Apache HttpClient4.5（一）__Java提高

建立HTTP用戶端

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

// 也可以為用戶端配置請求的參數,作為所有請求的預設值RequestConfig requestConfig = RequestConfig.custom()        .setConnectionRequestTimeout(5000)        .setConnectTimeout(5000)        .setSocketTimeout(5000)        .setCookieSpec(CookieSpecs.DEFAULT)        .build();CloseableHttpClient httpClient = HttpClients.custom()        .setDefaultRequestConfig(requestConfig)        .build();

建立GET請求

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

HttpClient提供URIBuilder工具類來簡化uri的建立

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);

如果參數中含有中文，需將參數進行URLEncoding處理

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

可以為單個請求設定一些配置

httpGet.setConfig(RequestConfig.DEFAULT);

建立POST請求

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

httpPost的uri和RequestConfig設定同httpGet。可以為httpGet和httpPost設定訊息頭

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

執行請求

CloseableHttpResponse response = null;try {    response = httpClient.execute(httpGet);    // 擷取HTTP響應的狀態代碼    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
當執行一個完整內容的Http請求或者Http請求已經成功，伺服器要發送響應到用戶端時，Http實體就會被建立。通過HttpResponse的getEntity()方法可以擷取HttpEntity，可以利用HttpEntity類的getContent方法來擷取實體的輸入資料流（java.io.InputStream)，或者利用HttpEntity類的writeTo(OutputStream)方法來擷取輸出資料流，這個方法會把所有的內容寫入到給定的流中或則使用EntityUtils。

// 擷取響應的HttpEntityHttpEntity entity = response.getEntity();Header type = entity.getContentType();//Content-Typelong length = entity.getContentLength();//Content-LengthHeader encoding = entity.getContentEncoding();// 擷取響應的媒體類型, 例如：text/htmlString contentMimeType = ContentType.getOrDefault(entity).getMimeType();// 擷取響應的BODY部分String bodyAsString = EntityUtils.toString(entity);

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

有些情況下，希望可以重複讀取Http實體的內容。這就需要把Http實體內容緩衝在記憶體或者磁碟上。最簡單的方法就是把Http Entity轉化成BufferedHttpEntity，這樣就把原Http實體的內容緩衝到了記憶體中。後面就可以重複讀取BufferedHttpEntity中的內容。

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

類比提交Html表單請求

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

發送二進位

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

ResponseHandler
最簡單也是最方便的處理http響應的方法就是使用ResponseHandler介面，這個介面中有handleResponse(HttpResponse response)方法。使用這個方法，使用者完全不用關心http連線管理員。當使用ResponseHandler時，HttpClient會自動地將Http串連釋放給Http管理器，即使http請求失敗了或者拋出了異常。

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);}};//設定responseHandler，當執行http方法時，就會返回MyJsonObject對象。MyJsonObject myjson = client.execute(httpget, rh);

       HttpClient已經實現了安全執行緒。所以在執行個體化HttpClient時，也要支援為多個請求使用。當一個CloseableHttpClient的執行個體不再被使用，並且它的作用範圍即將失效，和它相關的串連必須被關閉，關閉方法可以調用CloseableHttpClient的close()方法。

CloseableHttpClient httpclient = HttpClients.createDefault();try {<...>} finally {//關閉串連httpclient.close();}

HttpClient介面沒有對Http請求的過程做特別的限制和詳細的規定，串連管理、狀態管理、授權資訊和重新導向處理這些功能都單獨實現。這樣使用者就可以更簡單地拓展介面的功能（比如緩衝響應內容）。
一般說來，HttpClient實際上就是一系列特殊的handler或者說策略介面的實現，這些handler（測試介面）負責著處理Http協議的某一方面，比如重新導向、認證處理、有關串連持久性和keep alive期間的決策。這樣就允許使用者使用自訂的參數來代替預設配置，實現個人化的功能。

ConnectionKeepAliveStrategy keepAliveStrat = new DefaultConnectionKeepAliveStrategy() {@Overridepublic long getKeepAliveDuration(HttpResponse response,HttpContext context) {long keepAlive = super.getKeepAliveDuration(response, context);if (keepAlive == -1) {//如果伺服器沒有設定keep-alive這個參數，我們就把它設定成5秒keepAlive = 5000;}return keepAlive;}};//定製我們自己的httpclientCloseableHttpClient httpclient = HttpClients.custom().setKeepAliveStrategy(keepAliveStrat).build();

參考： http://www.yeetrack.com/?p=779