BeansLinker (Java SE 23 & JDK 23)
Description: declaration: module: jdk.dynalink, package: jdk.dynalink.beans, class: BeansLinker
Keywords: jdk.dynalink.beans.BeansLinker class

# Class BeansLinker

java.lang.Object
jdk.dynalink.beans.BeansLinker

All Implemented Interfaces:
  `GuardingDynamicLinker`

public class BeansLinker extends Object implements GuardingDynamicLinker
A linker for ordinary Java objects. Normally used as the ultimate fallback linker by the `DynamicLinkerFactory` so it is given the chance to link calls to all objects that no other linker recognized. Specifically, this linker will:

- if the object is a `record`, expose all public accessors of record components as property getters for `StandardOperation.GET` operations in the `StandardNamespace.PROPERTY` namespace;
- expose all public methods of form `setXxx()`, `getXxx()`, and `isXxx()` as property setters and getters for `StandardOperation.SET` and `StandardOperation.GET` operations in the `StandardNamespace.PROPERTY` namespace, except for getters for properties with names already handled by record component getters;
- expose all public methods for retrieval for `StandardOperation.GET` operation in the `StandardNamespace.METHOD` namespace; the methods thus retrieved can then be invoked using `StandardOperation.CALL`.
- expose all public fields as properties, unless there are getters or setters for the properties of the same name;
- expose elements of native Java arrays, `List` and `Map` objects as `StandardOperation.GET` and `StandardOperation.SET` operations in the `StandardNamespace.ELEMENT` namespace;
- expose removal of elements of `List` and `Map` objects as `StandardOperation.REMOVE` operation in the `StandardNamespace.ELEMENT` namespace;
- expose a virtual property named `length` on Java arrays, `Collection` and `Map` objects;
- expose `StandardOperation.NEW` on instances of `StaticClass` as calls to constructors, including those static class objects that represent Java arrays (their constructors take a single `int` parameter representing the length of the array to create);
- expose static methods, fields, and properties of classes in a similar manner to how instance method, fields, and properties are exposed, on `StaticClass` objects.
- expose a virtual property named `static` on instances of `Class` to access their `StaticClass`.

Overloaded method resolution is performed automatically for property setters, methods, and constructors. Additionally, manual overloaded method selection is supported by having a call site specify a name for a method that contains an explicit signature, e.g. `StandardOperation.GET.withNamespace(METHOD).named("parseInt(String,int)")` You can use non-qualified class names in such signatures regardless of those classes' packages, they will match any class with the same non-qualified name. You only have to use a fully qualified class name in case non-qualified class names would cause selection ambiguity (that is extremely rare). Overloaded resolution for constructors is not automatic as there is no logical place to attach that functionality to but if a language wishes to provide this functionality, it can use `getConstructorMethod(Class, String)` as a useful building block for it.

Variable argument invocation is handled for both methods and constructors.

Caller sensitive methods can be linked as long as they are otherwise public and link requests have call site descriptors carrying full-strength `MethodHandles.Lookup` objects and not weakened lookups or the public lookup.

The behavior for handling missing members can be customized by passing a `MissingMemberHandlerFactory` to the `constructor`.

The class also exposes various methods for discovery of available property and method names on classes and class instances, as well as access to per-class linkers using the `getLinkerForClass(Class)` method.

Since:
  9

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `BeansLinker()`
  Creates a new beans linker.
  `BeansLinker(MissingMemberHandlerFactory missingMemberHandlerFactory)`
  Creates a new beans linker with the specified factory for creating missing member handlers.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static Object`
  `getConstructorMethod(Class<?> clazz, String signature)`
  Return the dynamic method of constructor of the given class and the given signature.
  `GuardedInvocation`
  `getGuardedInvocation(LinkRequest request, LinkerServices linkerServices)`
  Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.
  `static Set<String>`
  `getInstanceMethodNames(Class<?> clazz)`
  Returns a set of names of all instance methods of a class.
  `TypeBasedGuardingDynamicLinker`
  `getLinkerForClass(Class<?> clazz)`
  Returns a bean linker for a particular single class.
  `static Set<String>`
  `getReadableInstancePropertyNames(Class<?> clazz)`
  Returns a set of names of all readable instance properties of a class.
  `static Set<String>`
  `getReadableStaticPropertyNames(Class<?> clazz)`
  Returns a set of names of all readable static properties of a class.
  `static Set<String>`
  `getStaticMethodNames(Class<?> clazz)`
  Returns a set of names of all static methods of a class.
  `static Set<String>`
  `getWritableInstancePropertyNames(Class<?> clazz)`
  Returns a set of names of all writable instance properties of a class.
  `static Set<String>`
  `getWritableStaticPropertyNames(Class<?> clazz)`
  Returns a set of names of all writable static properties of a class.
  `static boolean`
  `isDynamicConstructor(Object obj)`
  Returns true if the object is a Java constructor (obtained through `getConstructorMethod(Class, String)`}.
  `static boolean`
  `isDynamicMethod(Object obj)`
  Returns true if the object is a Java dynamic method (e.g., one obtained through a `GET:METHOD` operation on a Java object or `StaticClass` or through `getConstructorMethod(Class, String)`.

