Module org.apache.sis.storage
Package org.apache.sis.storage

Class ProbeResult

Object
ProbeResult
All Implemented Interfaces:
Serializable
public class ProbeResult extends Object implements Serializable
Tells whether a storage (file, database) appears to be supported by a Data­Store. Probe­Result may also provide additional information, like file MIME type and the format version.

Usage

When a Data­Stores​.open(…) method is invoked, SIS will iterate over the list of known providers and invoke the Data­Store­Provider​.probe­Content(Storage­Connector) method for each of them. The Probe­Result value returned by probe­Content(…) tells to SIS whether a particular Data­Store­Provider instance has reasonable chances to be able to handle the given storage.

Whether a storage appears to be supported or not is given by the is­Supported() property. Other properties like get­Version() are sometimes available for both supported and unsupported storages. For example, a file may be encoded in a known format, but may be using an unsupported version of that format.

Special values

In addition to the supported/unsupported information, Probe­Result defines two constants having a special meaning: INSUFFICIENT_BYTES and UNDETERMINED, which indicate that the provider does not have enough information for telling whether the storage can be opened. In such cases, SIS will revisit those providers only if no better suited provider is found.
Since:
0.4
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final Probe­Result
    INSUFFICIENT_BYTES
    The open capability cannot be determined because the Byte­Buffer contains an insufficient amount of bytes.
    static final Probe­Result
    SUPPORTED
    The Data­Store­Provider recognizes the given storage, but has no additional information.
    static final Probe­Result
    UNDETERMINED
    The open capability cannot be determined.
    static final Probe­Result
    UNSUPPORTED_STORAGE
    The Data­Store­Provider does not recognize the given storage object, file format or database schema.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Probe­Result(boolean is­Supported, String mime­Type, Version version)
    Creates a new Probe­Result with the given support status, MIME type and version number.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    equals(Object object)
    Compares this Probe­Result with the given object for equality.
    String
    get­Mime­Type()
    Returns the MIME type of the storage file format, or null if unknown or not applicable.
    Version
    get­Version()
    Returns the version of file format or database schema used by the storage, or null if unknown or not applicable.
    int
    hash­Code()
    Returns a hash code value for this instance.
    boolean
    is­Supported()
    Returns true if the storage is supported by the Data­Store­Provider.
    String
    to­String()
    Returns a string representation of this Probe­Result for debugging purpose.

    Methods inherited from class Object

    clone, finalize, get­Class, notify, notify­All, wait, wait, wait

  • Field Details

    • SUPPORTED

      public static final ProbeResult SUPPORTED
      The Data­Store­Provider recognizes the given storage, but has no additional information. The is­Supported() method returns true, but the MIME type and version properties are null.

      Data­Store­Provider​.probe­Content(Storage­Connector) implementations should consider returning a new instance instead of this constant if they can provide the file MIME type or the format version number.

    • UNSUPPORTED_STORAGE

      public static final ProbeResult UNSUPPORTED_STORAGE
      The Data­Store­Provider does not recognize the given storage object, file format or database schema. No other information is available: the is­Supported() method returns false, and the MIME type and version properties are null.

      Examples:

      • The storage is a file while the provider expected a database connection (or conversely).
      • The file does not contains the expected magic number.
      • The database schema does not contain the expected tables.
      Data­Store­Provider​.probe­Content(Storage­Connector) implementations should consider returning a new instance instead of this constant if the Data­Store­Provider recognizes the given storage, but the data are structured according a file or schema version not yet supported by the current implementation.

