Asynchronous processing in java

Asynchronous programming is very popular these days, primarily because of its ability to improve the overall throughput on a multi-core system. Asynchronous programming is a programming paradigm that facilitates fast and responsive user interfaces. The asynchronous programming model in Java provides a consistent programming model to write programs that support asynchrony.

Asynchronous programming provides a non-blocking, event-driven programming model. This programming model leverages the multiple cores in your system to provide parallelization by using multiple CPU cores to execute the tasks, thus increasing the application’s throughput. Note that throughput is a measure of the amount of work done in unit time. In this programming paradigm, a unit of work would execute separately from the main application thread and notify the calling thread about its execution state: success, in progress or failure.

Application of asynchronous can be a situation where we want to execute multiple things in parellel without waiting for 1 task to finish such that it increase the throughput of the system. Consider we want to send email to 100k+ users and at the same time need to process other data, such that we don’t want to wait for email task to complete to proceed.

Another good example of this can be logging frameworks: You typically would want to log exceptions and errors into your log targets; in other words, file, database, or something similar. There is no point for your application to wait till the logging tasks are over. In doing so, the application’s responsiveness would be affected. On the contrary, if the call to the logging framework can be made asynchronously, the application can proceed with other tasks concurrently, without having to wait. This is an example of a non-blocking mode of execution.

1. Future is a base interface and defines abstraction of an object which promises result to be available in future while FutureTask is an implementation of the Future interface.

2. Future is a parametric interface and type-safe written as Future<V>, where V denotes value.

3. Future provides get() method to get result, which is blocking method and blocks until result is available to Future.

4. Future interface also defines cancel() method to cancel task.

5. isDone() and isCancelled() method is used to query Future task states. isDone() returns true if task is completed and result is available to Future. If you call get() method, after isDone() returned true then it should return immediately. On the other hand, isCancelled() method returns true, if this task is cancelled before its completion.

6. Future has four sub interfaces, each with additional functionality e.g. Response, RunnableFuture, RunnableScheduledFuture and ScheduledFuture. RunnableFuture also implements Runnable and successful finish of run() method cause completion of this Future.

7. FutureTask and SwingWorker are two well known implementation of Future interface. FutureTask also implements RunnableFuture interface, which means this can be used as Runnable and can be submitted to ExecutorService for execution.

8. Though most of the time ExecutorService creates FutureTask for you, i.e. when you submit() Callable or Runnable object. You can also created it manually.

9. FutureTask is normally used to wrap Runnable or Callable object and submit them to ExecutorService for asynchronous execution.

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.logging.Level;
import java.util.logging.Logger; /** * Java program to show how to use Future in Java. Future allows to write * asynchronous code in Java, where Future promises result to be available in * future * * @author Javin */
public class FutureDemo {
private static final ExecutorService threadpool = Executors.newFixedThreadPool(2);
public static void main(String args[]) throws InterruptedException, ExecutionException {
FactorialCalculator task = new FactorialCalculator(1000);

System.out.println(“Submitting Task …”);
Future future = threadpool.submit(task);
System.out.println(“Task is submitted”);
while (!future.isDone()) {
System.out.println(“Task is not completed yet….”);
Thread.sleep(1); //sleep for 1 millisecond before checking again
}
System.out.println(“Task is completed, let’s check result”);
long factorial = (long) future.get();
System.out.println(“Factorial of 1000000 is : ” + factorial);
threadpool.shutdown();
}
private static class FactorialCalculator implements Callable {
private final int number;
public FactorialCalculator(int number) {
this.number = number;
}

@Override public Long call() {
long output = 0;
try {
output = factorial(number);
} catch (InterruptedException ex) {
//Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
}
return output;
}

private long factorial(int number) throws InterruptedException {
if (number < 0) {
throw new IllegalArgumentException(“Number must be greater than zero”);
}
long result = 1;
while (number > 0) {
Thread.sleep(1); // adding delay for example
result = result * number;
number–;
}
return result;

}
}
}

Usage in spring framework is given in below link :

 

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Developing RESTful service in Spring

The service will handle GET requests for /greeting, optionally with a name parameter in the query string. The GET request should return a 200 OK response with JSON in the body that represents a greeting. It should look something like this:

{
    "id": 1,
    "content": "Hello, World!"
}

The id field is a unique identifier for the greeting, and content is the textual representation of the greeting.

To model the greeting representation, you create a resource representation class. Provide a plain old java object with fields, constructors, and accessors for the id and content data:

src/main/java/hello/Greeting.java

package hello;

public class Greeting {

    private final long id;
    private final String content;

    public Greeting(long id, String content) {
        this.id = id;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }
}

Create a resource controller

In Spring’s approach to building RESTful web services, HTTP requests are handled by a controller. These components are easily identified by the @RestController annotation, and the GreetingController below handles GET requests for /greeting by returning a new instance of the Greeting class:

src/main/java/hello/GreetingController.java

package hello;

import java.util.concurrent.atomic.AtomicLong;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    private static final String template = "Hello, %s!";
    private final AtomicLong counter = new AtomicLong();

    @RequestMapping("/greeting")
    public Greeting greeting(@RequestParam(value="name", defaultValue="World") String name) {
        return new Greeting(counter.incrementAndGet(),
                            String.format(template, name));
    }
}

This controller is concise and simple, but there’s plenty going on under the hood. Let’s break it down step by step.

The @RequestMapping annotation ensures that HTTP requests to /greeting are mapped to the greeting() method.

The above example does not specify GET vs. PUT, POST, and so forth, because @RequestMapping maps all HTTP operations by default. Use @RequestMapping(method=GET) to narrow this mapping.

@RequestParam binds the value of the query string parameter name into the name parameter of the greeting() method. This query string parameter is not required; if it is absent in the request, the defaultValue of “World” is used.

The implementation of the method body creates and returns a new Greeting object with id and content attributes based on the next value from the counter, and formats the given name by using the greeting template.

A key difference between a traditional MVC controller and the RESTful web service controller above is the way that the HTTP response body is created. Rather than relying on a view technology to perform server-side rendering of the greeting data to HTML, this RESTful web service controller simply populates and returns a Greeting object. The object data will be written directly to the HTTP response as JSON.

This code uses Spring 4’s new @RestController annotation, which marks the class as a controller where every method returns a domain object instead of a view. It’s shorthand for @Controller and @ResponseBody rolled together.

The Greeting object must be converted to JSON. Thanks to Spring’s HTTP message converter support, you don’t need to do this conversion manually. Because Jackson 2 is on the classpath, Spring’s MappingJackson2HttpMessageConverter is automatically chosen to convert the Greeting instance to JSON.

Make the application executable

Although it is possible to package this service as a traditional WAR file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main() method. Along the way, you use Spring’s support for embedding the Tomcat servlet container as the HTTP runtime, instead of deploying to an external instance.

src/main/java/hello/Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration tags the class as a source of bean definitions for the application context.
  • @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.
  • Normally you would add @EnableWebMvc for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as setting up a DispatcherServlet.
  • @ComponentScan tells Spring to look for other components, configurations, and services in the the hello package, allowing it to find the GreetingController.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.

Build an executable JAR

If you are using Gradle, you can run the application using ./gradlew bootRun.

You can build a single executable JAR file that contains all the necessary dependencies, classes, and resources. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

./gradlew build

Then you can run the JAR file:

java -jar build/libs/gs-rest-service-0.1.0.jar

If you are using Maven, you can run the application using mvn spring-boot:run. Or you can build the JAR file with mvn clean package and run the JAR by typing:

java -jar target/gs-rest-service-0.1.0.jar