IntrospectionHelper (Apache Ant API)
Description: declaration: package: org.apache.tools.ant, class: IntrospectionHelper

# Class IntrospectionHelper

java.lang.Object
org.apache.tools.ant.IntrospectionHelper

public final class IntrospectionHelper extends Object
Helper class that collects the methods a task or nested element holds to set attributes, create nested elements or hold PCDATA elements. It contains hashtables containing classes that use introspection to handle all the invocation of the project-component specific methods. This class is somewhat complex, as it implements the O/X mapping between Ant XML and Java class instances. This is not the best place for someone new to Ant to start contributing to the codebase, as a change here can break the entire system in interesting ways. Always run a full test of Ant before checking in/submitting changes to this file. The class is final and has a private constructor. To get an instance for a specific (class,project) combination, use `getHelper(Project,Class)`. This may return an existing version, or a new one ...do not make any assumptions about its uniqueness, or its validity after the Project instance has finished its build.

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static final class`
  `IntrospectionHelper.Creator`
  creator - allows use of create/store external to IntrospectionHelper.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected static final String`
  `NOT_SUPPORTED_CHILD_POSTFIX`
  part of the error message created by `throwNotSupported`.
  `protected static final String`
  `NOT_SUPPORTED_CHILD_PREFIX`
  part of the error message created by `throwNotSupported`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addText(Project project, Object element, String text)`
  Adds PCDATA to an element, using the element's `void addText(String)` method, if it has one.
  `static void`
  `clearCache()`
  Clears the static cache of on build finished.
  `Object`
  `createElement(Project project, Object parent, String elementName)`
  Deprecated.
  since 1.6.x.
  `Method`
  `getAddTextMethod()`
  Returns the addText method when the introspected class supports nested text.
  `Map<String,Class<?>>`
  `getAttributeMap()`
  Returns a read-only map of attributes supported by the introspected class.
  `Method`
  `getAttributeMethod(String attributeName)`
  Returns the setter method of a named attribute.
  `Enumeration<String>`
  `getAttributes()`
  Returns an enumeration of the names of the attributes supported by the introspected class.
  `Class<?>`
  `getAttributeType(String attributeName)`
  Returns the type of a named attribute.
  `IntrospectionHelper.Creator`
  `getElementCreator(Project project, String parentUri, Object parent, String elementName, UnknownElement ue)`
  returns an object that creates and stores an object for an element of a parent.
  `Method`
  `getElementMethod(String elementName)`
  Returns the adder or creator method of a named nested element.
  `Class<?>`
  `getElementType(String elementName)`
  Returns the type of a named nested element.
  `List<Method>`
  `getExtensionPoints()`
  Returns a read-only list of extension points supported by the introspected class.
  `static IntrospectionHelper`
  `getHelper(Class<?> c)`
  Returns a helper for the given class, either from the cache or by creating a new instance.
  `static IntrospectionHelper`
  `getHelper(Project p, Class<?> c)`
  Returns a helper for the given class, either from the cache or by creating a new instance.
  `Map<String,Class<?>>`
  `getNestedElementMap()`
  Returns a read-only map of nested elements supported by the introspected class.
  `Enumeration<String>`
  `getNestedElements()`
  Returns an enumeration of the names of the nested elements supported by the introspected class.
  `boolean`
  `isContainer()`
  Indicates whether the introspected class is a task container, supporting arbitrary nested tasks/types.
  `boolean`
  `isDynamic()`
  Indicates whether the introspected class is a dynamic one, supporting arbitrary nested elements and/or attributes.
  `void`
  `setAttribute(Project p, Object element, String attributeName, Object value)`
  Sets the named attribute in the given element, which is part of the given project.
  `void`
  `setAttribute(Project p, Object element, String attributeName, String value)`
  Sets the named attribute in the given element, which is part of the given project.
  `void`
  `storeElement(Project project, Object parent, Object child, String elementName)`
  Stores a named nested element using a storage method determined by the initial introspection.
  `boolean`
  `supportsCharacters()`
  Returns whether or not the introspected class supports PCDATA.
  `boolean`
  `supportsNestedElement(String elementName)`
  Indicates if this element supports a nested element of the given name.
  `boolean`
  `supportsNestedElement(String parentUri, String elementName)`
  Indicate if this element supports a nested element of the given name.
  `boolean`
  `supportsNestedElement(String parentUri, String elementName, Project project, Object parent)`
  Indicate if this element supports a nested element of the given name.
  `boolean`
  `supportsReflectElement(String parentUri, String elementName)`
  Check if this element supports a nested element from reflection.
  `void`
  `throwNotSupported(Project project, Object parent, String elementName)`
  Utility method to throw a NotSupported exception

