使用OpenFeign Client调用合法GET URL时出现400 Bad Request错误

环境与依赖 #

基于Spring 3.1.5搭建的应用，启用@EnableFeignClients，核心POM依赖如下：

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<dependency>
    <!-- Required to use PATCH over default HttpURLConnection -->
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-hc5</artifactId> 
</dependency>

配置与代码 #

Feign客户端配置类 #

自定义配置类SoConfig，未添加@Configuration注解避免影响其他Feign客户端：

@Import(FeignClientsConfiguration.class)
public class SoConfig {

    @Bean
    public RequestInterceptor intercept(CustomInterceptor interceptor) {
        return interceptor;
    }
}

注：CustomInterceptor本身标记为@Component，负责为请求添加Bearer Token。

Feign客户端接口 #

@FeignClient(name = "so-client", url = "${config.url}", configuration = SoConfig.class)
public interface SoClient {

    @GetMapping(value = "?$filter=Identifier eq '{param}'")
    SoData getSoData(@PathVariable("param") String param);
}

调用网关类 #

@Component
@RequiredArgsConstructor
public class SoGateway {

    private final SoClient client;

    public SoData getSoData(@NonNull String param) {
        try {
            return client.getSoData(param);
        } catch (FeignException e) {
            // 自定义异常处理逻辑
        }
    }
}

运行时错误 #

调用过程中抛出400 Bad Request异常：

Caused by: feign.FeignException$BadRequest: [400 Bad Request] during [GET] to [https://resolved-config-url?%24filter=Identifier%20eq%20'testParam'] [SoClient#getSoData(String)]: [<!DOCTYPE html>
<html>
<body>
<p>Sorry, the page you are looking for is currently unavailable.<br/>
Please try again later.</p>
</body>
</html>
]

测试验证结果 #

• 将日志中的请求URL复制到Postman，携带Bearer Token发起GET请求，可正常获取预期响应（编码/解码后的URL均能访问SAP系统）
• 不带Bearer Token在Postman请求时，会收到需要提供JWT的提示，符合预期逻辑

已尝试的无效方案 #

• 替换feign-hc5为okhttp，无论是否配置spring.cloud.openfeign.httpclient.(hc5.)enabled=true
• 在配置类中显式指定默认编码器/解码器
• 设置spring.cloud.openfeign.lazy-attributes-resolution=true
• 修改SoClient，传入完整URL而非在@GetMapping中设置value

求助需求 #

恳请帮忙排查Feign调用返回400 Bad Request的原因，并提供可行的解决方案。

内容的提问来源于stack exchange，提问作者MarcelTon