java - 使用 HttpClientBuilder 时出现“ClassNotFoundException

Question

老程序员，Java新手。我正在尝试运行我认为非常常见的示例代码，该代码在网络上的许多地方都很相似，HttpClient httpClient = HttpClientBuilder.create().build() 抛出异常，我可以弄清楚为什么。我正在使用 HttpClient 4.3。

import java.io.IOException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.util.EntityUtils;

public class ATest{

   public static void main(String[] args) throws Exception {
      String strURL  = "http://192.9.10.11/cgi-bin/echo";
      String message = "hello world";
      // next line throwsClassNotFoundException, why?
      HttpClient httpClient = HttpClientBuilder.create().build();
      HttpPost   httpPost   = new  HttpPost(strURL);
      httpPost.setEntity(new StringEntity(message));
      HttpResponse response = httpClient.execute(httpPost);
      try {
         System.out.println(response.getStatusLine());
         HttpEntity entity = response.getEntity();
         // do something useful with the response body
         // and ensure it is fully consumed
         EntityUtils.consume(entity);
      } finally {
         response.close();
      }
   }
}

Answer 1

Java VM 带有很多类但没有 org.apache.http.* .

你必须帮助 Java VM，就像你帮助 gcc 将 C 或 C++ 中的二进制文件与 -lxxx 链接起来一样和 LD_LIBRARY_PATH , 与类路径概念。 java -cp <path>:<path>:<path>指定需要的类在哪里(例如 Unix 下二进制文件的 .so)。

org.apache.http.*类位于一个 jar 里。您必须将此 jar 路径指定到 cp <path> 中规范。

apache http client 4.3 delivery 中包含的 jar 位于 lib 目录中:

• httpclient-4.3.jar
• httpmime-4.3.jar
• fluent-hc-4.3.jar
• httpclient-cache-4.3.jar
• httpcore-4.3.jar
• commons-logging-1.1.3.jar
• commons-codec-1.6.jar

如果您的代码只是示例，则不需要全部，我建议 commons-logging-1.1.3.jar和 httpclient-4.3.jar