I want to parse this JSON file in JAVA using GSON :
{
"descriptor" : {
"app1" : {
"name" : "mehdi",
"age" : 21,
"messages": ["msg 1","msg 2","msg 3"]
},
"app2" : {
"name" : "mkyong",
"age" : 29,
"messages": ["msg 11","msg 22","msg 33"]
},
"app3" : {
"name" : "amine",
"age" : 23,
"messages": ["msg 111","msg 222","msg 333"]
}
}
}
but I don't know how to acceed to the root element which is : descriptor, after that the app3 element and finally the name element.
I followed this tutorial http://www.mkyong.com/java/gson-streaming-to-read-and-write-json/, but it doesn't show the case of having a root and childs elements.
I'm using gson 2.2.3
public class Main {
/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
JsonReader jsonReader = new JsonReader(new FileReader("jsonFile.json"));
jsonReader.beginObject();
while (jsonReader.hasNext()) {
String name = jsonReader.nextName();
if (name.equals("descriptor")) {
readApp(jsonReader);
}
}
jsonReader.endObject();
jsonReader.close();
}
public static void readApp(JsonReader jsonReader) throws IOException{
jsonReader.beginObject();
while (jsonReader.hasNext()) {
String name = jsonReader.nextName();
System.out.println(name);
if (name.contains("app")){
jsonReader.beginObject();
while (jsonReader.hasNext()) {
String n = jsonReader.nextName();
if (n.equals("name")){
System.out.println(jsonReader.nextString());
}
if (n.equals("age")){
System.out.println(jsonReader.nextInt());
}
if (n.equals("messages")){
jsonReader.beginArray();
while (jsonReader.hasNext()) {
System.out.println(jsonReader.nextString());
}
jsonReader.endArray();
}
}
jsonReader.endObject();
}
}
jsonReader.endObject();
}
}
One thing that to be remembered while solving such problems is that in JSON file, a {
indicates a JSONObject
and a [
indicates JSONArray
. If one could manage them properly, it would be very easy to accomplish the task of parsing the JSON file. The above code was really very helpful for me and I hope this content adds some meaning to the above code.
The Gson JsonReader documentation explains how to handle parsing of JsonObjects
and JsonArrays
:
- Within array handling methods, first call beginArray() to consume the array's opening bracket. Then create a while loop that accumulates values, terminating when hasNext() is false. Finally, read the array's closing bracket by calling endArray().
- Within object handling methods, first call beginObject() to consume the object's opening brace. Then create a while loop that assigns values to local variables based on their name. This loop should terminate when hasNext() is false. Finally, read the object's closing brace by calling endObject().
Source: Stackoverflow.com