1. 概述

在本教程中，我們將演示如何在 Feign 客户端中使用 @RequestLine 註解。 @RequestLine 是定義與 RESTful Web 服務連接的 URI 和查詢參數的模板。

2. Maven 依賴

首先，我們創建一個 Spring Boot Web 項目，並將 spring-cloud-starter-openfeign 或 feign-core 依賴添加到我們的 pom.xml 文件中。 spring-cloud-starter-openfeign 依賴內包含 feign-core 依賴：

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
    <version>3.1.2</version>
</dependency>

或者

<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-core</artifactId>
    <version>13.1</version>
</dependency>

3. @RequestLine in Feign Client

The @RequestLine Feign annotation specifies the HTTP verb, path, and request parameters as arguments in the Feign client. The path and request parameters are specified using the @Param annotation.

Normally in a Spring Boot application, we’d use @FeignClient, but we can also use @RequestLine if we don’t want to use the spring-cloud-starter-openfeign dependency. Using that dependency will give us an IllegalStateException if we use @RequestLine with @FeignClient.

The @FeignClient annotation’s String value is an arbitrary name that is used to create a Spring Cloud LoadBalancer client. We may additionally specify a URL and other parameters based on the requirements.

Let’s create an interface for using @RequestLine:

public interface EmployeeClient {
    @RequestLine("GET /empployee/{id}?active={isActive}")
    @Headers("Content-Type: application/json")
    Employee getEmployee(@Param long id, @Param boolean isActive);
}

We should also provide @Headers where we define headers required by the rest API.

Now, we’ll call the interface thus created to call the actual API:

EmployeeClient employeeResource = Feign.builder().encoder(new SpringFormEncoder())
  .target(EmployeeClient.class, "http://localhost:8081");
Employee employee = employeeResource.getEmployee(id, true);

4. 結論

在本文中，我們展示瞭如何以及何時使用 RequestLine 註解在 Feign 客户端。