# Class ValidatorHandler

java.lang.Object
javax.xml.validation.ValidatorHandler

All Implemented Interfaces:
  `ContentHandler`

public abstract class ValidatorHandler extends Object implements ContentHandler
Streaming validator that works on SAX stream.

A `ValidatorHandler` object is not thread-safe and not reentrant. In other words, it is the application's responsibility to make sure that one `ValidatorHandler` object is not used from more than one thread at any given time.

`ValidatorHandler` checks if the SAX events follow the set of constraints described in the associated `Schema`, and additionally it may modify the SAX events (for example by adding default values, etc.)

`ValidatorHandler` extends from `ContentHandler`, but it refines the underlying `ContentHandler` in the following way:

1. startElement/endElement events must receive non-null String for `uri`, `localName`, and `qname`, even though SAX allows some of them to be null. Similarly, the user-specified `ContentHandler` will receive non-null Strings for all three parameters.
2. Applications must ensure that `ValidatorHandler`'s `ContentHandler.startPrefixMapping(String,String)` and `ContentHandler.endPrefixMapping(String)` are invoked properly. Similarly, the user-specified `ContentHandler` will receive startPrefixMapping/endPrefixMapping events. If the `ValidatorHandler` introduces additional namespace bindings, the user-specified `ContentHandler` will receive additional startPrefixMapping/endPrefixMapping events.
3. `Attributes` for the `ContentHandler.startElement(String,String,String,Attributes)` method may or may not include xmlns* attributes.

A `ValidatorHandler` is automatically reset every time the startDocument method is invoked.

## Recognized Properties and Features

This spec defines the following feature that must be recognized by all `ValidatorHandler` implementations.

### `http://xml.org/sax/features/namespace-prefixes`

This feature controls how a `ValidatorHandler` introduces namespace bindings that were not present in the original SAX event stream. When this feature is set to true, it must make sure that the user's `ContentHandler` will see the corresponding `xmlns*` attribute in the `Attributes` object of the `ContentHandler.startElement(String,String,String,Attributes)` callback. Otherwise, `xmlns*` attributes must not be added to `Attributes` that's passed to the user-specified `ContentHandler`.

(Note that regardless of this switch, namespace bindings are always notified to applications through `ContentHandler.startPrefixMapping(String,String)` and `ContentHandler.endPrefixMapping(String)` methods of the `ContentHandler` specified by the user.)

Note that this feature does NOT affect the way a `ValidatorHandler` receives SAX events. It merely changes the way it augments SAX events.

This feature is set to `false` by default.

Since:
  1.5

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `ValidatorHandler()`
  Constructor for derived classes.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract ContentHandler`
  `getContentHandler()`
  Gets the `ContentHandler` which receives the augmented validation result.
  `abstract ErrorHandler`
  `getErrorHandler()`
  Gets the current `ErrorHandler` set to this `ValidatorHandler`.
  `boolean`
  `getFeature(String name)`
  Look up the value of a feature flag.
  `Object`
  `getProperty(String name)`
  Look up the value of a property.
  `abstract LSResourceResolver`
  `getResourceResolver()`
  Gets the current `LSResourceResolver` set to this `ValidatorHandler`.
  `abstract TypeInfoProvider`
  `getTypeInfoProvider()`
  Obtains the `TypeInfoProvider` implementation of this `ValidatorHandler`.
  `abstract void`
  `setContentHandler(ContentHandler receiver)`
  Sets the `ContentHandler` which receives the augmented validation result.
  `abstract void`
  `setErrorHandler(ErrorHandler errorHandler)`
  Sets the `ErrorHandler` to receive errors encountered during the validation.
  `void`
  `setFeature(String name, boolean value)`
  Set a feature for this `ValidatorHandler`.
  `void`
  `setProperty(String name, Object object)`
  Set the value of a property.
  `abstract void`
  `setResourceResolver(LSResourceResolver resourceResolver)`
  Sets the `LSResourceResolver` to customize resource resolution while in a validation episode.

  ### Methods declared in class Object

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

  ### Methods declared in interface ContentHandler

  `characters, declaration, endDocument, endElement, endPrefixMapping, ignorableWhitespace, processingInstruction, setDocumentLocator, skippedEntity, startDocument, startElement, startPrefixMapping`

- ## Constructor Details

  - ### ValidatorHandler

    protected ValidatorHandler()

    Constructor for derived classes.

    The constructor does nothing.

    Derived classes must create `ValidatorHandler` objects that have `null` `ErrorHandler` and `null` `LSResourceResolver`.

- ## Method Details

  - ### setContentHandler

    public abstract void setContentHandler(ContentHandler receiver)
    Sets the `ContentHandler` which receives the augmented validation result.

