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Pause message consumption from main kafka stream and start from other kafka topic

I am using #StreamListener (spring cloud stream) to consume messages from a topic (input-channel), do some processing and save into some cache or database.
My requirement is, if DB goes down while processing the consumed message, I want to pause the main consumer(input-channel), and start consuming from another TOPIC (INPUT56-CHANNEL), and as soon as It consume all the message (doesn't have many) from INPUT56-CHANNEL, I want to resume the main consumer (input-channel) again.
Can that be achieved??

#StreamListener is deprecated; you should convert to the functional programming model instead.
Here is an example using that model (but the same techniques apply to the deprecated listeners).
spring.cloud.function.definition=input1;input2
spring.cloud.stream.bindings.input1-in-0.group=grp1
spring.cloud.stream.bindings.input2-in-0.consumer.auto-startup=false
spring.cloud.stream.bindings.input2-in-0.group=grp2
spring.cloud.stream.kafka.bindings.input2-in-0.consumer.idle-event-interval=5000
#SpringBootApplication
public class So69726610Application {
public static void main(String[] args) {
SpringApplication.run(So69726610Application.class, args);
}
boolean dbIsDown = true;
#Autowired
BindingsLifecycleController controller;
TaskExecutor exec = new SimpleAsyncTaskExecutor();
#Bean
public Consumer<String> input1() {
return str -> {
System.out.println(str);
if (this.dbIsDown) {
this.controller.changeState("input1-in-0", State.PAUSED);
this.controller.changeState("input2-in-0", State.STARTED);
throw new RuntimeException("Paused");
}
};
}
#Bean
public Consumer<String> input2() {
return System.out::println;
}
#EventListener
public void idle(ListenerContainerIdleEvent event) {
System.out.println(event);
// assumes concurrency = 1 (default)
if (event.getListenerId().contains("input2-in-0")) {
this.controller.changeState("input1-in-0", State.RESUMED);
this.exec.execute(() -> this.controller.changeState("input2-in-0", State.STOPPED));
}
}
}

Spring Boot: Kafka health indicator

I have something like below which works well, but I would prefer checking health without sending any message, (not only checking socket connection). I know Kafka has something like KafkaHealthIndicator out of the box, does someone have experience or example using it ?
public class KafkaHealthIndicator implements HealthIndicator {
private final Logger log = LoggerFactory.getLogger(KafkaHealthIndicator.class);
private KafkaTemplate<String, String> kafka;
public KafkaHealthIndicator(KafkaTemplate<String, String> kafka) {
this.kafka = kafka;
}
#Override
public Health health() {
try {
kafka.send("kafka-health-indicator", "❥").get(100, TimeUnit.MILLISECONDS);
} catch (InterruptedException | ExecutionException | TimeoutException e) {
return Health.down(e).build();
}
return Health.up().build();
}
}

In order to trip health indicator, retrieve data from one of the future objects otherwise indicator is UP even when Kafka is down!!!
When Kafka is not connected future.get() throws an exception which in turn set this indicator down.
#Configuration
public class KafkaConfig {
#Autowired
private KafkaAdmin kafkaAdmin;
#Bean
public AdminClient kafkaAdminClient() {
return AdminClient.create(kafkaAdmin.getConfigurationProperties());
}
#Bean
public HealthIndicator kafkaHealthIndicator(AdminClient kafkaAdminClient) {
final DescribeClusterOptions options = new DescribeClusterOptions()
.timeoutMs(1000);
return new AbstractHealthIndicator() {
#Override
protected void doHealthCheck(Health.Builder builder) throws Exception {
DescribeClusterResult clusterDescription = kafkaAdminClient.describeCluster(options);
// In order to trip health indicator DOWN retrieve data from one of
// future objects otherwise indicator is UP even when Kafka is down!!!
// When Kafka is not connected future.get() throws an exception which
// in turn sets the indicator DOWN.
clusterDescription.clusterId().get();
// or clusterDescription.nodes().get().size()
// or clusterDescription.controller().get();
builder.up().build();
// Alternatively directly use data from future in health detail.
builder.up()
.withDetail("clusterId", clusterDescription.clusterId().get())
.withDetail("nodeCount", clusterDescription.nodes().get().size())
.build();
}
};
}
}

Use the AdminClient API to check the health of the cluster via describing the cluster and/or the topic(s) you'll be interacting with, and verifying those topics have the required number of insync replicas, for example
Kafka has something like KafkaHealthIndicator out of the box
It doesn't. Spring's Kafka integration might

Updating Dropwizard config at runtime

Is it possible to have my app update the config settings at runtime? I can easily expose the settings I want in my UI but is there a way to allow the user to update settings and make them permanent ie save them to the config.yaml file? The only way I can see it to update the file by hand then restart the server which seems a bit limiting.

