public static boolean isProxyServer(String remoteAddr) { 
    if (proxyServers == null) {
      refresh(); 
    }
    return proxyServers.contains(remoteAddr);
  }
@Test
  public void testProxyServer() {
    Configuration conf = new Configuration();
    assertFalse(ProxyServers.isProxyServer("1.1.1.1"));
    conf.set(ProxyServers.CONF_HADOOP_PROXYSERVERS, "2.2.2.2, 3.3.3.3");
    ProxyUsers.refreshSuperUserGroupsConfiguration(conf);
    assertFalse(ProxyServers.isProxyServer("1.1.1.1"));
    assertTrue(ProxyServers.isProxyServer("2.2.2.2"));
    assertTrue(ProxyServers.isProxyServer("3.3.3.3"));
  }