我们得到连接池关闭错误，而执行超文本传输协议请求使用RestTemplate.

这不是一个频繁的错误。它在一个月内发生了大约3次，持续时间很短（不到一分钟）。

我们正在使用PoolingHttpClientConnectionManager，最大连接数为50，连接超时=60秒

  @Bean
  public RestTemplate restTemplate()
  {
    final RestTemplate restTemplate = new RestTemplate ( httpRequestFactory () );
    return restTemplate;
  }

  @Bean
  public ClientHttpRequestFactory httpRequestFactory()
  {
    return new HttpComponentsClientHttpRequestFactory ( httpClient () );
  }

  @Bean
  public CloseableHttpClient httpClient()
  {
    final SSLContext sslcontext = SSLContexts.createSystemDefault ();
    final X509HostnameVerifier hostnameVerifier = new BrowserCompatHostnameVerifier ();
    final Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder
      .<ConnectionSocketFactory> create ()
      .register ( "http", PlainConnectionSocketFactory.INSTANCE )
      .register ( "https", new SSLConnectionSocketFactory ( sslcontext, hostnameVerifier ) )
      .build ();

    final PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager (
      socketFactoryRegistry );
    connectionManager.setMaxTotal ( 50 );
    final RequestConfig config = RequestConfig.custom ()
      .setConnectTimeout ( 60000 ).build ();

    final CloseableHttpClient defaultHttpClient = HttpClientBuilder
      .create ().setConnectionManager ( connectionManager )
      .setDefaultRequestConfig ( config ).build ();

    LOGGER.info ( "Initializing CloseableHttpClient" );
    return defaultHttpClient;
  }

spring-webmvc版本4.0.6。释放；
httpclient版本4.3.5

确切的堆栈跟踪如下…

java.lang.IllegalStateException: Connection pool shut down
        at org.apache.http.util.Asserts.check(Asserts.java:34) ~[httpcore-4.3.2.jar:4.3.2]
        at org.apache.http.pool.AbstractConnPool.lease(AbstractConnPool.java:169) ~[httpcore-4.3.2.jar:4.3.2]
        at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.requestConnection(PoolingHttpClientConnectionManager.java:221) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:158) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:195) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:86) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:108) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184) ~[httpclient-4.3.5.jar:4.3.5]
        at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82) ~[httpclient-4.3.5.jar:4.3.5]
        at org.springframework.http.client.HttpComponentsClientHttpRequest.executeInternal(HttpComponentsClientHttpRequest.java:87) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]
        at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]
        at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:52) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:545) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]
        at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:506) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]
        at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:243) ~[spring-web-4.0.6.RELEASE.jar:4.0.6.RELEASE]