Spring WebFlux — WebClient

In this article, will see how we could use Spring WebFlux WebClient for making non-blocking HTTP requests.

WebClient — Non-blocking, reactive client to perform HTTP requests, exposing a fluent, reactive API over underlying HTTP client libraries such as Reactor Netty.
Use static factory methods create() or create(String), or builder() to prepare an instance.
For examples with a response body see:
- retrieve()
- exchangeToMono()
- exchangeToFlux()

For examples with a request body see:
- bodyValue(Object)
- body(Publisher,Class)

db.json

{
  "posts":[
    {
      "id":1,
      "title":"json-server",
      "author":"typicode"
    }
  ],
  "comments":[
    {
      "id":1,
      "body":"some comment",
      "postId":1
    }
  ]
}

Start the command using Docker

docker run -d -p 3000:80 -v ${PWD}/db.json:/data/db.json clue/json-server

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.5.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.vinsguru</groupId>
   <artifactId>r2dbc-transaction</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>r2dbc-transaction</name>
   <description>Demo project for Spring Boot</description>
   <properties>
      <java.version>11</java.version>
   </properties>
   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-data-r2dbc</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-webflux</artifactId>
      </dependency>
      <dependency>
         <groupId>com.h2database</groupId>
         <artifactId>h2</artifactId>
         <scope>runtime</scope>
      </dependency>
      <dependency>
         <groupId>io.r2dbc</groupId>
         <artifactId>r2dbc-h2</artifactId>
         <scope>runtime</scope>
      </dependency>
      <dependency>
         <groupId>org.projectlombok</groupId>
         <artifactId>lombok</artifactId>
         <optional>true</optional>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
      <dependency>
         <groupId>io.projectreactor</groupId>
         <artifactId>reactor-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
               <excludes>
                  <exclude>
                     <groupId>org.projectlombok</groupId>
                     <artifactId>lombok</artifactId>
                  </exclude>
               </excludes>
            </configuration>
         </plugin>
      </plugins>
   </build>

</project>

Post.java

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Post {
    private int id;
    private String title;
    private String author;
}

Comment.java

import lombok.Data;
import lombok.ToString;

@Data
@ToString
public class Comment {
    private int id;
    private String body;
    private int postId;
}

Test class

import com.vinsguru.r2dbctransaction.entity.Post;
import org.junit.jupiter.api.*;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.WebClient;

import java.time.Duration;
import java.util.Arrays;

@SpringBootTest
@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
@TestInstance(TestInstance.Lifecycle.PER_CLASS)
public class WebClientTest {
    private static final String BASE_URL = "http://localhost:3000/";

    private WebClient webClient;

    @BeforeAll
    public void beforeAll(){
        webClient = WebClient.builder()
                .baseUrl(BASE_URL).build();
    }

    @Test
    public void testGET(){
        this.webClient
                .get()
                .uri("/posts")
                .retrieve()
                .bodyToMono(Post[].class)
                .flatMapIterable(Arrays::asList)
                .subscribe(System.out::println);
    }

    @Test
    public void savePosts(){
        Post post = new Post();
        post.setId(3);
        post.setAuthor("Aravind");
        post.setTitle("Life of NTC");

        this.webClient
                .post()
                .uri("/posts")
                .bodyValue(post)
                .retrieve()
                .bodyToMono(String.class)
                .subscribe(System.out::println);
    }

    @Test
    public void updatePost(){
        Post post = new Post();
        post.setId(3);
        post.setAuthor("Aravind");
        post.setTitle("Life of NTC 11");

        webClient.put()
                .uri("/posts/3")
                .bodyValue(post)
                .retrieve()
                .bodyToMono(String.class)
                .subscribe(System.out::println);
    }

    @Test
    public void patchPosts(){
        this.webClient
                .patch()
                .uri("/posts/3")
                .bodyValue(BodyInserters.fromFormData("title", "Life of NTC 20"))
                .retrieve()
                .bodyToMono(String.class)
                .subscribe(System.out::println);
    }

    @Test
    public void deletePost(){
        this.webClient
                .delete()
                .uri("/posts/3")
                .retrieve()
                .bodyToMono(String.class)
                .subscribe(System.out::println);
    }

    @Test
    public void timeoutPost(){
        this.webClient
                .get()
                .uri("/posts")
                .retrieve()
                .bodyToMono(Post[].class)
                .timeout(Duration.ofSeconds(1))
                .flatMapIterable(Arrays::asList)
                .onErrorReturn(new Post(100, "Default", "Default"))
                .subscribe(System.out::println);
    }
}

All endpoints-

// all posts 
http://localhost:3000/posts 

// all comments 
http://localhost:3000/comments 

// post 1 comments 
http://localhost:3000/posts/1/comments