java - PoolingHttpClientConnectionManager 不释放连接

Question

我正在使用 Spring 来实现以下目标:

在服务器上，我通过 REST 接口(interface)以 XML 格式接收数据。我想将数据转换为 JSON 并将其发布到另一个服务器。我的代码(我删除了一些敏感的类名/URL 以避免雇主的愤怒)如下所示:

主/配置类:

package stateservice;

import org.apache.http.HttpHost;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class App {
    Logger log = LoggerFactory.getLogger(App.class);

    public static void main(String[] args) {
        System.out.println("Start!");
        SpringApplication.run(StateServiceApplication.class, args);
        System.out.println("End!");
    }

    @Bean
    public RestTemplate restTemplate() {
        log.trace("restTemplate()");
        HttpHost proxy = new HttpHost("proxy_url", 8080);
        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
        // Increase max total connection to 200
        cm.setMaxTotal(200);
        cm.setDefaultMaxPerRoute(50);

        RequestConfig requestConfig = RequestConfig.custom().setProxy(proxy).build();

        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
        httpClientBuilder.setDefaultRequestConfig(requestConfig);
        httpClientBuilder.setConnectionManager(cm);
        HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(
                httpClientBuilder.build());
        return new RestTemplate(requestFactory);
    }
}

代表RESTful接口(interface)的类:

package stateservice;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import foo.bar.XmlData

@RestController
public class StateController {

    private static Logger log = LoggerFactory.getLogger(DataController.class);

    @Autowired
    ForwarderService forwarder;


    @RequestMapping(value = "/data", method = RequestMethod.POST)
    public String postState(@RequestBody XmlData data) {
        forwarder.forward(data);
        return "Done!";
    }
}

最后是转发器:

package stateservice;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import foo.bar.Converter;
import foo.bar.XmlData;

@Service
public class ForwarderService {
    private static Logger log = LoggerFactory.getLogger(ForwarderService.class);

    String uri = "forward_uri";

    @Autowired
    RestTemplate restTemplate;

    @Async
    public String forward(XmlData data) {
        log.trace("forward(...) - start");
        String json = Converter.convert(data);
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);

        ResponseEntity<String> response = restTemplate.postForEntity(uri,
                new HttpEntity<String>(json, headers), String.class);
        // responseEntity.getBody();
        // log.trace(responseEntity.toString());
        log.trace("forward(...) - end");
        return response.getBody();
    }
}

但是，连接管理器似乎很少释放连接以供重用，此外，系统会充斥着处于 CLOSE_WAIT 状态的连接(可以使用 netstat 看到)。池中的所有连接都被租用，但未释放，并且一旦处于 CLOSE_WAIT 状态的连接数达到 ulimit，我就会得到“打开的文件太多”-异常

由于代码的多线程特性，我怀疑无法关闭套接字/释放连接，因为其他一些线程正在阻塞它们。

如果您能给我解决问题的任何帮助或提示，我将不胜感激。

Answer 1

Apache HttpEntity 有一个技巧 - 释放锁定的连接 - 响应必须完全消耗和关闭。见 EntityUtils和 HttpEntity有关详细信息的文档:

EntityUtils.consume(response);

从 4.3 版开始，当在 CloseableHttpResponse 上调用 #close() 方法时，Apache HttpClient 会释放与池的连接。

然而，Spring Web 仅从版本 4.0.0-RELEASE 开始支持此功能，请参阅 HttpComponentsClientHttpResponse.java 中的方法 #close() :

@Override
public void close() {
    // Release underlying connection back to the connection manager
    try {
        try {
            // Attempt to keep connection alive by consuming its remaining content
            EntityUtils.consume(this.httpResponse.getEntity());
        } finally {
            // Paranoia
            this.httpResponse.close();
        }
    }
    catch (IOException ignore) {
    }
}

成功的关键是“//偏执狂”标记的那一行——显式的.close()调用。它实际上将连接释放回池。