Class LOBStateTracker
- java.lang.Object
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- org.apache.derby.client.am.LOBStateTracker
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class LOBStateTracker extends java.lang.Object
An object that tracks the state of large objects (LOBs) for the current row in a result set.A LOB's state is either unpublished or published.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 methoddiscardState
makescheckCurrentRow
ignore all LOBs on the subsequent call.
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Field Summary
Fields Modifier and Type Field Description private int[]
columns
1-based column indexes for the LOBs to track.private boolean
doRelease
Tells whether locators shall be released.private boolean[]
isBlob
Tells whether the LOB is Blob or a Clob.private int[]
lastLocatorSeen
The last locator values seen when releasing.static LOBStateTracker
NO_OP_TRACKER
Instance to use when there are no LOBs in the result set, or when the server doesn't support locators.private boolean[]
published
Tells whether the LOB colum has been published for the current row.
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Constructor Summary
Constructors Constructor Description LOBStateTracker(int[] lobIndexes, boolean[] isBlob, boolean doRelease)
Creates a LOB state tracker for the specified configuration.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description (package private) void
checkCurrentRow(Cursor cursor)
Checks the current row, updating state and releasing locators on the server as required.(package private) void
discardState()
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 Detail
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NO_OP_TRACKER
public static final LOBStateTracker NO_OP_TRACKER
Instance to use when there are no LOBs in the result set, or when the server doesn't support locators.
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columns
private final int[] columns
1-based column indexes for the LOBs to track.
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isBlob
private final boolean[] isBlob
Tells whether the LOB is Blob or a Clob.
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published
private final boolean[] published
Tells whether the LOB colum has been published for the current row.
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doRelease
private final boolean doRelease
Tells whether locators shall be released. This will befalse
if locators are not supported by the server.
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lastLocatorSeen
private final int[] lastLocatorSeen
The 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 Detail
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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:
NO_OP_TRACKER
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Method Detail
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checkCurrentRow
void checkCurrentRow(Cursor cursor) throws SqlException
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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