Java – poolinghttpclientconnectionmanager does not release the connection

I use spring to achieve the following:

On the server, I receive data through the rest interface in XML format I want to convert the data into JSON and post it to another server My code (I deleted some sensitive class names / URLs to avoid the anger of the employer) looks like this:

Master / configuration class:

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);
    }
}

Classes representing restful interfaces:

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!";
    }
}

Finally, freight forwarder:

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();
    }
}

However, connection managers rarely seem to release reused connections. In addition, the system will close_ The connection in the wait state (which can be seen using netstat) All connections in the pool are leased, but not released, and once closed_ When the number of connections in the wait state reaches ulimit, I will receive 'too many open files' exceptions

Due to the multithreading nature of the code, I suspect that sockets cannot be closed / connections released because some other threads cannot block them

I really appreciate any help or tips. You can help me solve the problem

Solution

Apache httpentity has a trick - releasing locked connections - the response must be completely consumed and closed For more information, see the entityutils and httpentity documentation:

EntityUtils.consume(response);

Starting from version 4.3, when the #close () method is called on the closeablehttpresponse, Apache httpclient will release the connection back to the pool

However, spring version 4.0 only supports spring web functions. See httpcomponentsclienthttpresponse Method #close() in Java:

@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) {
    }
}

The key to success is "/ / paranoia" – explicit Close() call It actually frees the connection back to the pool