Test runtime change of maxTotal property of HttpClient's ConnectionManager -> it's working ;)

HttpClientTest.java

final PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
connectionManager.setMaxTotal(1);

final CloseableHttpClient httpClient = HttpClientBuilder.create()
        .setConnectionManager(connectionManager)
        .build();

final HttpGet get = new HttpGet("http://www.google.com");

final StopWatch stopWatch1 = new StopWatch();
stopWatch1.start();
IntStream.range(0, 10).parallel().forEach(i -> {
    try {
        httpClient.execute(get, response -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null;
        });
    } catch (IOException e) {
        e.printStackTrace();
    }
});
stopWatch1.stop();

connectionManager.setMaxTotal(10);
final StopWatch stopWatch2 = new StopWatch();
stopWatch2.start();
IntStream.range(0, 10).parallel().forEach(i -> {
    try {
        httpClient.execute(get, response -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null;
        });
    } catch (IOException e) {
        e.printStackTrace();
    }
});
stopWatch2.stop();
System.out.println("before: " + stopWatch1.getTime() + ", after: " + stopWatch2.getTime());
// before: 11888, after: 5802