Package jakarta.activation

Class DataHandler

  • public class DataHandler
extends Object
    The DataHandler class provides a consistent interface to data available in many different sources and formats. It manages simple stream to string conversions and related operations using DataContentHandlers. It provides access to commands that can operate on the data. The commands are found using a CommandMap.

    DataHandler and CommandMaps

    The DataHandler keeps track of the current CommandMap that it uses to service requests for commands (getCommand, getAllCommands, getPreferredCommands). Each instance of a DataHandler may have a CommandMap associated with it using the setCommandMap method. If a CommandMap was not set, DataHandler calls the getDefaultCommandMap method in CommandMap and uses the value it returns. See CommandMap for more information.

    DataHandler and URLs

    The current DataHandler implementation creates a private instance of URLDataSource when it is constructed with a URL.

    See Also:
    CommandMap, DataContentHandler, DataSource, URLDataSource

    • Constructor Detail

      • DataHandler

        public DataHandler​(DataSource ds)
        Create a DataHandler instance referencing the specified DataSource. The data exists in a byte stream form. The DataSource will provide an InputStream to access the data.
        Parameters:
        ds - the DataSource

      • DataHandler

        public DataHandler​(Object obj,
                   String mimeType)
        Create a DataHandler instance representing an object of this MIME type. This constructor is used when the application already has an in-memory representation of the data in the form of a Java Object.
        Parameters:
        obj - the Java Object
        mimeType - the MIME type of the object

      • DataHandler

        public DataHandler​(URL url)
        Create a DataHandler instance referencing a URL. The DataHandler internally creates a URLDataSource instance to represent the URL.
        Parameters:
        url - a URL object

    • Method Detail

      • getDataSource

        public DataSource getDataSource()
        Return the DataSource associated with this instance of DataHandler.

        For DataHandlers that have been instantiated with a DataSource, this method returns the DataSource that was used to create the DataHandler object. In other cases the DataHandler constructs a DataSource from the data used to construct the DataHandler. DataSources created for DataHandlers not instantiated with a DataSource are cached for performance reasons.

        Returns:
        a valid DataSource object for this DataHandler

      • getName

        public String getName()
        Return the name of the data object. If this DataHandler was created with a DataSource, this method calls through to the DataSource.getName method, otherwise it returns null.
        Returns:
        the name of the object

      • getContentType

        public String getContentType()
        Return the MIME type of this object as retrieved from the source object. Note that this is the full type with parameters.
        Returns:
        the MIME type

      • getInputStream

        public InputStream getInputStream()
                           throws IOException
        Get the InputStream for this object.

        For DataHandlers instantiated with a DataSource, the DataHandler calls the DataSource.getInputStream method and returns the result to the caller.

        For DataHandlers instantiated with an Object, the DataHandler first attempts to find a DataContentHandler for the Object. If the DataHandler can not find a DataContentHandler for this MIME type, it throws an UnsupportedDataTypeException. If it is successful, it creates a pipe and a thread. The thread uses the DataContentHandler's writeTo method to write the stream data into one end of the pipe. The other end of the pipe is returned to the caller. Because a thread is created to copy the data, IOExceptions that may occur during the copy can not be propagated back to the caller. The result is an empty stream.

        Returns:
        the InputStream representing this data
        Throws:
        IOException - if an I/O error occurs
        See Also:
        DataContentHandler.writeTo(java.lang.Object, java.lang.String, java.io.OutputStream), UnsupportedDataTypeException

      • writeTo

        public void writeTo​(OutputStream os)
             throws IOException
        Write the data to an OutputStream.

        If the DataHandler was created with a DataSource, writeTo retrieves the InputStream and copies the bytes from the InputStream to the OutputStream passed in.

        If the DataHandler was created with an object, writeTo retrieves the DataContentHandler for the object's type. If the DataContentHandler was found, it calls the writeTo method on the DataContentHandler.

        Parameters:
        os - the OutputStream to write to
        Throws:
        IOException - if an I/O error occurs

      • getOutputStream

        public OutputStream getOutputStream()
                             throws IOException
        Get an OutputStream for this DataHandler to allow overwriting the underlying data. If the DataHandler was created with a DataSource, the DataSource's getOutputStream method is called. Otherwise, null is returned.
        Returns:
        the OutputStream
        Throws:
        IOException - for failures creating the OutputStream
        See Also:
        DataSource.getOutputStream(), URLDataSource

      • getTransferDataFlavors

        public ActivationDataFlavor[] getTransferDataFlavors()
        Return the ActivationDataFlavors in which this data is available.

        Returns an array of ActivationDataFlavor objects indicating the flavors the data can be provided in. The array is usually ordered according to preference for providing the data, from most richly descriptive to least richly descriptive.

        The DataHandler attempts to find a DataContentHandler that corresponds to the MIME type of the data. If one is located, the DataHandler calls the DataContentHandler's getTransferDataFlavors method.

        If a DataContentHandler can not be located, and if the DataHandler was created with a DataSource (or URL), one ActivationDataFlavor is returned that represents this object's MIME type and the java.io.InputStream class. If the DataHandler was created with an object and a MIME type, getTransferDataFlavors returns one ActivationDataFlavor that represents this object's MIME type and the object's class.