Yes. It is possible to reload the service classes at runtime.
Dropwizard by itself does not have the way to reload the app, but jersey has.
Jersey uses a container object internally to maintain the running application. Dropwizard uses the ServletContainer class of Jersey to run the application.
How to reload the app without restarting it -
Get a handle to the container used internally by jersey
You can do this by registering a AbstractContainerLifeCycleListener in Dropwizard Environment before starting the app. and implement its onStartup method as below -
In your main method where you start the app -
//getting the container instance
environment.jersey().register(new AbstractContainerLifecycleListener() {
#Override
public void onStartup(Container container) {
//initializing container - which will be used to reload the app
_container = container;
}
});
Add a method to your app to reload the app. It will take in the list of string which are the names of the service classes you want to reload. This method will call the reload method of the container with the new custom DropWizardConfiguration instance.
In your Application class
public static synchronized void reloadApp(List<String> reloadClasses) {
DropwizardResourceConfig dropwizardResourceConfig = new DropwizardResourceConfig();
for (String className : reloadClasses) {
try {
Class<?> serviceClass = Class.forName(className);
dropwizardResourceConfig.registerClasses(serviceClass);
System.out.printf(" + loaded class %s.\n", className);
} catch (ClassNotFoundException ex) {
System.out.printf(" ! class %s not found.\n", className);
}
}
_container.reload(dropwizardResourceConfig);
}
For more details see the example documentation of jersey - jersey example for reload
Consider going through the code and documentation of following files in Dropwizard/Jersey for a better understanding -
Container.java
ContainerLifeCycleListener.java
ServletContainer.java
AbstractContainerLifeCycleListener.java
DropWizardResourceConfig.java
ResourceConfig.java

No.
Yaml file is parsed at startup and given to the application as Configuration object once and for all. I believe you can change the file after that but it wouldn't affect your application until you restart it.
Possible follow up question: Can one restart the service programmatically?
AFAIK, no. I've researched and read the code somewhat for that but couldn't find a way to do that yet. If there is, I'd love to hear that :).

I made a task that reloads the main yaml file (it would be useful if something in the file changes). However, it is not reloading the environment. After researching this, Dropwizard uses a lot of final variables and it's quite hard to reload these on the go, without restarting the app.
class ReloadYAMLTask extends Task {
private String yamlFileName;
ReloadYAMLTask(String yamlFileName) {
super("reloadYaml");
this.yamlFileName = yamlFileName;
}
#Override
public void execute(ImmutableMultimap<String, String> parameters, PrintWriter output) throws Exception {
if (yamlFileName != null) {
ConfigurationFactoryFactory configurationFactoryFactory = new DefaultConfigurationFactoryFactory<ReportingServiceConfiguration>();
ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
Validator validator = validatorFactory.getValidator();
ObjectMapper objectMapper = Jackson.newObjectMapper();
final ConfigurationFactory<ServiceConfiguration> configurationFactory = configurationFactoryFactory.create(ServiceConfiguration.class, validator, objectMapper, "dw");
File confFile = new File(yamlFileName);
configurationFactory.build(new File(confFile.toURI()));
}
}
}

