PoolingHttpClientConnectionManager原理剖析

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#pool #httpClient #manager #连接池 #回收与释放

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本文深入剖析了PoolingHttpClientConnectionManager的工作原理，包括其在HttpClient中的继承体系和连接的租用与释放过程。当创建CloseableHttpClient时，重点讨论了HttpClientBuilder的构建方法，并在execute方法中揭示了连接的获取和回收触发点。

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- PoolingHttpClientConnectionManager原理剖析
  - 继承体系
  - 连接是如何租用和释放的？
    - 获取连接,回收连接触发时机

PoolingHttpClientConnectionManager原理剖析

继承体系

poolingHttpClientConnManager

public class HttpClientUtil{
//全局参数
private PoolingHttpClientConnectionManager connectionManager;
//用来释放不用的连接 closeExpiredConnections() closeIdleConnections(long idletime, TimeUnit tunit)
private HttpClientConnectionMonitorThread thread;
//连接配置
private RequestConfig requestConfig;

//单例模式创建资源
    @PostConstruct
    private void init() {//bean初始化
        if (connectionManager == null) {
            connectionManager = new PoolingHttpClientConnectionManager();
            // 整个连接池最大连接数
            connectionManager.setMaxTotal(MAX_TOTAL);
            // 每路由最大连接数，默认值是2
            connectionManager.setDefaultMaxPerRoute(MAX_PER_ROUTE);
            /** 管理 http连接池 */
            thread = new HttpClientConnectionMonitorThread(connectionManager);
            requestConfig = RequestConfig.custom()
                    .setConnectionRequestTimeout(REQ_TIMEOUT)
                    .setConnectTimeout(CONN_TIMEOUT).setSocketTimeout(SOCK_TIMEOUT)
                    .build();
        }
    }

//下次获取httpClient的时候是这样的
    public CloseableHttpClient getHttpClient() {
        return HttpClients.custom().setConnectionManager(connectionManager)
          .setDefaultRequestConfig(requestConfig).build();
    }
}

/**
 * @ClassName: HttpClientConnectionMonitorThread
 * @Description: TODO(使用管理器，管理HTTP连接池 无效链接定期清理功能)
 * @author xiangqi
 * @date 2018-01-29 下午 2:10
 */
public class HttpClientConnectionMonitorThread extends Thread {

    private final HttpClientConnectionManager connManager;
    private volatile boolean shutdown = false;

    public HttpClientConnectionMonitorThread(HttpClientConnectionManager connManager) {
        super();
        this.setName("http-connection-monitor");
        this.setDaemon(true);
        this.connManager = connManager;
        this.start();
    }

    @Override
    public void run() {
        try {
            while (!shutdown) {
                synchronized (this) {
                    // 等待5秒
                    wait(5000);
                    // 关闭过期的链接
                    connManager.closeExpiredConnections();
                    // 选择关闭 空闲30秒的链接
                    connManager.closeIdleConnections(30, TimeUnit.SECONDS);
                }
            }
        } catch (InterruptedException ex) {
            //ignore ex
        }
    }
}

连接是如何租用和释放的？

创建CloseableHttpClient时，一个重要的方法是HttpClientBuilder#build():CloseableHttpClient。发现源码里面都是初始化以下函数的入参：

 public InternalHttpClient(
            final ClientExecChain execChain,
            final HttpClientConnectionManager connManager,
            final HttpRoutePlanner routePlanner,
            final Lookup<CookieSpecProvider> cookieSpecRegistry,
            final Lookup<AuthSchemeProvider> authSchemeRegistry,
            final CookieStore cookieStore,
            final CredentialsProvider credentialsProvider,
            final RequestConfig defaultConfig,
            final List<Closeable> closeables) {
        super();
        Args.notNull(execChain, "HTTP client exec chain");
        Args.notNull(connManager, "HTTP connection manager");
        Args.notNull(routePlanner, "HTTP route planner");
        this.execChain = execChain;
        this.connManager = connManager;
        this.routePlanner = routePlanner;
        this.cookieSpecRegistry = cookieSpecRegistry;
        this.authSchemeRegistry = authSchemeRegistry;
        this.cookieStore = cookieStore;
        this.credentialsProvider = credentialsProvider;
        this.defaultConfig = defaultConfig;
        this.closeables = closeables;
    }

获取连接,回收连接触发时机

CloseableHttpClient#execute( HttpUriRequest request):CloseableHttpResponse，断点调试发现，其实底层调用的是
- InternalHttpClient#doExecute( HttpHost , HttpRequest ,HttpContext )
- this.execChain.execute(route, wrapper, localcontext, execAware)
- MainClinetExec#execute*(HttpRoute,HttpRequestWrapper,HttpClientContext,HttpExecutionAware)
- HttpClientConnectionManager#requestConnection(HttpRoute,Object):ConnectionRequest
- ConnectionRequest#get(long,TimeUnit):HttpClientConnection，这就是租用时机
- CloseableHttpResponse#close(),这是回收链接时机
- ConnectionHolder#close()
- ConnectionHolder#releaseConnection()
- releaseConnection$releaseConnection(boolean)