InternetAddressResolutionSPI.java

package java18.internetaddress;

/**
 * Java 18 Internet-Address Resolution SPI
 * Demonstrates custom hostname resolution
 * 
 * NOTE: This is a Service Provider Interface (SPI)
 * The classes InetAddressResolver and InetAddressResolverProvider are in java.net.spi package
 * which may require Java 18+ and proper module configuration.
 * 
 * To use this, you need to register it via ServiceLoader:
 * 1. Create file: META-INF/services/java.net.spi.InetAddressResolverProvider
 * 2. Add line: java18.internetaddress.CustomResolverProvider
 * 3. The ServiceLoader will automatically discover and use it
 */
public class InternetAddressResolutionSPI {
    public static void main(String[] args) {
        System.out.println("=== Java 18 Internet-Address Resolution SPI ===\n");
        
        System.out.println("This SPI allows custom hostname resolution implementations.");
        System.out.println("\nExample Custom Resolver Provider Code:");
        System.out.println("""
            import java.net.*;
            import java.net.spi.InetAddressResolver;
            import java.net.spi.InetAddressResolverProvider;
            
            public class CustomResolverProvider extends InetAddressResolverProvider {
                @Override
                public InetAddressResolver get(Configuration configuration) {
                    return new InetAddressResolver() {
                        @Override
                        public InetAddress[] lookupByName(String host, LookupPolicy lookupPolicy) 
                                throws UnknownHostException {
                            // Custom resolution logic
                            if (host.equals("example.com")) {
                                return new InetAddress[]{InetAddress.getByName("93.184.216.34")};
                            }
                            // Fall back to default resolution
                            return InetAddress.getAllByName(host);
                        }
            
                        @Override
                        public String lookupByAddress(byte[] addr) throws UnknownHostException {
                            return InetAddress.getByAddress(addr).getHostName();
                        }
                    };
                }
                
                @Override
                public String name() {
                    return "custom-resolver";
                }
            }
            """);
        
        System.out.println("\nTo register the provider:");
        System.out.println("1. Create file: META-INF/services/java.net.spi.InetAddressResolverProvider");
        System.out.println("2. Add line: java18.internetaddress.CustomResolverProvider");
        System.out.println("3. The ServiceLoader will automatically discover and use it");
        
        System.out.println("\nUse Cases:");
        System.out.println("- Custom DNS resolution");
        System.out.println("- Testing and mocking");
        System.out.println("- Network address translation");
        System.out.println("- Load balancing");
        System.out.println("- Security filtering");
        
        System.out.println("\nBenefits:");
        System.out.println("- Flexible hostname resolution");
        System.out.println("- Customizable network behavior");
        System.out.println("- Useful for testing");
        System.out.println("- Service provider pattern");
        
        System.out.println("\nNote: The actual implementation requires:");
        System.out.println("- Java 18 or later");
        System.out.println("- java.net.spi module access");
        System.out.println("- Proper ServiceLoader configuration");
    }
}

/**
 * Example Custom Resolver Provider Structure
 * 
 * NOTE: This is a conceptual example. The actual implementation requires:
 * - java.net.spi.InetAddressResolver interface
 * - java.net.spi.InetAddressResolverProvider abstract class
 * - These classes are part of Java 18+ and may require module configuration
 * 
 * For a working implementation, ensure you have:
 * 1. Java 18 or later
 * 2. Proper module configuration (if using modules)
 * 3. ServiceLoader registration file
 */