2916. Design Pattern - Proxy
Proxy Pattern

Structural Pattern: Proxy Pattern.

1. Proxy Pattern

In proxy pattern, a class represents functionality of another class. The Proxy class provides a surrogate or place holder to provide access to an object.

2. Example

2.1 Internet

public interface Internet {
    public void connect(String host) throws Exception;
}

public class RealInternet implements Internet
{
    @Override
    public void connect(String host)
    {
        System.out.println("Connecting to '"+ host + "' ...");
    }
}

2.2 Proxy

public class ProxyInternet implements Internet
{
    private Internet internet = new RealInternet();
    private static List<String> bannedSites;

    static
    {
        bannedSites = new ArrayList<String>();
        bannedSites.add("abc.com");
        bannedSites.add("def.com");
        bannedSites.add("ijk.com");
        bannedSites.add("lnm.com");
    }

    @Override
    public void connect(String host) throws Exception
    {
        if(bannedSites.contains(host.toLowerCase()))
        {
            throw new Exception("Access Denied: unable to connect to '" + host + "'");
        }

        internet.connect(host);
    }
}

2.3 Client

public class ClientTest {

    @Test
    public void testClient() {
        Internet internet = new ProxyInternet();
        System.out.println("Internet is working now ...");
        try
        {
            internet.connect("jojozhuang.github.io");
            internet.connect("abc.com");
        }
        catch (Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
}

Output.

Internet is working now ...
Connecting to 'jojozhuang.github.io' ...
Access Denied: unable to connect to 'abc.com'

4. Source Files

5. References