在Java开发中，访问第三方HTTP协议的网络接口，通常使用的连接工具为JDK自带的HttpURLConnection、HttpClient（现在应该称之为HttpComponents）和OKHttp。

这些Http连接工具，使用起来都比较复杂，如果项目中使用的是Spring框架，可以使用Spring自带的RestTemplate来进行Http连接请求。

RestTemplate底层默认的连接方式是Java中的HttpURLConnection，可以使用ClientHttpRequestFactory来指定底层使用不同的HTTP连接方式。

RestTemplate中默认的连接方式

RestTemplate中默认使用的是SimpleClientHttpRequestFactory，我们这里手动创建SimpleClientHttpRequestFactory可以指定连接的超时时间，读数据的超时时间。

package com.morris.user.demo;import com.morris.user.entity.Order;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.client.SimpleClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;/*** restTemplate+httpUrlConnection*/
@Slf4j
public class RestTemplateDemo1 {public static void main(String[] args) {SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();factory.setConnectTimeout(3000);factory.setReadTimeout(5000);RestTemplate restTemplate = new RestTemplate(factory);Order[] orders = restTemplate.getForObject("http://127.0.0.1:8020/order/findOrderByUserId?userId=", Order[].class, 1);log.info("orders :{}", orders);}}

SimpleClientHttpRequestFactory底层在创建请求的时候使用的就是HttpURLConnection。

org.springframework.http.client.SimpleClientHttpRequestFactory#createRequest

public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {HttpURLConnection connection = openConnection(uri.toURL(), this.proxy);prepareConnection(connection, httpMethod.name());if (this.bufferRequestBody) {return new SimpleBufferingClientHttpRequest(connection, this.outputStreaming);}else {return new SimpleStreamingClientHttpRequest(connection, this.chunkSize, this.outputStreaming);}
}

RestTemplate与HttpClient的结合

只需要在构造RestTemplate实例时传入HttpComponentsClientHttpRequestFactory对象即可。

package com.morris.user.demo;import com.morris.user.entity.Order;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;/*** RestTemplate+HttpClient*/
@Slf4j
public class RestTemplateDemo2 {public static void main(String[] args) {HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory();RestTemplate restTemplate = new RestTemplate(factory);Order[] orders = restTemplate.getForObject("http://127.0.0.1:8020/order/findOrderByUserId?userId=", Order[].class, 1);log.info("orders :{}", orders);}}

HttpComponentsClientHttpRequestFactory底层在创建请求时使用了HttpClient。
org.springframework.http.client.HttpComponentsClientHttpRequestFactory#createRequest

public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {HttpClient client = getHttpClient();HttpUriRequest httpRequest = createHttpUriRequest(httpMethod, uri);postProcessHttpRequest(httpRequest);HttpContext context = createHttpContext(httpMethod, uri);if (context == null) {context = HttpClientContext.create();}// Request configuration not set in the contextif (context.getAttribute(HttpClientContext.REQUEST_CONFIG) == null) {// Use request configuration given by the user, when availableRequestConfig config = null;if (httpRequest instanceof Configurable) {config = ((Configurable) httpRequest).getConfig();}if (config == null) {config = createRequestConfig(client);}if (config != null) {context.setAttribute(HttpClientContext.REQUEST_CONFIG, config);}}if (this.bufferRequestBody) {return new HttpComponentsClientHttpRequest(client, httpRequest, context);}else {return new HttpComponentsStreamingClientHttpRequest(client, httpRequest, context);}
}

RestTemplate与HttpClient的在生产环境使用的最佳实践

在构建HttpClient时，经常需要配置很多信息，例如RequestTimeout、ConnectTimeout、SocketTimeout、代理、是否允许重定向、连接池等信息。

