Develop Reference

How to use Jawampa (Java WAMP implementation) to subcribe to an event

i want to use the poloniex API. https://poloniex.com/support/api/
So far i made Jawampa ( https://github.com/Matthias247/jawampa ) running with IntelliJ.
My first Question is, how to login successfuly? (The Docu of Jawampa doesnt help)
I got a API Key and a Secret. Which functions i have to use in the builder of Jawampa:
withRealm
withRoles
withConnectorProvider
withConnectionConfiguration
withSerializations
withStrictUriValidation
withAuthId
withAuthMethod
withObjectMapper
I have so far this code
try {
WampClientBuilder builder = new WampClientBuilder();
builder.withConnectorProvider(connectorProvider)
.withUri("wss://api.poloniex.com")
.withAuthId("APIKEY")
.withRealm("realm2")
.withInfiniteReconnects()
.withReconnectInterval(1, TimeUnit.SECONDS);
client1 = builder.build();
} catch (Exception e) {
e.printStackTrace();
return;
}
Is wss://api.poloniex.com correct or should i use wss://api.poloniex.com/returnTicker for that client?
Do I have to make always a new client for every URI?
Thank you so much in advance.

My first Question is, how to login successfuly?
You don't have to authenticate to access Poloniex Push API via WAMP protocol. Push API methods are public, so you don't have to supply the API key and secret. Just connect to wss://api.poloniex.com and subscribe to a desired feed (Ticker, Order Book and Trades, Trollbox).
Btw, you need to supply the API Key only with Trading API methods. And the Secret is used to sign a POST data.
Which functions i have to use in the builder of Jawampa:
This is how you connect to the Push API:
WampClient client;
try {
WampClientBuilder builder = new WampClientBuilder();
IWampConnectorProvider connectorProvider = new NettyWampClientConnectorProvider();
builder.withConnectorProvider(connectorProvider)
.withUri("wss://api.poloniex.com")
.withRealm("realm1")
.withInfiniteReconnects()
.withReconnectInterval(5, TimeUnit.SECONDS);
client = builder.build();
} catch (Exception e) {
return;
}
Once your client is connected, you subscribe to a feed like this:
client.statusChanged().subscribe(new Action1<WampClient.State>() {
#Override
public void call(WampClient.State t1) {
if (t1 instanceof WampClient.ConnectedState) {
subscription = client.makeSubscription("trollbox")
.subscribe((s) -> { System.out.println(s.arguments()); }
}
}
});
client.open();
Is wss://api.poloniex.com correct or should i use
wss://api.poloniex.com/returnTicker for that client?
wss://api.poloniex.com is correct. Besides, returnTicker belongs to the Public API and is accessed via HTTP GET requests.
Do I have to make always a new client for every URI?
In respect to the Push API, once you connected a client to wss://api.poloniex.com, you can use this client to make subscriptions to multiple feeds. For example:
client.statusChanged().subscribe(new Action1<WampClient.State>() {
#Override
public void call(WampClient.State t1) {
if (t1 instanceof WampClient.ConnectedState) {
client.makeSubscription("trollbox")
.subscribe((s) -> { System.out.println(s.arguments()); });
client.makeSubscription("ticker")
.subscribe((s) -> { System.out.println(s.arguments()); });
}
}
});
However, according to Jawampa Docs:
After a WampClient was closed it can not be reopened again. Instead of this a new instance of the WampClient should be created if necessary.

Logging exceptions in Windows Service with WinRun4j

I have been trying to get a Windows service running from my JAR file. WinRun4j seems to be able to do the job, but I can't get it to work. I am especially finding it quite difficult to debug. I tried several methods for logging (writing to a .txt file, WinRun4j's EventLog class) but I can't seem to generate any output.
The service installs fine (eventually..) and I can start it. It should start a Jetty server that generates an XML file that can be reached over HTTP. The app works for a stand-alone version, just not for the service. The service is started, but as soon as I call the URL it stops without generating an error.
This is my Service class:
package com.some.package;
import org.boris.winrun4j.AbstractService;
import org.boris.winrun4j.ServiceException;
/**
* A basic service.
*/
public class StockService extends AbstractService {
private StockServer srv;
public int serviceMain(String[] args) throws ServiceException {
while (!shutdown) {
try {
Thread.sleep(5000);
} catch(InterruptedException e) {
}
if(srv == null) {
try {
srv = new StockServer();
srv.start();
} catch (Exception e) {
}
}
}
return 0;
}
}
I found out that the service didn't want to start if I started the Jetty server from the serviceMain class. I had to start a new thread. So StockServer extends Thread:
public class StockServer extends Thread {
private Server server;
public void run() {
if (server == null) {
try {
server = new Server(8080);
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/example");
StockServlet stockServlet = new StockServlet();
context.addServlet(new ServletHolder(stockServlet), "/stock/*");
server.setHandler(context);
server.setStopAtShutdown(true);
server.start();
server.join();
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
}
Since it runs perfectly fine as Java application I just don't know how to get this thing debugged. I hope one of you can point me in the right direction :).

