在Feign接口中返回泛型类型——自定义Decoder


前几天对接了一套第三方接口,所有接口的请求地址一样,请求参数和响应结果中有很多共同的字段,所以就想把这些字段都抽出来,Feign定义的接口直接返回泛型类型。

Feign定义

@FeignClient(name = "demoFeign", url = "${config.demo.domain}")
public interface DemoFeign {

    @PostMapping(value = "/open/post")
    public <R extends BaseResponse, T extends BaseRequest> R invoke(@RequestBody T request);
            
}

请求参数父类 BaseRequest

@Data
public class BaseRequest{
    private String requestId;
    private String timeStamp;
    private String method;
}

接口1的请求参数定义 Request01

@Data
public class Request01 extends BaseRequest{
    private String merchantId;
}

接口2的请求参数定义 Request02

@Data
public class Request02 extends BaseRequest{
    private String orderNo;
}

响应结果父类 BaseRequest

@Data
public class BaseResponse{
    private String code;
    private String message;
}

接口1的响应结果定义 Response01

@Data
public class Response01 extends BaseResponse{
    private String merchantId;
    private String merchantName;
}

接口2的响应结果定义 Response02

@Data
public class Response02 extends BaseResponse{
    private String orderNo;
    private String orderTime;
}

调用的时候报错:feign.codec.DecodeException: type is not an instance of Class or ParameterizedType: R

feign.codec.DecodeException: type is not an instance of Class or ParameterizedType: R
	at org.springframework.cloud.openfeign.support.SpringDecoder.decode(SpringDecoder.java:61)
	at org.springframework.cloud.openfeign.support.ResponseEntityDecoder.decode(ResponseEntityDecoder.java:62)
	at feign.optionals.OptionalDecoder.decode(OptionalDecoder.java:36)
	at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:176)
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:140)
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:78)
	at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103)
	at com.sun.proxy.$Proxy129.invoke(Unknown Source)

原来是当接口返回类型定义成泛型时,Feign的解码器Decoder(Feign默认的解码器是SpringDecoder)在解析接口响应内容的时候,Type被解析成了TypeVariableImpl类型,导致反序列化响应内容失败。

在Feign接口中返回泛型类型——自定义Decoder_第1张图片

Feign的编码器和解码器是可插拔的,可以自定义一个Feign的解码器来解决这个问题。

1、定义一个 解析 返回类型为泛型Feign接口解码器GenericsFeignResultDecoder,需要实现Decoder接口;

public class GenericsFeignResultDecoder implements Decoder {

	private static NamedThreadLocal<Class> feignReturnTypeThreadLocal=new NamedThreadLocal<Class>("feignReturnTypeThreadLocal");

	// 调用Feign的泛型接口前,先调用GenericsFeignResultDecoder.setReturnType()方法设置接口返回类型
	public static void setReturnType(Class returnType){
        feignReturnTypeThreadLocal.set(returnType);
    }
    
    // 重写Decode
    @Override
    public Object decode(Response response, Type type) throws IOException, DecodeException, FeignException {
    	try{
	        if (response.body() == null) {
	            throw new DecodeException(response.status(), "no data response");
	        }
	        Class returnType=feignReturnTypeThreadLocal.get();
	        String bodyStr = Util.toString(response.body().asReader(Util.UTF_8));
	        return JSON.parseObject(bodyStr,returnType);
	    } catch (Exception e) {
            log.error("GenericsFeignResultDecoder.decode error", e);
        }finally {
            feignReturnTypeThreadLocal.remove();
        }
        return null;
    }
}

2、定义一个CustomizedConfiguration类,用于包装GenericsFeignResultDecoder实例,用configuration属性为Feign指定自当前配置类。

@FeignClient(name = "demoFeign", url = "${config.demo.domain}", configuration = CustomizedConfiguration.class)
public interface DemoFeign {

    @PostMapping(value = "/open/post")
    public <R extends BaseResponse, T extends BaseRequest> R invoke(@RequestBody T request);
    
    public class CustomizedConfiguration{
        @Bean
        public Decoder feignDecoder() {
            return new GenericsFeignResultDecoder();
        }
        @Bean
        @Scope("prototype")
        public Feign.Builder feignBuilder() {
            return Feign.builder();

        }
    }
}

如果要为当前Spring容器管理的所有Feign都指定这个解码器,就把CustomizedConfiguration类挪到Feign接口外面,再加@Configuration,我这里为了方便就写到Feign接口里了;如果只是为一个Feign Client指定自定义的解码器,GenericsFeignResultDecoder就不要加Spring注解(不要被Spring管理)了,否则就成了全局的了。

调用Feign的时候,需要先设置Feign接口返回的具体类型,这里通过ThreadLocal来传递Feign接口返回值的具体类型,在调用前把返回值类型放在ThreadLocal中,调用完再remove掉。

需要注意的是,用这种方法需要设置Hystrix的隔离策略为信号量隔离(默认为线程隔离),或者为当前FeignClient禁止Hystrix,上面的代码就为DemoFeign禁止了Hystrix。

调用Feign

@Service
public class DemoService{

	@Autowired
	private DemoFeign demoFeign;

    public void function01(Request01 request){
		GenericsFeignResultDecoder.setReturnType(Response01.class);
		Response01 response=demoFeign.invoke(request);
		// ……
	}

    public void function02(Request02 request){
		GenericsFeignResultDecoder.setReturnType(Response02.class);
		Response02 response=demoFeign.invoke(request);
		// ……
	}

}

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