Java REST Client Using Netflix Feign

Continue the series about Java REST client, I’d like to share how to implement Java REST client using Netflix Feign. As mentioned in the Feign site, Feign is a java to http client binder inspired by Retrofit, JAXRS-2.0, and WebSocket. In similar to other REST client frameworks, libraries, Feign aims to simplify the interaction between client code and http api.

1. Preparation

Assume that we have a RESTful web service with several API as below:

1.1 Get all books

GET http://localhost:8080/v1/books

1	GET http://localhost:8080/v1/books

Responses: application/json

1.2 Create a new book

POST http://localhost:8080/v1/books

1	POST http://localhost:8080/v1/books

Request

Example:

{
    "name": "Java How To Program",
    "author": "Paul Deitel"
}

{

"name": "Java How To Program",

"author": "Paul Deitel"

}

Responses: application/json

Example:

{
    "id": 5
    "name": "Java How To Program",
    "author": "Paul Deitel"
}

{

"id": 5

"name": "Java How To Program",

"author": "Paul Deitel"

}

STATUS 201 if the book is created successfully.

1.3 Update a book

PUT http://localhost:8080/v1/books/{id}

1	PUT http://localhost:8080/v1/books/{id}

Request

Example:

{   
    "id": 1,
    "name": "Java How To Program 2nd",
    "author": "Paul Deitel"
}

{

"id": 1,

"name": "Java How To Program 2nd",

"author": "Paul Deitel"

}

Responses: application/json

STATUS 200 if the book is updated successfully.

STATUS 400 if there is no book with given id

1.4 Delete a book

DELETE http://localhost:8080/v1/books/{id}

1	DELETE http://localhost:8080/v1/books/{id}

Responses: application/json

STATUS 204 if the book is deleted successfully.

STATUS 400 if there is no book with given id or cannot delete the book.

1.5 Source code

The demo source code can be found on the Github.

We use Netflix Feign to communicate with the REST service above, and we will use Jackson JSON providers to deal with JSON content.

<dependency>
	<groupId>com.netflix.feign</groupId>
	<artifactId>feign-core</artifactId>
	<version>8.18.0</version>
</dependency>
<dependency>
	<groupId>com.netflix.feign</groupId>
	<artifactId>feign-jackson</artifactId>
	<version>8.18.0</version>
</dependency>

<groupId>com.netflix.feign</groupId>

<artifactId>feign-core</artifactId>

</dependency>

<groupId>com.netflix.feign</groupId>

<artifactId>feign-jackson</artifactId>

</dependency>

2. Create REST Client Using Netflix Feign

2.1. Define a Proxy Interface at the client side.

We firstly base on the above RESTful API to create a Java interface, annotated with annotations provided by Feign. Feign will process those annotations to make requests and communicate with the remote http api. Let’s see a BookResourceFeign class I have just defined as following:

import feign.Headers;
import feign.Param;
import feign.RequestLine;

@Headers("Accept: application/json")
public interface BookResourceFeign {

  @RequestLine("GET /v1/books")
  List<Book> getAllBooks();

  @Headers("Content-Type: application/json")
  @RequestLine("POST /v1/books")
  Book createBook(Book book);

  @Headers("Content-Type: application/json")
  @RequestLine("PUT /v1/books/{id}")
  Book updateBook(@Param("id") Long id, Book book);

  @RequestLine("DELETE /v1/books/{id}")
  void deleteBook(@Param("id") Long id);

}

import feign.Headers;

import feign.Param;

import feign.RequestLine;

@Headers("Accept: application/json")

public interface BookResourceFeign {

@RequestLine("GET /v1/books")

List<Book> getAllBooks();

@Headers("Content-Type: application/json")

@RequestLine("POST /v1/books")

Book createBook(Book book);

@Headers("Content-Type: application/json")

@RequestLine("PUT /v1/books/{id}")

Book updateBook(@Param("id") Long id, Book book);

@RequestLine("DELETE /v1/books/{id}")

void deleteBook(@Param("id") Long id);

}

We can see that the annotations are a little bit different with ones provided by JAX-RS, but it’s pretty easy to understand those. Because this client will accept response as JSON, we annotated the interface: @Headers(“Accept: application/json”). For the Post and Put resources, we specify the request body as JSON, so we annotated @Headers(“Content-Type: application/json”) on those methods. The values of the @RequestLine are kinds of text, very simple to understand.

