XMLConstants (Java SE 21 & JDK 21)
Description: declaration: module: java.xml, package: javax.xml, class: XMLConstants
Keywords: javax.xml.XMLConstants class

Module java.xml
Package javax.xml

# Class XMLConstants

java.lang.Object
javax.xml.XMLConstants

public final class XMLConstants extends Object
Defines constants for XML Processing APIs.

## External Access Properties

The value of the external access properties, including `ACCESS_EXTERNAL_DTD`, `ACCESS_EXTERNAL_SCHEMA`, and `ACCESS_EXTERNAL_STYLESHEET`, is defined as follows.

### Value:

A list of protocols separated by comma. A protocol is the scheme portion of a `URI`, or in the case of the JAR protocol, "jar" plus the scheme portion separated by colon. A scheme is defined as:

> scheme = alpha *( alpha | digit | "+" | "-" | "." )
> where alpha = a-z and A-Z.
> And the JAR protocol:
> jar[:scheme]
> Protocols including the keyword "jar" are case-insensitive. Any whitespaces as defined by `Character.isSpaceChar(char)` in the value will be ignored. Examples of protocols are file, http, jar:file.

### Default value:

The default value is implementation specific and therefore not specified. The following options are provided for consideration:

> - an empty string to deny all access to external references;
> - a specific protocol, such as file, to give permission to only the protocol;
> - the keyword "all" to grant permission to all protocols.
> When FEATURE_SECURE_PROCESSING is enabled, it is recommended that implementations restrict external connections by default, though this may cause problems for applications that process XML/XSD/XSL with external references.

### Granting all access:

The keyword "all" grants permission to all protocols.

## Property Precedence

Properties, including the External Access Properties and `USE_CATALOG`, can be specified through multiple configuration sources. They follow the configuration process as defined in the Configuration section of the module summary.

Since:
  1.5
See Also:
  - Extensible Markup Language (XML) 1.1
  - Extensible Markup Language (XML) 1.0 (Second Edition)
  - XML 1.0 Second Edition Specification Errata
  - Namespaces in XML 1.1
  - Namespaces in XML
  - XML Schema Part 1: Structures

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final String`
  `ACCESS_EXTERNAL_DTD`
  Property: accessExternalDTD
  `static final String`
  `ACCESS_EXTERNAL_SCHEMA`
  Property: accessExternalSchema
  `static final String`
  `ACCESS_EXTERNAL_STYLESHEET`
  Property: accessExternalStylesheet
  `static final String`
  `DEFAULT_NS_PREFIX`
  Prefix to use to represent the default XML Namespace.
  `static final String`
  `FEATURE_SECURE_PROCESSING`
  Feature for secure processing.
  `static final String`
  `NULL_NS_URI`
  Namespace URI to use to represent that there is no Namespace.
  `static final String`
  `RELAXNG_NS_URI`
  RELAX NG Namespace URI.
  `static final String`
  `USE_CATALOG`
  Feature: useCatalog
  `static final String`
  `W3C_XML_SCHEMA_INSTANCE_NS_URI`
  W3C XML Schema Instance Namespace URI.
  `static final String`
  `W3C_XML_SCHEMA_NS_URI`
  W3C XML Schema Namespace URI.
  `static final String`
  `W3C_XPATH_DATATYPE_NS_URI`
  W3C XPath Datatype Namespace URI.
  `static final String`
  `XML_DTD_NS_URI`
  XML Document Type Declaration Namespace URI as an arbitrary value.
  `static final String`
  `XML_NS_PREFIX`
  The official XML Namespace prefix.
  `static final String`
  `XML_NS_URI`
  The official XML Namespace name URI.
  `static final String`
  `XMLNS_ATTRIBUTE`
  The official XML attribute used for specifying XML Namespace declarations.
  `static final String`
  `XMLNS_ATTRIBUTE_NS_URI`
  The official XML attribute used for specifying XML Namespace declarations, `XMLConstants.XMLNS_ATTRIBUTE`, Namespace name URI.

- ## Method Summary

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

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

- ## Field Details

  - ### NULL_NS_URI

    public static final String NULL_NS_URI
    Namespace URI to use to represent that there is no Namespace.

    Defined by the Namespace specification to be "".

    See Also:
      - Namespaces in XML, 5.2 Namespace Defaulting
      - Constant Field Values

  - ### DEFAULT_NS_PREFIX

    public static final String DEFAULT_NS_PREFIX
    Prefix to use to represent the default XML Namespace.

    Defined by the XML specification to be "".

    See Also:
      - Namespaces in XML, 3. Qualified Names
      - Constant Field Values

  - ### XML_NS_URI

    public static final String XML_NS_URI
    The official XML Namespace name URI.

    Defined by the XML specification to be "`http://www.w3.org/XML/1998/namespace`".

    See Also:
      - Namespaces in XML, 3. Qualified Names
      - Constant Field Values

  - ### XML_NS_PREFIX

    public static final String XML_NS_PREFIX
    The official XML Namespace prefix.

    Defined by the XML specification to be "`xml`".

    See Also:
      - Namespaces in XML, 3. Qualified Names
      - Constant Field Values

  - ### XMLNS_ATTRIBUTE_NS_URI

    public static final String XMLNS_ATTRIBUTE_NS_URI
    The official XML attribute used for specifying XML Namespace declarations, `XMLConstants.XMLNS_ATTRIBUTE`, Namespace name URI.

    Defined by the XML specification to be "`http://www.w3.org/2000/xmlns/`".

