javax.persistence

Enum LockModeType

java.lang.Object

java.lang.Enum<LockModeType>

javax.persistence.LockModeType

All Implemented Interfaces:

Serializable, Comparable<LockModeType>

public enum LockModeType
extends Enum<LockModeType>

Lock modes can be specified by means of passing a 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:

• P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains the modified value, before T1 has committed or rolled back. Transaction T2 eventually commits successfully; it does not matter whether T1 commits or rolls back and whether it does so before or after T2 commits.
P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes that row, before T1 has committed. Both transactions eventually commit successfully.

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:

• P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains the modified value, before T1 has committed or rolled back.
• P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes that row, before T1 has committed or rolled back.

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).

Since:

Java Persistence 1.0

Enum Constant Summary

Enum Constants

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.

Method Summary

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.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

READ

public static final LockModeType READ

Synonymous with OPTIMISTIC. OPTIMISTIC is to be preferred for new applications.

WRITE

public static final LockModeType WRITE

Synonymous with OPTIMISTIC_FORCE_INCREMENT. OPTIMISTIC_FORCE_IMCREMENT is to be preferred for new applications.

OPTIMISTIC

public static final LockModeType OPTIMISTIC

Optimistic lock.

Since:

Java Persistence 2.0

OPTIMISTIC_FORCE_INCREMENT

public static final LockModeType OPTIMISTIC_FORCE_INCREMENT

Optimistic lock, with version update.

Since:

Java Persistence 2.0

PESSIMISTIC_READ

public static final LockModeType PESSIMISTIC_READ

Pessimistic read lock.

Since:

Java Persistence 2.0

PESSIMISTIC_WRITE

public static final LockModeType PESSIMISTIC_WRITE

Pessimistic write lock.

Since:

Java Persistence 2.0

PESSIMISTIC_FORCE_INCREMENT

public static final LockModeType PESSIMISTIC_FORCE_INCREMENT

Pessimistic write lock, with version update.

Since:

Java Persistence 2.0

NONE

public static final LockModeType NONE

No lock.

Since:

Java Persistence 2.0

Method Detail

values

public static LockModeType[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (LockModeType c : LockModeType.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static LockModeType valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null