背景

在看nacos client的代码，发现网络相关http实现是包装HttpURLConnection，其中关闭连接是：

finally {
    if (null != conn) {
        conn.disconnect();
    }
}

很少直接用HttpURLConnection写代码了，但是记得之前写代码，通常只关闭流

finally {
    if (null != conn && conn.getInputSteam()!= null ) {
        conn.getInputSteam().close();
    }
}

于是复习下。

HttpURLConnection.disconnect()

HttpURLConnection对disconnect描述；

    /**
     * Indicates that other requests to the server
     * are unlikely in the near future. Calling disconnect()
     * should not imply that this HttpURLConnection
     * instance can be reused for other requests.
     */
    public abstract void disconnect();

具体实现类：sun.net.www.protocol.http.HttpURLConnection

    public void disconnect() {
        this.responseCode = -1;
        if (this.pi != null) {
            this.pi.finishTracking();
            this.pi = null;
        }

        if (this.http != null) {
            if (this.inputStream != null) {
                HttpClient var1 = this.http;
                boolean var2 = var1.isKeepingAlive();

                try {
                    this.inputStream.close();
                } catch (IOException var4) {
                }

                if (var2) {
                    var1.closeIdleConnection();
                }
            } else {
                this.http.setDoNotRetry(true);
                this.http.closeServer();
            }

            this.http = null;
            this.connected = false;
        }

        this.cachedInputStream = null;
        if (this.cachedHeaders != null) {
            this.cachedHeaders.reset();
        }

    }

sun.net.www.http.HttpClient


    protected static KeepAliveCache kac = new KeepAliveCache();

    public void closeIdleConnection() {
        HttpClient var1 = kac.get(this.url, (Object)null);
        if (var1 != null) {
            var1.closeServer();
        }

    }

    public void closeServer() {
        try {
            this.keepingAlive = false;
            this.serverSocket.close();
        } catch (Exception var2) {
        }

    }

小结：disconnect()清除keepingAlive，关闭serverSocket。

HttpURLConnection.getInputSteam().close()

HttpURLConnection的javadoc

Calling the close() methods

on the InputStream or OutputStream of an HttpURLConnection

after a request may free network resources associated with this

instance but has no effect on any shared persistent connection.

Calling the disconnect() method may close the underlying socket

if a persistent connection is otherwise idle at that time.

小结

在开启keep-alive的情况下：

HttpURLConnection.disconnect()会关闭底层socket。
HttpURLConnection.getInputSteam().close()只关闭输入流，可以重用底层socket。

回到nacos client，定时向nacos server轮询配置更新，查询结束主动关闭连接，不复用底层socket，见ClientWorker的构造函数

executor.scheduleWithFixedDelay(new Runnable() {
    @Override
    public void run() {
        try {
            checkConfigInfo();
        } catch (Throwable e) {
            LOGGER.error("[" + agent.getName() + "] [sub-check] rotate check error", e);
        }
    }
}, 1L, 10L, TimeUnit.MILLISECONDS);

checkConfigInfo()最终会访问nacos server。如果任务正常结束，那么10ms之后又会发起网络请求。

HttpURLConnection disconnect

HttpURLConnection.disconnect() 会关闭底层连接。如果要复用连接，使用 HttpURLConnection.getInputSteam().close()。

背景

HttpURLConnection.disconnect()

HttpURLConnection.getInputSteam().close()

小结

资料