RestTemplate是Spring提供的用于访问Rest服务的客户端，RestTemplate提供了多种便捷访问远程Http服务的方法，能够大大提高客户端的编写效率。

ClientHttpRequestFactory

RestTemplate可以通过使用ClientHttpRequestFactory指定不同的HTTP请求方式。

ClientHttpRequestFactory接口主要提供了两种实现方式：

SimpleClientHttpRequestFactory，使用J2SE提供的方式（既java.net包提供的方式）创建底层的Http请求连接。

HttpComponentsClientHttpRequestFactory方式，底层使用HttpClient访问远程的Http服务，使用HttpClient可以配置连接池和证书等信息。

HttpComponentsClientHttpRequestFactory方式

HttpClient配置连接池

@Component("httpClientFactory")public class HttpClientFactoryBean extends DefaultConnectionKeepAliveStrategy implements FactoryBean
    
     ,    Runnable, InitializingBean, DisposableBean{/** * 保持最多的连接数 */private static final int CONNECTION_MAX_TOTAL = 50;/** * domain最多连接数 */private static final int CONNECTION_MAX_ROUTE = 10;/** * 空闲时间 */private static final int IDLE_TIMEOUT = 30 * 1000;private ScheduledExecutorService service;private PoolingHttpClientConnectionManager connectionManager;private HttpClient httpClient;@Overridepublic HttpClient getObject(){    HttpClientBuilder builder = HttpClients.custom();    builder.setKeepAliveStrategy(this);    builder.setConnectionManager(connectionManager);    httpClient = builder.build();    return httpClient;}@Overridepublic void afterPropertiesSet(){    service = new ScheduledThreadPoolExecutor(1, new ThreadFactoryBuilder().setNameFormat("httpclient-%d").build());    service.scheduleWithFixedDelay(this, 60, 60, TimeUnit.SECONDS);    connectionManager = new PoolingHttpClientConnectionManager();    connectionManager.setDefaultSocketConfig(SocketConfig.custom().setSoTimeout(10 * 1000).build());    connectionManager.setDefaultConnectionConfig(ConnectionConfig.custom().setBufferSize(8 * 1024)            .setFragmentSizeHint(8 * 1024).build());    connectionManager.setMaxTotal(CONNECTION_MAX_TOTAL);    connectionManager.setDefaultMaxPerRoute(CONNECTION_MAX_ROUTE);}@Overridepublic void destroy() {    service.shutdownNow();    connectionManager.close();}@Overridepublic Class
     
       getObjectType() {    return HttpClient.class;}@Overridepublic boolean isSingleton() {    return true;}@Overridepublic void run() {    if (connectionManager == null) {        return;    }    connectionManager.closeExpiredConnections();    connectionManager.closeIdleConnections(IDLE_TIMEOUT, TimeUnit.SECONDS);}复制代码

}

配置RestTemplate

@Componentpublic class RestRequest extends RestTemplate {@Autowired@Qualifier("httpClientFactory")private HttpClientFactoryBean httpClientFactory;@PostConstructpublic void init() throws Exception {	HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClientFactory.getObject());	setRequestFactory(factory);	List
    
     > converters = new ArrayList
     
      >();	converters.add(new FastJsonHttpMessageConverter4());	setMessageConverters(converters);	setErrorHandler(new ResponseErrorHandler());}复制代码

}