public enum LockModeType extends Enum<LockModeType>
LockModeType
argument to one of the
EntityManager
methods that take locks (lock
, find
, or
refresh
) or to the Query.setLockMode()
or
TypedQuery.setLockMode()
method.
Lock modes can be used to specify either optimistic or pessimistic locks.
Optimistic locks are specified using LockModeType.OPTIMISTIC
and
LockModeType.OPTIMISTIC_FORCE_INCREMENT
. The lock mode type
values LockModeType.READ
and LockModeType.WRITE
are
synonyms of OPTIMISTIC
and OPTIMISTIC_FORCE_INCREMENT
respectively. The latter
are to be preferred for new applications.
The semantics of requesting locks of type LockModeType.OPTIMISTIC
and
LockModeType.OPTIMISTIC_FORCE_INCREMENT
are the following.
If transaction T1 calls for a lock of type LockModeType.OPTIMISTIC
on a versioned object, the
entity manager must ensure that neither of the following phenomena can occur:
Lock modes must always prevent the phenomena P1 and P2.
In addition, calling a lock of type LockModeType.OPTIMISTIC_FORCE_INCREMENT
on a versioned
object, will also force an update (increment) to the entity's version column.
The persistence implementation is not required to support the use of optimistic lock modes on non-versioned
objects. When it cannot support a such lock call, it must throw the PersistenceException
.
The lock modes LockModeType.PESSIMISTIC_READ
,
LockModeType.PESSIMISTIC_WRITE
, and
LockModeType.PESSIMISTIC_FORCE_INCREMENT
are used to
immediately obtain long-term database locks.
The semantics of requesting locks of type LockModeType.PESSIMISTIC_READ
,
LockModeType.PESSIMISTIC_WRITE
, and LockModeType.PESSIMISTIC_FORCE_INCREMENT
are
the following.
If transaction T1 calls for a lock of type LockModeType.PESSIMISTIC_READ
or
LockModeType.PESSIMISTIC_WRITE
on an object, the entity manager must ensure that neither of
the following phenomena can occur:
A lock with LockModeType.PESSIMISTIC_WRITE
can be obtained on an entity instance to force
serialization among transactions attempting to update the entity data. A lock with
LockModeType.PESSIMISTIC_READ
can be used to query data using repeatable-read semantics
without the need to reread the data at the end of the transaction to obtain a lock, and without blocking
other transactions reading the data. A lock with LockModeType.PESSIMISTIC_WRITE
can be used
when querying data and there is a high likelihood of deadlock or update failure among concurrent updating
transactions.
The persistence implementation must support use of locks of type LockModeType.PESSIMISTIC_READ
LockModeType.PESSIMISTIC_WRITE
on a non-versioned entity as well as on a versioned entity.
When the lock cannot be obtained, and the database locking failure results in transaction-level rollback,
the provider must throw the PessimisticLockException
and ensure that the JTA transaction or
EntityTransaction
has been marked for rollback.
When the lock cannot be obtained, and the database locking failure results in only statement-level
rollback, the provider must throw the LockTimeoutException
(and must not mark the transaction for
rollback).
Enum Constant and Description |
---|
NONE
No lock.
|
OPTIMISTIC
Optimistic lock.
|
OPTIMISTIC_FORCE_INCREMENT
Optimistic lock, with version update.
|
PESSIMISTIC_FORCE_INCREMENT
Pessimistic write lock, with version update.
|
PESSIMISTIC_READ
Pessimistic read lock.
|
PESSIMISTIC_WRITE
Pessimistic write lock.
|
READ
Synonymous with
OPTIMISTIC . |
WRITE
Synonymous with
OPTIMISTIC_FORCE_INCREMENT . |
Modifier and Type | Method and Description |
---|---|
static LockModeType |
valueOf(String name)
Returns the enum constant of this type with the specified name.
|
static LockModeType[] |
values()
Returns an array containing the constants of this enum type, in
the order they are declared.
|
public static final LockModeType READ
OPTIMISTIC
. OPTIMISTIC
is to be preferred for new
applications.public static final LockModeType WRITE
OPTIMISTIC_FORCE_INCREMENT
. OPTIMISTIC_FORCE_IMCREMENT
is to
be preferred for new applications.public static final LockModeType OPTIMISTIC
public static final LockModeType OPTIMISTIC_FORCE_INCREMENT
public static final LockModeType PESSIMISTIC_READ
public static final LockModeType PESSIMISTIC_WRITE
public static final LockModeType PESSIMISTIC_FORCE_INCREMENT
public static final LockModeType NONE
public static LockModeType[] values()
for (LockModeType c : LockModeType.values()) System.out.println(c);
public static LockModeType valueOf(String name)
name
- the name of the enum constant to be returned.IllegalArgumentException
- if this enum type has no constant with the specified nameNullPointerException
- if the argument is nullCopyright © 2016. All rights reserved.