This is typically the default setting of a transaction definition, and typically defines a transaction synchronization scope. 

NOTE: For transaction managers with transaction synchronization, PROPAGATION_SUPPORTS is slightly different from no transaction at all, as it defines a transaction scope that synchronization might apply to. As a consequence, the same resources (a JDBC Connection, a Hibernate Session, etc) will be shared for the entire specified scope. Note that the exact behavior depends on the actual synchronization configuration of the transaction manager!

In general, use PROPAGATION_SUPPORTS with care! In particular, do not rely on PROPAGATION_REQUIRED or PROPAGATION_REQUIRES_NEW within a PROPAGATION_SUPPORTS scope (which may lead to synchronization conflicts at runtime). If such nesting is unavoidable, make sure to configure your transaction manager appropriately (typically switching to "synchronization on actual transaction").

Also see:

org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
org.springframework.transaction.support.AbstractPlatformTransactionManager#SYNCHRONIZATION_ON_ACTUAL_TRANSACTION

Note that transaction synchronization within a PROPAGATION_MANDATORY scope will always be driven by the surrounding transaction. 

NOTE: Actual transaction suspension will not work out-of-the-box on all transaction managers. This in particular applies to org.springframework.transaction.jta.JtaTransactionManager , which requires the javax.transaction.TransactionManager to be made available it to it (which is server-specific in standard J2EE).

A PROPAGATION_REQUIRES_NEW scope always defines its own transaction synchronizations. Existing synchronizations will be suspended and resumed appropriately.

Also see:

org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager

NOTE: Actual transaction suspension will not work out-of-the-box on all transaction managers. This in particular applies to org.springframework.transaction.jta.JtaTransactionManager , which requires the javax.transaction.TransactionManager to be made available it to it (which is server-specific in standard J2EE).

Note that transaction synchronization is not available within a PROPAGATION_NOT_SUPPORTED scope. Existing synchronizations will be suspended and resumed appropriately.

Also see:

org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager

Note that transaction synchronization is not available within a PROPAGATION_NEVER scope. 

NOTE: Actual creation of a nested transaction will only work on specific transaction managers. Out of the box, this only applies to the JDBC org.springframework.jdbc.datasource.DataSourceTransactionManager when working on a JDBC 3.0 driver. Some JTA providers might support nested transactions as well.

Also see:

org.springframework.jdbc.datasource.DataSourceTransactionManager

Also see:

java.sql.Connection

This level allows a row changed by one transaction to be read by another transaction before any changes in that row have been committed (a "dirty read"). If any of the changes are rolled back, the second transaction will have retrieved an invalid row.

Also see:

java.sql.Connection#TRANSACTION_READ_UNCOMMITTED

This level only prohibits a transaction from reading a row with uncommitted changes in it.

Also see:

java.sql.Connection#TRANSACTION_READ_COMMITTED

This level prohibits a transaction from reading a row with uncommitted changes in it, and it also prohibits the situation where one transaction reads a row, a second transaction alters the row, and the first transaction rereads the row, getting different values the second time (a "non-repeatable read").

Also see:

java.sql.Connection#TRANSACTION_REPEATABLE_READ

This level includes the prohibitions in #ISOLATION_REPEATABLE_READ and further prohibits the situation where one transaction reads all rows that satisfy a WHERE condition, a second transaction inserts a row that satisfies that WHERE condition, and the first transaction rereads for the same condition, retrieving the additional "phantom" row in the second read.

Also see:

java.sql.Connection#TRANSACTION_SERIALIZABLE

 public int getIsolationLevel()
Return the isolation level.
Must return one of the ISOLATION_XXX constants
defined on this interface .
Only makes sense in combination with #PROPAGATION_REQUIRED 
or #PROPAGATION_REQUIRES_NEW .
Note that a transaction manager that does not support custom
isolation levels will throw an exception when given any other level
than #ISOLATION_DEFAULT .

 public String getName()
Return the name of this transaction. Can be null.
This will be used as the transaction name to be shown in a
transaction monitor, if applicable (for example, WebLogic's).
In case of Spring's declarative transactions, the exposed name
must (and will) be the
fully-qualified class name + "." + method name
(by default).

 public int getPropagationBehavior()
Return the propagation behavior.
Must return one of the PROPAGATION_XXX constants
defined on this interface .

 public int getTimeout()
Return the transaction timeout.
Must return a number of seconds, or #TIMEOUT_DEFAULT .
Only makes sense in combination with #PROPAGATION_REQUIRED 
or #PROPAGATION_REQUIRES_NEW .
Note that a transaction manager that does not support timeouts
will throw an exception when given any other timeout than
#TIMEOUT_DEFAULT .

 public boolean isReadOnly()
Return whether to optimize as a read-only transaction.
The read-only flag applies to any transaction context, whether
backed by an actual resource transaction
(#PROPAGATION_REQUIRED /#PROPAGATION_REQUIRES_NEW ) or
operating non-transactionally at the resource level
(#PROPAGATION_SUPPORTS ). In the latter case, the flag will
only apply to managed resources within the application, such as a
Hibernate Session.
This just serves as a hint for the actual transaction subsystem;
it will not necessarily cause failure of write access attempts.
A transaction manager that cannot interpret the read-only hint will
not throw an exception when asked for a read-only transaction.