I ended up using the Java Service Wrapper (JSW). This seemed a lot more complex but ended up to be quite easy. It also provides logging by default so I could easily fix the errors. The JSW had problems finding the correct JDK, since JSW is 32bit and I installed JDK1.7 64 bit (and 1.6 32bit). Installing JDK1.7 32bit fixed it. That might have been the problem with WinRun4j as well, but that is something I will never know :).

What can be the best approach to handle java.net.UnknownHostException for AWS users?

My application sends message to Amazon Simple Notification Service (SNS) topic but sometime (6/10) I get java.net.UnknownHostException:sqs.ap-southeast-1.amazonaws.com. The reason of exception is described in the amazon web services discussion forums, please look: https://forums.aws.amazon.com/thread.jspa?messageID=499290&#499290.
My problem is similar to what described in forums of amazon but my rate of publishing messages to topic is very dynamic. It can be 1 message/second or 1 message/minute or no message in an hour. I am looking for a cleaner, better and safe approach, which guaranties sending of message to SNS topic.
Description of problem in detail:
Topic_Arn= arn of SNS topic where application wants to publish message
msg = Message to send in topic
// Just a sample example which publish message to Amazon SNS topic
class SimpleNotificationService {
AmazonSNSClient mSnsClient = null;
static {
createSnsClient()
}
private void static createSnsClient() {
Region region = Region.getRegion(Regions.AP_SOUTHEAST_1);
AWSCredentials credentials = new
BasicAWSCredentials(AwsPropertyLoader.getInstance().getAccessKey(),
AwsPropertyLoader.getInstance().getSecretKey());
mSqsClient = new AmazonSQSClient(credentials);
mSqsClient.setRegion(region);
}
public void static publishMessage(String Topic_Arn, String msg) {
PublishRequest req = new PublishRequest(Topic_Arn, msg);
mSnsClient.publish(req);
}
}
class which calls SimpleNotificationService
class MessagingManager {
public void sendMessage(String message) {
String topic_arn = "arn:of:amazon:sns:topic";
SimpleNotificationService.publishMessage(topic_arn, message);
}
}
Please note that this is a sample code, not my actual code. Here can be class design issue but please ignore those if they are not related to problem.
My thought process says to have try-catch block inside sendMessage, so when we catch UnknownHostException then again retry but I am not sure how to write this in safer, cleaner and better way.
So MessagingManager class will look something like this:
class MessagingManager {
public void sendMessage(String message) {
String topic_arn = "arn:of:amazon:sns:topic";
try {
SimpleNotificationService.publishMessage(topic_arn, message);
} catch (UnknownHostException uhe) {
// I need to catch AmazonClientException as aws throws
//AmazonClientException when sees UnknownHostException.
// I am mentioning UnknownHostException for non-aws user to understand
// my problem in better way.
sendMessage(message); // Isn't unsafe? - may falls into infinite loop
}
}
}
I am open for answers like this: java.net.UnknownHostException: Invalid hostname for server: local but my concern is to dependent on solution at application code-level and less dependent on changes to machine. As my server application is going to run in many boxes (developer boxes, testing boxes or production boxes). If changes in machine host-files or etc is only guaranted solution then I prefer that to include with code level changes.

