How do you compare Rest Assured with HttpClient or RestTemplate

REST Assured is a high level Java DSL (domain-specific language) for simplified testing of REST based services built over HTTP.(Hypertext transfer protocol)

On the other hand, HttpClient is a low level client for simplifying Http Communication.

In-fact HttpClient is used by REST Assured under the hood for Http communication.

REST Assured and HttpClient are designed to solve different sets of problems.

1. What does HttpClient do?

HttpClient sends request to and get response from server over HTTP protocol, and also it takes care of the following stuff:

• HTTP protocol interception
• Secure HTTP connections - SSL/TLS
• HTTP proxy server handling
• Handles HTTP cookies
• Connection pooling for different hosts, keep alive strategy,
• multi-threaded request execution

SSL stands for Secure Sockets Layer and, in short, it's the standard technology for keeping an internet connection secure and safeguarding any sensitive data that is being sent between two systems, preventing criminals from reading and modifying any information transferred, including potential personal details. The two systems can be a server and a client (for example, a shopping website and browser) or server to server (for example, an application with personal identifiable information or with payroll information).

TLS (Transport Layer Security) is just an updated, more secure, version of SSL. We still refer to our security certificates as SSL because it is a more commonly used term, but when you are buying SSL from DigiCert you are actually buying the most up to date TLS certificates with the option of ECC, RSA or DSA encryption.

1. REST Assured

REST Assured is a Java DSL for simplifying testing of REST based services and is built on top of HttpClient. It offers the following additional capabilities:

• Validating REST API response using inbuilt Hamcrest Matchers
• JSON & XML serialization and deserialization
• Extracting JSON data using JsonPath and XML data using XmlPath
• Verifying response body, cookies, headers, content-type and http status
• Authentication using Basic Auth, Digest Auth, Form Authentication (CSRF support), OAuth (OAuth1 and OAuth2)
• verifying multipart form data
• Request and response logging for easy troubleshooting
• Session Filters
• Spring Mock Mvc Module
• Spring Web Test Client Module
• Kotlin support

1. RestTemplate

RestTemplate is also a high level REST client which uses HttpClient under the hood, but it is mostly used in development rather than testing. It lacks (don't have ) most of the testing related features readily (simply) available in REST Assured like - Assertion capabilities - inbuilt Hemcrest matchers support, ease of use from testing perspective, out of the box support for various authentication protocols, ease of logging requests response, measuring request time, etc.

If you are planning to do functional testing for your REST Endpoints, REST Assured might be the better choice than using HttpClient or RestTemplate.