最近使用到了HttpClient，看了一下官方文檔：HttpClient implementations are expected to be thread safe. It is recommended that the same instance of this class is reused for multiple request executions，翻譯過來的意思就是：HttpClient的實現是線程安全的，可以重用相同的實例來執行多次請求。遇到這種描述的話，我們就應該想到，需要對HttpClient來進行封裝了。由于是使用的spring boot，所以下面來結合spring boot來封裝HttpClient。

一、Request retry handler(請求重試處理)

為了使自定義異常機制生效，需要實現HttpRequestRetryHandler接口，代碼如下：

import java.io.IOException; import java.io.InterruptedIOException; import java.net.UnknownHostException; import javax.net.ssl.SSLException; import javax.net.ssl.SSLHandshakeException; import org.apache.http.HttpEntityEnclosingRequest; import org.apache.http.HttpRequest; import org.apache.http.NoHttpResponseException; import org.apache.http.client.HttpRequestRetryHandler; import org.apache.http.client.protocol.HttpClientContext; import org.apache.http.conn.ConnectTimeoutException; import org.apache.http.protocol.HttpContext; import org.springframework.beans.factory.annotation.Value; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration;  /**  * 描述：HttpClient的重試處理機制  */ @Configuration public class MyhttpRequestRetryHandler {    @Value("${httpclient.config.retryTime}")// 此處建議采用@ConfigurationProperties(prefix="httpclient.config")方式，方便復用   private int retryTime;      @Bean   public HttpRequestRetryHandler httpRequestRetryHandler() {     // 請求重試     final int retryTime = this.retryTime;     return new HttpRequestRetryHandler() {       public boolean retryRequest(IOException exception, int executionCount, HttpContext context) {         // Do not retry if over max retry count,如果重試次數超過了retryTime,則不再重試請求         if (executionCount >= retryTime) {           return false;         }         // 服務端斷掉客戶端的連接異常         if (exception instanceof NoHttpResponseException) {           return true;         }         // time out 超時重試         if (exception instanceof InterruptedIOException) {           return true;         }         // Unknown host         if (exception instanceof UnknownHostException) {           return false;         }         // Connection refused         if (exception instanceof ConnectTimeoutException) {           return false;         }         // SSL handshake exception         if (exception instanceof SSLException) {           return false;         }         HttpClientContext clientContext = HttpClientContext.adapt(context);         HttpRequest request = clientContext.getRequest();         if (!(request instanceof HttpEntityEnclosingRequest)) {           return true;         }         return false;       }     };   } } 

二、Pooling connection manager(連接池管理)

PoolingHttpClientConnectionManager用來管理客戶端的連接池，并且可以為多個線程的請求提供服務，代碼如下：