使用HttpClient4来构建Spring RestTemplate

Spring RestTemplate简单说明

现在REST服务已经很普及了，在我们的程序中，经常会需要调用REST API，这时候会有很多选择，原始一点的JDK自带的，再进一步点使用HttpClient，或者说如果我们使用Jersey这种框架的话，也会自带rest client。但是我们项目使用的SpringMVC，所以直接使用RestTemplate。使用RestTemplate比直接使用Httpclient简单很多，同时也可以借助httpclient来实现RestTemplate。

通过使用RestTemplate仅仅只需要写几行代码，就可以完成直接使用httpclient很多行代码的事情,具体见： https://spring.io/blog/2009/03/27/rest-in-spring-3-resttemplate

RestTemplate有三个构造函数：

1. 默认构造函数，默认使用SimpleClientHttpRequestFactory，使用JDK自带的java.net包进行网络传输。
2. public RestTemplate(ClientHttpRequestFactory requestFactory)。传入一个ClientHttpRequestFactory，ClientHttpRequestFactory在Spring中的实现有很多个，如HttpComponentsClientHttpRequestFactory，Netty4ClientHttpRequestFactory等，具体的可以看代码，这里只介绍HttpComponentsClientHttpRequestFactory，需要用到 HttpClient4.
3. public RestTemplate(List > messageConverters),使用SpringMvc的应该对HttpMessageConverter很熟悉了，RestTemplate默认会给我们设置好常用的HttpMessageConverter，我一般很少使用到这个构造方法。

HttpComponentsClientHttpRequestFactory

这里主要讨论的是通过第二个构造方法来使用HttpClient4 来进行网络传输。下面我们来看下HttpComponentsClientHttpRequestFactory这个类。先看看他的构造方法

  /**   * Create a new instance of the {@code HttpComponentsClientHttpRequestFactory}   * with a default {@link HttpClient}.   */  public HttpComponentsClientHttpRequestFactory() {   this(HttpClients.createSystem());  }   /**   * Create a new instance of the {@code HttpComponentsClientHttpRequestFactory}   * with the given {@link HttpClient} instance.   * <p>As of Spring Framework 4.0, the given client is expected to be of type   * {@link CloseableHttpClient} (requiring HttpClient 4.3+).   * @param httpClient the HttpClient instance to use for this request factory   */  public HttpComponentsClientHttpRequestFactory(HttpClient httpClient) {   Assert.notNull(httpClient, "'httpClient' must not be null");   Assert.isInstanceOf(CloseableHttpClient.class, httpClient, "'httpClient' is not of type CloseableHttpClient");   this.httpClient = (CloseableHttpClient) httpClient;  }

import org.apache.http.config.Registry; import org.apache.http.config.RegistryBuilder; 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.HttpClientBuilder; import org.apache.http.impl.conn.PoolingHttpClientConnectionManager; import org.apache.http.ssl.SSLContextBuilder; import org.apache.http.ssl.TrustStrategy; import javax.net.ssl.HostnameVerifier; import javax.net.ssl.SSLContext; import java.security.KeyManagementException; import java.security.KeyStoreException; import java.security.NoSuchAlgorithmException; import java.security.cert.CertificateException; import java.security.cert.X509Certificate; /**  * Created by Administrator on 2015/6/8.  */ public class HttpClientUtils {     public static CloseableHttpClient acceptsUntrustedCertsHttpClient() throws KeyStoreException, NoSuchAlgorithmException, KeyManagementException {  HttpClientBuilder b = HttpClientBuilder.create();  // setup a Trust Strategy that allows all certificates.  //  SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(null, new TrustStrategy() {      public boolean isTrusted(X509Certificate[] arg0, String arg1) throws CertificateException {   return true;      }  }).build();  b.setSSLContext(sslContext);  // don't check Hostnames, either.  //      -- use SSLConnectionSocketFactory.getDefaultHostnameVerifier(), if you don't want to weaken  HostnameVerifier hostnameVerifier = NoopHostnameVerifier.INSTANCE;  // here's the special part:  //      -- need to create an SSL Socket Factory, to use our weakened "trust strategy";  //      -- and create a Registry, to register it.  //  SSLConnectionSocketFactory sslSocketFactory = new SSLConnectionSocketFactory(sslContext, hostnameVerifier);  Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create()   .register("http", PlainConnectionSocketFactory.getSocketFactory())   .register("https", sslSocketFactory)   .build();  // now, we create connection-manager using our Registry.  //      -- allows multi-threaded use  PoolingHttpClientConnectionManager connMgr = new PoolingHttpClientConnectionManager( socketFactoryRegistry);  connMgr.setMaxTotal(200);  connMgr.setDefaultMaxPerRoute(100);  b.setConnectionManager( connMgr);  // finally, build the HttpClient;  //      -- done!  CloseableHttpClient client = b.build();  return client;     } } 

创建并使用RestTemplate

        CloseableHttpClient httpClient = HttpClientUtils.acceptsUntrustedCertsHttpClient();         HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);         RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory);         String result = restTemplate.getForObject("http://www.baidu.com",String.class);         System.out.println(result);

那么问题来了，我们既然是使用Spring，那肯定希望把他RestTemplate配置成Spring bean来使用，HttpClient是线程安全的，他可以在程序中共享，创建一个成Spring bean刚好。下面是xml配置。

   <bean id="httpClient" class="com.hupengcool.util.HttpClientUtils" factory-method="acceptsUntrustedCertsHttpClient"/>      <bean id="clientHttpRequestFactory" class="org.springframework.http.client.HttpComponentsClientHttpRequestFactory">         <constructor-arg ref="httpClient"/>     </bean>      <bean id="restTemplate" class=" org.springframework.web.client.RestTemplate">         <constructor-arg ref="clientHttpRequestFactory" />     </bean>

开始使用Spring RestTemplate吧。。。。。PS:项目中除了Spring相关jar包外。需要添加HttpClient4.5，jackson 2.x的jar包。