# Class XML

Object
XML

public final class XML extends Object
Provides convenience methods for marshalling and unmarshalling SIS objects. Marshalling operations use the standard versions listed below (for marshalling a document in a different version, see `MarshallerPool`). Unmarshalling detects the version automatically.

Versions of standards applied at marshalling time
Topic | SIS 0.3 to 0.8 | SIS 1.0 | Remarks
--- | --- | --- | ---
Metadata | ISO 19139:2007 | ISO 19115-3:2016 |
Referencing | ISO 19136:2007 | ISO 19136:2007 | Same as GML 3.2

This class defines also some property keys that can be given to the `Marshaller` and `Unmarshaller` instances created by `MarshallerPool`:

Supported (un)marshaller properties
Key | Value type | Purpose
--- | --- | ---
`LOCALE` | `Locale` | for specifying the locale to use for international strings and code lists.
`TIMEZONE` | `TimeZone` | for specifying the timezone to use for dates and times.
`SCHEMAS` | `Map` | for specifying the root URL of metadata schemas to use.
`GML_VERSION` | `Version` | for specifying the GML version of the document to be (un)marshalled.
`METADATA_VERSION` | `Version` | for specifying the metadata version of the document to be (un)marshalled.
`RESOLVER` | `ReferenceResolver` | for replacing `xlink` or `uuidref` attributes by the actual object to use.
`CONVERTER` | `ValueConverter` | for controlling the conversion of URL, UUID, Units or similar objects.
`STRING_SUBSTITUTES` | `String[]` | for specifying which code lists to replace by simpler `<gco:CharacterString>` elements.
`WARNING_FILTER` | `Filter` | for being notified about non-fatal warnings.

Since:
  0.3

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final String`
  `CONVERTER`
  Controls the behaviors of the (un)marshalling process when an element cannot be processed, or alter the element values.
  `static final String`
  `GML_VERSION`
  Specifies the GML version of the document to be marshalled or unmarshalled.
  `static final String`
  `LENIENT_UNMARSHAL`
  Specifies whether the unmarshalling process should accept any metadata or GML supported version if the user did not specify an explicit version.
  `static final String`
  `LOCALE`
  Specifies the locale to use for marshalling `InternationalString` and `CodeList` instances.
  `static final String`
  `METADATA_VERSION`
  Specifies the metadata version of the document to be marshalled or unmarshalled.
  `static final String`
  `RESOLVER`
  Allows client code to replace `xlink` or `uuidref` attributes by the actual objects to use.
  `static final String`
  `SCHEMAS`
  Specifies the root URLs of some schemas.
  `static final String`
  `STRING_SUBSTITUTES`
  Allows marshallers to substitute some code lists by the simpler `<gco:CharacterString>` element.
  `static final String`
  `TIMEZONE`
  Specifies the timezone to use for marshalling dates and times.
  `static final String`
  `WARNING_FILTER`
  Specifies a listener to be notified when a non-fatal error occurred during the (un)marshalling.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static String`
  `marshal(Object object)`
  Marshal the given object into a string.
  `static void`
  `marshal(Object object, File output)`
  Marshal the given object into a file.
  `static void`
  `marshal(Object object, OutputStream output)`
  Marshal the given object into a stream.
  `static void`
  `marshal(Object object, Path output)`
  Marshal the given object into a path.
  `static void`
  `marshal(Object object, Result output, Map<String,?> properties)`
  Marshal the given object to a stream, DOM or other destinations.
  `static Object`
  `unmarshal(File input)`
  Unmarshal an object from the given file.
  `static Object`
  `unmarshal(InputStream input)`
  Unmarshal an object from the given stream.
  `static Object`
  `unmarshal(String xml)`
  Unmarshal an object from the given string.
  `static Object`
  `unmarshal(URL input)`
  Unmarshal an object from the given URL.
  `static Object`
  `unmarshal(Path input)`
  Unmarshal an object from the given path.
  `static <T> JAXBElement<T>`
  `unmarshal(Source input, Class<T> declaredType, Map<String,?> properties)`
  Unmarshal an object from the given stream, DOM or other sources.
  `static Object`
  `unmarshal(Source input, Map<String,?> properties)`
  Unmarshal an object from the given stream, DOM or other sources.

