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How To Check Web Service Using Postman

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Understanding Web Services and Postman

Web services are the backbone of modern applications, facilitating communication and data exchange between various systems. Postman, a popular API testing platform, provides a powerful and user-friendly interface for interacting with these services. This guide will walk you through the essential steps of checking web services using Postman, enabling you to test, validate, and understand their functionality.

Setting Up Postman

Before you begin, ensure you have Postman installed on your machine. Download and install it from the official website: https://www.postman.com/downloads/

Choosing the Right HTTP Method

The first step is identifying the appropriate HTTP method for your web service interaction. Here are the most common methods and their uses:

  • GET: Retrieves data from the server.
  • POST: Sends data to the server to create or update a resource.
  • PUT: Completely replaces an existing resource on the server.
  • PATCH: Partially modifies an existing resource on the server.
  • DELETE: Removes a resource from the server.

Crafting Your Request

Let’s see an example of how to send a GET request to retrieve data from a weather API:

1. Creating a New Request

  • Click the ”+” button in the Postman interface.
  • Choose “GET” as the HTTP method.
  • Enter the API URL in the “Enter request URL” field: 
    https://api.openweathermap.org/data/2.5/weather?q=London,uk&appid=YOUR_API_KEY
    Replace “YOUR_API_KEY” with your actual API key from OpenWeatherMap.

2. Adding Headers (Optional)

Headers provide additional information about the request. For example, you can add a “Content-Type” header for JSON data:

{
 "Content-Type": "application/json"
}

3. Sending Your Request

Click the “Send” button to execute the request.

Analyzing the Response

Once the request is sent, Postman displays the response from the server. This includes:

  • Status Code: Indicates the success or failure of the request.
  • Headers: Provides information about the response.
  • Body: Contains the data returned by the server.

Example: Parsing a JSON Response

For the weather API example, we expect a JSON response. Postman provides tools for easy parsing:

  • Click the “Body” tab in the response section.
  • Select “JSON” as the response format.
  • The response body will be displayed as a structured JSON object:
{
 "coord": {
   "lon": -0.1257,
   "lat": 51.5074
 },
 "weather": [
   {
     "id": 803,
     "main": "Clouds",
     "description": "broken clouds",
     "icon": "04d"
   }
 ],
 "base": "stations",
 "main": {
   "temp": 282.55,
   "feels_like": 280.36,
   "temp_min": 280.15,
   "temp_max": 284.15,
   "pressure": 1021,
   "humidity": 77
 },
 "visibility": 10000,
 "wind": {
   "speed": 4.6,
   "deg": 270
 },
 "clouds": {
   "all": 75
 },
 "dt": 1701848397,
 "sys": {
   "type": 2,
   "id": 2019646,
   "country": "GB",
   "sunrise": 1701818065,
   "sunset": 1701857876
 },
 "timezone": 3600,
 "id": 2643743,
 "name": "London",
 "cod": 200
}

Validating with Assertions

Postman lets you create assertions to check properties of the response:

  • Click the “Tests” tab.
  • Write your assertion using JavaScript:
pm.test("Status code is 200", () => {
  pm.response.to.have.status(200);
});


pm.test("Response has 'temperature' property", () => {
  pm.expect(pm.response.json().main.temp).to.be.a('number');
});

This example asserts that the response status code is 200 and that the ‘temp’ property exists in the response body.

Generating API Documentation

Postman can automatically generate documentation from your requests and assertions.

  • Open the “Documentation” tab.
  • Click “Generate” to create a comprehensive document for your web service.

Conclusion

Postman is an indispensable tool for checking web services, simplifying API testing, and improving the quality of your applications. Through this guide, you’ve learned how to send requests, analyze responses, and validate the behavior of your web services. Remember to explore the vast capabilities of Postman, including features like environment variables, collections, and workflows, to streamline your API testing process even further.

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