    • INSUFFICIENT_BYTES

      public static final ProbeResult INSUFFICIENT_BYTES
      The open capability cannot be determined because the Byte­Buffer contains an insufficient amount of bytes. This value can be returned by Data­Store­Provider​.probe­Content(Storage­Connector) implementations as below: 
          public ProbeResult probeContent(StorageConnector storage) throws DataStoreException {
        final ByteBuffer buffer = storage.getStorageAs(ByteBuffer.class);
        if (buffer == null) {
            return ProbeResult.UNSUPPORTED_STORAGE;
        }
        if (buffer.remaining() < Integer.BYTES) {
            return ProbeResult.INSUFFICIENT_BYTES;
        }
        // Other verifications here.
    }
      When searching for a provider capable to read a given file, if at least one Data­Store­Provider returns INSUFFICIENT_BYTES, then:
      1. SIS will continue to search for another provider for which probe­Content(…) declares to support the storage, using only the available bytes.
      2. Only if no such provider can be found, then SIS will fetch more bytes and query again the providers that returned INSUFFICIENT_BYTES in the previous iteration.
      SIS tries to work with available bytes before to ask more in order to reduce latencies on network connections.

    • UNDETERMINED

      public static final ProbeResult UNDETERMINED
      The open capability cannot be determined. This value may be returned by Data­Store implementations that could potentially open anything, for example the RAW image format.

      This is a last resort value! probe­Content(…) implementations are strongly encouraged to return a more accurate enumeration value for allowing Data­Stores​.open(Object) to perform a better choice. Generally, this value should be returned only by the RAW image format.

  • Constructor Details

    • ProbeResult

      public ProbeResult(boolean isSupported, String mimeType, Version version)
      Creates a new Probe­Result with the given support status, MIME type and version number.
      Parameters:
      is­Supported - true if the storage is supported by the Data­Store­Provider.
      mime­Type - the storage MIME type, or null if unknown or not applicable.
      version - the version of file format or database schema used by the storage, or null if unknown or not applicable.

  • Method Details

    • isSupported

      public boolean isSupported()
      Returns true if the storage is supported by the Data­Store­Provider. Data­Store instances created by that provider are likely (but not guaranteed) to be able to read from - and eventually write to - the given storage.
      Returns:
      true if the storage is supported by the Data­Store­Provider.

    • getMimeType

      public String getMimeType()
      Returns the MIME type of the storage file format, or null if unknown or not applicable. The Data­Store­Provider may (at implementation choice) inspect the storage content for determining a more accurate MIME type.

      XML types

      A generic MIME type for XML documents is "application/xml". However, many other MIME types exist for XML documents compliant to some particular shema. Those types can be determined by inspecting the namespace of XML root element. The following table gives some examples:
      MIME type examples
      MIME type Description Namespace
      "application/gml+xml" Official mime type for OGC GML "http://www.opengis.net/gml/3.2"
      "application/vnd.eu.europa.ec.inspire.resource+xml" Official mime type for INSPIRE Resources
      "application/vnd.iso.19139+xml" Unofficial mime type for ISO 19139 metadata "http://www.isotc211.org/2005/gmd"
      "application/vnd.ogc.wms_xml" Unofficial mime type for OGC WMS
      "application/vnd.ogc.wfs_xml" Unofficial mime type for OGC WFS
      "application/vnd.ogc.csw_xml" Unofficial mime type for OGC CSW "http://www.opengis.net/cat/csw/3.0"
      "application/vnd.google-earth.kml+xml"
      "application/rdf+xml"
      "application/soap+xml"
      Returns:
      the storage MIME type, or null if unknown or not applicable.

    • getVersion

      public Version getVersion()
      Returns the version of file format or database schema used by the storage, or null if unknown or not applicable.
      Returns:
      the version of file format or database schema used by the storage, or null if unknown or not applicable.

    • hashCode

      public int hashCode()
      Returns a hash code value for this instance.
      Overrides:
      hash­Code in class Object

    • equals

      public boolean equals(Object object)
      Compares this Probe­Result with the given object for equality. Two Probe­Results are equal if they are instances of the same class and all their properties are equal.
      Overrides:
      equals in class Object
      Parameters:
      object - the object to compare with this Probe­Result.
      Returns:
      true if the two objects are equal.

    • toString

      public String toString()
      Returns a string representation of this Probe­Result for debugging purpose.
      Overrides:
      to­String in class Object