REST Service Client base on created HttpClient. Example for BookService

ServiceClient.java

import java.io.IOException;
import io.lenar.examples.spring.clients.response.BookResponse;
import io.lenar.examples.spring.clients.response.BooksResponse;
import io.lenar.examples.spring.clients.response.Response;
import io.lenar.examples.spring.http.HttpClient;
import io.lenar.examples.spring.model.Book;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class BookServiceClient {

    @Value("${bookService.url}")
    private String serviceUrl;

    @Autowired
    HttpClient http;

    public BooksResponse findBooks(String author) throws IOException {
        String url = author == null ? serviceUrl  : serviceUrl + "?author=" + author;
        return new BooksResponse(http.get(url));
    }

    public BooksResponse findBooks() throws IOException {
        return new BooksResponse(http.get(serviceUrl));
    }

    public BookResponse findBook(String id) throws IOException {
        return new BookResponse(http.get(serviceUrl + "/" + id));
    }

    public BookResponse createBook(Book book) throws IOException {
        return new BookResponse(http.post(serviceUrl, book));
    }

    public BookResponse updateBook(String id, Book book) throws IOException {
        return new BookResponse(http.put(serviceUrl + "/" + id, book));
    }

    public Response deleteBook(String id) throws IOException {
        return new Response(http.delete(serviceUrl + "/" + id));
    }
}

See also
REST API client for TestNG and Spring Boot using Apache Http Components. Part 2
Response classes for Service Client gist
HttpClient gist