  ### Methods inherited from class Object

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

- ## Field Details

  - ### LOCALE

    public static final String LOCALE
    Specifies the locale to use for marshalling `InternationalString` and `CodeList` instances. The value for this property shall be an instance of `Locale` or a `CharSequence` recognized by `Locales​.parse(String)`.

    This property is mostly for marshallers. However, this property can also be used at unmarshalling time, for example if a `<lan:PT_FreeText>` element containing many localized strings need to be represented in a Java `String` object. In such case, the unmarshaller will try to pickup a string in the language specified by this property.

    #### Default behavior

    If this property is never set, then (un)marshalling will try to use "unlocalized" strings - typically some programmatic strings like UML identifiers. While such identifiers often look like English words, they are not considered as the English localization. The algorithm attempting to find a "unlocalized" string is defined in the `DefaultInternationalString​.toString(Locale)` javadoc.

    #### Special case

    If the object to be marshalled is an instance of `DefaultMetadata`, then the value given to its `setLanguage(Locale)` method will have precedence over this property. This behavior is compliant with INSPIRE rules.
    See Also:
      - `OptionKey​.LOCALE`
      - `Marshaller​.setProperty(String, Object)`
      - `DefaultMetadata​.setLanguage(Locale)`
      - Constant Field Values

  - ### TIMEZONE

    public static final String TIMEZONE
    Specifies the timezone to use for marshalling dates and times. The value for this property shall be an instance of `ZoneId`, `TimeZone`, or a `CharSequence` recognized by `ZoneId​.of(String)` or `TimeZone​.getTimeZone(String)`.

    #### Default behavior

    If this property is never set, then (un)marshalling will use the default timezone.
    See Also:
      - `OptionKey​.TIMEZONE`
      - Constant Field Values

  - ### SCHEMAS

    public static final String SCHEMAS
    Specifies the root URLs of some schemas. This property modifies only the URL strings; it does not change the structure of marshalled XML documents (for content structure, see `METADATA_VERSION`). The value for this property shall be an instance of `Map<String,String>`. This property controls the URLs to be used when marshalling the following elements:
    - The value of the `codeList` attribute when marshalling subclasses of `CodeList`.
    - The value of the `uom` attribute when marshalling measures (for example `<gco:Distance>`).

    #### Examples

    URLs in code lists and is units of measurement may appear as below. The underlined fragment is the part that can be replaced by `SCHEMAS` values:
    - `http://standards​.iso​.org/iso/19115/resources/Codelist/cat/codelists​.xml#LanguageCode`
    - `http://www​.isotc211​.org/2005/resources/Codelist/gmxCodelists​.xml#LanguageCode`
    - `http://www​.isotc211​.org/2005/resources/uom/gmxUom​.xml#xpointer(//*[@gml:id='m'])`

    #### Implementation note

    The currently recognized keys are listed below. The entries to be used depend on the metadata version to be marshalled. For example, the `"cat"` entry is used when marshalling ISO 19115-3:2016 document, while the `"gmd"` and `"gmi"` entries are used when marshalling ISO 19139:2007 documents. The following table gives some typical URLs, with the default URL in bold characters:

    Supported root URLs
    Map key | Typical values (choose only one)
    --- | ---
    cat | http://standards.iso.org/iso/19115/
    gmd | http://www.isotc211.org/2005/ http://schemas.opengis.net/iso/19139/20070417/ http://standards.iso.org/ittf/PubliclyAvailableStandards/ISO_19139_Schemas/

    Additional keys, if any, are ignored. Future SIS versions may recognize more keys.
    See Also:
      - Constant Field Values

  - ### GML_VERSION

    public static final String GML_VERSION
    Specifies the GML version of the document to be marshalled or unmarshalled. The GML version may affect the set of XML elements to be marshalled and their namespaces. Note that GML 3.2 is identical to ISO 19136:2007. The value can be `String` or `Version` object. If no version is specified, then the most recent supported GML version is assumed.

