Microservice - remote invocation (feign component)

1. Feign brief introduction

a RestTemplate comparison ,Feign Provide more elegant sending Http Requested function .

    public Order queryOrderById(Long orderId) {
    
        // 1. According to the order id Query order 
        Order order = orderMapper.findById(orderId);
        //2. According to the user id Query user information 
        String url = "http://userserivce/user/" + order.getUserId(); // Will change , Without elegance .
        // The remote invocation 
        User user = restTemplate.getForObject(url,User.class).var;
        return order;
    }

2. Use Feign Instead of RestTemplate

1. Introduce dependency coordinates

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

2. Open the annotation

@SpringCloudApplication
@EnableFeignClients // Turn on OpenFeign annotation 
public class OrderApplication {
    

    public static void main(String[] args) {
    
        SpringApplication.run(OrderApplication.class, args);
    }
}

3. Create an interface 、 Declare the path of the remote call

@FeignClient("userservice") //service id
public interface UserClient {
    

    @GetMapping("/user/{id}")
    User findById(@PathVariable("id") Long id);
}

4. Use FeignClient The method defined in replaces RestTemplate

User user = userClient.findById(order.getUserId());

3. Feign To configure

type	effect	explain
feign.Logger.Level	Modify log level	Contains four different levels ：NONE、BASIC、HEADERS、FULL
feign.codec.Decoder	The parser that responds to the result	http Analyze the result of remote call , For example, parsing json String is java object
feign.codec.Encoder	Request parameter encoding	Encode the request parameters , Easy to pass http Request to send
feign. Contract	Supported annotation formats	The default is SpringMVC Annotations
feign. Retryer	Failure retry mechanism	Retry mechanism for request failure , The default is No , However, it will be used Ribbon Retry

In general , The default value can meet our use , If you want to customize , Just create a custom @Bean Override default Bean that will do .

There are four levels of logs ：

• NONE： No log information is recorded , This is the default .
• BASIC： Record only the requested method ,URL And the response status code and execution time
• HEADERS： stay BASIC On the basis of , Additionally, the request and response header information is recorded
• FULL： Record details of all requests and responses , Including header information 、 Request body 、 Metadata .

Mode one ： The configuration file

Modify based on the configuration file feign Log level of :

feign:  
  client:
    config: 
      userservice: #  Configuration for a microservice 
        loggerLevel: FULL #  The level of logging  

feign:  
  client:
    config: 
      default: #  Here we use default Global configuration , If you write the service name , It is the configuration for a micro service 
        loggerLevel: FULL #  The level of logging  

4. Feign Use optimization

Feign Bottom layer initiation http request , Rely on other frameworks . Its underlying client implementation includes ：

• URLConnection： Default implementation , Connection pooling is not supported

• Apache HttpClient ： Support connection pool

• OKHttp： Support connection pool

So improve Feign The main means of performance is to use Connection pool Instead of default URLConnection.

Use Apache HttpClient

1. Introduce dependencies

        <!--Apache HttpClient Dependence  -->
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-httpclient</artifactId>
        </dependency>

2. Configure connection pool

feign:
  client:
    config:
      userservice: #  Configuration for a microservice 
        loggerLevel: BASIC #  The level of logging 
  httpclient: # Configure connection pool 
    enabled: true #  Turn on feign Yes HttpClient Support for 
    max-connections: 200 #  Maximum number of connections 
    max-connections-per-route: 50 #  Maximum number of connections per path 

take Feign The interface is drawn into a module

1. Create a new module , Special preservation Feign Interface , Introduce dependencies

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

2. Open annotation when using , Add scan path

@SpringCloudApplication
@EnableFeignClients(basePackages = {
    "cn.xin.feign.clients"})
public class OrderApplication {
    

    public static void main(String[] args) {
    
        SpringApplication.run(OrderApplication.class, args);
    }
}