How to custom #FeignClient Expander to convert param？ - spring

Question

Feign default expander to convert param：
final class ToStringExpander implements Expander {
#Override
public String expand(Object value) {
return value.toString();
}
}
I want custom it to convert user to support GET param, like this
#FeignClient("xx")
interface UserService{
#RequestMapping(value="/users",method=GET)
public List<User> findBy(#ModelAttribute User user);
}
userService.findBy(user);
What can i do?

Answer 1

First,you must write a expander like ToJsonExpander:
public class ToJsonExpander implements Param.Expander {
private static ObjectMapper objectMapper = new ObjectMapper();
public String expand(Object value) {
try {
return objectMapper.writeValueAsString(value);
} catch (JsonProcessingException e) {
throw new ExpanderException(e);
}
}
}
Second, write a AnnotatedParameterProcessor like JsonArgumentParameterProcessor to add expander for your processor.
public class JsonArgumentParameterProcessor implements AnnotatedParameterProcessor {
private static final Class<JsonArgument> ANNOTATION = JsonArgument.class;
public Class<? extends Annotation> getAnnotationType() {
return ANNOTATION;
}
public boolean processArgument(AnnotatedParameterContext context, Annotation annotation) {
MethodMetadata data = context.getMethodMetadata();
String name = ANNOTATION.cast(annotation).value();
String method = data.template().method();
Util.checkState(Util.emptyToNull(name) != null,
"JsonArgument.value() was empty on parameter %s", context.getParameterIndex());
context.setParameterName(name);
if (method != null && (HttpMethod.POST.matches(method) || HttpMethod.PUT.matches(method) || HttpMethod.DELETE.matches(method))) {
data.formParams().add(name);
} else {
`data.indexToExpanderClass().put(context.getParameterIndex(), ToJsonExpander.class);`
Collection<String> query = context.setTemplateParameter(name, data.template().queries().get(name));
data.template().query(name, query);
}
return true;
}
}
Third,add it to Feign configuration.
#Bean
public Contract feignContract(){
List<AnnotatedParameterProcessor> processors = new ArrayList<>();
processors.add(new JsonArgumentParameterProcessor());
processors.add(new PathVariableParameterProcessor());
processors.add(new RequestHeaderParameterProcessor());
processors.add(new RequestParamParameterProcessor());
return new SpringMvcContract(processors);
}
Now, you can use #JsonArgument to send model argument like:
public void saveV10(#JsonArgument("session") Session session);

Answer 2

I don't know what #ModelAttribute does but I was looking for a way to convert #RequestParam values so I did this:
import com.google.i18n.phonenumbers.PhoneNumberUtil;
import com.google.i18n.phonenumbers.Phonenumber;
import org.springframework.cloud.netflix.feign.FeignFormatterRegistrar;
import org.springframework.format.FormatterRegistry;
import org.springframework.stereotype.Component;
import static com.google.i18n.phonenumbers.PhoneNumberUtil.PhoneNumberFormat.E164;
#Component
public class PhoneNumberFeignFormatterRegistrar implements FeignFormatterRegistrar {
private final PhoneNumberUtil phoneNumberUtil;
public PhoneNumberFeignFormatterRegistrar(PhoneNumberUtil phoneNumberUtil) {
this.phoneNumberUtil = phoneNumberUtil;
}
#Override
public void registerFormatters(FormatterRegistry registry) {
registry.addConverter(Phonenumber.PhoneNumber.class, String.class, source -> phoneNumberUtil.format(source, E164));
}
}
Now stuff like the following works
import com.google.i18n.phonenumbers.Phonenumber;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.hateoas.Resource;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
#FeignClient("data-service")
public interface DataClient {
#RequestMapping(method = RequestMethod.GET, value = "/phoneNumbers/search/findByPhoneNumber")
Resource<PhoneNumberRecord> getPhoneNumber(#RequestParam("phoneNumber") Phonenumber.PhoneNumber phoneNumber);
}

Answer 3

As the open feign issue and spring doc say：
The OpenFeign #QueryMap annotation provides support for POJOs to be used as GET parameter maps.
Spring Cloud OpenFeign provides an equivalent #SpringQueryMap annotation, which is used to annotate a POJO or Map parameter as a query parameter map since 2.1.0.
You can use it like this:
#GetMapping("user")
String getUser(#SpringQueryMap User user);
public class User {
private String name;
private int age;
...
}