    #### Supported GML versions

    Apache SIS currently supports GML 3.2.1 by default. SIS can read and write GML 3.2 if this property is set to "3.2". It is also possible to set this property to "3.1", but the marshalled XML is not GML 3.1.1 conformant because of the differences between the two schemas. See SIS-160: Need XSLT between GML 3.1 and 3.2 for information about the status of GML 3.1.1 support.

    #### Compatibility note

    Newer GML versions typically have more elements, but not always. For example, in `<gml:VerticalDatum>`, the `<gml:verticalDatumType>` property presents in GML 3.0 and 3.1 has been removed in GML 3.2.
    See Also:
      - Constant Field Values

  - ### METADATA_VERSION

    public static final String METADATA_VERSION
    Specifies the metadata version of the document to be marshalled or unmarshalled. The metadata version may affect the set of XML elements to be marshalled and their namespaces. The value can be `String` or `Version` object. If no version is specified, then the most recent supported metadata version is assumed.

    The metadata version may be ignored when the metadata to marshal is inside a GML element. For example, the `<gml:domainOfValidity>` element inside a coordinate reference system is always marshalled using ISO 19139:2007 if the enclosing element uses GML 3.2 schema.

    #### Supported metadata versions

    Apache SIS currently supports ISO 19115-3:2016 by default. This version can be explicitly set with value "2014" or above (because the abstract model was defined in ISO 19115-1:2014). SIS can write legacy ISO 19139:2007 documents if this property is set to a value less than "2014". Both versions can be read without the need to specify this property.
    Since:
      1.0
    See Also:
      - Constant Field Values

  - ### LENIENT_UNMARSHAL

    public static final String LENIENT_UNMARSHAL
    Specifies whether the unmarshalling process should accept any metadata or GML supported version if the user did not specify an explicit version. The value can be a `Boolean` instance, or `"true"` or `"false"` as a `String`. If this value is not specified, then the default is `true` for all `XML​.unmarshal` methods and `false` otherwise.

    Metadata and Geographic Markup Language have slightly different XML encoding depending on the OGC/ISO version in use. Often the namespaces are different, but not only. Internally, Apache SIS supports only the schema versions documented in this class javadoc, for example the ISO 19115-3:2016 version of metadata schema. For unmarshalling a document encoded according an older metadata schema (e.g. ISO 19139:2007), a transformation is applied on-the-fly. However this transformation may sometimes produce undesirable results or make debugging more difficult. For this reason `MarshallerPool` applies the transformation only if explicitly requested, either by setting a `METADATA_VERSION` or `GML_VERSION` explicitly, or by setting this `LENIENT_UNMARSHAL` property to `true` if the version to unmarshal is not known in advance.

    Since:
      1.0
    See Also:
      - Constant Field Values

  - ### RESOLVER

    public static final String RESOLVER
    Allows client code to replace `xlink` or `uuidref` attributes by the actual objects to use. The value for this property shall be an instance of `ReferenceResolver`.

    If a property in a XML document is defined only by `xlink` or `uuidref` attributes, without any concrete definition, then the default behavior is as below:

    - If the reference is of the form `xlink:href="#foo"` and an object with the `gml:id="foo"` attribute was previously found in the same XML document, then that object will be used.
    - Otherwise, if `xlink:href` references an external document, that document is unmarshalled. The URI resolution can be controlled with an `URIResolver` specified at construction time.
    - Otherwise, an empty element containing only the values of the above-cited attributes is created.
    Applications can sometimes do better by using some domain-specific knowledge, for example by searching in a database. Users can define their search algorithm by subclassing `ReferenceResolver` and configuring a unmarshaller as below:

        ReferenceResolver  myResolver = ...;
        Map<String,Object> properties = new HashMap<>();
        properties.put(XML.RESOLVER, myResolver);
        Object obj = XML.unmarshal(source, properties);

    See Also:
      - `Unmarshaller​.setProperty(String, Object)`
      - `ReferenceResolver`
      - Constant Field Values

  - ### CONVERTER

    public static final String CONVERTER
    Controls the behaviors of the (un)marshalling process when an element cannot be processed, or alter the element values. The value for this property shall be an instance of `ValueConverter`.