You can change the configuration in the YAML and read it while your application is running. This will not however restart the server or change any server configurations. You will be able to read any changed custom configurations and use them. For example, you can change the logging level at runtime or reload other custom settings.
My solution -
Define a custom server command. You should use this command to start your application instead of the "server" command.
ArgsServerCommand.java
public class ArgsServerCommand<WC extends WebConfiguration> extends EnvironmentCommand<WC> {
private static final Logger LOGGER = LoggerFactory.getLogger(ArgsServerCommand.class);
private final Class<WC> configurationClass;
private Namespace _namespace;
public static String COMMAND_NAME = "args-server";
public ArgsServerCommand(Application<WC> application) {
super(application, "args-server", "Runs the Dropwizard application as an HTTP server specific to my settings");
this.configurationClass = application.getConfigurationClass();
}
/*
* Since we don't subclass ServerCommand, we need a concrete reference to the configuration
* class.
*/
#Override
protected Class<WC> getConfigurationClass() {
return configurationClass;
}
public Namespace getNamespace() {
return _namespace;
}
#Override
protected void run(Environment environment, Namespace namespace, WC configuration) throws Exception {
_namespace = namespace;
final Server server = configuration.getServerFactory().build(environment);
try {
server.addLifeCycleListener(new LifeCycleListener());
cleanupAsynchronously();
server.start();
} catch (Exception e) {
LOGGER.error("Unable to start server, shutting down", e);
server.stop();
cleanup();
throw e;
}
}
private class LifeCycleListener extends AbstractLifeCycle.AbstractLifeCycleListener {
#Override
public void lifeCycleStopped(LifeCycle event) {
cleanup();
}
}
}
Method to reload in your Application -
_ymlFilePath = null; //class variable
public static boolean reloadConfiguration() throws IOException, ConfigurationException {
boolean reloaded = false;
if (_ymlFilePath == null) {
List<Command> commands = _configurationBootstrap.getCommands();
for (Command command : commands) {
String commandName = command.getName();
if (commandName.equals(ArgsServerCommand.COMMAND_NAME)) {
Namespace namespace = ((ArgsServerCommand) command).getNamespace();
if (namespace != null) {
_ymlFilePath = namespace.getString("file");
}
}
}
}
ConfigurationFactoryFactory configurationFactoryFactory = _configurationBootstrap.getConfigurationFactoryFactory();
ValidatorFactory validatorFactory = _configurationBootstrap.getValidatorFactory();
Validator validator = validatorFactory.getValidator();
ObjectMapper objectMapper = _configurationBootstrap.getObjectMapper();
ConfigurationSourceProvider provider = _configurationBootstrap.getConfigurationSourceProvider();
final ConfigurationFactory<CustomWebConfiguration> configurationFactory = configurationFactoryFactory.create(CustomWebConfiguration.class, validator, objectMapper, "dw");
if (_ymlFilePath != null) {
// Refresh logging level.
CustomWebConfiguration webConfiguration = configurationFactory.build(provider, _ymlFilePath);
LoggingFactory loggingFactory = webConfiguration.getLoggingFactory();
loggingFactory.configure(_configurationBootstrap.getMetricRegistry(), _configurationBootstrap.getApplication().getName());
// Get my defined custom settings
CustomSettings customSettings = webConfiguration.getCustomSettings();
reloaded = true;
}
return reloaded;
}

Although this feature isn't supported out of the box by dropwizard, you're able to accomplish this fairly easy with the tools they give you.
Before I get started, note that this isn't a complete solution for the question asked as it doesn't persist the updated config values to the config.yml. However, this would be easy enough to implement yourself simply by writing to the config file from the application. If anyone would like to write this implementation feel free to open a PR on the example project I've linked below.
Code
Start off with a minimal config:
config.yml
myConfigValue: "hello"
And it's corresponding configuration file:
ExampleConfiguration.java
public class ExampleConfiguration extends Configuration {
private String myConfigValue;
public String getMyConfigValue() {
return myConfigValue;
}
public void setMyConfigValue(String value) {
myConfigValue = value;
}
}
Then create a task which updates the config:
UpdateConfigTask.java
public class UpdateConfigTask extends Task {
ExampleConfiguration config;
public UpdateConfigTask(ExampleConfiguration config) {
super("updateconfig");
this.config = config;
}
#Override
public void execute(Map<String, List<String>> parameters, PrintWriter output) {
config.setMyConfigValue("goodbye");
}
}
Also for demonstration purposes, create a resource which allows you to get the config value:
ConfigResource.java
#Path("/config")
public class ConfigResource {
private final ExampleConfiguration config;
public ConfigResource(ExampleConfiguration config) {
this.config = config;
}
#GET
public Response handleGet() {
return Response.ok().entity(config.getMyConfigValue()).build();
}
}
Finally wire everything up in your application:
ExampleApplication.java (exerpt)
environment.jersey().register(new ConfigResource(configuration));
environment.admin().addTask(new UpdateConfigTask(configuration));
Usage
Start up the application then run:
$ curl 'http://localhost:8080/config'
hello
$ curl -X POST 'http://localhost:8081/tasks/updateconfig'
$ curl 'http://localhost:8080/config'
goodbye
How it works
This works simply by passing the same reference to the constructor of ConfigResource.java and UpdateConfigTask.java. If you aren't familiar with the concept see here:
Is Java "pass-by-reference" or "pass-by-value"?
The linked classes above are to a project I've created which demonstrates this as a complete solution. Here's a link to the project:
scottg489/dropwizard-runtime-config-example
Footnote: I haven't verified this works with the built in configuration. However, the dropwizard Configuration class which you need to extend for your own configuration does have various "setters" for internal configuration, but it may not be safe to update those outside of run().
Disclaimer: The project I've linked here was created by me.

