Rest API Automation in Java - Post Method

Using Rest-assured and TestNG

In this post, we will be using Rest-Assured library and TestNG to automate the http post method of a Rest-ful API. Rest Assured is a Java library using which we can test and validate the REST web services. Although Rest-assured provides its own validating mechanism(assertions for validating response) but we can combine Rest-assured with TestNG to get the best of both the libraries.

During the course of this tutorial, we will be using the following-

  • Sample Rest API to be used in Automation - RestCountries API
  • Rest-Assured and its dependencies ( (Remember to download and add to class path, the other dependencies also). POM dependencies for the Rest Assured and its dependencies-

  • TestNG as testing framework

Automating Rest API HTTP Post method

The following code snippet uses requestSpecBuilder to create a post request. We have used the following parameters in our code, you need to set them as per your requirement-

  • APIUrl - Set APIUrl variable with the URL of the Rest API
  • APIBody - Set APIBody variable with body of the Rest API containing parameters e.g. {"key1":"value1","key2":"value2"}
  • setContentType() - Pass the "application/json", "application/xml" or "text/html" etc. headers to setContenType() method
  • Authentication credentials - Pass the username and password to the basic() method and in case of no authentication leave them blank basic("","")

The comments in the following code make it self-explanatory.

public void httpPost() throws JSONException,InterruptedException {
	//Initializing Rest API's URL
	String APIUrl = "http://{API URL}";
	//Initializing payload or API body
	String APIBody = "{API Body}"; //e.g.- "{\"key1\":\"value1\",\"key2\":\"value2\"}"
	// Building request using requestSpecBuilder
	RequestSpecBuilder builder = new RequestSpecBuilder();
	//Setting API's body
	//Setting content type as application/json or application/xml
	builder.setContentType("application/json; charset=UTF-8");
	RequestSpecification requestSpec =;

	//Making post request with authentication, leave blank in case there are no credentials- basic("","")
	Response response = given().authentication().preemptive().basic({username}, {password})
	JSONObject JSONResponseBody = new JSONObject(response.body().asString());

	//Fetching the desired value of a parameter
	String result = JSONResponseBody.getString({key});
	//Asserting that result of Norway is Oslo
	Assert.assertEquals(result, "{expectedValue}");


For HTTP Get method automation refer to our tutorial - Rest API Get method Automation in Java.