1、httpclient总结：
一、基本知识准备(1)构建URI工具类，URIBuilder(2)HttpResponse类，可以添加Header信息获取所有Header信息的方法，调用HeaderIterator接口HeaderIterator it = response.headerIterator("Set-Cookie");while (it.hasNext()) {System.out.println(it.next());} (3)HttpEntity内容实体 可以被装入Request和Response中..只有独立的entity才可以被重复调用.当请求需要entity HttpEntity.writeTo(OutputStream)从响应中解析entity HttpEntity.getContent()HttpEntity.getContentType()HttpEntity.getContentLength()HttpEntity.getContentEncoding()对entity进行解析可采用流的方式或者调用EntityUtils，但后者有长度的限制2048利用 BufferedEntity可以将entity缓存到本地磁盘，用来进行多次读取.创建entity信息时需要指定meta信息，包括contentType(4)可以调用ResponseHandler写入响应统一处理 二、常用策略keep-Alieve策略:自定义ConnectionKeepAliveStrategy重定向策略:LaxRedirectStrategy三、资源分配当CloseableHttpClient不再需要，并且不再连接管理的范围，需要调用CloseableHttpClient.close()方法将其关闭..四、HttpClient状态管理1、在HTTP上下文中，很多有逻辑关系的请求都可以放入到同一个session中..HttpClient本身线程HttpContext 包含任意的键值对，因此线程不安全..通常建议每个线程拥有自己的上下文 2、自动恢复机制---->HttpRequestRetryHandler
HttpRequestRetryHandler myRetryHandler = new HttpRequestRetryHandler() {public boolean retryRequest(IOException exception,int executionCount,HttpContext context) {if (executionCount >= 5) {// Do not retry if over max retry countreturn false;}if (exception instanceof InterruptedIOException) {// Timeoutreturn false;}if (exception instanceof UnknownHostException) {// Unknown hostreturn false;}if (exception instanceof ConnectTimeoutException) {// Connection refusedreturn false;}if (exception instanceof SSLException) {// SSL handshake exceptionreturn false;}HttpClientContext clientContext = HttpClientContext.adapt(context);HttpRequest request = clientContext.getRequest();boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);if (idempotent) {// Retry if the request is considered idempotentreturn true;}return false;}};CloseableHttpClient httpclient = HttpClients.custom().setRetryHandler(myRetryHandler).build();
4、多线程中的应用AtomicInteger，，，，待研究...
从连接管理器中获取连接(1)通过HttpClientConnectionManager来管理一个连接HttpClientContext context = HttpClientContext.create();HttpClientConnectionManager connMrg = new BasicHttpClientConnectionManager();HttpRoute route = new HttpRoute(new HttpHost("www.yeetrack.com", 80));// 获取新的连接. 这里可能耗费很多时间ConnectionRequest connRequest = connMrg.requestConnection(route, null);// 10秒超时HttpClientConnection conn = connRequest.get(10, TimeUnit.SECONDS);try {// 如果创建连接失败if (!conn.isOpen()) {// establish connection based on its route infoconnMrg.connect(conn, route, 1000, context);// and mark it as route completeconnMrg.routeComplete(conn, route, context);}// 进行自己的操作.} finally {connMrg.releaseConnection(conn, null, 1, TimeUnit.MINUTES);}通过更复杂的PoolingHttpClientConnectionManager来管理多个连接，适合多线程中的请求PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();// 将最大连接数增加到200cm.setMaxTotal(200);// 将每个路由基础的连接增加到20cm.setDefaultMaxPerRoute(20);//将目标主机的最大连接数增加到50HttpHost localhost = new HttpHost("www.yeetrack.com", 80);cm.setMaxPerRoute(new HttpRoute(localhost), 50);CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(cm).build();示例1---------------------------------PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(cm).build();// URL列表数组String[] urisToGet = {"http://www.domain1.com/","http://www.domain2.com/","http://www.domain3.com/","http://www.domain4.com/"};// 为每个url创建一个线程，GetThread是自定义的类GetThread[] threads = new GetThread[urisToGet.length];for (int i = 0; i < threads.length; i++) {HttpGet httpget = new HttpGet(urisToGet[i]);threads[i] = new GetThread(httpClient, httpget);}// 启动线程for (int j = 0; j < threads.length; j++) {threads[j].start();}// join the threadsfor (int j = 0; j < threads.length; j++) {threads[j].join();}自定义类GetThreadstatic class GetThread extends Thread {private final CloseableHttpClient httpClient;private final HttpContext context;private final HttpGet httpget;public GetThread(CloseableHttpClient httpClient, HttpGet httpget) {this.httpClient = httpClient;this.context = HttpClientContext.create();this.httpget = httpget;}@Overridepublic void run() {try {CloseableHttpResponse response = httpClient.execute(httpget, context);try {HttpEntity entity = response.getEntity();} finally {response.close();}} catch (ClientProtocolException ex) {// Handle protocol errors} catch (IOException ex) {// Handle I/O errors}}}
注意：即使httpclient可以被多线程访问，仍建议每个httpclient采用自己的context
5、 public static class IdleConnectionMonitorThread extends Thread {private final HttpClientConnectionManager connMgr;private volatile boolean shutdown;public IdleConnectionMonitorThread(HttpClientConnectionManager connMgr) {super();this.connMgr = connMgr;}@Overridepublic void run() {try {while (!shutdown) {synchronized (this) {wait(5000);// 关闭失效的连接connMgr.closeExpiredConnections();// 可选的, 关闭30秒内不活动的连接connMgr.closeIdleConnections(30, TimeUnit.SECONDS);}}} catch (InterruptedException ex) {// terminate}}public void shutdown() {shutdown = true;synchronized (this) {notifyAll();}}}