Send JSON data in an HTTP GET request to a REST AP

Question

I am making the following curl request successfully to my API:

curl -v -X GET -H "Content-Type: application/json" -d {'"query":"some text","mode":"0"'} http://host.domain.abc.com:23423/api/start-trial-api/

I would like to know how can i make this request from inside JAVA code. I have tried searching through Google and stack overflow for the solution. All i have found is how to send data through a query string or how to send JSON data through a POST request.

Thanks

Answer 1

Spring's RESTTemplate is also useful for sending all REST requests i.e. GET , PUT , POST , DELETE

By using Spring REST template, You can pass JSON request with POST like below,

You can pass JSON representation serialized into java Object using JSON serializer such as jackson

RestTemplate restTemplate = new RestTemplate();
List<HttpMessageConverter<?>> list = new ArrayList<HttpMessageConverter<?>>();
list.add(new MappingJacksonHttpMessageConverter());
restTemplate.setMessageConverters(list);
Person person = new Person();
String url = "http://localhost:8080/add";
HttpEntity<Person> entity = new HttpEntity<Person>(person);

// Call to Restful web services with person serialized as object using jackson
ResponseEntity<Person> response = restTemplate.postForEntity(  url, entity, Person.class);
Person person = response.getBody();

Answer 2

Using below code you should be able to invoke any rest API.

Make a class called RestClient.java which will have method for get and post

package test;

import java.io.IOException;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

import com.javamad.utils.JsonUtils;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;

public class RestClient {

    public static <T> T post(String url,T data,T t){
        try {
        Client client = Client.create();
        WebResource webResource = client.resource(url);
        ClientResponse response = webResource.type("application/json").post(ClientResponse.class, JsonUtils.javaToJson(data));

        if (response.getStatus() != 200) {
            throw new RuntimeException("Failed : HTTP error code : "
                 + response.getStatus());
        }
        String output = response.getEntity(String.class);
        System.out.println("Response===post="+output);

            t=(T)JsonUtils.jsonToJavaObject(output, t.getClass());
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return t;
    }
    public static <T> T get(String url,T t)
    {
         try {
        Client client = Client.create();

        WebResource webResource = client.resource(url);

        ClientResponse response = webResource.accept("application/json").get(ClientResponse.class);

        if (response.getStatus() != 200) {
           throw new RuntimeException("Failed : HTTP error code : "
            + response.getStatus());
        }

        String output = response.getEntity(String.class);
        System.out.println("Response===get="+output);



            t=(T)JsonUtils.jsonToJavaObject(output, t.getClass());
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return t;
    }

}

invoke the get and post method

public class QuestionAnswerService {
    static String baseUrl="http://javamad.com/javamad-webservices-1.0";

    //final String baseUrl="http://javamad.com/javamad-webservices-1.0";
    @Test
    public void getQuestions(){
        System.out.println("javamad.baseurl="+baseUrl);
        GetQuestionResponse gqResponse=new GetQuestionResponse();

        gqResponse =RestClient.get(baseUrl+"/v1/questionAnswerService/getQuestions?questionType=2",gqResponse);


        List qList=new ArrayList<QuestionDetails>();
        qList=(List) gqResponse.getQuestionList();

        //System.out.println(gqResponse);

    }

    public void postQuestions(){
        PostQuestionResponse pqResponse=new PostQuestionResponse();
        PostQuestionRequest pqRequest=new PostQuestionRequest();
        pqRequest.setQuestion("maybe working");
        pqRequest.setQuestionType("2");
        pqRequest.setUser_id("2");
        //Map m= new HashMap();
        pqResponse =(PostQuestionResponse) RestClient.post(baseUrl+"/v1/questionAnswerService/postQuestion",pqRequest,pqResponse);

    }

    }

Make your own Request and response class.

for json to java and java to json use below class

package com.javamad.utils;

import java.io.IOException;

import org.apache.log4j.Logger;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

public class JsonUtils {

    private static Logger logger = Logger.getLogger(JsonUtils.class.getName());


    public static <T> T jsonToJavaObject(String jsonRequest, Class<T> valueType)
            throws JsonParseException, JsonMappingException, IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.configure(org.codehaus.jackson.map.DeserializationConfig.Feature.UNWRAP_ROOT_VALUE,false);     
        T finalJavaRequest = objectMapper.readValue(jsonRequest, valueType);
        return finalJavaRequest;

    }

    public static String javaToJson(Object o) {
        String jsonString = null;
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.configure(org.codehaus.jackson.map.DeserializationConfig.Feature.UNWRAP_ROOT_VALUE,true);  
            jsonString = objectMapper.writeValueAsString(o);

        } catch (JsonGenerationException e) {
            logger.error(e);
        } catch (JsonMappingException e) {
            logger.error(e);
        } catch (IOException e) {
            logger.error(e);
        }
        return jsonString;
    }

}

I wrote the RestClient.java class , to reuse the get and post methods. similarly you can write other methods like put and delete...

Hope it will help you.

Answer 3

You could use the Jersey client library, if your project is a Maven one just include in your pom.xml the jersey-client and jersey-json artifacts from the com.sun.jersey group id. To connect to a web service you need a WebResource object:

WebResource resource = ClientHelper.createClient().resource(UriBuilder.fromUri("http://host.domain.abc.com:23423/api/").build());

To make a call sending a payload you can model the payload as a POJO, i.e.

class Payload {
    private String query;
    private int mode;

    ... get and set methods
}

and then call the call using the resource object:

Payload payload = new Payload();

payload.setQuery("some text"); payload.setMode(0);

ResultType result = service  
    .path("start-trial-api").  
    .type(MediaType.APPLICATION_JSON)  
    .accept(MediaType.APPLICATION_JSON)  
    .get(ResultType.class, payload);

where ResultType is the Java mapped return type of the called service, in case it's a JSON object, otherwise you can remove the accept call and just put String.class as the get parameter and assign the return value to a plain string.