  ### Methods inherited from class Object

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

- ## Field Details

  - ### NOT_SUPPORTED_CHILD_PREFIX

    protected static final String NOT_SUPPORTED_CHILD_PREFIX
    part of the error message created by `throwNotSupported`.
    Since:
      Ant 1.8.0
    See Also:
      - Constant Field Values

  - ### NOT_SUPPORTED_CHILD_POSTFIX

    protected static final String NOT_SUPPORTED_CHILD_POSTFIX
    part of the error message created by `throwNotSupported`.
    Since:
      Ant 1.8.0
    See Also:
      - Constant Field Values

- ## Method Details

  - ### getHelper

    public static IntrospectionHelper getHelper(Class<?> c)
    Returns a helper for the given class, either from the cache or by creating a new instance.
    Parameters:
      `c` - The class for which a helper is required. Must not be `null`.
    Returns:
      a helper for the specified class

  - ### getHelper

    public static IntrospectionHelper getHelper(Project p, Class<?> c)
    Returns a helper for the given class, either from the cache or by creating a new instance. The method will make sure the helper will be cleaned up at the end of the project, and only one instance will be created for each class.
    Parameters:
      `p` - the project instance. Can be null, in which case the helper is not cached.
      `c` - The class for which a helper is required. Must not be `null`.
    Returns:
      a helper for the specified class

  - ### setAttribute

    public void setAttribute(Project p, Object element, String attributeName, Object value) throws BuildException
    Sets the named attribute in the given element, which is part of the given project.
    Parameters:
      `p` - The project containing the element. This is used when files need to be resolved. Must not be `null`.
      `element` - The element to set the attribute in. Must not be `null`.
      `attributeName` - The name of the attribute to set. Must not be `null`.
      `value` - The value to set the attribute to. This may be interpreted or converted to the necessary type if the setter method doesn't accept an object of the supplied type.
    Throws:
      `BuildException` - if the introspected class doesn't support the given attribute, or if the setting method fails.

  - ### setAttribute

    public void setAttribute(Project p, Object element, String attributeName, String value) throws BuildException
    Sets the named attribute in the given element, which is part of the given project.
    Parameters:
      `p` - The project containing the element. This is used when files need to be resolved. Must not be `null`.
      `element` - The element to set the attribute in. Must not be `null`.
      `attributeName` - The name of the attribute to set. Must not be `null`.
      `value` - The value to set the attribute to. This may be interpreted or converted to the necessary type if the setter method doesn't just take a string. Must not be `null`.
    Throws:
      `BuildException` - if the introspected class doesn't support the given attribute, or if the setting method fails.

  - ### addText

    public void addText(Project project, Object element, String text) throws BuildException
    Adds PCDATA to an element, using the element's `void addText(String)` method, if it has one. If no such method is present, a BuildException is thrown if the given text contains non-whitespace.
    Parameters:
      `project` - The project which the element is part of. Must not be `null`.
      `element` - The element to add the text to. Must not be `null`.
      `text` - The text to add. Must not be `null`.
    Throws:
      `BuildException` - if non-whitespace text is provided and no method is available to handle it, or if the handling method fails.

  - ### throwNotSupported

    public void throwNotSupported(Project project, Object parent, String elementName)
    Utility method to throw a NotSupported exception
    Parameters:
      `project` - the Project instance.
      `parent` - the object which doesn't support a requested element
      `elementName` - the name of the Element which is trying to be created.

