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.

Constructor Summary

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

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https://docs.oracle.com/en/java/javase/17/docs/api/jdk.dynalink/jdk/dynalink/beans/BeansLinker.html