    If an element in a XML document cannot be parsed (for example if a URL string is not valid), the default behavior is to throw an exception which cause the (un)marshalling of the entire document to fail. This default behavior can be customized by invoking `Marshaller​.setProperty(String, Object)` with this `CONVERTER` property key and a custom `ValueConverter` instance. `ValueConverter` can also be used for replacing an erroneous URL by a fixed URL. See the `ValueConverter` javadoc for more details.

    #### Example

    The following example collects the failures in a list without stopping the (un)marshalling process.

            class WarningCollector extends ValueConverter {
                // The warnings collected during (un)marshalling.
                List<String> messages = new ArrayList<String>();

                // Override the default implementation in order to
                // collect the warnings and allow the process to continue.
                @Override
                protected <T> boolean exceptionOccured(MarshalContext context,
                        T value, Class<T> sourceType, Class<T> targetType, Exception e)
                {
                    mesages.add(e.getLocalizedMessage());
                    return true;
                }
            }

            // Unmarshal a XML string, trapping some kind of errors.
            // Not all errors are trapped - see the ValueConverter
            // javadoc for more details.
            WarningCollector myWarningList = new WarningCollector();
            Map<String,Object> properties = new HashMap<>();
            properties.put(XML.CONVERTER, myWarningList);
            Object obj = XML.unmarshal(source, properties);
            if (!myWarningList.isEmpty()) {
                // Report here the warnings to the user.
            }

    See Also:
      - `Unmarshaller​.setProperty(String, Object)`
      - `ValueConverter`
      - Constant Field Values

  - ### STRING_SUBSTITUTES

    public static final String STRING_SUBSTITUTES
    Allows marshallers to substitute some code lists by the simpler `<gco:CharacterString>` element. The value for this property shall be a `String[]` array of any of the following values:
    - "`language`" for substituting `<lan:LanguageCode>` elements
    - "`country`" for substituting `<lan:Country>` elements
    - "`filename`" for substituting `<gcx:FileName>` elements
    - "`mimetype`" for substituting `<gcx:MimeFileType>` elements

    #### Example

    INSPIRE compliant language code shall be formatted like below (details may vary):

          <gmd:language>
            <gmd:LanguageCode
                codeList="http://www.isotc211.org/2005/resources/Codelist/gmxCodelists.xml#LanguageCode"
                codeListValue="fra">French</gmd:LanguageCode>
          </gmd:language>

    However if this property contains the "`language`" value, then the marshaller will format the language code like below (which is legal according OGC schemas, but is not INSPIRE compliant):

          <lan:language>
            <gco:CharacterString>fra</gco:CharacterString>
          </lan:language>

    See Also:
      - Constant Field Values

  - ### WARNING_FILTER

    public static final String WARNING_FILTER
    Specifies a listener to be notified when a non-fatal error occurred during the (un)marshalling. The value for this property shall be an instance of `Filter`.

    By default, warnings that occur during the (un)marshalling process are logged. However, if a property is set for this key, then the `Filter​.isLoggable(LogRecord)` method will be invoked. If that method returns `false`, then the warning will not be logged by the (un)marshaller.

    Since:
      1.0
    See Also:
      - Constant Field Values

- ## Method Details

  - ### marshal

    public static String marshal(Object object) throws JAXBException
    Marshal the given object into a string.
    Parameters:
      `object` - the root of content tree to be marshalled.
    Returns:
      the XML representation of the given object.
    Throws:
      `JAXBException` - if an error occurred during the marshalling.

  - ### marshal

    public static void marshal(Object object, OutputStream output) throws JAXBException
    Marshal the given object into a stream.
    Parameters:
      `object` - the root of content tree to be marshalled.
      `output` - the stream where to write.
    Throws:
      `JAXBException` - if an error occurred during the marshalling.

  - ### marshal

    public static void marshal(Object object, File output) throws JAXBException
    Marshal the given object into a file.
    Parameters:
      `object` - the root of content tree to be marshalled.
      `output` - the file to be written.
    Throws:
      `JAXBException` - if an error occurred during the marshalling.

