InetAddressResolverProvider (Java SE 21 & JDK 21)
Description: declaration: module: java.base, package: java.net.spi, class: InetAddressResolverProvider
Keywords: java.net.spi.InetAddressResolverProvider class

Module java.base
Package java.net.spi

# Class InetAddressResolverProvider

java.lang.Object
java.net.spi.InetAddressResolverProvider

public abstract class InetAddressResolverProvider extends Object
Service-provider class for InetAddress resolvers.

A resolver provider is a factory for custom implementations of InetAddress resolvers. A resolver defines operations for looking up (resolving) host names and IP addresses.

A resolver provider is a concrete subclass of this class that has a zero-argument constructor and implements the abstract methods specified below.

A given invocation of the Java virtual machine maintains a single system-wide resolver instance, which is used by InetAddress. It is set after the VM is fully initialized and when an invocation of a method in `InetAddress` class triggers the first lookup operation.

A resolver provider is located and loaded by `InetAddress` to create the system-wide resolver as follows:

1. The `ServiceLoader` mechanism is used to locate an `InetAddressResolverProvider` using the system class loader. The order in which providers are located is implementation specific. The first provider found will be used to instantiate the `InetAddressResolver` by invoking the `get(InetAddressResolverProvider.Configuration)` method. The returned `InetAddressResolver` will be set as the system-wide resolver.
2. If the previous step fails to find any resolver provider the built-in resolver will be set as the system-wide resolver.

If instantiating a custom resolver from a provider discovered in step 1 throws an error or exception, the system-wide resolver will not be set and the error or exception will be propagated to the caller of the method that triggered the lookup operation. Otherwise, any lookup operation will be performed using the system-wide resolver.

Implementation Note:
  `InetAddress` will use the built-in resolver for any lookup operation that might occur before the VM is fully booted.
Since:
  18

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static interface`
  `InetAddressResolverProvider.Configuration`
  A `Configuration` object is supplied to the `get(Configuration)` method when setting the system-wide resolver.

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `InetAddressResolverProvider()`
  Creates a new instance of `InetAddressResolverProvider`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract InetAddressResolver`
  `get(InetAddressResolverProvider.Configuration configuration)`
  Initialize and return an `InetAddressResolver` provided by this provider.
  `abstract String`
  `name()`
  Returns the name of this provider, or `null` if unnamed.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### InetAddressResolverProvider

    protected InetAddressResolverProvider()
    Creates a new instance of `InetAddressResolverProvider`.
    Implementation Note:
      It is recommended that an `InetAddressResolverProvider` service implementation initialization should be as simple as possible, in order to avoid possible risks of deadlock or class loading cycles during the instantiation of the service provider.
    Throws:
      `SecurityException` - if a security manager is present and its `checkPermission` method doesn't allow the `RuntimePermission("inetAddressResolverProvider")`.

- ## Method Details

  - ### get

    public abstract InetAddressResolver get(InetAddressResolverProvider.Configuration configuration)
    Initialize and return an `InetAddressResolver` provided by this provider. This method is called by `InetAddress` when installing the system-wide resolver implementation.

    Any error or exception thrown by this method is considered as a failure of `InetAddressResolver` instantiation and will be propagated to the caller of the method that triggered the lookup operation.

    Parameters:
      `configuration` - a `InetAddressResolverProvider.Configuration` instance containing platform built-in address resolution configuration.
    Returns:
      the resolver provided by this provider

  - ### name

    public abstract String name()
    Returns the name of this provider, or `null` if unnamed.
    Returns:
      the name of this provider, or `null` if unnamed