    When a `ContentHandler` is specified, a `ValidatorHandler` will work as a filter and basically copy the incoming events to the specified `ContentHandler`.

    In doing so, a `ValidatorHandler` may modify the events, for example by adding defaulted attributes.

    A `ValidatorHandler` may buffer events to certain extent, but to allow `ValidatorHandler` to be used by a parser, the following requirement has to be met.

    1. When `ContentHandler.startElement(String, String, String, Attributes)`, `ContentHandler.endElement(String, String, String)`, `ContentHandler.startDocument()`, or `ContentHandler.endDocument()` are invoked on a `ValidatorHandler`, the same method on the user-specified `ContentHandler` must be invoked for the same event before the callback returns.
    2. `ValidatorHandler` may not introduce new elements that were not present in the input.
    3. `ValidatorHandler` may not remove attributes that were present in the input.

    When a callback method on the specified `ContentHandler` throws an exception, the same exception object must be thrown from the `ValidatorHandler`. The `ErrorHandler` should not be notified of such an exception.

    This method can be called even during a middle of a validation.

    Parameters:
      `receiver` - A `ContentHandler` or a null value.

  - ### getContentHandler

    public abstract ContentHandler getContentHandler()
    Gets the `ContentHandler` which receives the augmented validation result.
    Returns:
      This method returns the object that was last set through the `getContentHandler()` method, or null if that method has never been called since this `ValidatorHandler` has created.
    See Also:
      - `setContentHandler(ContentHandler)`

  - ### setErrorHandler

    public abstract void setErrorHandler(ErrorHandler errorHandler)
    Sets the `ErrorHandler` to receive errors encountered during the validation.

    Error handler can be used to customize the error handling process during a validation. When an `ErrorHandler` is set, errors found during the validation will be first sent to the `ErrorHandler`.

    The error handler can abort further validation immediately by throwing `SAXException` from the handler. Or for example it can print an error to the screen and try to continue the validation by returning normally from the `ErrorHandler`

    If any `Throwable` is thrown from an `ErrorHandler`, the same `Throwable` object will be thrown toward the root of the call stack.

    `ValidatorHandler` is not allowed to throw `SAXException` without first reporting it to `ErrorHandler`.

    When the `ErrorHandler` is null, the implementation will behave as if the following `ErrorHandler` is set:

        class DraconianErrorHandler implements ErrorHandler {
            public void fatalError( SAXParseException e ) throws SAXException {
                throw e;
            }
            public void error( SAXParseException e ) throws SAXException {
                throw e;
            }
            public void warning( SAXParseException e ) throws SAXException {
                // noop
            }
        }

    When a new `ValidatorHandler` object is created, initially this field is set to null.

    Parameters:
      `errorHandler` - A new error handler to be set. This parameter can be null.

  - ### getErrorHandler

    public abstract ErrorHandler getErrorHandler()
    Gets the current `ErrorHandler` set to this `ValidatorHandler`.
    Returns:
      This method returns the object that was last set through the `setErrorHandler(ErrorHandler)` method, or null if that method has never been called since this `ValidatorHandler` has created.
    See Also:
      - `setErrorHandler(ErrorHandler)`

  - ### setResourceResolver

    public abstract void setResourceResolver(LSResourceResolver resourceResolver)
    Sets the `LSResourceResolver` to customize resource resolution while in a validation episode.

    `ValidatorHandler` uses a `LSResourceResolver` when it needs to locate external resources while a validation, although exactly what constitutes "locating external resources" is up to each schema language.

    When the `LSResourceResolver` is null, the implementation will behave as if the following `LSResourceResolver` is set:

        class DumbLSResourceResolver implements LSResourceResolver {
            public LSInput resolveResource(
                String publicId, String systemId, String baseURI) {

                return null; // always return null
            }
        }

    If a `LSResourceResolver` throws a `RuntimeException` (or instances of its derived classes), then the `ValidatorHandler` will abort the parsing and the caller of the `validate` method will receive the same `RuntimeException`.

    When a new `ValidatorHandler` object is created, initially this field is set to null.

    Parameters:
      `resourceResolver` - A new resource resolver to be set. This parameter can be null.

  - ### getResourceResolver

    public abstract LSResourceResolver getResourceResolver()
    Gets the current `LSResourceResolver` set to this `ValidatorHandler`.
    Returns:
      This method returns the object that was last set through the `setResourceResolver(LSResourceResolver)` method, or null if that method has never been called since this `ValidatorHandler` has created.
    See Also:
      - `setErrorHandler(ErrorHandler)`

  - ### getTypeInfoProvider

    public abstract TypeInfoProvider getTypeInfoProvider()
    Obtains the `TypeInfoProvider` implementation of this `ValidatorHandler`.

