Spring RestTemplate - Need to release connection?

Question

This is my Configuration for Rest Template,

    @Bean
    @Qualifier("myRestService")
    public RestTemplate createRestTemplate(@Value("${connection.timeout}") String maxConn) {
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
         connectionManager.setMaxTotal(maxTotalConn);
         connectionManager.setDefaultMaxPerRoute(maxPerChannel);

        RequestConfig config = RequestConfig.custom().setConnectTimeout(100000).build();
        CloseableHttpClient httpClient = HttpClientBuilder.create().setConnectionManager(connectionManager)
                .setDefaultRequestConfig(config).build();
        ClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClient);

        RestTemplate restTemplate = new RestTemplate(factory);

        restTemplate.setErrorHandler(new RestResponseErrorHandler());
         restTemplate.setMessageConverters(createMessageConverters());

        return restTemplate;
    }

Am using PoolingHttpClientConnectionManager for managing the connections.

Its being accessed by the following code,

ResponseEntity<String> response = restClient.exchange( url, HttpMethod.GET, entity , String.class );

Do i need to release the connection after the above call or is it taken care by RestTemplate. If we need to take care of releasing connection.

Please can some one explain/show how to release the connection.

Answer 1

You should declare the ClientHttpRequestFactory as a bean. By declaring it as a bean, it becomes managed by the Spring bean factory, which will call the factory's destroy method when the application is closed, or the bean goes out of scope. The destroy method of the ClientHttpRequestFactory will close the underlying ClientConnectionManager's connection pool. You can check the Spring API docs for this.

@Bean
public ClientHttpRequestFactory createRequestFactory(@Value("${connection.timeout}") String maxConn) {
    PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
     connectionManager.setMaxTotal(maxTotalConn);
     connectionManager.setDefaultMaxPerRoute(maxPerChannel);

    RequestConfig config = RequestConfig.custom().setConnectTimeout(100000).build();
    CloseableHttpClient httpClient = HttpClientBuilder.create().setConnectionManager(connectionManager)
            .setDefaultRequestConfig(config).build();
    return new HttpComponentsClientHttpRequestFactory(httpClient);
}

Then you can use this bean to create your RestTemplate:

@Bean
@Qualifier("myRestService")
public RestTemplate createRestTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);

    restTemplate.setErrorHandler(new RestResponseErrorHandler());
    restTemplate.setMessageConverters(createMessageConverters());

    return restTemplate;
}

Answer 2

The question which you have asked: Do i need to release the connection after the above call or is it taken care by RestTemplate. If we need to take care of releasing connection.

No, you do not need to close the connection on the response, if you use resttemplate.

From the apache httpclient, you need to consume the complete response (EntityUtils.consume(HttpEntity) and close the response.

This can be verified in the ClientConnectionRelease.java

But RestTemplate does this for you, to verify the same have a look into RestTemplate.java

Look for method

protected <T> T doExecute(URI url,...) {
 try {
        ClientHttpRequest request = this.createRequest(url, method);
        ...
        response = request.execute();
        ...
        if(responseExtractor != null) {
            var7 = responseExtractor.extractData(response);
            return var7;
        }
       ...
       ...
    } finally {
        if(response != null) {
            response.close();
        }

    }
}

Where response extractor does the work for you by consuming the response using responseExtractor.extractData(response);

And after extracting the data completely it is closing response.close() as well.