httpclient总结

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 count
return false;
}
if (exception instanceof InterruptedIOException) {
// Timeout
return false;
}
if (exception instanceof UnknownHostException) {
// Unknown host
return false;
}
if (exception instanceof ConnectTimeoutException) {
// Connection refused
return false;
}
if (exception instanceof SSLException) {
// SSL handshake exception
return false;
}
HttpClientContext clientContext = HttpClientContext.adapt(context);
HttpRequest request = clientContext.getRequest();
boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
if (idempotent) {
// Retry if the request is considered idempotent
return 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 info
connMrg.connect(conn, route, 1000, context);
// and mark it as route complete
connMrg.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200
cm.setMaxTotal(200);
// 将每个路由基础的连接增加到20
cm.setDefaultMaxPerRoute(20);
//将目标主机的最大连接数增加到50
HttpHost 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 threads
for (int j = 0; j < threads.length; j++) {
threads[j].join();
}
自定义类GetThread
static 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;
}

@Override
public 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;
}

@Override
public 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();
}
}

}