# Class AttachProvider

java.lang.Object
com.sun.tools.attach.spi.AttachProvider

public abstract class AttachProvider extends Object
Attach provider class for attaching to a Java virtual machine.

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

An attach provider implementation is typically tied to a Java virtual machine implementation, version, or even mode of operation. That is, a specific provider implementation will typically only be capable of attaching to a specific Java virtual machine implementation or version. For example, Oracle's JDK implementation ships with provider implementations that can only attach to Oracle's HotSpot virtual machine. In general, if an environment consists of Java virtual machines of different versions and from different vendors then there will be an attach provider implementation for each family of implementations or versions.

An attach provider is identified by its `name` and `type`. The name is typically, but not required to be, a name that corresponds to the VM vendor. The Oracle JDK implementation, for example, ships with attach providers that use the package name "sun" (for historical reasons). The type typically corresponds to the attach mechanism. For example, an implementation that uses the Doors inter-process communication mechanism might use the type "doors". The purpose of the name and type is to identify providers in environments where there are multiple providers installed.

AttachProvider implementations are loaded and instantiated at the first invocation of the `providers` method. This method attempts to load all provider implementations that are installed on the platform.

All of the methods in this class are safe for use by multiple concurrent threads.

Since:
  1.6

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `AttachProvider()`
  Initializes a new instance of this class.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `VirtualMachine`
  `attachVirtualMachine(VirtualMachineDescriptor vmd)`
  Attaches to a Java virtual machine.
  `abstract VirtualMachine`
  `attachVirtualMachine(String id)`
  Attaches to a Java virtual machine.
  `abstract List<VirtualMachineDescriptor>`
  `listVirtualMachines()`
  Lists the Java virtual machines known to this provider.
  `abstract String`
  `name()`
  Return this provider's name.
  `static List<AttachProvider>`
  `providers()`
  Returns a list of the installed attach providers.
  `abstract String`
  `type()`
  Return this provider's type.

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

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

- ## Constructor Details

  - ### AttachProvider

    protected AttachProvider()
    Initializes a new instance of this class.

- ## Method Details

  - ### name

    public abstract String name()
    Return this provider's name.
    Returns:
      The name of this provider

  - ### type

    public abstract String type()
    Return this provider's type.
    Returns:
      The type of this provider

  - ### attachVirtualMachine

    public abstract VirtualMachine attachVirtualMachine(String id) throws AttachNotSupportedException, IOException
    Attaches to a Java virtual machine.

    A Java virtual machine is identified by an abstract identifier. The nature of this identifier is platform dependent but in many cases it will be the string representation of the process identifier (or pid).

    This method parses the identifier and maps the identifier to a Java virtual machine (in an implementation dependent manner). If the identifier cannot be parsed by the provider then an `AttachNotSupportedException` is thrown. Once parsed this method attempts to attach to the Java virtual machine. If the provider detects that the identifier corresponds to a Java virtual machine that does not exist, or it corresponds to a Java virtual machine that does not support the attach mechanism implemented by this provider, or it detects that the Java virtual machine is a version to which this provider cannot attach, then an `AttachNotSupportedException` is thrown.

    Parameters:
      `id` - The abstract identifier that identifies the Java virtual machine.
    Returns:
      VirtualMachine representing the target virtual machine.
    Throws:
      `AttachNotSupportedException` - If the identifier cannot be parsed, or it corresponds to to a Java virtual machine that does not exist, or it corresponds to a Java virtual machine which this provider cannot attach.
      `IOException` - If some other I/O error occurs
      `NullPointerException` - If `id` is `null`

  - ### attachVirtualMachine

    public VirtualMachine attachVirtualMachine(VirtualMachineDescriptor vmd) throws AttachNotSupportedException, IOException
    Attaches to a Java virtual machine.

    A Java virtual machine can be described using a `VirtualMachineDescriptor`. This method invokes the descriptor's `provider()` method to check that it is equal to this provider. It then attempts to attach to the Java virtual machine.

    Parameters:
      `vmd` - The virtual machine descriptor
    Returns:
      VirtualMachine representing the target virtual machine.
    Throws:
      `AttachNotSupportedException` - If the descriptor's `provider()` method returns a provider that is not this provider, or it does not correspond to a Java virtual machine to which this provider can attach.
      `IOException` - If some other I/O error occurs
      `NullPointerException` - If `vmd` is `null`

  - ### listVirtualMachines

    public abstract List<VirtualMachineDescriptor> listVirtualMachines()
    Lists the Java virtual machines known to this provider.

    This method returns a list of `VirtualMachineDescriptor` elements. Each `VirtualMachineDescriptor` describes a Java virtual machine to which this provider can potentially attach. There isn't any guarantee that invoking `attachVirtualMachine` on each descriptor in the list will succeed.

    Returns:
      The list of virtual machine descriptors which describe the Java virtual machines known to this provider (may be empty).

  - ### providers

    public static List<AttachProvider> providers()
    Returns a list of the installed attach providers.

    An AttachProvider is installed on the platform if:

    - It is installed in a JAR file that is visible to the defining class loader of the AttachProvider type (usually, but not required to be, the `system class loader`).
    - The JAR file contains a provider configuration named `com.sun.tools.attach.spi.AttachProvider` in the resource directory `META-INF/services`.
    - The provider configuration file lists the full-qualified class name of the AttachProvider implementation.

    The format of the provider configuration file is one fully-qualified class name per line. Space and tab characters surrounding each class name, as well as blank lines are ignored. The comment character is `'#'` (`0x23`), and on each line all characters following the first comment character are ignored. The file must be encoded in UTF-8.

    AttachProvider implementations are loaded and instantiated (using the zero-arg constructor) at the first invocation of this method. The list returned by the first invocation of this method is the list of providers. Subsequent invocations of this method return a list of the same providers. The list is unmodifiable.

    Returns:
      A list of the installed attach providers.