        Returns:
        an array of data flavors in which this data can be transferred
        See Also:
        DataContentHandler.getTransferDataFlavors()

      • isDataFlavorSupported

        public boolean isDataFlavorSupported​(ActivationDataFlavor flavor)
        Returns whether the specified data flavor is supported for this object.

        This method iterates through the ActivationDataFlavors returned from getTransferDataFlavors, comparing each with the specified flavor.

        Parameters:
        flavor - the requested flavor for the data
        Returns:
        true if the data flavor is supported
        See Also:
        getTransferDataFlavors()

      • getTransferData

        public Object getTransferData​(ActivationDataFlavor flavor)
                       throws IOException
        Returns an object that represents the data to be transferred. The class of the object returned is defined by the representation class of the data flavor.

        For DataHandler's created with DataSources or URLs:

        The DataHandler attempts to locate a DataContentHandler for this MIME type. If one is found, the passed in ActivationDataFlavor and the type of the data are passed to its getTransferData method. If the DataHandler fails to locate a DataContentHandler and the flavor specifies this object's MIME type and the java.io.InputStream class, this object's InputStream is returned. Otherwise it throws an IOException.

        For DataHandler's created with Objects:

        The DataHandler attempts to locate a DataContentHandler for this MIME type. If one is found, the passed in ActivationDataFlavor and the type of the data are passed to its getTransferData method. If the DataHandler fails to locate a DataContentHandler and the flavor specifies this object's MIME type and its class, this DataHandler's referenced object is returned. Otherwise it throws an IOException.

        Parameters:
        flavor - the requested flavor for the data
        Returns:
        the object
        Throws:
        IOException - if the data could not be converted to the requested flavor
        IOException - if an I/O error occurs
        See Also:
        ActivationDataFlavor

      • setCommandMap

        public void setCommandMap​(CommandMap commandMap)
        Set the CommandMap for use by this DataHandler. Setting it to null causes the CommandMap to revert to the CommandMap returned by the CommandMap.getDefaultCommandMap method. Changing the CommandMap, or setting it to null, clears out any data cached from the previous CommandMap.
        Parameters:
        commandMap - the CommandMap to use in this DataHandler
        See Also:
        CommandMap.setDefaultCommandMap(jakarta.activation.CommandMap)

      • getPreferredCommands

        public CommandInfo[] getPreferredCommands()
        Return the preferred commands for this type of data. This method calls the getPreferredCommands method in the CommandMap associated with this instance of DataHandler. This method returns an array that represents a subset of available commands. In cases where multiple commands for the MIME type represented by this DataHandler are present, the installed CommandMap chooses the appropriate commands.
        Returns:
        the CommandInfo objects representing the preferred commands
        See Also:
        CommandMap.getPreferredCommands(java.lang.String)

      • getAllCommands

        public CommandInfo[] getAllCommands()
        Return all the commands for this type of data. This method returns an array containing all commands for the type of data represented by this DataHandler. The MIME type for the underlying data represented by this DataHandler is used to call through to the getAllCommands method of the CommandMap associated with this DataHandler.
        Returns:
        the CommandInfo objects representing all the commands
        See Also:
        CommandMap.getAllCommands(java.lang.String)

      • getCommand

        public CommandInfo getCommand​(String cmdName)
        Get the command cmdName. Use the search semantics as defined by the CommandMap installed in this DataHandler. The MIME type for the underlying data represented by this DataHandler is used to call through to the getCommand method of the CommandMap associated with this DataHandler.
        Parameters:
        cmdName - the command name
        Returns:
        the CommandInfo corresponding to the command
        See Also:
        CommandMap.getCommand(java.lang.String, java.lang.String)

      • getContent

        public Object getContent()
                  throws IOException
        Return the data in its preferred Object form.

        If the DataHandler was instantiated with an object, return the object.

        If the DataHandler was instantiated with a DataSource, this method uses a DataContentHandler to return the content object for the data represented by this DataHandler. If no DataContentHandler can be found for the the type of this data, the DataHandler returns an InputStream for the data.

        Returns:
        the content.
        Throws:
        IOException - if an IOException occurs during this operation.

      • getBean

        public Object getBean​(CommandInfo cmdinfo)
        A convenience method that takes a CommandInfo object and instantiates the corresponding command, usually a JavaBean component.

        This method calls the CommandInfo's getCommandObject method with the ClassLoader used to load the jakarta.activation.DataHandler class itself.

        Parameters:
        cmdinfo - the CommandInfo corresponding to a command
        Returns:
        the instantiated command object

      • setDataContentHandlerFactory

        public static void setDataContentHandlerFactory​(DataContentHandlerFactory newFactory)
        Sets the DataContentHandlerFactory. The DataContentHandlerFactory is called first to find DataContentHandlers. The DataContentHandlerFactory can only be set once.

        If the DataContentHandlerFactory has already been set, this method throws an Error.

        Parameters:
        newFactory - the DataContentHandlerFactory
        Throws:
        Error - if the factory has already been defined.
        See Also:
        DataContentHandlerFactory