Don't Wait! Develop responsive applications with Java EE7 instead
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The document discusses developing responsive applications using Java EE7, highlighting technologies such as JAX-RS 2.0 for asynchronous processing, WebSocket API, and non-blocking I/O from Servlet 3.1. It emphasizes the benefits of these technologies in maximizing resource utilization and enabling real-time updates through reactive programming with libraries like RxJava. Additionally, it provides code examples demonstrating the implementation of asynchronous processing, WebSocket endpoints, and non-blocking I/O in Java EE environments.
Don't Wait! Develop responsive applications with Java EE7 instead
- 1. Don’t Wait! Develop responsive applications with Java EE7 instead! Erin Schnabel [email protected] @ebullientworks
- 2. Focus on the server side • “Responsive” application • Maximize resource utilization • Technologies in EE7 can help JAX-RS 2.0 async processing Concurrency Utilities (JSR-236) WebSocket API (JSR-356) Non-blocking I/O added in Servlet 3.1 2
- 3. JAX-RS 2.0 Async Support Concurrency Utilities
- 4. REST application (client-server or server-server) 4 NativeNative HTML5 Front-End REST API REST API ** Service B Business Logic ** ** Service B Business Logic **HybridHybrid Service A
- 5. A (very) simple JAX-RS example 5 @Path(”items") public class ItemResource { // various ways to get this guy, play nice and assume we have one protected ItemService itemService; @GET @Produces(MediaType.APPLICATION_JSON) public Collection<Item> listItems() { return itemService.listItems(); } @POST @Consumes(MediaType.APPLICATION_JSON) public void addItem(Item item) { itemService.addItem(item); } ... }
- 6. A (very) simple JAX-RS example 6 @Path(”items") public class ItemResource { // various ways to get this guy, play nice and assume we have one protected ItemService itemService; @GET @Produces(MediaType.APPLICATION_JSON) public Collection<Item> listItems() { return itemService.listItems(); } @POST @Consumes(MediaType.APPLICATION_JSON) public void addItem(Item item) { itemService.addItem(item); } ... } What if this is an encapsulation of a remote service? What if this is an encapsulation of a remote service?
- 7. JAX-RS 2.0 Asynchronous processing 7 @GET @Produces(MediaType.APPLICATION_JSON) public void getItems(@Suspended final AsyncResponse ar) { Collection<Item> result = itemService.listItems(); ar.resume(result ); } • AsyncResponse.resume(…) to send the response to the client. • @Suspended annotation with AsyncResponse parameter • void return type (to allow this method to return immediately) • “suspend” the connection -- NOT DISCONNECTED!
- 8. JAX-RS 2.0 Asynchronous processing 8 @GET @Produces(MediaType.APPLICATION_JSON) public void getItems(@Suspended final AsyncResponse ar) { Collection<Item> result = itemService.listItems(); ar.resume(result ); } • AsyncResponse.resume(…) to send the response to the client. • @Suspended annotation with AsyncResponse parameter • void return type (to allow this method to return immediately) • “suspend” the connection -- NOT DISCONNECTED! Hmm…I don’t see any threading stuff. How is this asynchronous? Hmm…I don’t see any threading stuff. How is this asynchronous?
- 9. JAX-RS 2.0 and … 9 @GET @Produces(MediaType.APPLICATION_JSON) public void getItems(@Suspended final AsyncResponse ar) { Runnable r = () -> { Collection<Item> result = itemService.listItems(); Response resp = Response.ok(result).build(); ar.resume(resp); }; Executors.newSingleThreadExecutor().submit(r); } This would totally work: The long-running operation is definitely on a different thread. This would totally work: The long-running operation is definitely on a different thread. Hopefully we also know that this is a horrible idea! #notcontainerfriendly Hopefully we also know that this is a horrible idea! #notcontainerfriendly
- 10. JAX-RS 2.0 and EJB • For a local EJB, use the @Asynchronous method annotation. 10 The EJB Container will dispatch to a different thread before invoking the method. The EJB Container will dispatch to a different thread before invoking the method.
