HttpClient 4 简介

1. 概述

主要通过一些代码示例展示如何使用Apache HttpClient 4

2. 示例

创建 http client

CloseableHttpClient client = HttpClientBuilder.create().build();

发起基础 GET 请求

instance.execute(new HttpGet("http://www.mango.im"));

获取 HTTP 响应状态码

CloseableHttpResponse response = instance.execute(new HttpGet("http://www.google.com"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(200));

获取 HTTP 响应媒体类型

CloseableHttpResponse response = instance.execute(new HttpGet("http://www.google.com"));
String contentMimeType = ContentType.getOrDefault(response.getEntity()).getMimeType();
assertThat(contentMimeType, equalTo(ContentType.TEXT_HTML.getMimeType()));

获取 HTTP 响应body

CloseableHttpResponse response = instance.execute(new HttpGet("http://www.google.com"));
String bodyAsString = EntityUtils.toString(response.getEntity());
assertThat(bodyAsString, notNullValue());

配置请求超时

@Test(expected = SocketTimeoutException.class)
public void givenLowTimeout_whenExecutingRequestWithTimeout_thenException() 
    throws ClientProtocolException, IOException {
    RequestConfig requestConfig = RequestConfig.custom()
      .setConnectionRequestTimeout(1000).setConnectTimeout(1000).setSocketTimeout(1000).build();
    HttpGet request = new HttpGet(SAMPLE_URL);
    request.setConfig(requestConfig);
    instance.execute(request);
}

注：

setConnectionRequestTimeout 从连接池中获取可用连接超时
setConnectTimeout 连接目标超时
setSocketTimeout 等待响应超时（读取数据超时）

配置默认请求超时

RequestConfig requestConfig = RequestConfig.custom().
    setConnectionRequestTimeout(1000).setConnectTimeout(1000).setSocketTimeout(1000).build();
HttpClientBuilder builder = HttpClientBuilder.create().setDefaultRequestConfig(requestConfig);

发起 POST 请求

instance.execute(new HttpPost(SAMPLE_URL));

增加请求参数

List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("key1", "value1"));
params.add(new BasicNameValuePair("key2", "value2"));
request.setEntity(new UrlEncodedFormEntity(params, Consts.UTF_8));

配置如何处理HTTP请求的重定向

CloseableHttpClient instance = HttpClientBuilder.create().disableRedirectHandling().build();
CloseableHttpResponse response = instance.execute(new HttpGet("http://t.co/I5YYd9tddw"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(301));

配置请求头

HttpGet request = new HttpGet(SAMPLE_URL);
request.addHeader(HttpHeaders.ACCEPT, "application/xml");
response = instance.execute(request);

获取响应头

CloseableHttpResponse response = instance.execute(new HttpGet(SAMPLE_URL));
Header[] headers = response.getHeaders(HttpHeaders.CONTENT_TYPE);
assertThat(headers, not(emptyArray()));

释放资源

response = instance.execute(new HttpGet(SAMPLE_URL));
try {
    HttpEntity entity = response.getEntity();
    if (entity != null) {
        InputStream instream = entity.getContent();
        instream.close();
    }
} finally {
    response.close();
}

本文译制httpclient4