Each AWS SDK implements automatic retry logic. The AWS SDK for Java automatically retries requests, and you can configure the retry settings using the ClientConfiguration class.
Below is the sample example to create SNS client. It retries for 25 times if encounters UnKnownHostException. It uses default BackOff and retry strategy. If you want to have your own then you need to implement these two interfaces: http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/retry/RetryPolicy.html
private void static createSnsClient() {
Region region = Region.getRegion(Regions.AP_SOUTHEAST_1);
AWSCredentials credentials = new
BasicAWSCredentials(AwsPropertyLoader.getInstance().getAccessKey(),
AwsPropertyLoader.getInstance().getSecretKey());
ClientConfiguration clientConfiguration = new ClientConfiguration();
clientConfiguration.setMaxErrorRetry(25);
clientConfiguration.setRetryPolicy(new RetryPolicy(null, null, 25, true));
mSnsClient = new AmazonSNSClient(credentials, clientConfiguration);
mSnsClient.setRegion(region);
}

Have you considering looking into the JVM TTL for the DNS Cache?
http://docs.aws.amazon.com/AWSSdkDocsJava/latest//DeveloperGuide/java-dg-jvm-ttl.html

Tesseract implementing a web service to trigger OCR actions

I am trying to implement a web service which triggers OCR actions of the server side.
Client code:
...
sy = belgeArsivle(testServisIstegi, ab);
...
private static ServisYaniti belgeArsivle(com.ocr.ws.ServiceRequest serviceRequest,com.ocr.ws.Document document) {
com.ocr.ws.ServiceRequest service = new com.ocr.ws.OCRArsivWSService();
com.ocr.ws.OCRArsivWS port = service.getOCRArsivWSPort();
return port.docArchive(serviceRequest, document);
}
When I run the code on the server side there is no problem. But whenever I call the web service method from the client I got this error code:
Exception: javax.xml.ws.soap.SOAPFaultException: Unable to load library 'libtesseract302': The specified module could not be found.
The working server-side code is:
public static void main(String[] args) {
// TODO code application logic here
File imageFile = new File("...OCR\\testTurWithBarcodeScanned.png");
Tesseract instance = Tesseract.getInstance();
try {
String lang = "tur";
instance.setLanguage(lang);
String result = instance.doOCR(imageFile);
System.out.println(result);
// write in a file
try {
File file = new File("...MyOutputWithBarcode.txt");
BufferedWriter out = new BufferedWriter(new FileWriter(file));
out.write(result);
out.close();
} catch (IOException ex) {
}
} catch (TesseractException ep) {
System.err.println(ep.getMessage());
}
}
I know that this error code is about Tesseract libraries. I put the corresponding .dll files (liblept168 and libtesseract302) under the client project's folder, added corresponding libraries (jna, jai_imageio, ghost4j_0.3.1), did neccessary changes in classpath but still getting this error.
I run a test code on the server side, it works fine. But the client side code is not working. Do I need to make some extra adjustment on the client side to run this web service?

I found out that the actual problem was with the Tomcat Server. I had to put the jar files to the Tomcat's Sources under Properties, than voila!

BlazeDS - AMFConnection.call giving HTTP 400 status

I'm trying to use BlazeDS's AMFConnection class to connect to pyamf, but when I call AMFConnection.call(), I get HTTP status 400 (Bad Request - "The request body was unable to be successfully decoded."). I'm more or less following this example: (pyamf.org/wiki/ClientHowTo ... sorry, I'm a new user so I guess I can't use hyperlinks. append a "http://" to those if you want to follow them)
Here's my code:
package amfconnectiontest;
import flex.messaging.io.amf.client.AMFConnection;
import flex.messaging.io.amf.client.exceptions.*;
public class Main {
public static void main(String[] args) {
AMFConnection amfConnection = new AMFConnection();
String url = "http://demo.pyamf.org/gateway/recordset";
String service = "service.getLanguages";
try
{
amfConnection.connect(url);
}
catch (ClientStatusException cse)
{
System.out.println(cse);
return;
}
// Make a remoting call and retrieve the result.
try
{
Object result = amfConnection.call(service);
System.out.println("results: " + result.toString());
}
catch (ClientStatusException cse)
{
System.out.println(cse);
}
catch (ServerStatusException sse)
{
System.out.println(sse);
}
// Close the connection.
amfConnection.close();
}
}
Any ideas?

The ability to en/decode BlazeDS specific messages (implementing ISmallMessage) has landed on the PyAMF trunk (r2726 and up). See the related ticket - http://pyamf.org/ticket/581
This version or one very similar is likely to become 0.5. If you need to connect to a BlazeDS service I would suggest checking out the trunk.