Spring Integration DSL Cafe example -- how are channels wired?

The Spring DSL documentation provides a sample project -- café
I'm unsure of a couple of aspects of how this works. Pasting the relevant excerpts here: (Full source at the above link)
#Configuration
#EnableAutoConfiguration
#IntegrationComponentScan
public class Application {
public static void main(String[] args) throws InterruptedException {
ConfigurableApplicationContext ctx = SpringApplication.run(Application.class, args);
Cafe cafe = ctx.getBean(Cafe.class);
for (int i = 1; i <= 100; i++) {
Order order = new Order(i);
order.addItem(DrinkType.LATTE, 2, false);
order.addItem(DrinkType.MOCHA, 3, true);
cafe.placeOrder(order);
}
Thread.sleep(60000);
ctx.close();
}
#MessagingGateway
public interface Cafe {
#Gateway(requestChannel = "orders.input")
void placeOrder(Order order);
}
#Bean
public IntegrationFlow orders() {
return f -> f
.split(Order.class, Order::getItems)
.channel(c -> c.executor(Executors.newCachedThreadPool()))
// SNIP
}
Reading this example, I'm unclear on a couple of points:
The Cafe interface exposes a #Gateway that connects to requestChannel = "orders.input". However, this channnel is not defined anywhere. How does this work?
The DSL snippet does is not wired to consume from any channels, nor does it refer to the Cafe::placeOrder method -- how does this get connected to the orders.input channel to receive the inbound Order?

We just published (yesterday) a line-by-line tutorial for the cafe dsl sample which goes into a lot of details about the internals.
When using the lambda version (f -> f.split()...) the framework declares an implicit DirectChannel with the bean name ("orders") + ".input" as its id.
You can also use return IntegrationFlows.from("myChannel"). ... .get() instead of the lambda expression and, again, the framework will auto-generate the channel if not declared as a bean already.
See the InterationFlows javadoc for more information.
cafe.placeOrder() is invoked in the last line in the for loop in the main method. The framework creates a proxy for the interface that wraps the Order object in a message and sends it to the gateway's request channel.

How to get an existing websocket instance

I'm working on an application that uses Websockets (Java EE 7) to send messages to all the connected clients asynchronously. The server (Websocket endpoint) should send these messages whenever a new article (an engagement modal in my app) is created.
Everytime a connection is established to the websocket endpoint, I'm adding the corresponding session to a list, which I could be able to access outside.
But the problem I had is, when I'm accessing this created websocket endpoint to which all the clients connected from outside (any other business class), I've get the existing instance (like a singleton).
So, can you please suggest me a way I can get an existing instance of the websocket endpoint, as I can't create it as new MyWebsocketEndPoint() coz it'll be created by the websocket internal mechanism whenever the request from a client is received.
For a ref:
private static WebSocketEndPoint INSTANCE = null;
public static WebSocketEndPoint getInstance() {
if(INSTANCE == null) {
// Instead of creating a new instance, I need an existing one
INSTANCE = new WebSocketEndPoint ();
}
return INSTANCE;
}
Thanks in advance.

