Simple Json to Java Conversion Using GSON

Question

I recently started using the GSON library for JSON deserialization that comes from a web service, but I can't get it to work. I decided to test GSON on some simple input - it cannot make it simpler, and it still doesn't work. I looked at similar issues, such as Converting JSON to Java , all of which offer a similar approach to the solution. I guess I missed something really simple and obvious, so a fresh look at the code will probably help. So here is what I have:

Json

{"A":{"name":"qwrety","value1":1,"value2":2}} 

Java class

 import com.google.gson.Gson; public class Main { public static void main(String[] args) { String json = /*getting JSON from server*/ Gson gson = new Gson(); A obj = gson.fromJson(json, A.class); System.out.println(obj); } } class A { private String name; private int value1; private int value2; public String getName() { return name; } public int getValue1() { return value1; } public int getValue2() { return value2; } public void setName(String name) { this.name = name; } public void setValue1(int value1) { this.value1 = value1; } public void setValue2(int value2) { this.value2 = value2; } public String toString() { return String.format("name: %s, value1: %d, value2: %d", name, value1, value2); } } 

What I get in return

 name: null, value1: 0, value2: 0 

Can anyone tell what is wrong with this code?

UPD As @torbinsky and @ Kevin-Dolan pointed out, the problem was that the structure of the Java class did not conform to the Json format. To fix this, I added a new class

 class Container { private A a; public A getA() { return a; } public void setA(A a) { this.a = a; } } 

and changed the deserialization call to

 Gson gson = new Gson(); Container obj = gson.fromJson(json, Container.class); System.out.println(obj.getA()); 

However, I still get a "zero" fingerprint

Answer 1

I think your problem is your JSON string.

Try changing:

 {"A":{"name":"qwrety","value1":1,"value2":2}} 

in

 {"name":"qwrety","value1":1,"value2":2} 

EDIT: I think the problem may be that your JSON string has an "A" and this is case sensitive. Try changing the member variable to uppercase "A". Unfortunately, I can’t check at the moment to confirm this.

If the JSON format is fixed, try changing the classes to something like this:

 class Foo { private String name; private int value1; private int value2; public String getName() { return name; } public int getValue1() { return value1; } public int getValue2() { return value2; } public void setName(String name) { this.name = name; } public void setValue1(int value1) { this.value1 = value1; } public void setValue2(int value2) { this.value2 = value2; } public String toString() { return String.format("name: %s, value1: %d, value2: %d", name, value1, value2); } } 

and:

 class Container { private Foo A; public Foo getA() { return A; } public void setA(Foo A) { this.A = A; } } 

Answer 2

The problem is that it searches for a field in your object called "A", but instead it finds the fields "name", "value1" and "value2".

The json you want to send to gson:

 {"name":"qwrety","value1":1,"value2":2} 

Answer 3

After the changes, your field name is still "a", but JSON uses "A". So you need to either rename the field or add an annotation to indicate that JSON uses "A" as the name (@SerializedName ("A"), I think).