Class LazyConnectionDataSourceProxy
- All Implemented Interfaces:
Wrapper
,CommonDataSource
,DataSource
,InitializingBean
read-only DataSource
to use
during a read-only transaction, in addition to the regular target DataSource.
This DataSource proxy allows to avoid fetching JDBC Connections from
a pool unless actually necessary. JDBC transaction control can happen
without fetching a Connection from the pool or communicating with the
database; this will be done lazily on first creation of a JDBC Statement.
As a bonus, this allows for taking the transaction-synchronized read-only
flag and/or isolation level into account in a routing DataSource (for example,
IsolationLevelDataSourceRouter
).
If you configure both a LazyConnectionDataSourceProxy and a
TransactionAwareDataSourceProxy, make sure that the latter is the outermost
DataSource. In such a scenario, data access code will talk to the
transaction-aware DataSource, which will in turn work with the
LazyConnectionDataSourceProxy. As of 6.1.2, LazyConnectionDataSourceProxy will
initialize its default connection characteristics on first Connection access;
to enforce this on startup, call checkDefaultConnectionProperties()
.
Lazy fetching of physical JDBC Connections is particularly beneficial in a generic transaction demarcation environment. It allows you to demarcate transactions on all methods that could potentially perform data access, without paying a performance penalty if no actual data access happens.
This DataSource proxy gives you behavior analogous to JTA and a transactional JNDI DataSource (as provided by the Jakarta EE server), even with a local transaction strategy like DataSourceTransactionManager or HibernateTransactionManager. It does not add value with Spring's JtaTransactionManager as transaction strategy.
Lazy fetching of JDBC Connections is also recommended for read-only operations with Hibernate, in particular if the chances of resolving the result in the second-level cache are high. This avoids the need to communicate with the database at all for such read-only operations. You will get the same effect with non-transactional reads, but lazy fetching of JDBC Connections allows you to still perform reads in transactions.
NOTE: This DataSource proxy needs to return wrapped Connections
(which implement the ConnectionProxy
interface) in order to handle
lazy fetching of an actual JDBC Connection. Use Wrapper.unwrap(java.lang.Class<T>)
to retrieve the native JDBC Connection.
- Since:
- 1.1.4
- Author:
- Juergen Hoeller, Sam Brannen
- See Also:
-
Constructor Summary
ConstructorDescriptionCreate a new LazyConnectionDataSourceProxy.LazyConnectionDataSourceProxy
(DataSource targetDataSource) Create a new LazyConnectionDataSourceProxy. -
Method Summary
Modifier and TypeMethodDescriptionvoid
Determine default auto-commit and transaction isolation via a Connection from the target DataSource, if possible.protected void
Check the default connection properties (auto-commit, transaction isolation), keeping them to be able to expose them correctly without fetching an actual JDBC Connection from the target DataSource later on.protected Boolean
Expose the default auto-commit value.protected Integer
Expose the default transaction isolation value.Return a Connection handle that lazily fetches an actual JDBC Connection when asked for a Statement (or PreparedStatement or CallableStatement).getConnection
(String username, String password) Return a Connection handle that lazily fetches an actual JDBC Connection when asked for a Statement (or PreparedStatement or CallableStatement).void
setDefaultAutoCommit
(boolean defaultAutoCommit) Set the default auto-commit mode to expose when no target Connection has been fetched yet (when the actual JDBC Connection default is not known yet).void
setDefaultTransactionIsolation
(int defaultTransactionIsolation) Set the default transaction isolation level to expose when no target Connection has been fetched yet (when the actual JDBC Connection default is not known yet).void
setDefaultTransactionIsolationName
(String constantName) Set the default transaction isolation level by the name of the corresponding constant inConnection
— for example,"TRANSACTION_SERIALIZABLE"
.void
setReadOnlyDataSource
