java - 如何在 Apache httpclient 中使用指数退避策略？

Question

docs指定一个 ExponentialBackOffSchedulingStrategy 类，但它似乎不存在于版本 4.5 中。

此外，没有找到任何解释如何使用它的内容。

以前有人用过类似的东西吗？

Answer 1

如果您使用这样的 Maven 包安装 Apache HTTP Client 4.5.x(Grails Maven 依赖语法):

compile "org.apache.httpcomponents:httpclient:4.5.1"
compile "org.apache.httpcomponents:httpcore:4.4.3"

您需要添加另一个 jar 来获取这些类，如下所示:

compile 'org.apache.httpcomponents:httpclient-cache:4.5.1'

参见 https://hc.apache.org/httpcomponents-client-4.5.x/download.html

然后你可以这样连接它:

 import org.apache.http.impl.client.*;
 import org.apache.http.impl.client.cache.*;
 import org.apache.http.client.methods.*;

 CloseableHttpClient createClient() {
     CachingHttpClientBuilder hcb = new CachingHttpClientBuilder();
     CacheConfig cc = CacheConfig.DEFAULT;
     ExponentialBackOffSchedulingStrategy ebo = new ExponentialBackOffSchedulingStrategy(cc);
     hcb.setSchedulingStrategy(ebo);
     CloseableHttpClient hc = hcb.build();
     return hc;
 }

 // You'll need to replace the URL below with something that returns a 5xx error
 CloseableHttpClient client = createClient();
 HttpUriRequest request = new HttpGet("http://www.example.com/throwsServerError");
 for (int i=0; i<4; i++) {
     CloseableHttpResponse response =  client.execute(request);
     println new Date().toString() + " " + response.getStatusLine().getStatusCode();
 }