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

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

- ## Constructor Details

  - ### BeansLinker

    public BeansLinker()
    Creates a new beans linker. Equivalent to `BeansLinker(MissingMemberHandlerFactory)` with `null` passed as the missing member handler factory, resulting in the default behavior for linking and evaluating missing members.

  - ### BeansLinker

    public BeansLinker(MissingMemberHandlerFactory missingMemberHandlerFactory)
    Creates a new beans linker with the specified factory for creating missing member handlers. The passed factory can be null if the default behavior is adequate. See `MissingMemberHandlerFactory` for details.
    Parameters:
      `missingMemberHandlerFactory` - a factory for creating handlers for operations on missing members.

- ## Method Details

  - ### getLinkerForClass

    public TypeBasedGuardingDynamicLinker getLinkerForClass(Class<?> clazz)
    Returns a bean linker for a particular single class. Useful when you need to override or extend the behavior of linking for some classes in your language runtime's linker, but still want to delegate to the default behavior in some cases.
    Parameters:
      `clazz` - the class
    Returns:
      a bean linker for that class

  - ### isDynamicMethod

    public static boolean isDynamicMethod(Object obj)
    Returns true if the object is a Java dynamic method (e.g., one obtained through a `GET:METHOD` operation on a Java object or `StaticClass` or through `getConstructorMethod(Class, String)`.
    Parameters:
      `obj` - the object we want to test for being a Java dynamic method.
    Returns:
      true if it is a dynamic method, false otherwise.

  - ### isDynamicConstructor

    public static boolean isDynamicConstructor(Object obj)
    Returns true if the object is a Java constructor (obtained through `getConstructorMethod(Class, String)`}.
    Parameters:
      `obj` - the object we want to test for being a Java constructor.
    Returns:
      true if it is a constructor, false otherwise.

  - ### getConstructorMethod

    public static Object getConstructorMethod(Class<?> clazz, String signature)
    Return the dynamic method of constructor of the given class and the given signature. This method is useful for exposing a functionality for selecting an overloaded constructor based on an explicit signature, as this functionality is not otherwise exposed by Dynalink as `StaticClass` objects act as overloaded constructors without explicit signature selection. Example usage would be: `getConstructorMethod(java.awt.Color.class, "int, int, int")`.
    Parameters:
      `clazz` - the class
      `signature` - full signature of the constructor. Note how you can use names of primitive types, array names with normal Java notation (e.g. `"int[]"`), and normally you can even use unqualified class names (e.g. `"String, List"` instead of `"java.lang.String, java.util.List"` as long as they don't cause ambiguity in the specific parameter position.
    Returns:
      dynamic method for the constructor or null if no constructor with the specified signature exists.

  - ### getReadableInstancePropertyNames

    public static Set<String> getReadableInstancePropertyNames(Class<?> clazz)
    Returns a set of names of all readable instance properties of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all readable instance properties of a class.

  - ### getWritableInstancePropertyNames

    public static Set<String> getWritableInstancePropertyNames(Class<?> clazz)
    Returns a set of names of all writable instance properties of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all writable instance properties of a class.

  - ### getInstanceMethodNames

    public static Set<String> getInstanceMethodNames(Class<?> clazz)
    Returns a set of names of all instance methods of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all instance methods of a class.

  - ### getReadableStaticPropertyNames

    public static Set<String> getReadableStaticPropertyNames(Class<?> clazz)
    Returns a set of names of all readable static properties of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all readable static properties of a class.

  - ### getWritableStaticPropertyNames

    public static Set<String> getWritableStaticPropertyNames(Class<?> clazz)
    Returns a set of names of all writable static properties of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all writable static properties of a class.

  - ### getStaticMethodNames

    public static Set<String> getStaticMethodNames(Class<?> clazz)
    Returns a set of names of all static methods of a class.
    Parameters:
      `clazz` - the class
    Returns:
      a set of names of all static methods of a class.

  - ### getGuardedInvocation

    public GuardedInvocation getGuardedInvocation(LinkRequest request, LinkerServices linkerServices) throws Exception
    Description copied from interface: `GuardingDynamicLinker`
    Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.
    Specified by:
      `getGuardedInvocation` in interface `GuardingDynamicLinker`
    Parameters:
      `request` - the object describing the request for linking a particular invocation
      `linkerServices` - linker services
    Returns:
      a guarded invocation with a method handle suitable for the arguments, as well as a guard condition that if fails should trigger relinking. Must return null if it can't resolve the invocation. If the returned invocation is unconditional (which is actually quite rare), the guard in the return value can be null. The invocation can also have any number of switch points for asynchronous invalidation of the linkage, as well as a `Throwable` subclass that describes an expected exception condition that also triggers relinking (often it is faster to rely on an infrequent but expected `ClassCastException` than on an always evaluated `instanceof` guard). While the linker must produce an invocation with parameter types matching those in the call site descriptor of the link request, it should not try to match the return type expected at the call site except when it can do it with only the conversions that lose neither precision nor magnitude, see `LinkerServices.asTypeLosslessReturn(MethodHandle, MethodType)` for further explanation.
    Throws:
      `Exception` - if the operation fails for whatever reason