Java Run Multiple Tasks Simultaneously
Sometimes we may need to write a program that can process multiple tasks concurrently. Java supports multithreading which means that we can run multiple threads to do different task at the same time within a single program.
In this example, we will use Java built-in ExecutorService from the java.util.concurrent package to execute multiple tasks asynchronously at the same time in parallel.
Following is a Java example code to make 1000 GET request concurrently at one time:
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
public class ExecutorServiceExample {
public static void main(String[] args) {
// 50000 urls
List<String> urlList = new ArrayList<>();
urlList.add("http://www.example.com");
urlList.add("http://www.example1.com");
urlList.add("http://www.example2.com");
urlList.add("http://www.example50000.com");
// task start time
long startTime = System.currentTimeMillis();
initiateRequest(urlList);
// task end time
long endTime = System.currentTimeMillis();
double timeTaken = (endTime - startTime) / 1000;
System.out.println(
"Time taken to run " + urlList.size() + " urls = " + timeTaken + " seconds");
}
public static void initiateRequest(List<String> urlList) {
if (urlList.isEmpty()) {
return;
}
int numberOfThreads = 1000;
ExecutorService fixedPoolExecutor = Executors.newFixedThreadPool(numberOfThreads);
List<Future<String>> futureList = new ArrayList<>();
urlList.forEach(url -> {
Future<String> future = fixedPoolExecutor.submit(() -> myTask(url));
futureList.add(future);
});
for (Future<String> future : futureList) {
try {
System.out.println("Future = " + future.get());
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
System.out.println("Complete");
}
private static String myTask(String url) {
CloseableHttpClient client = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(url);
int responseCode = 00;
CloseableHttpResponse response = null;
try {
response = client.execute(httpGet);
responseCode = response.getStatusLine().getStatusCode();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (client != null) {
client.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return url + ", response code = " + responseCode;
}
}