As for the Book model, we have defined temporarily as follows:

@JacksonXmlRootElement(localName = "book")
public class Book {
  private Long id;
  private String name;
  private String author;

  //All getters and setters should be here
}

@JacksonXmlRootElement(localName = "book")

public class Book {

private Long id;

private String name;

private String author;

//All getters and setters should be here

}

2.2. Invoke methods on the Proxy

After having the proxy interface, we just need to invoke its methods to communicate with the RESTful API.

2.2.1. Make a GET request to the RESTful web service (Get all books)

public class BookRepositoryImplFeign {
  private static final String URI_BOOK = "http://localhost:8080";

  public List<Book> getAllBooks() throws Exception {
    BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())
        .decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);
    return bookResource.getAllBooks();

  }
}

public class BookRepositoryImplFeign {

private static final String URI_BOOK = "http://localhost:8080";

public List<Book> getAllBooks() throws Exception {

BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())

.decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);

return bookResource.getAllBooks();

}

We use Feign utility class to set Jackson Encoder, Decoder, target to the BookResourceFeign.class and resource URI to create a kind of proxy for that class.

We will create a main method to test as follows:

  public static void main(String[] args) throws Exception {
    BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();
    List<Book> books = bookRepository.getAllBooks();
    System.out.println(books);
  }

public static void main(String[] args) throws Exception {

BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();

List<Book> books = bookRepository.getAllBooks();

System.out.println(books);

}

Here is the output of my console:

[Book [id=1, name=Java How To Program, author=Paul Deitel], Book [id=2, name=Thinking in Java, author=Bruce Eckel]]

1	[Book [id=1, name=Java How To Program, author=Paul Deitel], Book [id=2, name=Thinking in Java, author=Bruce Eckel]]

2.2.2. Make a POST request to the RESTful web service (create a book)

public class BookRepositoryImplFeign {
  private static final String URI_BOOK = "http://localhost:8080";

  public Book createBook(Book book) throws Exception {
    BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())
        .decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);
    Book createdBook = bookResource.createBook(book);
    return createdBook;

  }
}

public class BookRepositoryImplFeign {

private static final String URI_BOOK = "http://localhost:8080";

public Book createBook(Book book) throws Exception {

BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())

.decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);

Book createdBook = bookResource.createBook(book);

return createdBook;

}

We simply invoked the createBook(book) method on the proxy to create new book by posting the JSON content to the REST API

We will update the main method to test:

  public static void main(String[] args) throws Exception {
    BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();
    Book book = new Book(null, "Effective Java", "Joshua Bloch");
    Book createdBook = bookRepository.createBook(book);
    System.out.println(createdBook);
  }

public static void main(String[] args) throws Exception {

BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();

Book book = new Book(null, "Effective Java", "Joshua Bloch");

Book createdBook = bookRepository.createBook(book);

System.out.println(createdBook);

}

The output of my console:

Book [id=4, name=Effective Java, author=Joshua Bloch]

1	Book [id=4, name=Effective Java, author=Joshua Bloch]

2.2.3. Make a PUT request to the RESTful web service (Update a book)

import feign.Feign;
import feign.jackson.JacksonDecoder;
import feign.jackson.JacksonEncoder;

public class BookRepositoryImplFeign {
  private static final String URI_BOOK = "http://localhost:8080";
  
  public Book updateBook(Book book) throws Exception {
    BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())
        .decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);
    Book updatedBook = bookResource.updateBook(book.getId(), book);
    return updatedBook;
  }