  - ### marshal

    public static void marshal(Object object, Path output) throws JAXBException
    Marshal the given object into a path.
    Parameters:
      `object` - the root of content tree to be marshalled.
      `output` - the file to be written.
    Throws:
      `JAXBException` - if an error occurred during the marshalling.

  - ### marshal

    public static void marshal(Object object, Result output, Map<String,?> properties) throws JAXBException
    Marshal the given object to a stream, DOM or other destinations. This is the most flexible marshalling method provided in this `XML` class. The destination is specified by the `output` argument implementation, for example `StreamResult` for writing to a file or output stream. The optional `properties` map can contain any key documented in this `XML` class, together with the keys documented in the supported properties section of the `Marshaller` class.
    Parameters:
      `object` - the root of content tree to be marshalled.
      `output` - the file to be written.
      `properties` - an optional map of properties to give to the marshaller, or `null` if none.
    Throws:
      `JAXBException` - if a property has an illegal value, or if an error occurred during the marshalling.
    Since:
      0.4

  - ### unmarshal

    public static Object unmarshal(String xml) throws JAXBException
    Unmarshal an object from the given string. Note that the given argument is the XML document itself, not a URL to a XML document.
    Parameters:
      `xml` - the XML representation of an object.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if an error occurred during the unmarshalling.

  - ### unmarshal

    public static Object unmarshal(InputStream input) throws JAXBException
    Unmarshal an object from the given stream.
    Parameters:
      `input` - the stream from which to read a XML representation.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if an error occurred during the unmarshalling.

  - ### unmarshal

    public static Object unmarshal(URL input) throws JAXBException
    Unmarshal an object from the given URL.
    Parameters:
      `input` - the URL from which to read a XML representation.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if an error occurred during the unmarshalling.

  - ### unmarshal

    public static Object unmarshal(File input) throws JAXBException
    Unmarshal an object from the given file.
    Parameters:
      `input` - the file from which to read a XML representation.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if an error occurred during the unmarshalling.

  - ### unmarshal

    public static Object unmarshal(Path input) throws JAXBException
    Unmarshal an object from the given path.
    Parameters:
      `input` - the path from which to read a XML representation.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if an error occurred during the unmarshalling.

  - ### unmarshal

    public static Object unmarshal(Source input, Map<String,?> properties) throws JAXBException
    Unmarshal an object from the given stream, DOM or other sources. Together with the Unmarshal by Declared Type variant, this is the most flexible unmarshalling method provided in this `XML` class. The source is specified by the `input` argument implementation, for example `StreamSource` for reading from a file or input stream. The optional `properties` map can contain any key documented in this `XML` class, together with the keys documented in the supported properties section of the `Unmarshaller` class.
    Parameters:
      `input` - the file from which to read a XML representation.
      `properties` - an optional map of properties to give to the unmarshaller, or `null` if none.
    Returns:
      the object unmarshalled from the given input.
    Throws:
      `JAXBException` - if a property has an illegal value, or if an error occurred during the unmarshalling.
    Since:
      0.4

  - ### unmarshal

    public static <T> JAXBElement<T> unmarshal(Source input, Class<T> declaredType, Map<String,?> properties) throws JAXBException
    Unmarshal an object from the given stream, DOM or other sources. Together with the Unmarshal Global Root Element variant, this is the most flexible unmarshalling method provided in this `XML` class. The source is specified by the `input` argument implementation, for example `StreamSource` for reading from a file or input stream. The optional `properties` map can contain any key documented in this `XML` class, together with the keys documented in the supported properties section of the `Unmarshaller` class.
    Type Parameters:
      `T` - compile-time value of the `declaredType` argument.
    Parameters:
      `input` - the file from which to read a XML representation.
      `declaredType` - the JAXB mapped class of the object to unmarshal.
      `properties` - an optional map of properties to give to the unmarshaller, or `null` if none.
    Returns:
      the object unmarshalled from the given input, wrapped in a JAXB element.
    Throws:
      `JAXBException` - if a property has an illegal value, or if an error occurred during the unmarshalling.
    Since:
      0.8