STRA

외부 API를 Spring RestTemplate로 호출하는데

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: 

Can not instantiate value of type java.util.HashMap from String value ('fail'); no single-String constructor/factory method

위의 Exception이 발생.

restTemplate.exchange에 세팅한 responseType class는 아래의 

TestResponse.java

package kr.co.sbs20011.jackson.model; import java.util.HashMap; import org.apache.commons.lang.builder.ToStringBuilder; import org.apache.commons.lang.builder.ToStringStyle; import com.fasterxml.jackson.annotation.JsonIgnoreProperties; import lombok.Data; @Data @JsonIgnoreProperties(ignoreUnknown = true) public class TestResponse { private HashMap<String, Object> result; }

API 호출 class

ApiTest.java

package kr.co.sbs20011.jackson.service; import javax.inject.Inject; import org.springframework.http.HttpEntity; import org.springframework.http.HttpHeaders; import org.springframework.http.HttpMethod; import org.springframework.http.ResponseEntity; import org.springframework.stereotype.Component; import org.springframework.web.client.RestTemplate; import com.fasterxml.jackson.databind.ObjectMapper; import kr.co.sbs20011.jackson.model.TestResponse; @Component public class ApiTest { @Inject RestTemplate restTemplate; public TestResponse callApi(){ try { HttpHeaders headers = new HttpHeaders(); headers.add("content-type", "application/json"); HttpEntity entity = new HttpEntity(headers); ResponseEntity<TestResponse> response = restTemplate.exchange("https://api.test.com/post", HttpMethod.POST, entity, TestResponse.class); // 이 부분에서 에러 발생 return response.getBody(); } catch(Exception e) { e.printStackTrace(); } } }

외부 API에서 응답 데이터를

{ "result": { "code" : "200", "msg" : "success" } }

위 처럼 넘겨줄 때는 정상적으로 변환되어 TestResponse의 HashMap<String, Object> result에 세팅되나,

아래와 같이 response가 오게되면

{ "result": "fail" }

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: 

Can not instantiate value of type java.util.HashMap from String value ('fail'); no single-String constructor/factory method

위 에러 발생(HashMap에 "fail" 이라는 String value 값을 세팅할 수 없다(?))

외부 API를 수정할 수 없어(?) 서버쪽에서 변환 시 예외 처리를 하도록 함.

CustomDeserializer.java

package kr.co.sbs20011.jackson.service; import java.io.IOException; import java.util.HashMap; import org.springframework.util.StringUtils; import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.core.JsonToken; import com.fasterxml.jackson.core.type.TypeReference; import com.fasterxml.jackson.databind.DeserializationContext; import com.fasterxml.jackson.databind.JsonDeserializer; public class CustomDeserializer extends JsonDeserializer<HashMap<String, Object>> { @Override public HashMap<String, Object> deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException { HashMap<String, Object> resultMap = new HashMap<String, Object>(); JsonToken jsonToken = jp.getCurrentToken(); if(jsonToken == JsonToken.VALUE_STRING) { // result가 String 형태이면 HashMap에 해당 값 추가하여 전달 ex) {"result" : "OK"} if(!StringUtils.isEmpty(jp.getValueAsString())) { resultMap.put("msg", jp.getValueAsString()); } return resultMap; }else if(jsonToken == JsonToken.START_OBJECT){ // result가 Object 형태 '{' 로 시작 ex) {"result" : { "code" : "200", msg : "success" }} return jp.readValueAs(new TypeReference<HashMap<String, Object>>(){}); }else { return null; } } }

생성한 CustomDeserializer를 TestResponse에 설정

TestResponse.java

package kr.co.sbs20011.jackson.model; import java.util.HashMap; import org.apache.commons.lang.builder.ToStringBuilder; import org.apache.commons.lang.builder.ToStringStyle; import com.fasterxml.jackson.annotation.JsonIgnoreProperties; import com.fasterxml.jackson.databind.annotation.JsonDeserialize; import kr.co.sbs20011.jackson.service.CustomDeserializer; import lombok.Data; @Data @JsonIgnoreProperties(ignoreUnknown = true) public class TestResponse { @JsonDeserialize(using = CustomDeserializer.class) // deserialize 할 때, CustomDeserializer를 사용하도록 함 private HashMap<String, Object> result; }

이제 {"result":"success"} 형태도 받을 수 있음.

result.get("msg").toString() == "success"