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How To Use Postman To Send Json

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Sending JSON Data with Postman: A Comprehensive Guide

Postman is a powerful tool that simplifies API testing and development. One of its crucial features is the ability to send JSON data to your API endpoints. This guide provides a comprehensive walkthrough on how to utilize Postman for this purpose, covering various aspects from basic sending to advanced techniques.

1. Creating a Basic JSON Request in Postman

Understanding JSON Structure

JSON (JavaScript Object Notation) is a lightweight data-interchange format that uses key-value pairs organized within curly braces {}. Values can be primitive data types (strings, numbers, booleans) or nested objects and arrays. Here’s a simple example:

{
  "name": "John Doe",
  "age": 30,
  "city": "New York"
}

Sending JSON Data with Postman

  1. Open Postman: Launch the Postman app or access the web version.
  2. Set the Request Method: Select the appropriate HTTP method from the dropdown (e.g., POST, PUT, PATCH).
  3. Input Endpoint URL: Enter the URL of the API endpoint you want to interact with.
  4. Switch to the “Body” Tab: In the request builder, click on the “Body” tab.
  5. Choose “raw” and “JSON”: Select “raw” as the body type and choose “JSON” from the dropdown.
  6. Paste Your JSON Data: Copy and paste your JSON data into the text editor.
  7. Send the Request: Click the “Send” button.

Example:

Let’s say you want to create a new user on an API with the following JSON data:

{
  "username": "testuser",
  "email": "test@example.com",
  "password": "password123"
}

After setting the method to “POST” and the endpoint URL, you would paste this JSON data in the “raw” body section and send the request.

2. Sending JSON Data with Variables and Environment Variables

Using Variables for Dynamic Data

Postman supports variables to make your requests more dynamic. This is especially useful when the JSON data needs to change frequently.

  1. Define Variables: Go to the “Variables” tab in the request builder.
  2. Add Variable: Click on “Add variables” and define a variable name and value.
  3. Use Variables in the Request Body: Replace the static values in your JSON data with variable names enclosed in double curly braces ({{variable_name}}).

Example:

Let’s create a variable called name with the value “Jane Doe” and use it in our JSON request:

{
  "name": "{{name}}",
  "age": 30,
  "city": "New York"
}

When you send the request, Postman will replace {{name}} with “Jane Doe”.

Using Environment Variables for Global Scope

Environment variables provide a global scope across multiple requests and collections.

  1. Create an Environment: Go to “Environments” in the sidebar and click “Add”. Name your environment and add variables as needed.
  2. Select Environment: Switch to the environment you created in the request builder.
  3. Use in JSON Data: Utilize environment variables in your JSON data just like regular variables.

Example:

Create an environment variable called base_url and use it in the endpoint URL:

{
  "username": "testuser",
  "email": "test@example.com",
  "password": "password123",
  "base_url": "{{base_url}}"
}

This approach helps manage your API environment settings systematically.

3. Iterating JSON Data with Collections and Data Files

Sending Multiple Requests with Collections

Collections in Postman are a powerful way to group your requests and organize your API workflows.

  1. Create a Collection: Go to “Collections” in the sidebar and create a new collection.
  2. Add Requests: Add your requests to the collection.
  3. Iterate Through Data: For sending multiple requests with different JSON data, use the “Collection Runner”. Specify a data file in JSON format and map data fields from the file to your request variables.

Example:

Suppose you have a JSON file (users.json) containing a list of user data:

[
  {
    "name": "John Doe",
    "email": "john.doe@example.com"
  },
  {
    "name": "Jane Doe",
    "email": "jane.doe@example.com"
  }
]

In your collection runner settings, specify users.json as the data source and map name and email from the file to your request variables. When you run the collection, Postman will send two requests, one for each user, using the corresponding data from the file.

4. Handling JSON Responses with Postman

Postman provides features for inspecting and validating JSON responses.

Examining JSON Data

  1. View the Response: After sending a request, review the response in the “Body” section.
  2. Use the “Pretty” Button: Format the JSON response for better readability.
  3. Navigate Through Nested Objects: Use the expandable tree structure to easily access nested JSON objects and arrays.

Asserting JSON Data

Postman’s powerful assertions allow you to verify the JSON response according to your expectations.

  1. Add Assertions: Go to the “Tests” tab and add your assertions using the built-in JavaScript language.
  2. Use pm.response.json(): Access the JSON response body using pm.response.json().
  3. Write Conditions: Use assertion methods like pm.test() or pm.expect() to verify specific data points or check if the response contains expected keys and values.

Example:

pm.test("Status code is 200", function () {
  pm.response.to.have.status(200);
});


pm.test("Response has a message", function () {
  pm.expect(pm.response.json().message).to.be.a('string');
});


pm.test("User name is correct", function () {
  pm.expect(pm.response.json().name).to.be.equal("Jane Doe");
});

These tests will validate the response code, check if a “message” key exists in the response, and assert that the “name” value is “Jane Doe”.

5. Advanced JSON Use Cases for Postman

Sending Multipart/Form-Data with JSON

Sometimes you need to send JSON data along with files.

  1. Set “form-data” Body Type: In the “Body” tab, select “form-data” as the body type.
  2. Add Key-Value Pairs: Add your JSON data as a key-value pair where the value is the JSON string.
  3. Include Files: Add additional key-value pairs to include files, specifying the file path.

Example:

You can add a key called “user_data” with the value being your JSON string and include a file called “profile_picture.jpg”.

Generating JSON-Based Dynamic Data

Postman’s scripting capabilities allow generating dynamic JSON data.

  1. Use JavaScript in Pre-Request Scripts: Utilize pm.request.body.json() to access and modify the JSON data before the request is sent.
  2. Write Custom Logic: Implement JavaScript code to create random data, generate timestamps, or perform other manipulations based on your requirements.

Example:

In a Pre-Request Script, you can use the Date() object to generate a timestamp and update the timestamp key in your JSON data:

const timestamp = new Date().toISOString();
pm.request.body.json().timestamp = timestamp;

Conclusion

Postman is an invaluable tool for sending and handling JSON data in API testing and development. Its intuitive interface, support for variables, collections, and data files, combined with robust testing and scripting capabilities, makes it a powerful choice for interacting with your APIs. By mastering these techniques, you can streamline your API testing workflow and ensure the reliability and functionality of your applications.

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