Generic RestTemplate wrapper

RestTemplateHelper.java

import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.CollectionType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Component;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.RestClientException;
import org.springframework.web.client.RestTemplate;

import java.io.IOException;
import java.util.List;

@Component
public class RestTemplateHelper {

    private static final Logger LOGGER = LoggerFactory.getLogger(RestTemplateHelper.class);

    private RestTemplate restTemplate;
    private ObjectMapper objectMapper;

    @Autowired
    public RestTemplateHelper(RestTemplateBuilder restTemplateBuilder, ObjectMapper objectMapper) {
        this.restTemplate = restTemplateBuilder.build();
        this.objectMapper = objectMapper;
    }

    public <T> T getForEntity(Class<T> clazz, String url, Object... uriVariables) {
        try {
            ResponseEntity<String> response = restTemplate.getForEntity(url, String.class, uriVariables);
            JavaType javaType = objectMapper.getTypeFactory().constructType(clazz);
            return readValue(response, javaType);
        } catch (HttpClientErrorException exception) {
            if (exception.getStatusCode() == HttpStatus.NOT_FOUND) {
                LOGGER.info("No data found {}", url);
            } else {
                LOGGER.info("rest client exception", exception.getMessage());
            }
        }
        return null;
    }

    public <T> List<T> getForList(Class<T> clazz, String url, Object... uriVariables) {
        try {
            ResponseEntity<String> response = restTemplate.getForEntity(url, String.class, uriVariables);
            CollectionType collectionType = objectMapper.getTypeFactory().constructCollectionType(List.class, clazz);
            return readValue(response, collectionType);
        } catch (HttpClientErrorException exception) {
            if (exception.getStatusCode() == HttpStatus.NOT_FOUND) {
                LOGGER.info("No data found {}", url);
            } else {
                LOGGER.info("rest client exception", exception.getMessage());
            }
        }
        return null;
    }

    public <T, R> T postForEntity(Class<T> clazz, String url, R body, Object... uriVariables) {
        HttpEntity<R> request = new HttpEntity<>(body);
        ResponseEntity<String> response = restTemplate.postForEntity(url, request, String.class, uriVariables);
        JavaType javaType = objectMapper.getTypeFactory().constructType(clazz);
        return readValue(response, javaType);
    }

    public <T, R> T putForEntity(Class<T> clazz, String url, R body, Object... uriVariables) {
        HttpEntity<R> request = new HttpEntity<>(body);
        ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.PUT, request, String.class, uriVariables);
        JavaType javaType = objectMapper.getTypeFactory().constructType(clazz);
        return readValue(response, javaType);
    }

    public void delete(String url, Object... uriVariables) {
        try {
            restTemplate.delete(url, uriVariables);
        } catch (RestClientException exception) {
            LOGGER.info(exception.getMessage());
        }
    }

    private <T> T readValue(ResponseEntity<String> response, JavaType javaType) {
        T result = null;
        if (response.getStatusCode() == HttpStatus.OK ||
                response.getStatusCode() == HttpStatus.CREATED) {
            try {
                result = objectMapper.readValue(response.getBody(), javaType);
            } catch (IOException e) {
                LOGGER.info(e.getMessage());
            }
        } else {
            LOGGER.info("No data found {}", response.getStatusCode());
        }
        return result;
    }

}

RestTemplateUsage.java

private RestTemplateHelper restTemplateHelper;

// other codes...

// find by id
UserDto userDto = restTemplateHelper.getForEntity(UserDto.class, "http://localhost:8080/users/{id}", id);

// find all
UserDto userDto = restTemplateHelper.getForList(UserDto.class, "http://localhost:8080/users");

// save
UserDto userDto = restTemplateHelper.postForEntity(UserDto.class, "http://localhost:8080/users", userDto);
                                                   
// update
UserDto userDto = restTemplateHelper.putForEntity(UserDto.class, "http://localhost:8080/users/{id}", userDto, id);

// delete
restTemplateHelper.delete("http://localhost:8080/users/{id}", id);

Great!!!

Hello! I'm trying to consume an API, and found its wrapper class, the api I'm consuming has a complex JSON
https://bittrex.com/api/v1.1/public/getmarkets
so I have a model with generics ApiResult that has the attributes success, message and T result how to use your wrapper and for this Pojo?
ApiResult apiResult

Thank you
Robson C

Good job!

Nice one :)

Thank you!!!!!!!!!!!!!!!!!!!!!!
You've saved my life.

Great! I found this very useful

Great!
Thanks!

Maybe someone have exchange implementation?

Maybe someone have exchange implementation?

restTemplate.exchange(url, HttpMethod.GET, new HttpEntity<>(headers), String.class);

If you want to return something like ResponseWrapper<T> you can use this:

 public <T> ListWrapperDTO<T> getForWrapper(String url, HttpHeaders headers,  Class<T> clazz) {
        return restTemplate.exchange(url, HttpMethod.GET, new HttpEntity<>(headers),
                new ParameterizedTypeReference<ListWrapperDTO<T>>() {
                    public Type getType() {
                        return new CustomParameterizedType((ParameterizedType) super.getType(), new Type[]{clazz});
                    }
                }
        ).getBody();
    }

where

class CustomParameterizedType implements ParameterizedType {
    private final ParameterizedType delegate;
    private final Type[] actualTypeArguments;
    
    CustomParameterizedType(ParameterizedType delegate, Type[] actualTypeArguments) {
        this.delegate = delegate;
        this.actualTypeArguments = actualTypeArguments;
    }
    
    @Override
    public Type[] getActualTypeArguments() {
        return actualTypeArguments;
    }
    
    @Override
    public Type getRawType() {
        return delegate.getRawType();
    }
    
    @Override
    public Type getOwnerType() {
        return delegate.getOwnerType();
    }
    
}