- java.lang.Object
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- jakarta.activation.DataHandler
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public class DataHandler extends java.lang.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 thesetCommandMap
method. If a CommandMap was not set, DataHandler calls thegetDefaultCommandMap
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
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Constructor Summary
Constructors Constructor Description DataHandler(DataSource ds)
Create aDataHandler
instance referencing the specified DataSource.DataHandler(java.lang.Object obj, java.lang.String mimeType)
Create aDataHandler
instance representing an object of this MIME type.DataHandler(java.net.URL url)
Create aDataHandler
instance referencing a URL.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description CommandInfo[]
getAllCommands()
Return all the commands for this type of data.java.lang.Object
getBean(CommandInfo cmdinfo)
A convenience method that takes a CommandInfo object and instantiates the corresponding command, usually a JavaBean component.CommandInfo
getCommand(java.lang.String cmdName)
Get the command cmdName.java.lang.Object
getContent()
Return the data in its preferred Object form.java.lang.String
getContentType()
Return the MIME type of this object as retrieved from the source object.DataSource
getDataSource()
Return the DataSource associated with this instance of DataHandler.java.io.InputStream
getInputStream()
Get the InputStream for this object.java.lang.String
getName()
Return the name of the data object.java.io.OutputStream
getOutputStream()
Get an OutputStream for this DataHandler to allow overwriting the underlying data.CommandInfo[]
getPreferredCommands()
Return the preferred commands for this type of data.java.lang.Object
getTransferData(ActivationDataFlavor flavor)
Returns an object that represents the data to be transferred.ActivationDataFlavor[]
getTransferDataFlavors()
Return the ActivationDataFlavors in which this data is available.boolean
isDataFlavorSupported(ActivationDataFlavor flavor)
Returns whether the specified data flavor is supported for this object.void
setCommandMap(CommandMap commandMap)
Set the CommandMap for use by this DataHandler.static void
setDataContentHandlerFactory(DataContentHandlerFactory newFactory)
Sets the DataContentHandlerFactory.void
writeTo(java.io.OutputStream os)
Write the data to anOutputStream
.
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Constructor Detail
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DataHandler
public DataHandler(DataSource ds)
Create aDataHandler
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
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DataHandler
public DataHandler(java.lang.Object obj, java.lang.String mimeType)
Create aDataHandler
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 ObjectmimeType
- the MIME type of the object
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DataHandler
public DataHandler(java.net.URL url)
Create aDataHandler
instance referencing a URL. The DataHandler internally creates aURLDataSource
instance to represent the URL.- Parameters:
url
- a URL object
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Method Detail
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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
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getName
public java.lang.String getName()
Return the name of the data object. If this DataHandler was created with a DataSource, this method calls through to theDataSource.getName
method, otherwise it returns null.- Returns:
- the name of the object
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getContentType
public java.lang.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
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getInputStream
public java.io.InputStream getInputStream() throws java.io.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:
java.io.IOException
- if an I/O error occurs- See Also:
DataContentHandler.writeTo(java.lang.Object, java.lang.String, java.io.OutputStream)
,UnsupportedDataTypeException
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writeTo
public void writeTo(java.io.OutputStream os) throws java.io.IOException
Write the data to anOutputStream
.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 theDataContentHandler
.- Parameters:
os
- the OutputStream to write to- Throws:
java.io.IOException
- if an I/O error occurs
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getOutputStream
public java.io.OutputStream getOutputStream() throws java.io.IOException
Get an OutputStream for this DataHandler to allow overwriting the underlying data. If the DataHandler was created with a DataSource, the DataSource'sgetOutputStream
method is called. Otherwise,null
is returned.- Returns:
- the OutputStream
- Throws:
java.io.IOException
- for failures creating the OutputStream- See Also:
DataSource.getOutputStream()
,URLDataSource
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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()
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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()
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getTransferData
public java.lang.Object getTransferData(ActivationDataFlavor flavor) throws java.io.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 thejava.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:
java.io.IOException
- if the data could not be converted to the requested flavorjava.io.IOException
- if an I/O error occurs- See Also:
ActivationDataFlavor
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setCommandMap
public void setCommandMap(CommandMap commandMap)
Set the CommandMap for use by this DataHandler. Setting it tonull
causes the CommandMap to revert to the CommandMap returned by theCommandMap.getDefaultCommandMap
method. Changing the CommandMap, or setting it tonull
, 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)
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getPreferredCommands
public CommandInfo[] getPreferredCommands()
Return the preferred commands for this type of data. This method calls thegetPreferredCommands
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)
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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 thegetAllCommands
method of the CommandMap associated with this DataHandler.- Returns:
- the CommandInfo objects representing all the commands
- See Also:
CommandMap.getAllCommands(java.lang.String)
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getCommand
public CommandInfo getCommand(java.lang.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 thegetCommand
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)
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getContent
public java.lang.Object getContent() throws java.io.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:
java.io.IOException
- if an IOException occurs during this operation.
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getBean
public java.lang.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 theClassLoader
used to load thejakarta.activation.DataHandler
class itself.- Parameters:
cmdinfo
- the CommandInfo corresponding to a command- Returns:
- the instantiated command object
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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:
java.lang.Error
- if the factory has already been defined.- See Also:
DataContentHandlerFactory
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