introduction

We used RestTemplate Realization REST API call , The code looks like this ：

@GetMapping("/buy/{id}")
public Product order() {
    Product product = restTemplate.getForObject("http://shop-service- product/product/1", Product.class);
    return product;
}

From the code , We use concatenated strings to construct URL Of , The URL There is only one parameter . however , In reality ,URL It often contains multiple parameters . At this time, if we still construct in this way URL, Then it will be very painful . Then how to solve ？ We take this question into the study of this chapter .  

1. Feign brief introduction

Feign yes Netflix Developed declarative , templated HTTP client , It's inspired by Retrofit,JAXRS-2.0 as well as WebSocket.

• Feign Can help us more convenient , Elegant call HTTP API.
• stay SpringCloud in , Use Feign It's simple — Create an interface , And add some comments to the interface , The code is over a .
• Feign Support multiple annotations , for example Feign Own notes or JAX-RS Annotations etc. .
• SpringCloud Yes Feign Enhanced , send Feign Support SpringMVC annotation , And integrated Ribbon and Eureka, So that Feign It is more convenient to use .

2. be based on Feign Service call for

2.1 Introduce dependencies

In serving consumers shop_service_order add to Fegin rely on

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

2.2 Startup class add Feign Support for

adopt @EnableFeignClients Annotations to open Spring Cloud Feign Support functions of

@SpringBootApplication
@EnableFeignClients// Turn on feign function 
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

2.3 Start class activation FeignClient

Create a Feign Interface , This interface is in Feign The core interface for invoking microservices in

In serving consumers shop_service_order Add one ProductFeginClient Interface

@FeignClient(name = "shop-service-product")
public interface  ProductFeginClient {
    @RequestMapping("/shop-service-product/product/{id}")
    public Product findById(@PathVariable("id") Long id);
}

When defining the binding of each parameter ,@PathVariable、@RequestParam、@RequestHeader And so on, you can specify the parameter belongs to sex , stay Feign The binding parameter in must pass value Property to specify the specific parameter name , Otherwise, an exception will be thrown

@FeignClient： Comments by name Specify the name of the micro service to be called , Used to create Ribbon Load balancer for . therefore Ribbon Will be able to shop-service-product Service resolved to registry .

2.4 Configure the calling interface of the request provider

modify OrderController , add to ProductFeginClient Automatic injection , And in order Method used in

ProductFeginClient Complete the microservice call

@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private ProductFeginClient productFeginClient;

    @GetMapping("/buy/{id}")
    public Product order(@PathVariable	Long id) {
        return  productFeginClient.findById(id);
    }
}

2.5 Run the test

3. Feign and Ribbon contact

Ribbon It's based on HTTP and TCP client Load balancing tools . It can Configure... On the client side

RibbonServerList（ Server list ）, Use HttpClient or RestTemplate simulation http request , The steps are rather tedious .

Feign Is in Ribbon Based on this, an improvement is made , It is more convenient to use HTTP client . Interface mode , Just create an interface , Then add comments on it , Define the methods of other services that need to be called as abstract parties Just do it , You don't need to build it yourself http request . Then it's like calling the method call of your own project , And I don't feel it's calling the remote party Law , It makes it very easy to write the client

4.  Load balancing

Feign Has been integrated in Ribbon Dependency and auto configuration , So we don't need to introduce additional dependencies , No need to register again RestTemplate object . in addition , We can configure it as we did in the last lesson Ribbon, Can pass ribbon.xx For global configuration . It can also be done through service name .ribbon.xx To configure the specified service ：

Start two shop_service_product , Retesting can reveal the use of Ribbon The polling strategy is used for load balancing

5. Feign Configuration of

from Spring Cloud Edgware Start ,Feign Support the use of custom attributes Feign. For a named Feign Client（ For example Feign Client For the name of the feignName ）,Feign The following configuration items are supported ：

feign:
 client: 
  config:
   feignName: ## Definition FeginClient The name of 
   connectTimeout: 5000	#  amount to Request.Options
   readTimeout: 5000	#  amount to Request.Options
   loggerLevel: full    #  To configure Feign Log level of , It's equivalent to Logger
   decode404: false 

• feignName：FeginClient The name of
• connectTimeout ： The timeout for establishing a link
• readTimeout ： Read timeout duration
• loggerLevel: Fegin Log level of
• errorDecoder ：Feign Error decoder for
• retryer ： Configuration retry
• requestInterceptors ： Add a request interceptor
• decode404 ： Configuration fusing is not handled 404 abnormal

6. Request compression  

Spring Cloud Feign Support for requests and responses GZIP Compress , To reduce the performance loss in the communication process . Through the following parameters You can turn on the compression function of request and response ：

feign:
 compression:
  request:
   enabled: true #  Turn on request compression 
  response:
   enabled: true #  Turn on response compression 

meanwhile , We can also request the data type , And the lower limit of the size to trigger compression ：

feign:
 compression: 
  request:
   enabled: true #  Turn on request compression 
   mime-types: text/html,application/xml,application/json #  Set compressed data type 
   min-request-size: 2048 #  Set the lower size limit for triggering compression 

notes ： Data type above 、 The lower limit of compression size is the default value .

7. The level of logging  

In the development or operation phase, you often want to see Feign Logging of the request process , By default Feign Your log is not open . If you want to use attribute configuration to achieve logging effect , Just in application.yml Add the following to ：

feign:
 client: 
  config:
   shop-service-product: 
    loggerLevel: FULL
logging: 
 level:
  com.suke.order.fegin.ProductFeginClient:  debug

logging.level.xx : debug : Feign Log will only be used for log level debug In response

feign.client.config.shop-service-product.loggerLevel : To configure Feign Log Feign There are four logging levels ：

• NONE【 Best performance , Suitable for production 】： Don't log anything （ The default value is ）
• BASIC【 Applicable to production environment tracking problems 】： Only the request method is recorded 、URL、 Response status code and execution time
• HEADERS： Record BASIC Level based , Recording requests and responses header.
• FULL【 It is more suitable for positioning problems in development and test environment 】： Recording requests and responses header、body And the quaternion According to the .