    See Also:
      - Namespaces in XML, 3. Qualified Names
      - Constant Field Values

  - ### XMLNS_ATTRIBUTE

    public static final String XMLNS_ATTRIBUTE
    The official XML attribute used for specifying XML Namespace declarations.

    It is NOT valid to use as a prefix. Defined by the XML specification to be "`xmlns`".

    See Also:
      - Namespaces in XML, 3. Qualified Names
      - Constant Field Values

  - ### W3C_XML_SCHEMA_NS_URI

    public static final String W3C_XML_SCHEMA_NS_URI
    W3C XML Schema Namespace URI.

    Defined to be "`http://www.w3.org/2001/XMLSchema`".

    See Also:
      - XML Schema Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated
      - Constant Field Values

  - ### W3C_XML_SCHEMA_INSTANCE_NS_URI

    public static final String W3C_XML_SCHEMA_INSTANCE_NS_URI
    W3C XML Schema Instance Namespace URI.

    Defined to be "`http://www.w3.org/2001/XMLSchema-instance`".

    See Also:
      - XML Schema Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated
      - Constant Field Values

  - ### W3C_XPATH_DATATYPE_NS_URI

    public static final String W3C_XPATH_DATATYPE_NS_URI
    W3C XPath Datatype Namespace URI.

    Defined to be "`http://www.w3.org/2003/11/xpath-datatypes`".

    See Also:
      - XQuery 1.0 and XPath 2.0 Data Model
      - Constant Field Values

  - ### XML_DTD_NS_URI

    public static final String XML_DTD_NS_URI
    XML Document Type Declaration Namespace URI as an arbitrary value.

    Since not formally defined by any existing standard, arbitrarily define to be "`http://www.w3.org/TR/REC-xml`".

    See Also:
      - Constant Field Values

  - ### RELAXNG_NS_URI

    public static final String RELAXNG_NS_URI
    RELAX NG Namespace URI.

    Defined to be "`http://relaxng.org/ns/structure/1.0`".

    See Also:
      - RELAX NG Specification
      - Constant Field Values

  - ### FEATURE_SECURE_PROCESSING

    public static final String FEATURE_SECURE_PROCESSING
    Feature for secure processing.
    - `true` instructs the implementation to process XML securely. This may set limits on XML constructs to avoid conditions such as denial of service attacks.
    - `false` instructs the implementation to process XML in accordance with the XML specifications ignoring security issues such as limits on XML constructs to avoid conditions such as denial of service attacks.
    Implementation Note:
      when the Java Security Manager is present, the JDK sets the value of this feature to true and does not allow it to be turned off.
    See Also:
      - Constant Field Values

  - ### ACCESS_EXTERNAL_DTD

    public static final String ACCESS_EXTERNAL_DTD
    Property: accessExternalDTD

    Restrict access to external DTDs and external Entity References to the protocols specified. If access is denied due to the restriction of this property, a runtime exception that is specific to the context is thrown. In the case of `SAXParser` for example, `SAXException` is thrown.

    Value: as defined in the class description.

    System Property: `javax.xml.accessExternalDTD`.

    Configuration File: Yes. The property can be set in the configuration file.

    Since:
      1.7
    See Also:
      - Constant Field Values

  - ### ACCESS_EXTERNAL_SCHEMA

    public static final String ACCESS_EXTERNAL_SCHEMA

    Property: accessExternalSchema

    Restrict access to the protocols specified for external reference set by the schemaLocation attribute, Import and Include element. If access is denied due to the restriction of this property, a runtime exception that is specific to the context is thrown. In the case of `SchemaFactory` for example, org.xml.sax.SAXException is thrown.

    Value: as defined in the class description.

    System Property: `javax.xml.accessExternalSchema`

    Configuration File: Yes. The property can be set in the configuration file.

    Since:
      1.7
    See Also:
      - Constant Field Values

  - ### ACCESS_EXTERNAL_STYLESHEET

    public static final String ACCESS_EXTERNAL_STYLESHEET
    Property: accessExternalStylesheet

    Restrict access to the protocols specified for external references set by the stylesheet processing instruction, Import and Include element, and document function. If access is denied due to the restriction of this property, a runtime exception that is specific to the context is thrown. In the case of constructing new `Transformer` for example, `TransformerConfigurationException` will be thrown by the `TransformerFactory`.

    Value: as defined in the class description.

    System Property: `javax.xml.accessExternalStylesheet`

    Configuration File: Yes. The property can be set in the configuration file.

    Since:
      1.7
    See Also:
      - Constant Field Values

  - ### USE_CATALOG

    public static final String USE_CATALOG
    Feature: useCatalog

    Instructs XML processors to use XML Catalogs to resolve entity references. Catalogs may be set through JAXP factories, system properties, or configuration file by using the `javax.xml.catalog.files` property defined in `CatalogFeatures`. The following code enables Catalog on SAX parser:

             SAXParserFactory spf = SAXParserFactory.newInstance();
             spf.setFeature(XMLConstants.USE_CATALOG, true);
             SAXParser parser = spf.newSAXParser();
             parser.setProperty(CatalogFeatures.Feature.FILES.getPropertyName(), "catalog.xml");

    Value: a boolean. If the value is true, and a catalog is set, the XML parser will resolve external references using `CatalogResolver`. If the value is false, XML Catalog is ignored even if one is set. The default value is true.

    System Property: `javax.xml.useCatalog`

    Configuration File: Yes. The property can be set in the configuration file.

    Since:
      9
    See Also:
      - Constant Field Values