package com.avangate.api.samples;

import com.avangate.api.rest.ApiClient;
import javax.ws.rs.core.Response;

public class ListProducts
{
    public static void main( String[] args )
    {
        String merchantCode = "AVLRNG";
        String merchantSecret = "1sGC*[c_T0)J9(k+]6Kw";
        String apiUrl = "https://api.avangate.com/rest/3.0/";

        ApiClient client = new ApiClient(merchantCode, merchantSecret, apiUrl);

        Response response = client.get("products/");

        String products = response.readEntity(String.class);

        System.out.println("status: " + response.getStatus());
        System.out.println("headers: " + response.getHeaders());
        System.out.println("body:" + products);

    }
}

package com.avangate.api.samples;

import com.avangate.api.rest.ApiClient;
import javax.ws.rs.core.Response;

public class ListProducts
{
    public static void main( String[] args )
    {
        String merchantCode = "";
        String merchantSecret = "";
        String apiUrl = "";

        ApiClient client = new ApiClient(merchantCode, merchantSecret, apiUrl);

        Response response = client.get("products/");

        String products = response.readEntity(String.class);

        System.out.println("status: " + response.getStatus());
        System.out.println("headers: " + response.getHeaders());
        System.out.println("body:" + products);

    }
}

Update ListProducts.java