Apache HttpClient4.5（一）

创建HTTP客户端

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

// 也可以为客户端配置请求的参数,作为所有请求的默认值RequestConfig requestConfig = RequestConfig.custom()        .setConnectionRequestTimeout(5000)        .setConnectTimeout(5000)        .setSocketTimeout(5000)        .setCookieSpec(CookieSpecs.DEFAULT)        .build();CloseableHttpClient httpClient = HttpClients.custom()        .setDefaultRequestConfig(requestConfig)        .build();

创建GET请求

HttpGet httpGet = new HttpGet("http://localhost/index.html?param1=value1¶m2=value2");

HttpClient提供URIBuilder工具类来简化uri的创建

URI uri = null;try {    uri= new URIBuilder()            .setScheme("http")            .setHost("localhost")            .setPath("/index.html")            .setParameter("param1", "value1")            .setParameter("param2", "value2")            .build();} catch (URISyntaxException e) {    e.printStackTrace();}HttpGet httpGet = new HttpGet(uri);

如果参数中含有中文，需将参数进行URLEncoding处理

URI uri = null;try {    uri = new URIBuilder()            .setScheme("http")            .setHost("localhost")            .setPath("/index.html")            .setParameter("param1", URLEncoder.encode("中国", "UTF-8"))            .setParameter("param2", "value2")            .build();} catch (UnsupportedEncodingException | URISyntaxException e) {    e.printStackTrace();}HttpGet httpGet = new HttpGet(uri);

可以为单个请求设置一些配置

httpGet.setConfig(RequestConfig.DEFAULT);

创建POST请求

HttpPost httpPost = new HttpPost("http://www.baidu.com");

httpPost的uri和RequestConfig设置同httpGet。可以为httpGet和httpPost设置消息头

httpPost.addHeader(HttpHeaders.CONTENT_TYPE, "application/octet-stream;charset=utf-8");httpGet.addHeader(HttpHeaders.ACCEPT, "application/xml");

执行请求

CloseableHttpResponse response = null;try {    response = httpClient.execute(httpGet);    // 获取HTTP响应的状态码    int status = response.getStatusLine().getStatusCode();    System.out.println(status);} catch (IOException e) {    e.printStackTrace();} finally {    try {        if (response != null) response.close();    } catch (IOException e) {        e.printStackTrace();    }}

CloseableHttpResponse response = null;try {    CloseableHttpResponse response = httpClient.execute(httpPost);    System.out.println(response.getStatusLine());    System.out.println(response.getAllHeaders());    System.out.println(response. getHeaders(HttpHeaders.CONTENT_TYPE);    System.out.println(response.getEntity());} catch (IOException e) {    e.printStackTrace();} finally {    try {        if (response != null) response.close();    } catch (IOException e) {        e.printStackTrace();    }}

使用HttpEntity
当执行一个完整内容的Http请求或者Http请求已经成功，服务器要发送响应到客户端时，Http实体就会被创建。通过HttpResponse的getEntity()方法可以获取HttpEntity，可以利用HttpEntity类的getContent方法来获取实体的输入流（java.io.InputStream)，或者利用HttpEntity类的writeTo(OutputStream)方法来获取输出流，这个方法会把所有的内容写入到给定的流中或则使用EntityUtils。

// 获取响应的HttpEntityHttpEntity entity = response.getEntity();Header type = entity.getContentType();//Content-Typelong length = entity.getContentLength();//Content-LengthHeader encoding = entity.getContentEncoding();// 获取响应的媒体类型, 例如：text/htmlString contentMimeType = ContentType.getOrDefault(entity).getMimeType();// 获取响应的BODY部分String bodyAsString = EntityUtils.toString(entity);

InputStream instream = entity.getContent();try {    // do something useful  } finally {    instream.close();}

有些情况下，希望可以重复读取Http实体的内容。这就需要把Http实体内容缓存在内存或者磁盘上。最简单的方法就是把Http Entity转化成BufferedHttpEntity，这样就把原Http实体的内容缓冲到了内存中。后面就可以重复读取BufferedHttpEntity中的内容。

HttpEntity entity = response.getEntity();  if (entity != null) {      entity = new BufferedHttpEntity(entity);  }

模拟提交Html表单请求

HttpPost httpPost = new HttpPost("http://www.baidu.com");// 拼接参数List<NameValuePair> formparams = new ArrayList<>();formparams.add(new BasicNameValuePair("username", "vip"));formparams.add(new BasicNameValuePair("password", "secret"));UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);httpPost.setEntity(entity);

发送二进制

httpPost.addHeader("Content-Type", "application/octet-stream;charset=utf-8");httpPost.setEntity(new ByteArrayEntity(bytes));

ResponseHandler
最简单也是最方便的处理http响应的方法就是使用ResponseHandler接口，这个接口中有handleResponse(HttpResponse response)方法。使用这个方法，用户完全不用关心http连接管理器。当使用ResponseHandler时，HttpClient会自动地将Http连接释放给Http管理器，即使http请求失败了或者抛出了异常。

CloseableHttpClient httpclient = HttpClients.createDefault();HttpGet httpget = new HttpGet("http://www.yeetrack.com/json");ResponseHandler<MyJsonObject> rh = new ResponseHandler<MyJsonObject>() {@Overridepublic JsonObject handleResponse(final HttpResponse response) throws IOException {StatusLine statusLine = response.getStatusLine();HttpEntity entity = response.getEntity();if (statusLine.getStatusCode() >= 300) {throw new HttpResponseException(statusLine.getStatusCode(),statusLine.getReasonPhrase());}if (entity == null) {throw new ClientProtocolException("Response contains no content");}Gson gson = new GsonBuilder().create();ContentType contentType = ContentType.getOrDefault(entity);Charset charset = contentType.getCharset();Reader reader = new InputStreamReader(entity.getContent(), charset);return gson.fromJson(reader, MyJsonObject.class);}};//设置responseHandler，当执行http方法时，就会返回MyJsonObject对象。MyJsonObject myjson = client.execute(httpget, rh);

       HttpClient已经实现了线程安全。所以在实例化HttpClient时，也要支持为多个请求使用。当一个CloseableHttpClient的实例不再被使用，并且它的作用范围即将失效，和它相关的连接必须被关闭，关闭方法可以调用CloseableHttpClient的close()方法。

CloseableHttpClient httpclient = HttpClients.createDefault();try {<...>} finally {//关闭连接httpclient.close();}

HttpClient接口没有对Http请求的过程做特别的限制和详细的规定，连接管理、状态管理、授权信息和重定向处理这些功能都单独实现。这样用户就可以更简单地拓展接口的功能（比如缓存响应内容）。
一般说来，HttpClient实际上就是一系列特殊的handler或者说策略接口的实现，这些handler（测试接口）负责着处理Http协议的某一方面，比如重定向、认证处理、有关连接持久性和keep alive持续时间的决策。这样就允许用户使用自定义的参数来代替默认配置，实现个性化的功能。

ConnectionKeepAliveStrategy keepAliveStrat = new DefaultConnectionKeepAliveStrategy() {@Overridepublic long getKeepAliveDuration(HttpResponse response,HttpContext context) {long keepAlive = super.getKeepAliveDuration(response, context);if (keepAlive == -1) {//如果服务器没有设置keep-alive这个参数，我们就把它设置成5秒keepAlive = 5000;}return keepAlive;}};//定制我们自己的httpclientCloseableHttpClient httpclient = HttpClients.custom().setKeepAliveStrategy(keepAliveStrat).build();

参考：http://www.yeetrack.com/?p=779