How to set the proxy of a wifi in android 4.x?

This is the code. Type is an enum that contains two DHCP and PAC values. The problem is that this code tells me that the call requires android 21 and I need this to work on 18. Is there any way? Thanks in advance.

private static WifiConfiguration setProxy(WifiConfiguration conf, String hostname, int port, List<String> bypass, PROXY_TYPE type) {
try {
    Class proxyInfoClass = Class.forName("android.net.ProxyInfo");
    Class[] setHttpProxyParams = new Class[1];
    setHttpProxyParams[0] = proxyInfoClass;
    Class wifiConfigClass = Class.forName("android.net.wifi.WifiConfiguration");
    Method setHttpProxy = wifiConfigClass.getDeclaredMethod("setHttpProxy", setHttpProxyParams);
    setHttpProxy.setAccessible(true);

    //Get the ENUM ProxySettings in IpConfiguration
    Class ipConfigClass = Class.forName("android.net.IpConfiguration");
    Field f = ipConfigClass.getField("proxySettings");
    Class proxySettingsClass = f.getType();

    Class[] setProxySettingsParams = new Class[1];
    setProxySettingsParams[0] = proxySettingsClass;
    Method setProxySettings = wifiConfigClass.getDeclaredMethod("setProxySettings", setProxySettingsParams);
    setProxySettings.setAccessible(true);


    ProxyInfo pi = null;
    String Type = null;
    switch (type) {
        case MANUAL:
            Type = "DHCP";
            //esta es la llamada que me dice API21
            pi = ProxyInfo.buildDirectProxy(hostname, port, bypass);
            break;
        case PAC_URL:
            Type = "PAC";
            //esta tambien
            pi = ProxyInfo.buildPacProxy(Uri.parse(hostname));
    }

    //pass the new object to setHttpProxy
    Object[] params_SetHttpProxy = new Object[1];
    params_SetHttpProxy[0] = pi;
    setHttpProxy.invoke(conf, params_SetHttpProxy);

    //pass the enum to setProxySettings
    Object[] params_setProxySettings = new Object[1];
    params_setProxySettings[0] = Enum.valueOf((Class<Enum>) proxySettingsClass, Type);
    setProxySettings.invoke(conf, params_setProxySettings);
} catch (Exception e) {
    e.printStackTrace();
}
return conf;

}