Validate JSON Input

How it works

Many APIs have an endpoint whose only job is to check a payload: it reads the JSON you send, applies its rules and tells you whether the input passed. The testkru /validate/json endpoint works that way. It wants a non-empty name and an email in a valid address format, and on success it answers 200 with a top-level boolean valid plus a data object that repeats your payload, including any extra fields you added.

Two REST Assured details decide whether the server even sees your JSON. First, body() with a String sends that text exactly as written, so the quotes must be escaped inside the Java literal. Second, the request needs a JSON content type. Without contentType(ContentType.JSON), REST Assured labels a String body as text/plain with an ISO-8859-1 charset, the server finds no JSON to parse and replies 400 with a plain error message instead of a valid flag.

Reading the answer is a JsonPath job. getBoolean("valid") gives a Java boolean, and dotted paths such as data.name walk into the nested object. If you prefer to assert rather than read, then().body("valid", equalTo(true)) checks the same field with a Hamcrest matcher.

About the assignment

Send a correct name and email to the validation endpoint, confirm the server accepted them, and print the flag and the two values it echoed back inside data.

What you will do

1. 1Start from given(), set the content type to ContentType.JSON and pass the Alice payload from the starter comment to body().
2. 2Call post() with the /validate/json path and keep the Response.
3. 3Assert the result through then(): status 200, and valid equal to true.
4. 4Print three labelled lines, Valid:, Name: and Email:, reading valid with getBoolean() and the nested data.name and data.email with getString().

Common mistakes

• Leaving out the content type

  The request still goes out, but as plain text. The endpoint answers 400 with an error field and no valid key, and getBoolean("valid") then throws a NullPointerException because there is no value to unbox.

• Reading name at the top level

  The echoed values sit under data. A path of plain name finds nothing at the root and getString() returns null, so the label prints with null after it.

• Testing only the happy path

  An email such as not-an-email passes the empty check but fails the format rule, giving 400 and one entry in errors. A validation endpoint deserves at least one negative case, and the next lesson sends one.

In a real test suite

Related lessons

• Handle Validation ErrorsSends a broken payload to the same endpoint and walks the errors array.
• Echo Request BodyPOSTs JSON to /echo and reads back the fields the server returns unchanged.
• Send POJO as Request BodyReplaces the hand-written JSON string with a POJO that REST Assured serialises.

To try one of these calls on any API endpoint without a task, open the Online Selenium Java Compiler (REST Assured is included).

Starter code

The editor above opens with this code. Fill in the TODO lines, then run and submit it.

import io.restassured.RestAssured;
import io.restassured.response.Response;
import io.restassured.specification.RequestSpecification;
import io.restassured.http.ContentType;
import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;

public class Main {
    public static void main(String[] args) {
        RestAssured.baseURI = "https://testkru.com/api";

        // TODO: POST to /validate/json with body: {"name": "Alice", "email": "alice@test.com"}
        // TODO: Validate status 200
        // TODO: Print valid, data.name, and data.email
    }
}