- 11. JAX-RS 2.0 and Concurrency Utilities 11 @Path("execitems") public class ItemsExecutorResource { private ExecutorService getExecutor() throws NamingException { return (ExecutorService) new InitialContext() .lookup("java:comp/DefaultManagedExecutorService"); } @GET @Produces(MediaType.APPLICATION_JSON) public void getItems(@Suspended final AsyncResponse ar) { Runnable r = () -> {...}; try { ExecutorService executor = getExecutor(); executor.submit(r); } catch (NamingException e) { r.run(); } } ... } JNDI lookup for managed executor #oldschool JNDI lookup for managed executor #oldschool
- 12. JAX-RS 2.0, CDI, and Concurrency Utilities • Enable CDI (beans.xml), and have an Executor provided 12
- 13. JAX-RS 2.0: Time out! 13
- 14. JAX-RS 2.0: Callbacks • Register callbacks on AsyncResponse: 14 Support for ConnectionCallback is optional. #YMMV Support for ConnectionCallback is optional. #YMMV
- 15. Concurrency Utilities • Extension of java.util.concurrent (familiar API) – ManagedExecutorService java:comp/DefaultManagedExecutorService – ManagedScheduledExecutorService java:comp/DefaultManagedScheduledExecutorService – ManagedThreadFactory java:comp/DefaultManagedThreadFactory – ContextService java:comp/DefaultContextService • Container-friendly mechanisms to queue and manage work – Java EE Context propagation • JNDI, classloader, security, etc. – Allows container to manage async work, too! 15
- 16. WebSocket APIs
- 17. Server Endpoint: Annotated • Simple POJO with @ServerEndpoint annotation • Annotations for notifications: lifecycle and messages 17 @ServerEndpoint(value = "/SimpleAnnotated") public class SimpleEndpoint { @OnOpen public void onOpen(Session session, EndpointConfig ec) { } @OnClose public void onClose(Session session, CloseReason reason) { } @OnMessage public void receiveMessage(String message, Session session) { } @OnError public void onError(Throwable t) { } }
- 18. • @OnMessage method is called when a message is received – If message is ‘stop’: close the session – Otherwise, echo the message along with a hit count • Broadcast – iterate over open sessions 18 Simple echo + server provided data (using annotations)
- 20. Non-blocking I/O in Servlet 3.1 • Builds on Asynchronous processing from Servlet 3.0 – Only works for async-enabled apps • Enables reading/writing data without blocking a thread – ReadListener on ServletInputStream – WriteListener on ServletOutputStream • Best used with slow clients – For clients that are slow to read data, use a WriteListener – For clients that are slow to write data, use a ReadListener 20
- 21. Code Samples – Aync Servlet Listener 21 // start async AsyncContext ac = request.startAsync(); // set up async listener ac.addListener(new AsyncListener() { @Override public void onComplete(AsyncEvent event) throws IOException { System.out.println("AsyncServlet onComplete() called"); } @Override public void onError(AsyncEvent event) { System.out.println("AsyncServlet onError() " + event.getThrowable()); } @Override public void onStartAsync(AsyncEvent event) { System.out.println("AsyncServlet onStartAsync()"); } @Override public void onTimeout(AsyncEvent event) { System.out.println("AsyncServlet onTimeout()"); } }, request, response);
- 22. Code Samples – Non-Blocking I/O: Input 22
- 23. Code Samples – Non-Blocking I/O: Output 23
- 24. RxJava + EE7
- 25. Reactive Programming • Reactive programming focuses on data flows and propagation of change. • Java 8 has introduced lambdas and a new java.util.stream package, which help reactive programmers get started. • For highly concurrent stream processing and more advanced scenarios, ReactiveX is the library of choice. • RxJava is the Java implementation of ReactiveX. 25
- 26. RxJava and JEE7 • RxJava and EE7 go hand-in-hand: – Inject (CDI) and ExecutorServices from Concurrency Utilities into your app – Encapsulate these concurrent artifacts with a RxJava Scheduler – Use Websockets to provide real-time updates as observables are completed 26
- 27. RxJava and Liberty • Applications deployed in Liberty can include the RxJava library and seamlessly tap into its EE7 framework 27
- 28. RxJava and Liberty • GitHub sample: https://github.com/WASdev/sample.rxjava • App provides reviews and weather information about vacation destinations – concurrent-1.0 – websocket-1.1 – cdi-1.2 28
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Editor's Notes
- #5: REST over HTTP is an incredibly popular transport RESTful interactions take place both between client devices, either in browsers or in web applications, or between individual services in the backend of a microservices application.
- #6: JAX-RS annotations make creating a RESTful service easy and obvious.
- #14: If you are submitting the async work via an executor, you can set a timeout, and optionally register a timeout handler. If a handler isn’t present, a ServiceUnavailableException will be thrown with status code 503. The TimeoutHandler is given the AsyncResponse as a parameter, which must still be resumed to send a response back to the client. The AsyncResponse can also be cancelled, with an accompanying indication of how long a client should wait before retrying. A cancelled AsyncResponse sends a 503 / Service Unvaliable response to the client.
- #15: If you are submitting the async work via an executor, you can set a timeout, and optionally register a timeout handler. If a handler isn’t present, a ServiceUnavailableException will be thrown with status code 503. The TimeoutHandler is given the AsyncResponse as a parameter, which must still be resumed to send a response back to the client.
- #16: Unmanaged threads and timers can cause problems for containers: they inhibit an app server’s ability to track and manage resources. Concurrency Utilities provided in EE7 extend the mechanisms java.util.concurrent to provide a familiar API to applications that allows easy creation of container-managed resources to support async activities. Java EE Concurrency utilities provide context propagation, so that new threads inherit the container thread context of the originating application component thread (which is important for referencing other EE).
- #19: @OnMessage methods are single threaded for an endpoint… Note the broadcast! Easy as pie to send the same data around to different sessions. Also note that each connection will have it’s own Endpoint instance, but that instances can see each other through sessions: Endpoints are not thread safe, but Sessions are.
- #30: Create a new stream from the input destination Map them into internal populated POJOs, using a custom scheduler / executor.
- #31: Concat previous observable of destinations (from previous inputs) with current stream Sort the aggregated list of destinations Flatten the list of destination streams into a single stream Subscribe (ie: push results back to client via websocket) using a different scheduler / executor.