  - ### createElement

    @Deprecated public Object createElement(Project project, Object parent, String elementName) throws BuildException
    Deprecated.
    since 1.6.x. This is not a namespace aware method.
    Creates a named nested element. Depending on the results of the initial introspection, either a method in the given parent instance or a simple no-arg constructor is used to create an instance of the specified element type.
    Parameters:
      `project` - Project to which the parent object belongs. Must not be `null`. If the resulting object is an instance of ProjectComponent, its Project reference is set to this parameter value.
      `parent` - Parent object used to create the instance. Must not be `null`.
      `elementName` - Name of the element to create an instance of. Must not be `null`.
    Returns:
      an instance of the specified element type
    Throws:
      `BuildException` - if no method is available to create the element instance, or if the creating method fails.

  - ### getElementCreator

    public IntrospectionHelper.Creator getElementCreator(Project project, String parentUri, Object parent, String elementName, UnknownElement ue)
    returns an object that creates and stores an object for an element of a parent.
    Parameters:
      `project` - Project to which the parent object belongs.
      `parentUri` - The namespace uri of the parent object.
      `parent` - Parent object used to create the creator object to create and store and instance of a subelement.
      `elementName` - Name of the element to create an instance of.
      `ue` - The unknown element associated with the element.
    Returns:
      a creator object to create and store the element instance.

  - ### isDynamic

    public boolean isDynamic()
    Indicates whether the introspected class is a dynamic one, supporting arbitrary nested elements and/or attributes.
    Returns:
      `true` if the introspected class is dynamic; `false` otherwise.
    Since:
      Ant 1.6.3
    See Also:
      - `DynamicElement`
      - `DynamicElementNS`

  - ### isContainer

    public boolean isContainer()
    Indicates whether the introspected class is a task container, supporting arbitrary nested tasks/types.
    Returns:
      `true` if the introspected class is a container; `false` otherwise.
    Since:
      Ant 1.6.3
    See Also:
      - `TaskContainer`

  - ### supportsNestedElement

    public boolean supportsNestedElement(String elementName)
    Indicates if this element supports a nested element of the given name.
    Parameters:
      `elementName` - the name of the nested element being checked
    Returns:
      true if the given nested element is supported

  - ### supportsNestedElement

    public boolean supportsNestedElement(String parentUri, String elementName)
    Indicate if this element supports a nested element of the given name.

    Note that this method will always return true if the introspected class is `dynamic` or contains a method named "add" with void return type and a single argument. To ge a more thorough answer, use the four-arg version of this method instead.

    Parameters:
      `parentUri` - the uri of the parent
      `elementName` - the name of the nested element being checked
    Returns:
      true if the given nested element is supported

  - ### supportsNestedElement

    public boolean supportsNestedElement(String parentUri, String elementName, Project project, Object parent)
    Indicate if this element supports a nested element of the given name.

    Note that this method will always return true if the introspected class is `dynamic`, so be prepared to catch an exception about unsupported children when calling `getElementCreator`.

    Parameters:
      `parentUri` - the uri of the parent
      `elementName` - the name of the nested element being checked
      `project` - currently executing project instance
      `parent` - the parent element
    Returns:
      true if the given nested element is supported
    Since:
      Ant 1.8.0.

  - ### supportsReflectElement

    public boolean supportsReflectElement(String parentUri, String elementName)
    Check if this element supports a nested element from reflection.
    Parameters:
      `parentUri` - the uri of the parent
      `elementName` - the name of the nested element being checked
    Returns:
      true if the given nested element is supported
    Since:
      Ant 1.8.0

  - ### storeElement

    public void storeElement(Project project, Object parent, Object child, String elementName) throws BuildException
    Stores a named nested element using a storage method determined by the initial introspection. If no appropriate storage method is available, this method returns immediately.
    Parameters:
      `project` - Ignored in this implementation. May be `null`.
      `parent` - Parent instance to store the child in. Must not be `null`.
      `child` - Child instance to store in the parent. Should not be `null`.
      `elementName` - Name of the child element to store. May be `null`, in which case this method returns immediately.
    Throws:
      `BuildException` - if the storage method fails.

