How to call a GraphQL query/mutation with Java code

Question

I know we can use the /graphiql endpoint to test the created or deployed GraphQL API.

1. I need to consume a GraphQL API which is already there using a Java code. How can I do it.
2. How can I test a GraphQL end-point using a postman like application, or is it even possible.

Answer 1

Depending on your situation, utilizing Spring RestTemplate might be simplest thing to do.

public class Person {
    @JsonProperty("query")
    public final String query = "mutation($name:String, $gender:String, $age:Int) { updateDetails (name: $name, gender: $gender, age: $age) }";
    @JsonProperty("variables")
    public final Map<String, String> variables;
...
}
...
(new RestTemplate()).postForEntity("http://example.com/graphql", new Person("David", "male", 12));

Could go even simpler by avoiding Spring and using HttpClient, building same JSON document using StringBuilder.

Alternatively Apollo Andoid can autogenerate client code for you.

Answer 2

An example, to work for me... username and password are wrong :) But, URL is ok...

with that, I don't use RestTemplate, any jars, etc..

private static void test_LivePharma() {
    try {
        URL url = new URL("https://stores-hml.funcionalmais.com/graphql");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setDoOutput(true);
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Content-Type", "application/json");

        String input="{\"query\":\"mutation{createToken(login:\\\"112233\\\",password:\\\"112233\\\"){  token}}\\n\"}";

        OutputStream os = conn.getOutputStream();
        os.write(input.getBytes());
        os.flush();
        BufferedReader br = new BufferedReader(new InputStreamReader(
                (conn.getInputStream())));
        String output;
        System.out.println("Output from Server .... \n");
        while ((output = br.readLine()) != null) {
            System.out.println(output);
        }
        conn.disconnect();
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }       
}

Answer 3

Consuming graphql API in your backend code, will require multiple steps such as.

1. Defining the schema
2. Installing the dependencies
3. Defining the graphql endpoint

import com.coxautodev.graphql.tools.SchemaParser;
import javax.servlet.annotation.WebServlet;
import graphql.servlet.SimpleGraphQLServlet;


@WebServlet(urlPatterns = "/graphql")
public class GraphQLEndpoint extends SimpleGraphQLServlet {

    public GraphQLEndpoint() {
        super(SchemaParser.newParser()
                .file("schema.graphqls") //parse the schema file created earlier
                .build()
                .makeExecutableSchema());
    }
}

Here is a detailed guide to do the same : Graphql-java-backend-implementation

Yes, it is possible to send the request using postman. You can simply copy the schema in the body. Doing GraphQL request using Postman