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 ??
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.
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.
Related
I have this array list in java
[ {"pname":"7", "qty":"222"},
{"pname":"8", "qty":"5"},
{"pname":"9", "qty":"60"} ]
I can access the first index which is object, how can I access the first element inside the first object which is "pname" key in java syntax. Please give me sample codes. Thanks.
I tried:
mylist.get(0)
but it only gives me the first object. I don't know how to access the first index inside the object.
here is my whole code from getting the data to parse it into json array and convert to array list
String data = request.getParameter("data");
JSONArray jsonArray = new JSONArray(data);
ArrayList<String> mylist = new ArrayList<String>();
JSONArray this_is_jsonArray = (JSONArray)jsonArray;
if (jsonArray == null) {
System.out.println("json is empty");
}
else
{
int length = this_is_jsonArray.length();
for (int i=0;i<length;i++){
mylist.add(this_is_jsonArray.get(i).toString());
}
}
output.append(mylist);
Basically I'm trying to do a function similar output to this mylist[0].pname in javascript. the expected output all in all is to save those pnames and qtys to a variable for me to able to send each value to the database
In order to write a proper answer you need to be very clear about the input and output you have and you expect.
I don't understand why you want to create a parallel data structure instead of using the parsed JSON but from what I read in comments I think that you need to change the structure of your ArrayList content in order to obtain the result you want to achieve.
String data = "[ {\"pname\":\"7\", \"qty\":\"222\"}, {\"pname\":\"8\", \"qty\":\"5\"}, {\"pname\":\"9\", \"qty\":\"60\"} ]" ;
HashMap<String, String> item = new HashMap<String, String>();
JSONArray jsonArray = new JSONArray(data);
ArrayList<HashMap> mylist = new ArrayList<HashMap>();
if (jsonArray == null) {
System.out.println("json is empty");
} else {
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
item.put("pname", jsonObject.getString("pname"));
item.put("qty", jsonObject.getString("qty"));
mylist.add(item);
}
}
System.out.println(mylist);
First thing to consider is JSON object is not ordered.The first object can be pname or qty, in successive request. To access the fields, give field name as an associative array.
JSONArray jsonArray = new JSONArray(data);
ArrayList<String> mylist = new ArrayList<String>();
JSONArray this_is_jsonArray = (JSONArray)jsonArray;
if (jsonArray == null) {
System.out.println("json is empty");
}
else
{
int length = this_is_jsonArray.length();
for (int i=0;i<length;i++){
// Just this line is modified
mylist.add(this_is_jsonArray.getJSONObject(i).getString("pname").toString());
}
}
I have seen that both of them is used to red key value pair of a json file. For example:
The use of JsonParser to read key value of JSON file:
try {
// read the json file
FileReader reader = new FileReader(filePath);
JSONParser jsonParser = new JSONParser();
JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);
// get a String from the JSON object
String firstName = (String) jsonObject.get("firstname");
System.out.println("The first name is: " + firstName);
// get a number from the JSON object
long id = (long) jsonObject.get("id");
System.out.println("The id is: " + id);
// get an array from the JSON object
JSONArray lang= (JSONArray) jsonObject.get("languages");
// take the elements of the json array
for(int i=0; i<lang.size(); i++){
System.out.println("The " + i + " element of the array: "+lang.get(i));
}
Iterator i = lang.iterator();
// take each value from the json array separately
while (i.hasNext()) {
JSONObject innerObj = (JSONObject) i.next();
System.out.println("language "+ innerObj.get("lang") +
" with level " + innerObj.get("knowledge"));
}
// handle a structure into the json object
JSONObject structure = (JSONObject) jsonObject.get("job");
System.out.println("Into job structure, name: " + structure.get("name"));
}
And the use of JsonReader to read key and value of JSON file:
try
{
InputStream isr=new FileInputStream("
C:\\Users\\DELL\\Documents\\NetBeansProjects\\WaterNetwork
\\web\\kusha.json");
JsonReader jsr=Json.createReader(isr);
JsonObject job=jsr.readObject();
jsr.close();
isr.close();
System.out.println("Name is: "+job.getString("name"));
}
I searched on net but not get any useful answers till now. So I want a full explanation on working and difference between JsonReader and JsonParser in java.
As the name suggests, JsonReader is used to identify and read a JSON object present as a string or stream and then convert it to a proper JSON object before returning it.
You cannot parse the JSON object, that is, the values and arrays under an object cannot be read using getters to extract value from JSON object which, say you might get from a JSONReader object.
But this is all abstract as we are talking about interfaces here.
Look at the functions available in both of them to gain some clarity.
I am returning an JSON array which contains many objects, I'm looking to be able to search the attributes in each object and then return the objects that meet this criteria.
I am able to return the JSON array but I'm having trouble on how to then search through the objects to match the attribute values to a given value.