  - ### getElementType

    public Class<?> getElementType(String elementName) throws BuildException
    Returns the type of a named nested element.
    Parameters:
      `elementName` - The name of the element to find the type of. Must not be `null`.
    Returns:
      the type of the nested element with the specified name. This will never be `null`.
    Throws:
      `BuildException` - if the introspected class does not support the named nested element.

  - ### getAttributeType

    public Class<?> getAttributeType(String attributeName) throws BuildException
    Returns the type of a named attribute.
    Parameters:
      `attributeName` - The name of the attribute to find the type of. Must not be `null`.
    Returns:
      the type of the attribute with the specified name. This will never be `null`.
    Throws:
      `BuildException` - if the introspected class does not support the named attribute.

  - ### getAddTextMethod

    public Method getAddTextMethod() throws BuildException
    Returns the addText method when the introspected class supports nested text.
    Returns:
      the method on this introspected class that adds nested text. Cannot be `null`.
    Throws:
      `BuildException` - if the introspected class does not support the nested text.
    Since:
      Ant 1.6.3

  - ### getElementMethod

    public Method getElementMethod(String elementName) throws BuildException
    Returns the adder or creator method of a named nested element.
    Parameters:
      `elementName` - The name of the attribute to find the setter method of. Must not be `null`.
    Returns:
      the method on this introspected class that adds or creates this nested element. Can be `null` when the introspected class is a dynamic configurator!
    Throws:
      `BuildException` - if the introspected class does not support the named nested element.
    Since:
      Ant 1.6.3

  - ### getAttributeMethod

    public Method getAttributeMethod(String attributeName) throws BuildException
    Returns the setter method of a named attribute.
    Parameters:
      `attributeName` - The name of the attribute to find the setter method of. Must not be `null`.
    Returns:
      the method on this introspected class that sets this attribute. This will never be `null`.
    Throws:
      `BuildException` - if the introspected class does not support the named attribute.
    Since:
      Ant 1.6.3

  - ### supportsCharacters

    public boolean supportsCharacters()
    Returns whether or not the introspected class supports PCDATA.
    Returns:
      whether or not the introspected class supports PCDATA.

  - ### getAttributes

    public Enumeration<String> getAttributes()
    Returns an enumeration of the names of the attributes supported by the introspected class.
    Returns:
      an enumeration of the names of the attributes supported by the introspected class.
    See Also:
      - `getAttributeMap()`

  - ### getAttributeMap

    public Map<String,Class<?>> getAttributeMap()
    Returns a read-only map of attributes supported by the introspected class.
    Returns:
      an attribute name to attribute `Class` unmodifiable map. Can be empty, but never `null`.
    Since:
      Ant 1.6.3

  - ### getNestedElements

    public Enumeration<String> getNestedElements()
    Returns an enumeration of the names of the nested elements supported by the introspected class.
    Returns:
      an enumeration of the names of the nested elements supported by the introspected class.
    See Also:
      - `getNestedElementMap()`

  - ### getNestedElementMap

    public Map<String,Class<?>> getNestedElementMap()
    Returns a read-only map of nested elements supported by the introspected class.
    Returns:
      a nested-element name to nested-element `Class` unmodifiable map. Can be empty, but never `null`.
    Since:
      Ant 1.6.3

  - ### getExtensionPoints

    public List<Method> getExtensionPoints()
    Returns a read-only list of extension points supported by the introspected class.

    A task/type or nested element with void methods named `add()` or `addConfigured()`, taking a single class or interface argument, supports extensions point. This method returns the list of all these void add[Configured](type) methods.

    Returns:
      a list of void, single argument add() or addConfigured() `Method`s of all supported extension points. These methods are sorted such that if the argument type of a method derives from another type also an argument of a method of this list, the method with the most derived argument will always appear first. Can be empty, but never `null`.
    Since:
      Ant 1.6.3

  - ### clearCache

    public static void clearCache()
    Clears the static cache of on build finished.