I want to map below Json data to java object of List<Map<String, String>> type.
Sample Json:
{
{
a:b,
c:d
},
{
e:f,
g:h,
i:j
},
{
h:k
}
}
Here a:b represents key-value pair. So a:b and c:d will be mapped to first map of the list and so on.
one way to do this is by building JSON tree and access each node and store the pair into the map.
Is there a better way to do this (cleaner approach)?
Here is the code to read a List<Map<String, String>> using the Jackson library, with your example data as input:
public class JsonTest {
public static void main(String[] args) throws Exception {
final String json
= "[\n"
+ " {\n"
+ " \"a\":\"b\",\n"
+ " \"c\":\"d\"\n"
+ " },\n"
+ " {\n"
+ " \"e\":\"f\",\n"
+ " \"g\":\"h\",\n"
+ " \"i\":\"j\"\n"
+ " },\n"
+ " {\n"
+ " \"h\":\"k\"\n"
+ " }\n"
+ "]"; // [{a:b,c:d},{e:f,g:h,i:j},{h:k}]
ObjectMapper mapper = new ObjectMapper();
TypeFactory factory = TypeFactory.defaultInstance();
List<Map<String, String>> list = mapper.readValue(json,factory
.constructCollectionType(List.class, factory
.constructMapType(Map.class, String.class, String.class)));
System.out.println(list.toString());
}
}
Note: I had to fix your outermost braces from {} to [], which is the correct JSON list syntax.
You can use Jackson to achieve this task through below example code
public class JacksonExample {
public static void main(String[] args) {
ObjectMapper mapper = new ObjectMapper();
try {
// Convert JSON string from file to Object
User user = mapper.readValue(new File("C:\\user.json"), User.class);
System.out.println(user);
// Convert JSON string to Object
String jsonInString = "{\"age\":33,\"messages\":[\"msg 1\",\"msg 2\"],\"name\":\"xyz\"}";
User user1 = mapper.readValue(jsonInString, User.class);
System.out.println(user1);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
First I made few changes to your json to make it valid
{
"key":
[{
"a": "b",
"c": "d"
},
{
"e": "f",
"g": "h",
"i": "j"
},
{
"h": "k"
}]
}
Please find the below code that I have tried out :
ObjectMapper mapper = new ObjectMapper();
ObjectNode objectNode1 = mapper.createObjectNode();
Map<String, Object> i = mapper.readValue(new File("J:/temp/sample.json"), Map.class);
System.out.println(i.get("key"));
System.out.println(i.values());
//For System.out.println(i.get("key"));
[{a=b, c=d}, {e=f, g=h, i=j}, {h=k}]
//For System.out.println(i.values());
[[{a=b, c=d}, {e=f, g=h, i=j}, {h=k}]]
If the above approach helps you, Make a right decision based on your needs either i.get("key") or i.values()
Just use gson library to Json to object and object to Json
import java.lang.reflect.Type;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
Object to Json
Gson gson = new Gson();
Student obj=new Student();
String jsonInString = gson.toJson(obj);
Json To Object
Student obj = gson.fromJson(jsonInString, Student.class);
List<Map<String, String>>, it's more of aMap<String, Object>, whereObjectcan be aList<Map<String, Object>>or aList<Object>(and those nestedObjects can be the same two things as well). As for parsing it, I would personally use a json library but it's basically down to a state machine at that point (on the input symbols)