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About Harsh Raval

Simple REST client in Java

Today most of the mobile applications that used to communicate to some server use REST services. These services are also common practice to use with JavaScript or jQuery. Right now I know 2 ways to create client for REST service in java and in this article I will try to demonstrate both the ways I know hoping that it will help someone in some way.

1. Using Apache HttpClient

The Apache HttpClient library simplifies handling HTTP requests. To use this library you have to download the binaries with dependencies from their website.
Here is the code for HTTP GET method:

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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  HttpClient client = new DefaultHttpClient();
  HttpGet request = new HttpGet('http://restUrl');
  HttpResponse response = client.execute(request);
  BufferedReader rd = new BufferedReader (new InputStreamReader(response.getEntity().getContent()));
  String line = '';
  while ((line = rd.readLine()) != null) {
    System.out.println(line);
  }
 }
}

And for Post method; for sending simple string in post:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  HttpClient client = new DefaultHttpClient();
  HttpPost post = new HttpPost('http://restUrl');
  StringEntity input = new StringEntity('product');
  post.setEntity(input);
  HttpResponse response = client.execute(post);
  BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
  String line = '';
  while ((line = rd.readLine()) != null) {
   System.out.println(line);
  }
 }
}

You can also send full JSON or XML of a POJO by putting String representing JSON or XML as a parameter of StringEntity and then set the input content type. Something like this:

StringEntity input = new StringEntity('{\'name1\':\'value1\',\'name2\':\'value2\'}'); //here instead of JSON you can also have XML
input.setContentType('application/json');

For JSON you can use JSONObject to create string representation of JSON.

JSONObject json = new JSONObject();
json.put('name1', 'value1');
json.put('name2', 'value2');
StringEntity se = new StringEntity( json.toString());

And for sending multiple parameter in post request:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  HttpClient client = new DefaultHttpClient();
  HttpPost post = new HttpPost('http://restUrl');
  List nameValuePairs = new ArrayList(1);
  nameValuePairs.add(new BasicNameValuePair('name', 'value')); //you can as many name value pair as you want in the list.
  post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
  HttpResponse response = client.execute(post);
  BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
  String line = '';
  while ((line = rd.readLine()) != null) {
   System.out.println(line);
  }
 }
}

2. Using Jersey

Jersey is the reference implementation forJSR-311 specification, the specification of REST support in Java. Jersey contains basically a REST server and a REST client. it provides a library to communicate with the server producing REST services. For http get method:

import java.io.IOException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.UriBuilder;
import org.apache.http.client.ClientProtocolException;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  ClientConfig config = new DefaultClientConfig();
  Client client = Client.create(config);
  WebResource service = client.resource(UriBuilder.fromUri('http://restUrl').build());
  // getting XML data
  System.out.println(service. path('restPath').path('resourcePath').accept(MediaType.APPLICATION_JSON).get(String.class));
  // getting JSON data
  System.out.println(service. path('restPath').path('resourcePath').accept(MediaType.APPLICATION_XML).get(String.class));
 }
}

There are also other media formats in which you can get the response like PLAIN or HTML.
And for HTTP POST method:

import java.io.IOException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.core.UriBuilder;
import org.apache.http.client.ClientProtocolException;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;
import com.sun.jersey.core.util.MultivaluedMapImpl;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  ClientConfig config = new DefaultClientConfig();
  Client client = Client.create(config);
  WebResource webResource = client.resource(UriBuilder.fromUri('http://restUrl').build());
  MultivaluedMap formData = new MultivaluedMapImpl();
  formData.add('name1', 'val1');
  formData.add('name2', 'val2');
  ClientResponse response = webResource.type(MediaType.APPLICATION_FORM_URLENCODED_TYPE).post(ClientResponse.class, formData);
  System.out.println('Response ' + response.getEntity(String.class));
 }
}

If you are using your POJO in the POST then you can do something like following:

ClientResponse response = webResource.path('restPath').path('resourcePath').
type(MediaType.APPLICATION_JSON).accept(MediaType.APPLICATION_JSON).post(ClientResponse.class, myPojo);
System.out.println('Response ' + response.getEntity(String.class));

Here myPojo is an instance of custom POJO class.
You can also use Form class from Jersey to submit multiple parameters in POST request:

import java.io.IOException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.UriBuilder;
import org.apache.http.client.ClientProtocolException;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;
import com.sun.jersey.api.representation.Form;
public class Test {
 public static void main(String[] args) throws ClientProtocolException, IOException {
  ClientConfig config = new DefaultClientConfig();
  Client client = Client.create(config);
  WebResource service = client.resource(UriBuilder.fromUri('http://restUrl').build());
  Form form = new Form();
  form.add('name1', 'value1');
  form.add('name2', 'value1');
  ClientResponse response = service.path('restPath').path('resourcePath').
  type(MediaType.APPLICATION_FORM_URLENCODED).post(ClientResponse.class, form);
  System.out.println('Response ' + response.getEntity(String.class));
 }
}

Happy coding and don’t forget to share!

Reference: Simple REST client in java from our JCG partner Harsh Raval at the harryjoy blog.

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14 comments

  1. The Fluent API which is part of the Http Client 4.x lib is also pretty good

  2. This indeed is helpful. Thanks Harsh.

  3. Your tutorial is really helpful but please give the link of the JAR’s to use along with the code.

  4. Thanks Harsh. It is useful to me

  5. Try looking at http-rest-client

    https://github.com/g00dnatur3/http-rest-client

    Here is a simple example:

    RestClient client = RestClient.builder().build();
    String geocoderUrl = “http://maps.googleapis.com/maps/api/geocode/json”
    Map params = Maps.newHashMap();
    params.put(“address”, “beverly hills 90210”);
    params.put(“sensor”, “false”);
    JsonNode node = client.get(geocoderUrl, params, JsonNode.class);

    Cheers!

  6. In section 2. the line for GET calls in XML and JSON format respectively, seems to have been switched.

  7. Its working ,Code is accurate….

  8. Excellent Post.. one last stop to all query related rest api, Thanks Harsh, Keep posting good technical blog content.

  9. Hi Thanks for the post. Its works just fine. I am using your HTTP get and post.

    In your : ” sending simple string in post: ” How can I send source frame as source data? Thanks

  10. Alchemy-HTTP is a really nice library for making Web calls from Java

    https://github.com/SirWellington/alchemy-http

    From the ReadMe:
    Coffee myCoffee = http.go()
    .get()
    .expecting(Coffee.class)
    .at(“http://aroma.tech/orders?orderNumber=99”);

  11. Hi Thanks for the post. Excellent.

  12. DefaultHttpClient is deprecated.

    It is better to use HttpClientBuilder:

    HttpClient httpClient= HttpClientBuilder.create().build();

  13. Hi!
    It’s a clear post and helpful!
    Thanks a lot!

  14. I am very new to java. Please let me know how to solve the issue . When i try to run below code , I get error import org.apache.http. cannot be resolved. How to overcome this. I have just typed in eclipse

    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;

    import org.apache.http.HttpResponse;
    import org.apache.http.client.ClientProtocolException;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.impl.client.DefaultHttpClient;
    public class myget1 {
    public static void main(String[] args) throws ClientProtocolException, IOException {
    HttpClient client = new DefaultHttpClient();
    HttpGet request = new HttpGet(‘http://restUrl’);
    HttpResponse response = client.execute(request);
    BufferedReader rd = new BufferedReader (new InputStreamReader(response.getEntity().getContent()));
    String line = ”;
    while ((line = rd.readLine()) != null) {
    System.out.println(line);
    }
    }
    }

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