I am trying to validate this string below. Actually I am receiving this string in my servlet, now I need to validate these values at backend. What is the right way to do so. Shall I first convert it to JSON Object then to HashMap? Please suggest the correct/appropriate approach to be used here. I am quite new to Java and JSON.
String is
"{"if_ack":4},{"if_cmd":1,"if_state":1},{"if_cmd":1,"if_state":5}"
I am using GSON for processing JSON at server. For example:
InputStream is (send by client, JSON format)
Reader reader = new InputStreamReader(is);
Gson gson = new Gson();
List<YourClass> items = gson.fromJson(reader, new TypeToken<List<YourClass>>()
YourClass should have attributes like if_ack, if_state, if_cmd,...
Then you use as simple as this:
for (YourClass item : items) {
//do whatever you want
}
EDIT: your string should be in correct JSON format like this (JSON array): [{"if_ack":4}, {"if_cmd":1,"if_state":1}, {"if_cmd":1,"if_state":5}]
EXAMPLE:
You have JSON like this : [{"id": "1", "image": "test1"}, {"id": "2", "image": "test2"}]
YourClass.java should be:
public class YourClass{
private int id;
private String image;
//+ constructor, getters, setters,...
}
On server you can receive JSON from client side by InputStream is:
Reader reader = new InputStreamReader(is, "UTF-8");
Gson gson = new Gson();
List<YourClass> items = gson.fromJson(reader, new TypeToken<List<YourClass>>();
and then:
for (YourClass item: items){
//acces to item properties like item.id, item.image
}
Related
I'm connecting to some APIs. These calls return an already "prettyprinted" JSON instead of a one-line JSON.
Example:
[
{
"Field1.1": "Value1.1",
"Field1.2": "value1.2",
"Field1.3": "Value1.3"
},
{
"Field2.1": "Value2.1",
"Field2.2": "value2.2",
"Field2.3": "Value2.3"
}
]
When I try to parse a JSON like this with GSON it throws JsonSyntaxException.
Code example:
BufferedReader br = /*Extracting response from server*/
JsonElement jelement = new JsonParser().parse(br.readLine())
Is there a way to parse JSON files formatted like this?
EDIT:
I tried using Gson directly:
BufferedReader jsonBuf = ....
Gson gson = new Gson();
JsonObject jobj = gson.fromJson(jsonBuf, JsonObject.class)
But jobj is NULL when the code terminates.
I also tried to parse the string contained into the BufferedReader into a single line string and then using JsonParser on that:
import org.apache.commons.io.IOUtils
BufferedReader jsonBuf = ....
JsonElement jEl = new JsonParser().parse(IOUtils.toString(jsonBuf).replaceAll("\\s+", "");
But the JsonElement I get in the end is a NULL pointer...
I can't understand what I'm doing wrong...
BufferedReader::nextLine reads only one line. Either you read whole json from your reader to some String variable or you will use for example Gson::fromJson(Reader, Type) and pass reader directly to this method.
As your json looks like an array of json objects it can be deserialized to List<Map<String,String>> with usage of TypeToken :
BufferedReader bufferedReader = ...
Type type = new TypeToken<List<Map<String,String>>>(){}.getType();
Gson gson = new Gson();
List<Map<String,String>> newMap = gson.fromJson(bufferedReader, type);
You could also use some custom object instead of Map depending on your needs.
I am trying to parse a JSON response in Java but am facing difficulty due to the response being array format, not object. I, first, referenced the this link but couldn't find a solution for parsing the JSON properly. Instead, I am receiving this error when trying to display the parsed data...
Exception in thread "main" org.json.JSONException: JSONObject["cardBackId"] not found.
Snippet for displaying data:
JSONObject obj = new JSONObject(response);
JSONArray cardBackId = (JSONArray) obj.get("cardBackId");
System.out.println(cardBackId);
Data response via Postman:
[
{
"cardBackId": "0",
"name": "Classic",
"description": "The only card back you'll ever need.",
"source": "startup",
"sourceDescription": "Default",
"enabled": true,
"img": "http://wow.zamimg.com/images/hearthstone/backs/original/Card_Back_Default.png",
"imgAnimated": "http://wow.zamimg.com/images/hearthstone/backs/animated/Card_Back_Default.gif",
"sortCategory": "1",
"sortOrder": "1",
"locale": "enUS"
},
While without JSONObject I am pulling the data fine in Java and verified by using response.toString in STDOUT, this is my first time using json library in Java and it is important I parse this data as json. Any advice with this is helpful.
The response is an array and not object itself, try this:
JSONObject obj = new JSONArray(response).getJSONObject(0);
String cardBackId = obj.getString("cardBackId");
Here is the output, along with relevant files used:
First parse the response as JsonArray, instead of JsonObject.
Get JsonObject by iterating through the array.
Now get the value using the key.
Look at this example using Gson library, where you need to define the Datatype to define how to parse the JSON.
The key part of the example is: Data[] data = gson.fromJson(json, Data[].class);
package foo.bar;
import com.google.gson.Gson;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
public class Main {
private class Data {
long cardBackId;
String name;
}
public static void main(String[] args) throws FileNotFoundException {
// reading the data from a file
BufferedReader reader = new BufferedReader(new FileReader("data.json"));
StringBuffer buffer = new StringBuffer();
reader.lines().forEach(line -> buffer.append(line));
String json = buffer.toString();
// parse the json array
Gson gson = new Gson();
Data[] data = gson.fromJson(json, Data[].class);
for (Data item : data) {
System.out.println("data=" + item.name);
}
}
}
When I use JSONArray and JSONObject to generate a JSON, whole JSON will be generated in one line. How can I have each record on a separate line?