    The obtained `TypeInfoProvider` can be queried during a parse to access the type information determined by the validator.

    Some schema languages do not define the notion of type, for those languages, this method may not be supported. However, to be compliant with this specification, implementations for W3C XML Schema 1.0 must support this operation.

    Returns:
      null if the validator / schema language does not support the notion of `TypeInfo`. Otherwise a non-null valid `TypeInfoProvider`.

  - ### getFeature

    public boolean getFeature(String name) throws SAXNotRecognizedException, SAXNotSupportedException
    Look up the value of a feature flag.

    The feature name is any fully-qualified URI. It is possible for a `ValidatorHandler` to recognize a feature name but temporarily be unable to return its value. Some feature values may be available only in specific contexts, such as before, during, or after a validation.

    Implementors are free (and encouraged) to invent their own features, using names built on their own URIs.

    Parameters:
      `name` - The feature name, which is a non-null fully-qualified URI.
    Returns:
      The current value of the feature (true or false).
    Throws:
      `SAXNotRecognizedException` - If the feature value can't be assigned or retrieved.
      `SAXNotSupportedException` - When the `ValidatorHandler` recognizes the feature name but cannot determine its value at this time.
      `NullPointerException` - When `name` is `null`.
    See Also:
      - `setFeature(String, boolean)`

  - ### setFeature

    public void setFeature(String name, boolean value) throws SAXNotRecognizedException, SAXNotSupportedException

    Set a feature for this `ValidatorHandler`.

    Feature can be used to control the way a `ValidatorHandler` parses schemas. The feature name is any fully-qualified URI. It is possible for a `SchemaFactory` to expose a feature value but to be unable to change the current value. Some feature values may be immutable or mutable only in specific contexts, such as before, during, or after a validation.

    All implementations are required to support the `XMLConstants.FEATURE_SECURE_PROCESSING` feature. When the feature is:

    - `true`: the implementation will limit XML processing to conform to implementation limits. Examples include entity expansion limits and XML Schema constructs that would consume large amounts of resources. If XML processing is limited for security reasons, it will be reported via a call to the registered `ErrorHandler.fatalError(SAXParseException exception)`. See `setErrorHandler(ErrorHandler errorHandler)`.
    - `false`: the implementation will processing XML according to the XML specifications without regard to possible implementation limits.
    Parameters:
      `name` - The feature name, which is a non-null fully-qualified URI.
      `value` - The requested value of the feature (true or false).
    Throws:
      `SAXNotRecognizedException` - If the feature value can't be assigned or retrieved.
      `SAXNotSupportedException` - When the `ValidatorHandler` recognizes the feature name but cannot set the requested value.
      `NullPointerException` - When `name` is `null`.
    See Also:
      - `getFeature(String)`

  - ### setProperty

    public void setProperty(String name, Object object) throws SAXNotRecognizedException, SAXNotSupportedException
    Set the value of a property.

    The property name is any fully-qualified URI. It is possible for a `ValidatorHandler` to recognize a property name but to be unable to change the current value. Some property values may be immutable or mutable only in specific contexts, such as before, during, or after a validation.

    `ValidatorHandler`s are not required to recognize setting any specific property names.

    Parameters:
      `name` - The property name, which is a non-null fully-qualified URI.
      `object` - The requested value for the property.
    Throws:
      `SAXNotRecognizedException` - If the property value can't be assigned or retrieved.
      `SAXNotSupportedException` - When the `ValidatorHandler` recognizes the property name but cannot set the requested value.
      `NullPointerException` - When `name` is `null`.

  - ### getProperty

    public Object getProperty(String name) throws SAXNotRecognizedException, SAXNotSupportedException
    Look up the value of a property.

    The property name is any fully-qualified URI. It is possible for a `ValidatorHandler` to recognize a property name but temporarily be unable to return its value. Some property values may be available only in specific contexts, such as before, during, or after a validation.

    `ValidatorHandler`s are not required to recognize any specific property names.

    Implementors are free (and encouraged) to invent their own properties, using names built on their own URIs.

    Parameters:
      `name` - The property name, which is a non-null fully-qualified URI.
    Returns:
      The current value of the property.
    Throws:
      `SAXNotRecognizedException` - If the property value can't be assigned or retrieved.
      `SAXNotSupportedException` - When the XMLReader recognizes the property name but cannot determine its value at this time.
      `NullPointerException` - When `name` is `null`.
    See Also:
      - `setProperty(String, Object)`