JSON array. Right now you parse an object, not an array. Show us the code you use to parse an array of objects. — user1907906
– user1907906, Commented Mar 2, 2015 at 9:22
i just want to parse this {"l1":"1","l2":"0","f1":"0","connected":"0","all":"0"}. I have added the code used in the question. — Alfred Francis
– Alfred Francis, Commented Mar 2, 2015 at 9:25
If it starts with { and ends with }, that is a JavaScript/JSON Object, not an Array; JavaScript Arrays use [ and ], and do not need : to separate keys and values. — tucuxi
– tucuxi, Commented Mar 2, 2015 at 9:26

Community · Accepted Answer · 2017-05-23 12:08:09Z

4

It is simple JSON object, not an array. You need to iterate through keys and print data:

    JSONObject root = new JSONObject(tokener);
    Iterator<?> keys = root.keys();

    while(keys.hasNext()){
        String key = (String)keys.next();
        System.out.println(key + "=" + root.getString(key));
    }

Please note that above solution prints keys in a random order, due to usage of HashMap internally. Please refer to this SO question describing this behavior.

edited May 23, 2017 at 12:08

CommunityBot

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answered Mar 2, 2015 at 9:26

udalmik

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3 Comments

Alfred Francis Over a year ago

error : can only iterate over an array or any instance or java.lang.iterable

Alfred Francis Over a year ago

Why the array is printing in random order ?? I got output as connected=0 all=0 l1=1 l2=1 f1=0

udalmik Over a year ago

Because values are stored in a HashMap internally, so keys are not ordered.

DNA · Accepted Answer · 2015-03-02 09:38:47Z

4

Your JSON file does not contain an array - it contains an object.

JSON arrays are enclosed in [] brackets; JSON objects are enclosed in {} brackets.

[1, 2, 3]                     // array
{ one:1, two:2, three:3 }     // object

Your code currently extracts the names from this object, then prints those out:

JSONObject root = new JSONObject(tokener);
JSONArray jsonArray = root.names();

Instead of looping over just the names, you need to use the names (keys) to extract each value from the object:

JSONObject root = new JSONObject(tokener);
for (Iterator<?> keys= root.keys(); keys.hasNext();){
  System.out.println(key + "=" + root.get(keys.next()));
}

Note that the entries will not print out in any particular order, because JSON objects are not ordered:

An object is an unordered set of name/value pairs -- http://json.org/

See also the documentation for the JSONObject class.

edited Mar 2, 2015 at 9:38

answered Mar 2, 2015 at 9:31

DNA

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2 Comments

Alfred Francis Over a year ago

error : can only iterate over an array or any instance or java.lang.iterable

DNA Over a year ago

It's the same error, but I didn't see your answer until afterwards, so too late to avoid! Shame the library doesn't implement Iterable...

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