How to call rest api from java code

REST API (Representational State Transfer Application Programming Interface) is important for several reasons, primarily revolving around its simplicity, scalability, and interoperability. Here are some key reasons why REST APIs are crucial in modern software development:

1. Simplicity and Ease of Use

• Human-Readable: REST APIs use standard HTTP methods (GET, POST, PUT, DELETE) and URLs, making them easy to understand and use.
• Statelessness: Each request from a client to a server must contain all the information needed to understand and process the request. This stateless nature simplifies the server design.

2. Scalability

• Horizontal Scaling: REST APIs can handle a large number of clients and requests. Since they are stateless, servers can be added or removed as needed without affecting client interactions.
• Load Balancing: The stateless nature of REST allows for easy distribution of requests across multiple servers.

3. Interoperability

• Cross-Platform: REST APIs are language-agnostic and can be used across different programming languages and platforms. This allows different systems to communicate seamlessly.
• Standard Protocols: REST APIs use standard web protocols, making it easy to integrate with other web services and applications.

4. Flexibility and Extensibility

• Resource-Based: REST APIs are centered around resources (data entities), allowing developers to build APIs that can be extended without breaking existing functionality.
• Modularity: RESTful principles encourage a modular approach, making it easier to update, maintain, and scale the application.

5. Performance

• Caching: REST APIs can leverage HTTP caching mechanisms to improve performance and reduce server load.
• Efficient Data Transfer: With REST, data can be transferred in various formats (JSON, XML, etc.), allowing for efficient and optimized data exchange.

6. Security

• Authentication and Authorization: REST APIs can use various authentication mechanisms (OAuth, JWT, API keys) to ensure secure access.
• HTTPS: By using HTTPS, REST APIs can ensure secure data transfer between the client and server.

7. Broad Adoption and Community Support

• Widespread Use: REST is widely adopted across the industry, making it easier to find resources, libraries, and tools for development.
• Community Support: A large community and extensive documentation are available, aiding developers in troubleshooting and enhancing their API implementations.

Examples of REST API Use Cases

1. Web Applications
• Backend Services: REST APIs provide backend services for web applications, allowing front-end clients to interact with databases and servers.
• Content Management Systems: Platforms like WordPress and Drupal offer REST APIs to interact with their content management systems programmatically.
2. Mobile Applications
• Data Synchronization: Mobile apps use REST APIs to synchronize data with cloud services, ensuring consistency across devices.
• Third-Party Integrations: Mobile apps integrate with external services (e.g., social media, payment gateways) through REST APIs.
3. Microservices Architecture
• Service Communication: In a microservices architecture, different services communicate with each other using REST APIs, enabling modular and scalable system design.
• API Gateway: An API gateway can route requests to appropriate microservices, providing a single entry point for clients.
4. Internet of Things (IoT)
• Device Communication: IoT devices use REST APIs to send and receive data to and from cloud services, enabling real-time monitoring and control.
5. Data Services
• Public APIs: Many organizations provide public APIs (e.g., Google Maps API, Twitter API) to allow developers to access and utilize their data and services.

 

How to call  REST API in java code

Calling a REST API in Java can be accomplished using various libraries and frameworks. Here are some common approaches:

1. Using HttpURLConnection (Standard Java Library)
2. Using Apache HttpClient
3. Using Spring RestTemplate
4. Using Spring WebClient (part of Spring WebFlux)

1. Using HttpURLConnection

This is the most basic way to call a REST API using standard Java libraries.

java

import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL;   public class HttpURLConnectionExample {     public static void main(String[] args) {         try {             URL url = new URL("https://jsonplaceholder.typicode.com/posts/1");             HttpURLConnection conn = (HttpURLConnection) url.openConnection();             conn.setRequestMethod("GET");               int responseCode = conn.getResponseCode();             System.out.println("Response Code : " + responseCode);               BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));             String inputLine;             StringBuffer response = new StringBuffer();               while ((inputLine = in.readLine()) != null) {                 response.append(inputLine);             }             in.close();               // Print result             System.out.println(response.toString());         } catch (Exception e) {             e.printStackTrace();         }     } }

 

2. Using Apache HttpClient

Apache HttpClient is a more flexible and feature-rich HTTP client.

1. Add dependency (in pom.xml):

xml

<dependency>     <groupId>org.apache.httpcomponents</groupId>     <artifactId>httpclient</artifactId>     <version>4.5.13</version> </dependency>

 

2. Make the API call:

java

import org.apache.http.HttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import org.apache.http.util.EntityUtils;   public class ApacheHttpClientExample {     public static void main(String[] args) {         try (CloseableHttpClient httpClient = HttpClients.createDefault()) {             HttpGet request = new HttpGet("https://jsonplaceholder.typicode.com/posts/1");             HttpResponse response = httpClient.execute(request);               String result = EntityUtils.toString(response.getEntity());             System.out.println(result);         } catch (Exception e) {             e.printStackTrace();         }     } }

 

3. Using Spring RestTemplate

RestTemplate is part of the Spring framework and simplifies the process of making HTTP calls.

1. Add dependency (in pom.xml):

xml

<dependency>     <groupId>org.springframework.boot</groupId>     <artifactId>spring-boot-starter-web</artifactId> </dependency>

 

2. Make the API call:

java

import org.springframework.web.client.RestTemplate; import org.springframework.http.ResponseEntity;   public class RestTemplateExample {     public static void main(String[] args) {         RestTemplate restTemplate = new RestTemplate();         String url = "https://jsonplaceholder.typicode.com/posts/1";                 ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);         System.out.println(response.getBody());     } }

 

4. Using Spring WebClient (part of Spring WebFlux)

WebClient is a modern, asynchronous and non-blocking client designed for making REST calls.

1. Add dependency (in pom.xml):

xml

<dependency>     <groupId>org.springframework.boot</groupId>     <artifactId>spring-boot-starter-webflux</artifactId> </dependency>

 

2. Make the API call:

java

import org.springframework.web.reactive.function.client.WebClient; import reactor.core.publisher.Mono;   public class WebClientExample {     public static void main(String[] args) {         WebClient client = WebClient.create("https://jsonplaceholder.typicode.com");         Mono<String> response = client.get()             .uri("/posts/1")             .retrieve()             .bodyToMono(String.class);         response.subscribe(System.out::println);     } }

 

Choosing the Right Approach

• For simplicity and minimal dependencies: Use HttpURLConnection.
• For a feature-rich and flexible client: Use Apache HttpClient.
• For Spring applications: Use RestTemplate (for synchronous calls) or WebClient (for asynchronous/non-blocking calls).

Each method has its own pros and cons, so choose the one that best fits your application's needs.