Class LOBStateTracker
A LOB's state is either unpublished or published. When a LOB is published, it
means that the end-user has been given a reference to the LOB object. This
implies that the LOB cannot be automatically freed/released when the
result set position changes (i.e. typically rs.next()
), because the
LOB object must be kept valid/alive until the transaction is ended or the
LOB object is explicitly freed.
This class covers two types of functionality regarding LOBs;
- Keep track of whether a LOB column has been published or not.
- Release LOB locators on the server.
checkCurrentRow(org.apache.derby.client.am.Cursor)
is
called.
The tracker has a notion of current row. The current row is changed by
calling checkCurrentRow
. The owner of the tracker
is repsonsible for invoking the method at the correct time, and only when
the cursor is positioned on a valid data row. The method must be invoked
before the cursor changes the position. Note that calling the method
discardState
makes checkCurrentRow
ignore all
LOBs on the subsequent call.
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate final int[]
1-based column indexes for the LOBs to track.private final boolean
Tells whether locators shall be released.private final boolean[]
Tells whether the LOB is Blob or a Clob.private final int[]
The last locator values seen when releasing.static final LOBStateTracker
Instance to use when there are no LOBs in the result set, or when the server doesn't support locators.private final boolean[]
Tells whether the LOB colum has been published for the current row. -
Constructor Summary
ConstructorsConstructorDescriptionLOBStateTracker
(int[] lobIndexes, boolean[] isBlob, boolean doRelease) Creates a LOB state tracker for the specified configuration. -
Method Summary
Modifier and TypeMethodDescription(package private) void
checkCurrentRow
(Cursor cursor) Checks the current row, updating state and releasing locators on the server as required.(package private) void
Discards all recorded dynamic state about LOBs.(package private) void
markAsPublished
(int index) Marks the specified column of the current row as published, which implies that the tracker should not release the associated locator.
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Field Details
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NO_OP_TRACKER
Instance to use when there are no LOBs in the result set, or when the server doesn't support locators. -
columns
private final int[] columns1-based column indexes for the LOBs to track. -
isBlob
private final boolean[] isBlobTells whether the LOB is Blob or a Clob. -
published
private final boolean[] publishedTells whether the LOB colum has been published for the current row. -
doRelease
private final boolean doReleaseTells whether locators shall be released. This will befalse
if locators are not supported by the server. -
lastLocatorSeen
private final int[] lastLocatorSeenThe last locator values seen when releasing. These values are used to detect if checkCurrentRow(org.apache.derby.client.am.Cursor) is being executed more than once on the same row.
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Constructor Details
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LOBStateTracker
LOBStateTracker(int[] lobIndexes, boolean[] isBlob, boolean doRelease) Creates a LOB state tracker for the specified configuration.- Parameters:
lobIndexes
- the 1-based indexes of the LOB columnsisBlob
- whether the LOB is a Blob or a ClobdoRelease
- whether locators shall be released- See Also:
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Method Details
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checkCurrentRow
Checks the current row, updating state and releasing locators on the server as required.This method should only be called once per valid row in the result set.
- Parameters:
cursor
- the cursor object to use for releasing the locators- Throws:
SqlException
- if releasing the locators on the server fails
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discardState
void discardState()Discards all recorded dynamic state about LOBs.Typically called after connection commit or rollback, as those operations will release all locators on the server automatically. There is no need to release them from the client side in this case.
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markAsPublished
void markAsPublished(int index) Marks the specified column of the current row as published, which implies that the tracker should not release the associated locator.Columns must be marked as published when a LOB object is created on the client, to avoid releasing the corresponding locator too early.
- Parameters:
index
- 1-based column index
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