title: How to use HttpClientBuilder with Http proxy?
body: <p>I am trying to set proxy for a request I am making using <code>HttpClientBuilder</code> as follows:</p>
  
  <pre><code>        CredentialsProvider credsProvider = new BasicCredentialsProvider();
          UsernamePasswordCredentials usernamePasswordCredentials = new UsernamePasswordCredentials(proxyUser, proxyPassword);
          credsProvider.setCredentials(new AuthScope(proxyHost, proxyPort), usernamePasswordCredentials);
  
          builder.useSystemProperties();
          builder.setProxy(new HttpHost(proxyHost, proxyPort));
          builder.setDefaultCredentialsProvider(credsProvider);
          builder.setProxyAuthenticationStrategy(new ProxyAuthenticationStrategy());
  </code></pre>
  
  <p>where builder is:</p>
  
  <pre><code>    HttpClientBuilder builder = HttpClientBuilder.create();
  </code></pre>
  
  <p>However, I get this exception when I execute this request:</p>
  
  <pre><code>java.lang.RuntimeException: org.apache.http.conn.UnsupportedSchemeException: http protocol is not supported
  Caused by: org.apache.http.conn.UnsupportedSchemeException: http protocol is not supported
          at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:108) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.conn.BasicHttpClientConnectionManager.connect(BasicHttpClientConnectionManager.java:338) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:388) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107) ~[httpclient-4.5.1.jar:4.5.1]
          at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:55) ~[httpclient-4.5.1.jar:4.5.1]
  </code></pre>
  
  <p>(exception shortened for brevity)</p>
  
  <p>Since this is an HTTP proxy, I don't want to change the scheme to HTTPS, which anyways won't work. How do I get this working?</p>