It generates like this:
[{"key1":"value1","key2":"value2"}]
I need it to be like following:
[{
"key1":"value1",
"key2":"value2"
}]
You can use Pretty Print JSON Output (Jackson).
Bellow are some examples
Convert Object and print its output in JSON format.
User user = new User();
//...set user data
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user));
Pretty Print JSON String
String test = "{\"age\":29,\"messages\":[\"msg 1\",\"msg 2\",\"msg 3\"],\"name\":\"myname\"}";
Object json = mapper.readValue(test, Object.class);
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json));
Reference : http://www.mkyong.com/java/how-to-enable-pretty-print-json-output-jackson/
You may use of the google-gson library for beautifying your JSON string.
You can download the library from here
Sample code :
Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonParser jp = new JsonParser();
JsonElement je = jp.parse(uglyJSONString);
String prettyJsonString = gson.toJson(je);
OR
you can use org.json
Sample code :
JSONTokener tokener = new JSONTokener(uglyJsonString); //tokenize the ugly JSON string
JSONObject finalResult = new JSONObject(tokener); // convert it to JSON object
System.out.println(finalResult.toString(4)); // To string method prints it with specified indentation.
Refer answer from this post :
Pretty-Print JSON in Java
The JSON.stringify method supported by many modern browsers (including IE8) can output a beautified JSON string:
JSON.stringify(jsObj, null, "\t"); // stringify with tabs inserted at each level
JSON.stringify(jsObj, null, 4); // stringify with 4 spaces at each level
and please refer this : https://stackoverflow.com/a/2614874/3164682
you can also beautify your string online here.. http://codebeautify.org/jsonviewer
For gettting a easy to read json file you can configure the ObjectMapper to Indent using the following:
objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
I am creating a java project which writes data to an already existing json file.I am using gson libraries to write.The problem is when i write the json it written at the end of the file not inside.Here is my json before i run the program
{
"trips":[
{
"tripname":"Goa",
"members":"john"}
]
}
here is my java code
FileOutputStream os=new FileOutputStream(file,true);
BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(os));
Gson gson=new GsonBuilder().setPrettyPrinting().create();
String temp=gson.toJson(trips);
bw.append(temp);
bw.close();
and here is my output json
{
"trips":[
{
"tripname":"Goa",
"members":"john"}
]
}{
"tripname": "trip1",
"members": "xyzxyz"
}
the newly added must be inside the trips array how can i achieve it.
The problem is that you are not using Gson. You need to have Java Bean with proper Gson annotaions and with this use Gson to serialize.
Look at this example: https://sites.google.com/site/gson/gson-user-guide#TOC-Object-Examples
Edit
More or less it would look like this:
public class Trip implements Serializable {
private String tripName;
private String members;
// getters setters
}
Using Gson:
List<Trip> trips = new ArrayList<>();
// add to list
Gson gson = new Gson();
// to json
String json = gson.toJson(trips)
// from json
Type collectionType = new TypeToken<Collection<Trip>>(){}.getType();
List<Trip> trips2 = gson.fromJson(json, collectionType);
I have a servlet in Java and I would like to know how I can do the following.
I have a String variable with the value of a name and want to create a Json with the variable being something like {"name": "David"}.
How do I do this?
I have the following code but I get an error :
Serious: Servlet.service () for servlet threw
exception servlet.UsuarioServlet java.lang.NullPointerException
at servlet.UsuarioServlet.doPost (UsuarioServlet.java: 166):
at line
String myString = new JSONObject().put("name", "Hello, World!").toString();
Your exact problem is described by Chandra.
And you may use the JSONObject using his suggestion.
As you now see, its designers hadn't in mind the properties, like chaining, which made the success of other languages or libs.
I'd suggest you use the very good Google Gson one. It makes both decoding and encoding very easy :
The idea is that you may define your class for example as :
public class MyClass {
public String name = "Hello, World!";
}
private Gson gson = new GsonBuilder().create();
PrintWriter writer = httpServletResponse.getWriter();
writer.write( gson.toJson(yourObject));
The json library based on Map. So, put basically returns the previous value associated with this key, which is null, so null pointer exception.( http://docs.oracle.com/javase/1.4.2/docs/api/java/util/HashMap.html#put%28java.lang.Object,%20java.lang.Object%29)
You can rewrite the code as follows to resolve the issue.
JSONObject jsonObject1 = new JSONObject();
jsonObject1.put("name", "Hello, World");
String myString = jsonObject1.toString();
I tried with GSON, GSON is directly convert your JSONString to java class object.
Example:
String jsonString = {"phoneNumber": "8888888888"}
create a new class:
class Phone {
#SerializedName("phoneNumber")
private String phoneNumebr;
public void setPhoneNumber(String phoneNumebr) {
this.phoneNumebr = phoneNumebr;
}
public String getPhoneNumebr(){
return phoneNumber;
}
}
// in java
Gson gson = new Gson();
Phone phone = gson.fromJson(jsonString, Phone.class);
System.out.println(" Phone number is "+phone.getPhoneNumebr());