Service call feign of "micro service"

One 、feign summary

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

@GetMapping("/buy/{id}")
public Product order() {
    
    Product product = restTemplate.getForObject("http://shop-serviceproduct/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 .

1.1 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 done .

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 .

1.2 be based on Feign Service call for

（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） Startup class add Feign Support for

@SpringBootApplication(scanBasePackages="cn.itcast.order")
@EntityScan("cn.itcast.entity")
@EnableFeignClients
public class OrderApplication {
    
public static void main(String[] args) {
    
SpringApplication.run(OrderApplication.class, args);
 }
}

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

（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

// Specify the name of the micro service to be called  
@FeignClient(name="shop-service-product") 
public interface ProductFeginClient {
     
	// The requested path of the call  
	@RequestMapping(value = "/product/{id}",method = RequestMethod.GET) 
	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 .

（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); 
	} 
} 

（5） The test results

	 A successful call ～ No screenshots , The computer is too laggy. 

1.3 Feign and Ribbon The connection of

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

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 methods , You don't need to build it yourself http request . Then it's like calling the method call of your own project , It doesn't feel like a remote method call , It makes it very easy to write the client

1.4 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 Come on in
Row global configuration . It can also be done through service name .ribbon.xx To configure the specified service ：

feign:
  client:
    config:
   	  ## Definition FeginClient The name of 
      service-product:
        # amount to Request.Options
        connect-timeout: 5000
        # amount to Request.Options
        readTimeout: 5000
        # To configure Feign Log level of , It's equivalent to Logger
        loggerLevel: full
        #Feign Error decoder for , It's equivalent to ErrorDecoder
        errorDecoder: com.example.SimpleErrorDecoder
        # Configuration retry , It's equivalent to Retryer
        retryer: com.example.SimpleRetryer
        # Configure interceptors , It's equivalent to RequestInterceptor
        requestInterceptors:
          -com.example.FooRequestInterceptor
          -com.example.BarRequestInterceptor
        decode404: false

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

Two 、Feign Advanced

2.1Feign Configuration of

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

feign:
  client:
    config:
      service-product:
        # amount to Request.Options
        connect-timeout: 5000
        # amount to Request.Options
        readTimeout: 5000
        # To configure Feign Log level of , It's equivalent to Logger
        loggerLevel: full
        #Feign Error decoder for , It's equivalent to ErrorDecoder
        errorDecoder: com.example.SimpleErrorDecoder
        # Configuration retry , It's equivalent to Retryer
        retryer: com.example.SimpleRetryer
        # Configure interceptors , It's equivalent to RequestInterceptor
        requestInterceptors:
          -com.example.FooRequestInterceptor
          -com.example.BarRequestInterceptor
        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

2.2 Request compression

SpringCloudFeign Support for requests and responses GZIP Compress , To reduce the performance loss in the communication process . The compression function of request and response can be turned on through the following parameters ：

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

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

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

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

2.3 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:
      service-product:
        #  amount to Request.Options
        connect-timeout: 5000
        #  amount to Request.Options
        readTimeout: 5000
        #  To configure Feign Log level of , It's equivalent to Logger
        loggerLevel: full

logging:
  level:
    # Feign Log will only be used for log level debug In response 
    cn.itcast.order.fegin.ProductFeginClient: debug

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 metadata .