private void selectHttpProxy() {
		AbstractHttp defaultProxy = null;
		ClassLoader classLoader = HttpUtil.class.getClassLoader();
		// 基于 java 11 HttpClient
		if (ClassUtil.isPresent("java.net.http.HttpClient", classLoader)) {
			defaultProxy = getHttpProxy(com.xkcoding.http.support.java11.HttpClientImpl.class);
		}
		// 基于 okhttp3
		if (null == defaultProxy && ClassUtil.isPresent("okhttp3.OkHttpClient", classLoader)) {
			defaultProxy = getHttpProxy(com.xkcoding.http.support.okhttp3.OkHttp3Impl.class);
		}
		// 基于 httpclient
		if (null == defaultProxy && ClassUtil.isPresent("org.apache.http.impl.client.HttpClients", classLoader)) {
			defaultProxy = getHttpProxy(com.xkcoding.http.support.httpclient.HttpClientImpl.class);
		}
		// 基于 hutool
		if (null == defaultProxy && ClassUtil.isPresent("cn.hutool.http.HttpRequest", classLoader)) {
			defaultProxy = getHttpProxy(com.xkcoding.http.support.hutool.HutoolImpl.class);
		}

		if (defaultProxy == null) {
			throw new SimpleHttpException("Has no HttpImpl defined in environment!");
		}

		proxy = defaultProxy;
	}