# Interface Reference

All Superinterfaces:
  `URIReference, XMLStructure`

public interface Reference extends URIReference, XMLStructure
A representation of the `Reference` element as defined in the W3C Recommendation for XML-Signature Syntax and Processing. The XML schema is defined as:

    <element name="Reference" type="ds:ReferenceType"/>
    <complexType name="ReferenceType">
      <sequence>
        <element ref="ds:Transforms" minOccurs="0"/>
        <element ref="ds:DigestMethod"/>
        <element ref="ds:DigestValue"/>
      </sequence>
      <attribute name="Id" type="ID" use="optional"/>
      <attribute name="URI" type="anyURI" use="optional"/>
      <attribute name="Type" type="anyURI" use="optional"/>
    </complexType>

    <element name="DigestValue" type="ds:DigestValueType"/>
    <simpleType name="DigestValueType">
      <restriction base="base64Binary"/>
    </simpleType>

A `Reference` instance may be created by invoking one of the `newReference` methods of the `XMLSignatureFactory` class; for example:

      XMLSignatureFactory factory = XMLSignatureFactory.getInstance("DOM");
      Reference ref = factory.newReference
        ("http://www.ietf.org/rfc/rfc3275.txt",
         factory.newDigestMethod(DigestMethod.SHA1, null));

Since:
  1.6
See Also:
  - `XMLSignatureFactory.newReference(String, DigestMethod)`
  - `XMLSignatureFactory.newReference(String, DigestMethod, List, String, String)`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `byte[]`
  `getCalculatedDigestValue()`
  Returns the calculated digest value of this `Reference` after a validation operation.
  `Data`
  `getDereferencedData()`
  Returns the dereferenced data, if reference caching is enabled.
  `InputStream`
  `getDigestInputStream()`
  Returns the pre-digested input stream, if reference caching is enabled.
  `DigestMethod`
  `getDigestMethod()`
  Returns the digest method of this `Reference`.
  `byte[]`
  `getDigestValue()`
  Returns the digest value of this `Reference`.
  `String`
  `getId()`
  Returns the optional `Id` attribute of this `Reference`, which permits this reference to be referenced from elsewhere.
  `List<Transform>`
  `getTransforms()`
  Returns an `unmodifiable list` of `Transform`s that are contained in this `Reference`.
  `boolean`
  `validate(XMLValidateContext validateContext)`
  Validates this reference.

  ### Methods declared in interface URIReference

  `getType, getURI`
  Modifier and Type
  Method
  Description
  `String`
  `getType()`
  Returns the type of data referenced by this URI.
  `String`
  `getURI()`
  Returns the URI of the referenced data object.

  ### Methods declared in interface XMLStructure

  `isFeatureSupported`
  Modifier and Type
  Method
  Description
  `boolean`
  `isFeatureSupported(String feature)`
  Indicates whether a specified feature is supported.

- ## Method Details

  - ### getTransforms

    List<Transform> getTransforms()
    Returns an `unmodifiable list` of `Transform`s that are contained in this `Reference`.
    Returns:
      an unmodifiable list of `Transform`s (may be empty but never `null`)

  - ### getDigestMethod

    DigestMethod getDigestMethod()
    Returns the digest method of this `Reference`.
    Returns:
      the digest method

  - ### getId

    String getId()
    Returns the optional `Id` attribute of this `Reference`, which permits this reference to be referenced from elsewhere.
    Returns:
      the `Id` attribute (may be `null` if not specified)

  - ### getDigestValue

    byte[] getDigestValue()
    Returns the digest value of this `Reference`.
    Returns:
      the raw digest value, or `null` if this reference has not been digested yet. Each invocation of this method returns a new clone to protect against subsequent modification.

  - ### getCalculatedDigestValue

    byte[] getCalculatedDigestValue()
    Returns the calculated digest value of this `Reference` after a validation operation. This method is useful for debugging if the reference fails to validate.
    Returns:
      the calculated digest value, or `null` if this reference has not been validated yet. Each invocation of this method returns a new clone to protect against subsequent modification.

  - ### validate

    boolean validate(XMLValidateContext validateContext) throws XMLSignatureException
    Validates this reference. This method verifies the digest of this reference.

    This method only validates the reference the first time it is invoked. On subsequent invocations, it returns a cached result.

    Parameters:
      `validateContext` - the validating context
    Returns:
      `true` if this reference was validated successfully; `false` otherwise
    Throws:
      `NullPointerException` - if `validateContext` is `null`
      `XMLSignatureException` - if an unexpected exception occurs while validating the reference

  - ### getDereferencedData

    Data getDereferencedData()
    Returns the dereferenced data, if reference caching is enabled. This is the result of dereferencing the URI of this reference during a validation or generation operation.
    Returns:
      the dereferenced data, or `null` if reference caching is not enabled or this reference has not been generated or validated

  - ### getDigestInputStream

    InputStream getDigestInputStream()
    Returns the pre-digested input stream, if reference caching is enabled. This is the input to the digest operation during a validation or signing operation.
    Returns:
      an input stream containing the pre-digested input, or `null` if reference caching is not enabled or this reference has not been generated or validated