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:

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));
	}
}

Let me know if you find any difficulty while using these code samples. Feel free to comment. 🙂

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SOAP Client in java

If you are looking for java client for RESTful web service then you should visit this article:

Simple REST client in java

This article will teach you how to create a SOAP client in java. That is creating a client in java which requests soap server (no need to be in java) and get response from it. First create request message as follows:

SOAPMessage message = MessageFactory.newInstance().createMessage();
SOAPHeader header = message.getSOAPHeader();
header.detachNode();

If you have namespace required in SOAP request then add those namespaces to envelope element as follows:

SOAPEnvelope envelope = message.getSOAPPart().getEnvelope();
envelope.setAttribute("namspace","namespaceUrl");

You can add as many attribute as you want. Now time to create request message body.
Following body is made assuming that SOAP server where this client will connect will have a public service method called getResponse(name) available.

SOAPBody body = message.getSOAPBody();
QName bodyName = new QName("getResponse");
SOAPBodyElement bodyElement = body.addBodyElement(bodyName);
SOAPElement symbol = bodyElement.addChildElement("name");
symbol.addTextNode(“Harry joy”);

Now that request message is ready it’s time to connect to soap server and send request. Following code will do this:

SOAPConnection connection = SOAPConnectionFactory.newInstance().createConnection();
SOAPMessage response = connection.call(message, endpoint);
connection.close();

In above code endpoint is the SOAP server URL without “?wsdl”. To parse response you can do as follows:

SOAPBody responseBody = response.getSOAPBody();
SOAPBodyElement responseElement = (SOAPBodyElement)responseBody.getChildElements().next();
SOAPElement returnElement = (SOAPElement)responseElement.getChildElements().next();
if(responseBody.getFault() != null) { //-- If response has any fault.
 	System.out.println(returnElement.getValue()+" "+responseBody.getFault().getFaultString());
}  else  {
   	System.out.println(returnElement.getValue());
}

Here request/response messages are totally dependent on SOAP server, how you have configured it.


Bonus: How to print request/response xml?

String getXmlFromSOAPMessage(SOAPMessage msg) throws SOAPException, IOException {
	ByteArrayOutputStream byteArrayOS = new ByteArrayOutputStream();
	msg.writeTo(byteArrayOS);
	return new String(byteArrayOS.toByteArray());
}

Use:

System.out.println(getXmlFromSOAPMessage(message));
System.out.println(getXmlFromSOAPMessage(response));

Full source code:

public class SOAPClient {

	private static final String endpoint = "http://localhost/SOAPService/MySoapService";

	public static void main(String[] args) throws SOAPException {
		SOAPMessage message = MessageFactory.newInstance().createMessage();
		SOAPHeader header = message.getSOAPHeader();
		header.detachNode();

		SOAPEnvelope envelope = message.getSOAPPart().getEnvelope();
		envelope.setAttribute("namespace","namespaceUrl");

		SOAPBody body = message.getSOAPBody();
		QName bodyName = new QName("getResponse");
		SOAPBodyElement bodyElement = body.addBodyElement(bodyName);
		SOAPElement symbol = bodyElement.addChildElement("name");
		symbol.addTextNode("Harry Joy");

		SOAPConnection connection = SOAPConnectionFactory.newInstance().createConnection();
		SOAPMessage response = connection.call(message, endpoint);
		connection.close();

		SOAPBody responseBody = response.getSOAPBody();
		SOAPBodyElement responseElement = (SOAPBodyElement)responseBody.getChildElements().next();
		SOAPElement returnElement = (SOAPElement)responseElement.getChildElements().next();
		if(responseBody.getFault()!=null){
			System.out.println(returnElement.getValue()+" "+responseBody.getFault().getFaultString());
		} else {
			System.out.println(returnElement.getValue());
		}

		try {
			System.out.println(getXmlFromSOAPMessage(message));
			System.out.println(getXmlFromSOAPMessage(response));
		} catch (IOException e) {
			e.printStackTrace();
		}

	}

	private static String getXmlFromSOAPMessage(SOAPMessage msg) throws SOAPException, IOException {
		ByteArrayOutputStream byteArrayOS = new ByteArrayOutputStream();
		msg.writeTo(byteArrayOS);
		return new String(byteArrayOS.toByteArray());
	}

}
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