/*
 * http://localhost:8080/AppContext
 */
String host = "localhost";
int port = 8080;
String uri = "/AppContext";

// Create a client
HohRawClientSimple client = new HohRawClientSimple(host, port, uri);

// Optionally, if credentials should be sent, they 
// can be provided using a credential callback
IAuthorizationClientCallback authCalback = new SingleCredentialClientCallback("ausername", "somepassword");
client.setAuthorizationCallback(authCalback);

// The ISendable defines the object that provides the actual
// message to send
String message = 
	"MSH|^~\\&|||||200803051508||ADT^A31|2|P|2.5\r" + 
	"EVN||200803051509\r" + 
	"PID|||ZZZZZZ83M64Z148R^^^SSN^SSN^^20070103\r";
ISendable sendable = new RawSendable(message);

try {
	// sendAndReceive actually sends the message
	IReceivable<String> receivable = client.sendAndReceive(sendable);
	
	// receivavle.getRawMessage() provides the response
	System.out.println("Response was:\n" + receivable.getRawMessage());
	
	// IReceivable also stores metadata about the message
	String remoteHostIp = (String) receivable.getMetadata().get(MessageMetadataKeys.REMOTE_HOST_ADDRESS);
	System.out.println("From:\n" + remoteHostIp);
	
} catch (DecodeException e) {
	// Thrown if the response can't be read
	e.printStackTrace();
} catch (IOException e) {
	// Thrown if communication fails
	e.printStackTrace();
} catch (EncodeException e) {
	// Thrown if the message can't be encoded (generally a programming bug)
	e.printStackTrace();
}
	    	

/**
 * This class illustrates an example HL7 over HTTP
 * raw message servlet for receiving and responding to messages
 */
public class ExampleRawHl7OverHttpServlet extends HohRawServlet {

	/**
	 * Constructor
	 */
	public ExampleRawHl7OverHttpServlet() {
		
		/*
		 * The servlet must be provided an implementation
		 * of IMessageHandler<String>, such as the one which
		 * is nested below
		 */
		setMessageHandler(new ExampleMessageHandler());
		
		/* 
		 * Optionally, if we want to verify HTTP authentication,
		 * we can specify an authorization callback
		 */
		IAuthorizationServerCallback callback = 
		   new SingleCredentialServerCallback("someusername", "apassword");
		setAuthorizationCallback(callback);
		
	}

	/**
	 * IMessageHandler defines the interface for the class which receives
	 * and processes messages which come in
	 */
	private static class ExampleMessageHandler implements IMessageHandler<String> {

		/**
		 * This method is fired every time a message is received. The return value
		 * contains the HL7 response value 
		 */
		public IResponseSendable<String> messageReceived(IReceivable<String> theReceived) 
		        throws MessageProcessingException {
			
			String incomingRawMsg = theReceived.getRawMessage();
			System.out.println("Received message:\n" + incomingRawMsg);
			
			// ... do some processing ...
			
			/*
			 * Your application should generate an appropriate 
			 * HL7 ACK message here
			 */
			String ack = "MSH|....."; 
			
			/*
			 * If something goes horribly wrong, you can throw an 
			 * exception and an HTTP 500 error will be generated.
			 * However, it is preferable to return a normal HL7 ACK 
			 * message with an "AE" response code to note an error. 
			 */
			boolean somethingFailed = false;
			if (somethingFailed) {
				throw new MessageProcessingException("");
			}
			
			// Return the raw response message
			return new RawSendable(ack);
		}
		
	}
	
}

<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="2.5">
    <servlet>
        <servlet-name>hl7_listener</servlet-name>
        <servlet-class>ca.uhn.hl7v2.examples.hoh.ExampleRawHl7OverHttpServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hl7_listener</servlet-name>
        <url-pattern>/hl7list</url-pattern>
    </servlet-mapping>
</web-app>