}

import feign.Feign;

import feign.jackson.JacksonDecoder;

import feign.jackson.JacksonEncoder;

public class BookRepositoryImplFeign {

private static final String URI_BOOK = "http://localhost:8080";

public Book updateBook(Book book) throws Exception {

BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())

.decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);

Book updatedBook = bookResource.updateBook(book.getId(), book);

return updatedBook;

}

We update the main method to test:

  public static void main(String[] args) throws Exception {
    BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();
    // Getting the first book from the RESTful service
    Book book = bookRepository.getAllBooks().get(0);
    System.out.println(book);
    // Change the name
    book.setName(book.getName() + " 3rd");
    // Then update the book
    book = bookRepository.updateBook(book);
    System.out.println(book);
  }

public static void main(String[] args) throws Exception {

BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();

// Getting the first book from the RESTful service

Book book = bookRepository.getAllBooks().get(0);

System.out.println(book);

// Change the name

book.setName(book.getName() + " 3rd");

// Then update the book

book = bookRepository.updateBook(book);

System.out.println(book);

}

Here is the output of my console:

Book [id=1, name=Java How To Program, author=Paul Deitel]
Book [id=1, name=Java How To Program 3rd, author=Paul Deitel]

1 2	Book [id=1, name=Java How To Program, author=Paul Deitel] Book [id=1, name=Java How To Program 3rd, author=Paul Deitel]

Note that the book was updated with the new name: Java How To Program 3rd

2.2.4. Make a DELETE request to the RESTful web service (delete a book)

  public void deleteBook(Long id) {
    BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())
        .decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);
    bookResource.deleteBook(id);
  }

public void deleteBook(Long id) {

BookResourceFeign bookResource = Feign.builder().encoder(new JacksonEncoder())

.decoder(new JacksonDecoder()).target(BookResourceFeign.class, URI_BOOK);

bookResource.deleteBook(id);

}

The main method is updated to test as below:

  public static void main(String[] args) throws Exception {
    BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();
    Book book = bookRepository.getAllBooks().get(0);
    bookRepository.deleteBook(book.getId());
  }

public static void main(String[] args) throws Exception {

BookRepositoryImplFeign bookRepository = new BookRepositoryImplFeign();

Book book = bookRepository.getAllBooks().get(0);

bookRepository.deleteBook(book.getId());

}

3. Conclusion

We have learned how to implement Java REST Client using Netflix Feign. Note that we have used Feign Jackson Json message converter to deal with JSON content from REST API. There are a lot of choices. We can use Gson, Sax, JAXB, JAX-RS if we prefer. In future, I will share how to implement Java REST client with another framework like Retrofit and summarize all the common frameworks, tools that can be used to implement Java REST client.

Below are other articles which related to the Java REST client for your references:

Using Netflix Feign with Spring Cloud

Basic Authentication with Open Feign

File Uploading with Open Feign

Java REST Client Using Retrofit 2

Simple Java REST Client Using java.net.URL package

Java REST Client Using Spring RestTemplate

Java REST Client Using Apache HttpClient

Java REST Client Using Jersey Client

Java REST Client Using Resteasy Client

Java REST Client Using Resteasy Client Proxy Framework

Java REST Client Using Apache CXF Proxy-based API

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Java REST Client Using Netflix Feign

1. Preparation

1.1 Get all books

1.2 Create a new book

1.3 Update a book

1.4 Delete a book

1.5 Source code

2. Create REST Client Using Netflix Feign

2.1. Define a Proxy Interface at the client side.

2.2. Invoke methods on the Proxy

2.2.1. Make a GET request to the RESTful web service (Get all books)

2.2.2. Make a POST request to the RESTful web service (create a book)

2.2.3. Make a PUT request to the RESTful web service (Update a book)

2.2.4. Make a DELETE request to the RESTful web service (delete a book)

3. Conclusion

howtoprogram