[FIXED] Unable to receive data out of api call with webclient

Issue

So I'm trying to get my head around the webclient, but I keep getting a nullpointerexception, though my test work fine and say that object is not null. I also see my console making connection to the api. But when I ask the value, I get null.

Here are the two objects I use for it:

import com.fasterxml.jackson.annotation.JsonProperty;

public class Data {
    @JsonProperty("message")
    private String message;
    @JsonProperty("status")
    private String status;
    
    
    public String getMessage() {
        return message;
    }

    public String getStatus() {
        return status;
    }

    
}

public class Foto {
    private Data data;

    public Data getData() {
        return data;
    }

    
}

and then here I have my api call, I've put in my psvm to get console results:

        try {
        var test =  client.get()
                .uri("https://dog.ceo/api/breeds/image/random")
                .retrieve()
                .bodyToMono(Foto.class)
                .block();
        System.out.println(test.getData().getMessage());
    } catch (WebClientResponseException.NotFound ex) {
        ex.getMessage();
    }
        
        
    }

But as a console output for the system.out.println I keep receiving: Exception in thread "main" java.lang.NullPointerException: Cannot invoke "be.hi10.apiesTest.domain.Data.getMessage()" because the return value of "be.hi10.apiesTest.domain.Foto.getData()" is null at be.hi10.apiesTest.ApiesTestApplication.main(ApiesTestApplication.java:31)

What am I doing wrong here? I should be receiving a String representing a url to an image.

Solution

Notice that your api returns response like this :

{
"message": "https://images.dog.ceo/breeds/collie-border/n02106166_346.jpg",
"status": "success"
}

Since you are trying to convert your response to Foto class which looks like this :

public class Foto {
    private Data data;

    public Data getData() {
        return data;
    }

    
}

For that to work your JSON should have to look like this :

"data":{
     "message": "https://images.dog.ceo/breeds/collie-border/n02106166_346.jpg",
    "status": "success"
}

but it doesnt and thats why your deserilization fails and you are getting NullPointerException.

To make this work, change response type to Data :

var test =  client.get()
                .uri("https://dog.ceo/api/breeds/image/random")
                .retrieve()
                .bodyToMono(Data.class)
                .block();

Answered By - Nemanja
Answer Checked By - Timothy Miller (JavaFixing Admin)