在HttpClient，对这些参数进行配置需要使用到RequestConfig类的一个内部类Builder。

这里将这些常用的配置抽取出来放到配置文件中：

package com.morris.user.config;import lombok.extern.slf4j.Slf4j;
import org.apache.http.HeaderElement;
import org.apache.http.HeaderElementIterator;
import org.apache.http.HttpHost;
import org.apache.http.client.HttpClient;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.ConnectionKeepAliveStrategy;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.DefaultHttpRequestRetryHandler;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicHeaderElementIterator;
import org.apache.http.protocol.HTTP;
import org.apache.http.ssl.SSLContextBuilder;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;import javax.annotation.Resource;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLContext;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;@EnableConfigurationProperties(HttpClientConfig.class)
@ConditionalOnClass(RestTemplate.class)
@Configuration
@Slf4j
public class RestTemplateAutoConfiguration {@Resourceprivate HttpClientConfig httpClientConfig;@Bean@ConditionalOnClass(CloseableHttpClient.class)public RestTemplate httpClientRestTemplate(ClientHttpRequestFactory clientHttpRequestFactory){return new RestTemplate(clientHttpRequestFactory);}@Bean@ConditionalOnClass(CloseableHttpClient.class)public ClientHttpRequestFactory clientHttpRequestFactory(HttpClient httpClient) {HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();clientHttpRequestFactory.setHttpClient(httpClient);clientHttpRequestFactory.setConnectTimeout(httpClientConfig.getRequest().getConnectTimeout());clientHttpRequestFactory.setReadTimeout(httpClientConfig.getRequest().getReadTimeout());clientHttpRequestFactory.setConnectionRequestTimeout(httpClientConfig.getRequest().getConnectionRequestTimeout());clientHttpRequestFactory.setBufferRequestBody(httpClientConfig.getRequest().isBufferRequestBody());return clientHttpRequestFactory;}@Bean@Primary@ConditionalOnClass(CloseableHttpClient.class)public HttpClient httpClient() throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException {HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();try {// 设置信任SSL访问SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(null, (arg0, arg1) -> true).build();httpClientBuilder.setSSLContext(sslContext);// 任何主机都不会抛出SSLException异常HostnameVerifier hostnameVerifier = NoopHostnameVerifier.INSTANCE;SSLConnectionSocketFactory sslConnectionSocketFactory = new SSLConnectionSocketFactory(sslContext, hostnameVerifier);Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create()// 注册HTTP和HTTPS请求.register("http", PlainConnectionSocketFactory.getSocketFactory()).register("https", sslConnectionSocketFactory).build();// 使用Httpclient连接池的方式配置PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);poolingHttpClientConnectionManager.setMaxTotal(httpClientConfig.getPool().getMaxTotalConnect());poolingHttpClientConnectionManager.setDefaultMaxPerRoute(httpClientConfig.getPool().getMaxConnectPerRoute());poolingHttpClientConnectionManager.setValidateAfterInactivity(httpClientConfig.getPool().getValidateAfterInactivity());httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager);httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(httpClientConfig.getPool().getRetryTimes(), true));httpClientBuilder.setKeepAliveStrategy(connectionKeepAliveStrategy());return httpClientBuilder.build();} catch (KeyManagementException | NoSuchAlgorithmException | KeyStoreException e) {log.error("初始化HTTP连接池出错", e);throw e;}}/*** 配置长连接保持策略* @return ConnectionKeepAliveStrategy*/public ConnectionKeepAliveStrategy connectionKeepAliveStrategy(){return (response, context) -> {// Honor 'keep-alive' headerHeaderElementIterator it = new BasicHeaderElementIterator(response.headerIterator(HTTP.CONN_KEEP_ALIVE));while (it.hasNext()) {HeaderElement he = it.nextElement();String param = he.getName();String value = he.getValue();if (value != null && "timeout".equalsIgnoreCase(param)) {try {return Long.parseLong(value) * 1000;} catch(NumberFormatException error) {log.error("解析长连接过期时间异常", error);}}}HttpHost target = (HttpHost) context.getAttribute(HttpClientContext.HTTP_TARGET_HOST);//如果请求目标地址,单独配置了长连接保持时间,使用该配置Optional<Map.Entry<String, Integer>> any = Optional.ofNullable(httpClientConfig.getPool().getKeepAliveTargetHost()).orElseGet(HashMap::new).entrySet().stream().filter(e -> e.getKey().equalsIgnoreCase(target.getHostName())).findAny();//否则使用默认长连接保持时间return any.map(en -> en.getValue() * 1000L).orElse(httpClientConfig.getPool().getKeepAliveTime() * 1000L);};}}