Question

This is really unexpected behavior. I’m writing a simple web browser using the JavaFX WebView. To make the web requests go through a local proxy, I wrote code similar to this:

System.setProperty("http.proxyHost", "localhost");
System.setProperty("http.proxyPort", "8080");

It appears to work fine if the proxy is running. However, if it isn’t, Java silently reverts to not using a proxy at all! How can I force Java to fail if the proxy is not available?

Answer 1

You may be able to do this with a custom ProxySelector which only allows your proxy, and doesn’t offer Proxy.NO_PROXY as an alternative:

import java.net.*;
import java.util.*;

public class AlwaysProxySelector implements ProxySelector {
  private List<Proxy> proxies = Arrays.asList(new Proxy[] {
        new Proxy(Proxy.Type.HTTP, new InetSocketAddress("localhost", 8080))
      });

  public List<Proxy> select(URI u) { return proxies; }
  public void connectFailed(URI u, SocketAddress a, IOException e) {}
}

You install this selector using ProxySelector.setDefault(new AlwaysProxySelector());