Sending Data with POST Requests in Java Using HttpClient and Gson

Welcome to this lesson on sending data with POST requests. As you continue your exploration of interacting with RESTful APIs, you'll learn how to send data to a server using the POST method. POST requests are essential when you want to create new resources or submit data, such as filling out a web form or adding a new entry to a database. Unlike GET requests, POST requests do not solely retrieve information; they transmit data to an API.

Understanding these differences is crucial as you expand your skill set in HTTP methods. Let’s dive deeper into utilizing POST requests to comprehend how they stand apart from GET requests.

Before diving into POST requests, let's briefly compare them to GET requests:

• GET Requests:

  • Purpose: Retrieve data from a server.
  • Data Location: Data is sent in the URL as path or query parameters.
  • Success Status: Expect a 200 status code for successful data retrieval.

• POST Requests:

  • Purpose: Send data to a server to create or update a resource, such as submitting a form, uploading a file, or adding a new item to a database.
  • Data Location: Data is sent in the request body.
  • Success Status: Expect a 201 status code for successful resource creation.

These differences clarify when to use each method. POST requests, in particular, require careful handling of the request body.

For POST requests, the request body is crucial as it holds the data you want to send to the server. This data is usually structured in formats like JSON, XML, or form data, with JSON being a common choice due to its readability and compatibility.

Here's an example of creating a JSON request body in Java using Gson:

Todo newTodo = new Todo("Learn Java HttpClient", "Complete a course on Java API calls.", false);
String requestBody = gson.toJson(newTodo);

This represents a new todo item, including a title, completion status, and description. Noticeably, we are not sending an id, as this is typically managed by the server upon resource creation. For this, we are using a simple Todo POJO class:

public class Todo {
    public String title;
    public String description;
    public boolean done;

    public Todo(int id, String title, String description, boolean done) {
        this.title = title;
        this.description = description;
        this.done = done;
    }
}