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Tapio Rautonen
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iluwatar#68: Implementation of Async Method Invocation pattern
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‎async-method-invocation/pom.xml‎

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<?xml version="1.0"?>
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.3.0</version>
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</parent>
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<artifactId>async-method-invocation</artifactId>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java‎

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package com.iluwatar.async.method.invocation;
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import java.util.concurrent.Callable;
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public class App {
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public static void main(String[] args) throws Exception {
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AsyncExecutor executor = new ThreadAsyncExecutor();
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AsyncResult<Integer> asyncResult1 = executor.startProcess(lazyval(10, 500));
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AsyncResult<String> asyncResult2 = executor.startProcess(lazyval("test", 300));
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AsyncResult<Long> asyncResult3 = executor.startProcess(lazyval(50L, 700));
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AsyncResult<Integer> asyncResult4 = executor.startProcess(lazyval(20, 400), callback("Callback result 4"));
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AsyncResult<String> asyncResult5 = executor.startProcess(lazyval("callback", 600), callback("Callback result 5"));
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Thread.sleep(350); // Oh boy I'm working hard here
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log("Some hard work done");
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Integer result1 = executor.endProcess(asyncResult1);
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String result2 = executor.endProcess(asyncResult2);
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Long result3 = executor.endProcess(asyncResult3);
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asyncResult4.await();
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asyncResult5.await();
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log("Result 1: " + result1);
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log("Result 2: " + result2);
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log("Result 3: " + result3);
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}
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private static <T> Callable<T> lazyval(T value, long delayMillis) {
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return () -> {
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Thread.sleep(delayMillis);
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log("Task completed with: " + value);
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return value;
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};
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}
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private static <T> AsyncCallback<T> callback(String name) {
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return (value, ex) -> {
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if (ex.isPresent()) {
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log(name + " failed: " + ex.map(Exception::getMessage).orElse(""));
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} else {
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log(name + ": " + value);
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}
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};
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}
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private static void log(String msg) {
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System.out.println(String.format("[%1$-10s] - %2$s", Thread.currentThread().getName(), msg));
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}
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}

‎async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/AsyncCallback.java‎

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package com.iluwatar.async.method.invocation;
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import java.util.Optional;
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public interface AsyncCallback<T> {
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void onComplete(T value, Optional<Exception> ex);
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}

‎async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/AsyncExecutor.java‎

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package com.iluwatar.async.method.invocation;
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import java.util.concurrent.Callable;
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import java.util.concurrent.ExecutionException;
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public interface AsyncExecutor {
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<T> AsyncResult<T> startProcess(Callable<T> task);
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<T> AsyncResult<T> startProcess(Callable<T> task, AsyncCallback<T> callback);
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<T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException, InterruptedException;
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}

‎async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/AsyncResult.java‎

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package com.iluwatar.async.method.invocation;
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import java.util.concurrent.ExecutionException;
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public interface AsyncResult<T> {
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boolean isCompleted();
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T getValue() throws ExecutionException;
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void await() throws InterruptedException;
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}

‎async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/ThreadAsyncExecutor.java‎

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package com.iluwatar.async.method.invocation;
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import java.util.Optional;
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import java.util.concurrent.Callable;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.atomic.AtomicInteger;
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public class ThreadAsyncExecutor implements AsyncExecutor {
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private final AtomicInteger idx = new AtomicInteger(0);
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@Override
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public <T> AsyncResult<T> startProcess(Callable<T> task) {
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return startProcess(task, null);
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}
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@Override
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public <T> AsyncResult<T> startProcess(Callable<T> task, AsyncCallback<T> callback) {
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CompletableResult<T> result = new CompletableResult<>(callback);
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new Thread(() -> {
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try {
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result.setValue(task.call());
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} catch (Exception ex) {
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result.setException(ex);
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}
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}, "executor-" + idx.incrementAndGet()).start();
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return result;
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}
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@Override
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public <T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException, InterruptedException {
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if (asyncResult.isCompleted()) {
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return asyncResult.getValue();
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} else {
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asyncResult.await();
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return asyncResult.getValue();
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}
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}
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private static class CompletableResult<T> implements AsyncResult<T> {
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static final int RUNNING = 1;
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static final int FAILED = 2;
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static final int COMPLETED = 3;
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final Object lock;
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final Optional<AsyncCallback<T>> callback;
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volatile int state = RUNNING;
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T value;
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Exception exception;
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CompletableResult(AsyncCallback<T> callback) {
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this.lock = new Object();
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this.callback = Optional.ofNullable(callback);
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}
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void setValue(T value) {
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this.value = value;
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this.state = COMPLETED;
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this.callback.ifPresent(ac -> ac.onComplete(value, Optional.<Exception>empty()));
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synchronized (lock) {
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lock.notifyAll();
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}
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}
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void setException(Exception exception) {
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this.exception = exception;
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this.state = FAILED;
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this.callback.ifPresent(ac -> ac.onComplete(null, Optional.of(exception)));
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synchronized (lock) {
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lock.notifyAll();
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}
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}
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@Override
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public boolean isCompleted() {
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return (state > RUNNING);
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}
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@Override
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public T getValue() throws ExecutionException {
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if (state == COMPLETED) {
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return value;
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} else if (state == FAILED) {
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throw new ExecutionException(exception);
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} else {
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throw new IllegalStateException("Execution not completed yet");
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}
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}
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@Override
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public void await() throws InterruptedException {
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synchronized (lock) {
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if (!isCompleted()) {
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lock.wait();
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}
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}
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}
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}
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}

‎async-method-invocation/src/test/java/com/iluwatar/async/method/invocation/AppTest.java‎

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package com.iluwatar.async.method.invocation;
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import org.junit.Test;
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public class AppTest {
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@Test
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public void test() throws Exception {
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String[] args = {};
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App.main(args);
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}
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}

‎pom.xml‎

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<module>naked-objects</module>
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<module>front-controller</module>
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<module>repository</module>
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<module>async-method-invocation</module>
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</modules>
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<dependencyManagement>

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