public class BackupDataInput extends Object
BackupAgent
reads
information from the backup data set, via its
onRestore()
method. The data is presented as a set of "entities," each
representing one named record as previously stored by the agent's
onBackup()
implementation. An entity is composed of a descriptive header plus a
byte array that holds the raw data saved in the remote backup.
The agent must consume every entity in the data stream, otherwise the restored state of the application will be incomplete.
A typical
onRestore()
implementation might be structured something like this:
public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState) { while (data.readNextHeader()) { String key = data.getKey(); int dataSize = data.getDataSize(); if (key.equals(MY_BACKUP_KEY_ONE)) { // process this kind of record here byte[] buffer = new byte[dataSize]; data.readEntityData(buffer, 0, dataSize); // reads the entire entity at once // now 'buffer' holds the raw data and can be processed however // the agent wishes processBackupKeyOne(buffer); } else if (key.equals(MY_BACKUP_KEY_TO_IGNORE) { // a key we recognize but wish to discard data.skipEntityData(); } // ... etc. } }
Constructor and Description |
---|
BackupDataInput(FileDescriptor fd) |
Modifier and Type | Method and Description |
---|---|
protected void |
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
int |
getDataSize()
Report the size in bytes of the data associated with the current entity in the
restore stream.
|
String |
getKey()
Report the key associated with the current entity in the restore stream
|
int |
readEntityData(byte[] data,
int offset,
int size)
Read a record's raw data from the restore stream.
|
boolean |
readNextHeader()
Extract the next entity header from the restore stream.
|
void |
skipEntityData()
Consume the current entity's data without extracting it into a buffer
for further processing.
|
public BackupDataInput(FileDescriptor fd)
protected void finalize() throws Throwable
Object
finalize
method to dispose of
system resources or to perform other cleanup.
The general contract of finalize
is that it is invoked
if and when the JavaTM virtual
machine has determined that there is no longer any
means by which this object can be accessed by any thread that has
not yet died, except as a result of an action taken by the
finalization of some other object or class which is ready to be
finalized. The finalize
method may take any action, including
making this object available again to other threads; the usual purpose
of finalize
, however, is to perform cleanup actions before
the object is irrevocably discarded. For example, the finalize method
for an object that represents an input/output connection might perform
explicit I/O transactions to break the connection before the object is
permanently discarded.
The finalize
method of class Object
performs no
special action; it simply returns normally. Subclasses of
Object
may override this definition.
The Java programming language does not guarantee which thread will
invoke the finalize
method for any given object. It is
guaranteed, however, that the thread that invokes finalize will not
be holding any user-visible synchronization locks when finalize is
invoked. If an uncaught exception is thrown by the finalize method,
the exception is ignored and finalization of that object terminates.
After the finalize
method has been invoked for an object, no
further action is taken until the Java virtual machine has again
determined that there is no longer any means by which this object can
be accessed by any thread that has not yet died, including possible
actions by other objects or classes which are ready to be finalized,
at which point the object may be discarded.
The finalize
method is never invoked more than once by a Java
virtual machine for any given object.
Any exception thrown by the finalize
method causes
the finalization of this object to be halted, but is otherwise
ignored.
public boolean readNextHeader() throws IOException
getKey()
and getDataSize()
methods can
be used to inspect the entity that is now available for processing.true
when there is an entity ready for consumption from the
restore stream, false
if the restore stream has been fully consumed.IOException
- if an error occurred while reading the restore streampublic String getKey()
IllegalStateException
- if the next record header has not yet been readpublic int getDataSize()
IllegalStateException
- if the next record header has not yet been readpublic int readEntityData(byte[] data, int offset, int size) throws IOException
readNextHeader()
method. Multiple calls to
this method may be made in order to process the data in chunks; not all of it
must be read in a single call. Once all of the raw data for the current entity
has been read, further calls to this method will simply return zero.data
- An allocated byte array of at least 'size' bytesoffset
- Offset within the 'data' array at which the data will be placed
when read from the streamsize
- The number of bytes to read in this passIOException
- if an error occurred when trying to read the restore data streampublic void skipEntityData() throws IOException
BackupAgent
to
efficiently discard obsolete or otherwise uninteresting records during the
restore operation.IOException
- if an error occurred when trying to read the restore data stream