简述

本文介绍Apache HttpAsyncClient的最常见用例，从基本用法到如何设置代理，如何使用SSL证书以及最后如何使用异步客户端进行身份验证。

简单Demo

首先，让我们看一下如何在一个简单的例子中使用HttpAsyncClient，发送一个GET请求：

@Test
public void test() throws Exception {
    CloseableHttpAsyncClient client = HttpAsyncClients.createDefault();
    client.start();
    HttpGet request = new HttpGet("http://localhost:8080");
     
    Future<HttpResponse> future = client.execute(request, null);
    HttpResponse response = future.get();
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

注意我们在使用之前需要启动HttpAsyncClients ; 没有它，我们会得到以下异常：

java.lang.IllegalStateException: Request cannot be executed; I/O reactor status: INACTIVE
    at o.a.h.u.Asserts.check(Asserts.java:46)
    at o.a.h.i.n.c.CloseableHttpAsyncClientBase.
      ensureRunning(CloseableHttpAsyncClientBase.java:90)

使用HttpAsyncClient进行多线程处理

现在，让我们看看如何使用HttpAsyncClient同时执行多个请求。

在以下示例中，我们使用HttpAsyncClient和PoolingNHttpClientConnectionManager向三个不同的主机发送三个GET请求：

@Test
public void test() throws Exception {
    ConnectingIOReactor ioReactor = new DefaultConnectingIOReactor();
    PoolingNHttpClientConnectionManager cm = 
      new PoolingNHttpClientConnectionManager(ioReactor);
    CloseableHttpAsyncClient client = 
      HttpAsyncClients.custom().setConnectionManager(cm).build();
    client.start();
     
    String[] toGet = {
            "192.168.0.101:8080",
            "192.168.0.102:8080",
            "192.168.0.103:8080"
    };
 
    GetThread[] threads = new GetThread[toGet.length];
    for (int i = 0; i < threads.length; i++) {
        HttpGet request = new HttpGet(toGet[i]);
        threads[i] = new GetThread(client, request);
    }
 
    for (GetThread thread : threads) {
        thread.start();
    }
    for (GetThread thread : threads) {
        thread.join();
    }
}

以下是我们的GetThread实现来处理响应：

static class GetThread extends Thread {
    private CloseableHttpAsyncClient client;
    private HttpContext context;
    private HttpGet request;
 
    public GetThread(CloseableHttpAsyncClient client,HttpGet req){
        this.client = client;
        context = HttpClientContext.create();
        this.request = req;
    }
 
    @Override
    public void run() {
        try {
            Future<HttpResponse> future = client.execute(request, context, null);
            HttpResponse response = future.get();
            assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
        } catch (Exception ex) {
            System.out.println(ex.getLocalizedMessage());
        }
    }
}

使用HttpAsyncClient的代理

接下来，让我们来看看如何设置和使用代理服务器与HttpAsyncClient。

在以下示例中，我们通过代理发送HTTP GET请求：

@Test
public void test() throws Exception {
    CloseableHttpAsyncClient client = HttpAsyncClients.createDefault();
    client.start();
     
    HttpHost proxy = new HttpHost("74.50.126.248", 3127);
    RequestConfig config = RequestConfig.custom().setProxy(proxy).build();
    HttpGet request = new HttpGet("http://192.168.0.101");
    request.setConfig(config);
     
    Future<HttpResponse> future = client.execute(request, null);
    HttpResponse response = future.get();
     
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

使用HttpAsyncClient的SSL证书

现在，让我们来看看如何使用SSL证书与HttpAsyncClient。

在以下示例中， 我们将HttpAsyncClient配置为接受所有证书：

@Test
public void test() throws Exception {
    TrustStrategy acceptingTrustStrategy = new TrustStrategy() {
        public boolean isTrusted(X509Certificate[] certificate,  String authType) {
            return true;
        }
    };
    SSLContext sslContext = SSLContexts.custom()
      .loadTrustMaterial(null, acceptingTrustStrategy).build();
 
    CloseableHttpAsyncClient client = HttpAsyncClients.custom()
      .setSSLHostnameVerifier(SSLConnectionSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER)
      .setSSLContext(sslContext).build();
    client.start();
     
    HttpGet request = new HttpGet("");
    Future<HttpResponse> future = client.execute(request, null);
    HttpResponse response = future.get();
     
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

使用HttpAsyncClient的Cookie

接下来，让我们看看如何在HttpAsyncClient中使用cookie 。

在以下示例中，我们在发送请求之前设置cookie值：

@Test
public void test() throws Exception {
    BasicCookieStore cookieStore = new BasicCookieStore();
    BasicClientCookie cookie = new BasicClientCookie("JSESSIONID", "1234");
    cookie.setDomain(".william.com");
    cookie.setPath("/");
    cookieStore.addCookie(cookie);
     
    CloseableHttpAsyncClient client = HttpAsyncClients.custom().build();
    client.start();
     
    HttpGet request = new HttpGet("http://localhost:8080");
    HttpContext localContext = new BasicHttpContext();
    localContext.setAttribute(HttpClientContext.COOKIE_STORE, cookieStore);
    Future<HttpResponse> future = client.execute(request, localContext, null);
    HttpResponse response = future.get();
     
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

使用HttpAsyncClient进行身份验证

接下来，让我们看看如何使用HttpAsyncClient进行身份验证。

在以下示例中，我们使用CredentialsProvider通过基本身份验证访问主机：

@Test
public void test() throws Exception {
    CredentialsProvider provider = new BasicCredentialsProvider();
    UsernamePasswordCredentials creds = new UsernamePasswordCredentials("user", "pass");
    provider.setCredentials(AuthScope.ANY, creds);
     
    CloseableHttpAsyncClient client = 
      HttpAsyncClients.custom().setDefaultCredentialsProvider(provider).build();
    client.start();
     
    HttpGet request = new HttpGet("http://localhost:8080");
    Future<HttpResponse> future = client.execute(request, null);
    HttpResponse response = future.get();
     
    assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
    client.close();
}

结论

本文介绍的内容希望你对HttpAsyncClient有深刻的了解