The container creates a separate instance of the endpoint for every client connection, so you can't do what you're trying to do. But I think what you're trying to do is send a message to all the active client connections when an event occurs, which is fairly straightforward.
The javax.websocket.Session class has the getBasicRemote method to retrieve a RemoteEndpoint.Basic instance that represents the endpoint associated with that session.
You can retrieve all the open sessions by calling Session.getOpenSessions(), then iterate through them. The loop will send each client connection a message. Here's a simple example:
#ServerEndpoint("/myendpoint")
public class MyEndpoint {
#OnMessage
public void onMessage(Session session, String message) {
try {
for (Session s : session.getOpenSessions()) {
if (s.isOpen()) {
s.getBasicRemote().sendText(message);
}
} catch (IOException ex) { ... }
}
}
But in your case, you probably want to use CDI events to trigger the update to all the clients. In that case, you'd create a CDI event that a method in your Websocket endpoint class observes:
#ServerEndpoint("/myendpoint")
public class MyEndpoint {
// EJB that fires an event when a new article appears
#EJB
ArticleBean articleBean;
// a collection containing all the sessions
private static final Set<Session> sessions =
Collections.synchronizedSet(new HashSet<Session>());
#OnOpen
public void onOpen(final Session session) {
// add the new session to the set
sessions.add(session);
...
}
#OnClose
public void onClose(final Session session) {
// remove the session from the set
sessions.remove(session);
}
public void broadcastArticle(#Observes #NewArticleEvent ArticleEvent articleEvent) {
synchronized(sessions) {
for (Session s : sessions) {
if (s.isOpen()) {
try {
// send the article summary to all the connected clients
s.getBasicRemote().sendText("New article up:" + articleEvent.getArticle().getSummary());
} catch (IOException ex) { ... }
}
}
}
}
}
The EJB in the above example would do something like:
...
#Inject
Event<ArticleEvent> newArticleEvent;
public void publishArticle(Article article) {
...
newArticleEvent.fire(new ArticleEvent(article));
...
}
See the Java EE 7 Tutorial chapters on WebSockets and CDI Events.
Edit: Modified the #Observer method to use an event as a parameter.
Edit 2: wrapped the loop in broadcastArticle in synchronized, per #gcvt.
Edit 3: Updated links to Java EE 7 Tutorial. Nice job, Oracle. Sheesh.

Actually, WebSocket API provides a way how you can control endpoint instantiation. See https://tyrus.java.net/apidocs/1.2.1/javax/websocket/server/ServerEndpointConfig.Configurator.html
simple sample (taken from Tyrus - WebSocket RI test):
public static class MyServerConfigurator extends ServerEndpointConfig.Configurator {
public static final MyEndpointAnnotated testEndpoint1 = new MyEndpointAnnotated();
public static final MyEndpointProgrammatic testEndpoint2 = new MyEndpointProgrammatic();
#Override
public <T> T getEndpointInstance(Class<T> endpointClass) throws InstantiationException {
if (endpointClass.equals(MyEndpointAnnotated.class)) {
return (T) testEndpoint1;
} else if (endpointClass.equals(MyEndpointProgrammatic.class)) {
return (T) testEndpoint2;
}
throw new InstantiationException();
}
}
You need to register this to an endpoint:
#ServerEndpoint(value = "/echoAnnotated", configurator = MyServerConfigurator.class)
public static class MyEndpointAnnotated {
#OnMessage
public String onMessage(String message) {
assertEquals(MyServerConfigurator.testEndpoint1, this);
return message;
}
}
or you can use it with programmatic endpoints as well:
public static class MyApplication implements ServerApplicationConfig {
#Override
public Set<ServerEndpointConfig> getEndpointConfigs(Set<Class<? extends Endpoint>> endpointClasses) {
return new HashSet<ServerEndpointConfig>
(Arrays.asList(ServerEndpointConfig.Builder
.create(MyEndpointProgrammatic.class, "/echoProgrammatic")
.configurator(new MyServerConfigurator())
.build()));
}
#Override
public Set<Class<?>> getAnnotatedEndpointClasses(Set<Class<?>> scanned) {
return new HashSet<Class<?>>(Arrays.asList(MyEndpointAnnotated.class));
}
Of course it is up to you if you will have one configurator used for all endpoints (ugly ifs as in presented snippet) or if you'll create separate configurator for each endpoint.
Please do not copy presented code as it is - this is only part of Tyrus tests and it does violate some of the basic OOM paradigms.
See https://github.com/tyrus-project/tyrus/blob/1.2.1/tests/e2e/src/test/java/org/glassfish/tyrus/test/e2e/GetEndpointInstanceTest.java for complete test.