Serializing JSON string to object

Question

I am trying to parse through a JSON string and convert it to the following POJO:

package apicall;
//POJO representation of OAuthAccessToken
public class OAuthAccessToken {
    private String tokenType;
    private String tokenValue;
    public OAuthAccessToken(String tokenType,String tokenValue) {
        this.tokenType=tokenType;
        this.tokenValue=tokenValue;
    }

    public String toString() {
        return "tokenType="+tokenType+"\ntokenValue="+tokenValue;

    }

    public String getTokenValue() {
        return tokenValue;
    }

    public String getTokenType() {
        return tokenType;
    }

}

In order to do this I have written the following code:

Gson gson=new Gson();
String responseJSONString="{\"access_token\" : \"2YotnFZFEjr1zCsicMWpAA\",\"token_type\" : \"bearer\"}";
OAuthAccessToken token=gson.fromJson(responseJSONString, OAuthAccessToken.class);
System.out.println(token);

When I run the code, I get the following output:

tokenType=null
tokenValue=null

Instead of 
tokenType=bearer
tokenValue=2YotnFZFEjr1zCsicMWpAA

I don't understand if there's anything I've done wrong. Please help.

Francisco Spaeth · Accepted Answer · 2012-07-08 09:24:31Z

3

You can get the expected result by annotating your fields like:

@SerializedName("token_type")
private final String tokenType;
@SerializedName("access_token")
private final String tokenValue;

answered Jul 8, 2012 at 9:24

Francisco Spaeth

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Comments

JB Nizet · Accepted Answer · 2012-07-08 09:20:10Z

1

How is Gson supposed to know how to populate your object? You don't have a no-arg constructor, and the fields of your object don't match the fields in the JSON object.

Make your object as following:

public class OAuthAccessToken {
    private String accessToken;
    private String tokenType;

    OAuthAccessToken() {
    }

    ...
}

answered Jul 8, 2012 at 9:20

JB Nizet

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2 Comments

Francisco Spaeth Over a year ago

This isn't the problem, in fact Gson doesn't require that you have a empty parameter constructor, when objects are restored no constructor is executed.

JB Nizet Over a year ago

That's not what the documantations says: While deserializing an Object, Gson needs to create a default instance of the class Well-behaved classes that are meant for serialization and deserialization should have a no-argument constructor. Doesn't matter whether public or private. Typically, Instance Creators are needed when you are dealing with a library class that does NOT define a no-argument constructor. See sites.google.com/site/gson/… Anyway, the main point is that JSON and Java fields don't match at all.

Tomer · Accepted Answer · 2012-07-08 09:22:17Z

0

The class should have the exact field name as the json, so if your json have 2 keys: "access_token" and "token_type", the class should have 2 fields:

private String access_token;
private String token_type;

And, of course you need to change the getters/setters accordingly.

answered Jul 8, 2012 at 9:22

Tomer

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