(DataSource readOnlyDataSource) Specify a variant of the target DataSource to use for read-only transactions.Methods inherited from class org.springframework.jdbc.datasource.DelegatingDataSource
afterPropertiesSet, createConnectionBuilder, createShardingKeyBuilder, getLoginTimeout, getLogWriter, getParentLogger, getTargetDataSource, isWrapperFor, obtainTargetDataSource, setLoginTimeout, setLogWriter, setTargetDataSource, unwrap
-
Constructor Details
-
LazyConnectionDataSourceProxy
public LazyConnectionDataSourceProxy()Create a new LazyConnectionDataSourceProxy. -
LazyConnectionDataSourceProxy
Create a new LazyConnectionDataSourceProxy.- Parameters:
targetDataSource
- the target DataSource- See Also:
-
-
Method Details
-
setReadOnlyDataSource
Specify a variant of the target DataSource to use for read-only transactions.If available, a Connection from such a read-only DataSource will be lazily obtained within a Spring-managed transaction that has been marked as read-only. The
Connection.setReadOnly(boolean)
flag will be left untouched, expecting it to be pre-configured as a default on the read-only DataSource, avoiding the overhead of switching it at the beginning and end of every transaction. Also, the default auto-commit and isolation level settings are expected to match the default connection properties of the primary target DataSource. -
setDefaultAutoCommit
public void setDefaultAutoCommit(boolean defaultAutoCommit) Set the default auto-commit mode to expose when no target Connection has been fetched yet (when the actual JDBC Connection default is not known yet).If not specified, the default gets determined by checking lazily on first access of a Connection.
- See Also:
-
setDefaultTransactionIsolationName
Set the default transaction isolation level by the name of the corresponding constant inConnection
— for example,"TRANSACTION_SERIALIZABLE"
.- Parameters:
constantName
- name of the constant- See Also:
-
setDefaultTransactionIsolation
public void setDefaultTransactionIsolation(int defaultTransactionIsolation) Set the default transaction isolation level to expose when no target Connection has been fetched yet (when the actual JDBC Connection default is not known yet).This property accepts the int constant value (for example, 8) as defined in the
Connection
interface; it is mainly intended for programmatic use. Consider using the "defaultTransactionIsolationName" property for setting the value by name (for example,"TRANSACTION_SERIALIZABLE"
).If not specified, the default gets determined by checking lazily on first access of a Connection.
-
checkDefaultConnectionProperties
public void checkDefaultConnectionProperties()Determine default auto-commit and transaction isolation via a Connection from the target DataSource, if possible.- Since:
- 6.1.2
- See Also:
-
checkDefaultConnectionProperties
Check the default connection properties (auto-commit, transaction isolation), keeping them to be able to expose them correctly without fetching an actual JDBC Connection from the target DataSource later on.- Parameters:
con
- the Connection to use for checking- Throws:
SQLException
- if thrown by Connection methods
-
defaultAutoCommit
Expose the default auto-commit value. -
defaultTransactionIsolation
Expose the default transaction isolation value. -
getConnection
Return a Connection handle that lazily fetches an actual JDBC Connection when asked for a Statement (or PreparedStatement or CallableStatement).The returned Connection handle implements the ConnectionProxy interface, allowing to retrieve the underlying target Connection.
- Specified by:
getConnection
in interfaceDataSource
- Overrides:
getConnection
in classDelegatingDataSource
- Returns:
- a lazy Connection handle
- Throws:
SQLException
- See Also:
-
getConnection
Return a Connection handle that lazily fetches an actual JDBC Connection when asked for a Statement (or PreparedStatement or CallableStatement).The returned Connection handle implements the ConnectionProxy interface, allowing to retrieve the underlying target Connection.
- Specified by:
getConnection
in interfaceDataSource
- Overrides:
getConnection
in classDelegatingDataSource
- Parameters:
username
- the per-Connection usernamepassword
- the per-Connection password- Returns:
- a lazy Connection handle
- Throws:
SQLException
- See Also:
-