Some example values from the array:
[
{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"136199","timeStamp":1.483384640123117E9,"uID":"136199_3_10"},
{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"136199","timeStamp":1.483379834470379E9,"uID":"136199_3_10"},
{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"136199","timeStamp":1.483384639621985E9,"uID":"136199_3_10"}
]
I'm using the following code to return the array, which works as expected:
JsonParser jp = new JsonParser();
JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));
JsonArray rootArr = root.getAsJsonArray();
The following block of code is what I'm using to search through an object for the given attribute value, this code works when only an object is returned but gives an error when the whole array is returned:
JsonObject rootObj = rootArr.getAsJsonObject();
for (String attribute : attributes) {
System.out.println(rootObj.get(attribute).getAsString());
}
It is giving the error:
java.lang.IllegalStateException: Not a JSON Object:
I've tried changing rootObj.get(attribute) to rootArr.get(attribute) but that returns the error:
incompatible types: java.lang.String cannot be converted to int
This is the method call:
method("136199", Arrays.asList("blobJson", "deviceMfg", "uID"));
Method declaration:
void method(String sensor, List<String> attributes)
The issue is that you're trying to treat JsonArray to JsonObject. Try the below code and see if it works for you. Point of interest for now is - JsonObject rootObj = rootArr.get(0).getAsJsonObject();
public static void main(String[] args) {
String json = "[{\"blobJson\":\"x\",\"deviceMfg\":10,\"eventCode\":0,\"sensorClass\":3,\"sensorUUID\":\"136199\",\"timeStamp\":1.483384640123117E9,\"uID\":\"136199_3_10\"},{\"blobJson\":\"x\",\"deviceMfg\":10,\"eventCode\":0,\"sensorClass\":3,\"sensorUUID\":\"136199\",\"timeStamp\":1.483379834470379E9,\"uID\":\"136199_3_10\"},{\"blobJson\":\"x\",\"deviceMfg\":10,\"eventCode\":0,\"sensorClass\":3,\"sensorUUID\":\"136199\",\"timeStamp\":1.483384639621985E9,\"uID\":\"136199_3_10\"}]";
JsonParser jp = new JsonParser();
JsonElement root = jp.parse(json);
JsonArray rootArr = root.getAsJsonArray();
JsonObject rootObj = rootArr.get(0).getAsJsonObject();
rootObj.entrySet().forEach(entry -> System.out.println(entry.getKey()+": "+entry.getValue().getAsString()));
}
Here is what you can try
try {
JSONArray jsonArray = new JSONArray(data);
for (int i = 0; i < jsonArray.length(); i++) {
Log.e("JSON Count", jsonArray.get(i).toString());
}
} catch (Exception e) {
}
I'm trying to use JSON simple as part of a Java application to pull specific data from a .json file. Whenever I run the program, I get an unexpected token error message when it tries to parse.
A simplified version of the JSON file is as follows:
{"id":123,"text":"sample1","user":{"id":111,"name":"username"},"lang":"en"}
{"id":345,"text":"sample2","user":{"id":555,"name":"user2"},"lang":"en"}
My code is as follows:
public static void readJSON() {
JSONParser jsonParser = new JSONParser();
try {
FileReader reader = new FileReader(fileLocation);
JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);
JSONArray jsonArray = (JSONArray) jsonObject.get("");
Iterator<?> i = jsonArray.iterator();
while (i.hasNext()) {
JSONObject obj = (JSONObject) i.next();
int tweetID = (int) obj.get("id");
String lang = (String) obj.get("lang");
}
} catch (Exception e) {
e.printStackTrace();
}
}
In this example, the line of code:
JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);
throws an error due to an unexpected token at the first left brace ({) of the second JSON object (i.e, at the brace before "id":345).
How could I go about resolving this issue?
And, as a follow up, how would one also pull the information for the username in this example?
Thanks for taking the time to read through this, and for any assistance provided!
That file is an invalid JSON file, it contains an entire object on each line.
What you'll need to do is read the file line by line, and then passing each line to the parser to create a new object.
If you fix your code, you can solve unexpected token error.
public static void readJSON() {
JSONParser jsonParser = new JSONParser();
try {
FileReader reader = new FileReader(fileLocation);
//You need to fix this part
JSONArray jsonArray = (JSONArray) jsonParser.parse(reader);
Iterator<?> i = jsonArray.iterator();
while (i.hasNext()) {
JSONObject obj = (JSONObject) i.next();
int tweetID = (int) obj.get("id");
String lang = (String) obj.get("lang");
}
} catch (Exception e) {
e.printStackTrace();
}
}
You are trying to parse JSON object, and you actually have two JSON objects.
And in your code you are actually expect an array of JSON objects.
So, use the proper JSON array:
[
{"id":123,"text":"sample1","user":{"id":111,"name":"username"},"lang":"en"},
{"id":345,"text":"sample2","user":{"id":555,"name":"user2"},"lang":"en"}
]
In order to quickly check your JSON syntax, you can use some online tool.
Your JSON is indeed wrong. It actually contains 2 valid JSONs. If you want to create one valid JSON document you have to wrap your input with { and } or [ ] if this is an array or collection. Please note the comma that separates 2 different entities.
[
{"id":123,"text":"sample1","user":{"id":111,"name":"username"},"lang":"en"},
{"id":345,"text":"sample2","user":{"id":555,"name":"user2"},"lang":"en"}
]
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.
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");
}
}
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
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);