How to Convert gson to LinkedHashMap<String, List<String>>? - gson

Question

i'm new to gson and i wonder how convert json data to LinkedHashMap<String, List<String>>
my json data is show like below:
{ "data":
{
"data1": ["asdf", "qwer"],
"data2": ["xczv", "aweqrfds123", "sfdgq234"],
"data3": ["dsafasd", "xcvr123", "sdfa324123"]
}
}
field names of json data of data are dynamic, so i want to convert json data of data to LinkedHashMap<String, List<String>>
how can i do that ?

Answer 1

You can use TypeToken to convert it into expected type with Gson#fromJson(Reader,Type)
As per JSON string it is LinkedHashMap<String,LinkedHashMap<String,ArrayList<String>>>
Sample code:
BufferedReader reader = new BufferedReader(new FileReader(new File("json.txt")));
Type type = new TypeToken<LinkedHashMap<String,LinkedHashMap<String,ArrayList<String>>>>() {}.getType();
LinkedHashMap<String,LinkedHashMap<String,ArrayList<String>>> data = new Gson().fromJson(reader, type);
LinkedHashMap<String,ArrayList<String>> innerMap = data.get("data");
System.out.println(new GsonBuilder().setPrettyPrinting().create().toJson(innerMap));

Answer 2

This is not how it works in Gson world - you can't convert JSON to any Java class you want, unless you want to do all of that manually. The common approach works as described below:
Create a Java class, which matches your JSON format, e.g. you can use a Java class generator described here: http://jsongen.byingtondesign.com/
Use GsonBuilder to read your Json from a file and to import it to the generated class
I've used that approach and the Java file that has been generated (after I've fixed a minor syntax error in your initial JSON) looks like this:
package com.json;
import java.util.List;
public class Data{
private List data1;
private List data2;
private List data3;
public List getData1(){
return this.data1;
}
public void setData1(List data1){
this.data1 = data1;
}
public List getData2(){
return this.data2;
}
public void setData2(List data2){
this.data2 = data2;
}
public List getData3(){
return this.data3;
}
public void setData3(List data3){
this.data3 = data3;
}
}
To start working with the newly created class you can use the template below:
is = new InputStreamReader(new FileInputStream(new File('<path-to-json>')), "UTF-8")/;
Gson gson = new GsonBuilder().create();
Data d = gson.fromJson(is, Data.class);
// Start using your d instance here