Parse data from embedded generics in Java

[supereagle]

When design REST APIs, two points should be considered:

• There are enough informations for client, include code, message, data and so on.
• The response format for ALL APIs is unified.

The response from ALL APIs with the same format, but with different fields (empty will be omitted in some case) and data type/struct. So we need to correctly parse the data from the response. Here is an example implemented in Java.

[supereagle]

User.java

package com.generic.demo;

public class User {
    private String username;
    private int age;
    private String address;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

Result.java

package com.generic.demo;

import java.io.Serializable;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;

public class Result<T> implements Serializable {
    private static final long serialVersionUID = 1L;

    @JsonProperty("message")
    private String msg;

    @JsonProperty("data")
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private T t;

    private long code;

    @JsonInclude(JsonInclude.Include.NON_NULL)
    private String errorCode;

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public T getT() {
        return t;
    }

    public void setT(T t) {
        this.t = t;
    }

    public long getCode() {
        return code;
    }

    public void setCode(long code) {
        this.code = code;
    }

    public String getErrorCode() {
        return errorCode;
    }

    public void setErrorCode(String errorCode) {
        this.errorCode = errorCode;
    }
}

[supereagle]

EmbeddedGenericTest.java

package com.generic.demo;

import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.junit.Assert;
import org.junit.Test;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class EmbeddedGenericTest {

    private final static Log LOGGER = LogFactory.getLog(EmbeddedGenericTest.class);

    protected final ObjectMapper mapper = new ObjectMapper();

    protected RestTemplate template = new RestTemplate();

    @Test
    public void testParseDataFromResponse() {
        String tokenUrl = "http://example.auth.com?username=robin";

        // Test GET request for user
        MultiValueMap<String, String> headers = new LinkedMultiValueMap<String, String>();
        headers.add("Authorization", "Basic abcdefg123456");
        HttpEntity<User> requestWithAuthorization = new HttpEntity<User>(null, headers);
        ResponseEntity<Result> response = template.exchange(tokenUrl, HttpMethod.GET, requestWithAuthorization,
                Result.class);

        // Check the response and parse user from it
        User user = EmbeddedGeneric.parseDataFromResponse(response, User.class);
        if (user == null) {
            Assert.fail("Fail to parse data from response");
        }
    }

    public <T> T parseDataFromResponse(ResponseEntity<Result> response, Class<T> dataType) {
        if (HttpStatus.OK != response.getStatusCode()) {
            LOGGER.error("Error: respose status code is no 200, as " + response.getStatusCode());
            return null;
        }

        if (response.getBody().getCode() != 0) {
            LOGGER.error("Error: respose code is not 0, as " + response.getStatusCode());
            return null;
        }

        try {
            return mapper.readValue(mapper.writeValueAsString(response.getBody().getT()), dataType);
        } catch (JsonParseException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }
}