Class LazyConnectionDataSourceProxy

java.lang.Object

org.springframework.jdbc.datasource.DelegatingDataSource

org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy

All Implemented Interfaces:

Wrapper, CommonDataSource, DataSource, InitializingBean

public class LazyConnectionDataSourceProxy
extends DelegatingDataSource

Proxy for a target DataSource, fetching actual JDBC Connections lazily, i.e. not until first creation of a Statement. Connection initialization properties like auto-commit mode, transaction isolation, read-only mode, catalog, schema, holdability, client info, and network timeout will be kept and applied to the actual JDBC Connection as soon as an actual Connection is fetched (if ever). Consequently, commit and rollback calls will be ignored if no Statements have been created.

Once a property has been set, the corresponding getter method returns the set value until the actual Connection is fetched. If the property has not been set, invoking the getter triggers a fetch of the actual connection in order to obtain the default value.

Although client info is listed among the deferred properties above, the following methods are exceptions to the lazy acquisition behavior and force immediate acquisition of the underlying Connection. The Connection.getClientInfo() and Connection.getClientInfo(java.lang.String) methods are read operations whose values cannot be reliably cached due to driver defaults, remnants from pooled connections, or external session modifications.

The Connection.setClientInfo(java.util.Properties) method also forces immediate acquisition. JDBC driver implementations are inconsistent: some treat it as an overwrite, while others treat it as an append/merge. To guarantee behavior identical to that of a non-lazy DataSource across all drivers, the proxy does not cache or replay it, thereby avoiding any risk of semantic mismatch.

As of 6.1.2, there is also special support for a 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.

As of 6.2.6, this DataSource proxy also suppresses a rollback attempt in case of a timeout where the connection has been closed in the meantime.

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(Class) to retrieve the native JDBC Connection.

Since:

1.1.4

Author:

Juergen Hoeller, Sam Brannen, Chengang Guan

See Also:

• DataSourceTransactionManager
• DelegatingDataSource.setTargetDataSource(DataSource)
• setReadOnlyDataSource(DataSource)

Constructor Summary

Constructors

Constructor	Description
LazyConnectionDataSourceProxy()	Create a new LazyConnectionDataSourceProxy.
LazyConnectionDataSourceProxy(DataSource targetDataSource)	Create a new LazyConnectionDataSourceProxy.

Method Summary

Modifier and Type	Method	Description
void	checkDefaultConnectionProperties()	Determine default auto-commit and transaction isolation via a Connection from the target DataSource, if possible.
protected void	checkDefaultConnectionProperties(Connection con)	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 @Nullable Boolean	defaultAutoCommit()	Expose the default auto-commit value.
protected @Nullable Integer	defaultTransactionIsolation()	Expose the default transaction isolation value.
Connection	getConnection()	Return a Connection handle that lazily fetches an actual JDBC Connection when asked for a Statement (or PreparedStatement or CallableStatement).
Connection	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 in Connection — for example, "TRANSACTION_SERIALIZABLE".
void	setReadOnlyDataSource(@Nullable DataSource readOnlyDataSource)	Specify a variant of the target DataSource to use for read-only transactions.

Methods inherited from class DelegatingDataSource

afterPropertiesSet, createConnectionBuilder, createShardingKeyBuilder, getLoginTimeout, getLogWriter, getParentLogger, getTargetDataSource, isWrapperFor, obtainTargetDataSource, setLoginTimeout, setLogWriter, setTargetDataSource, unwrap

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LazyConnectionDataSourceProxy

public LazyConnectionDataSourceProxy()

Create a new LazyConnectionDataSourceProxy.

See Also:

• DelegatingDataSource.setTargetDataSource(DataSource)
• setReadOnlyDataSource(DataSource)

LazyConnectionDataSourceProxy

public LazyConnectionDataSourceProxy(DataSource targetDataSource)

Create a new LazyConnectionDataSourceProxy.

Parameters:

targetDataSource - the target DataSource

See Also:

• DelegatingDataSource.setTargetDataSource(DataSource)

Method Details

setReadOnlyDataSource

public void setReadOnlyDataSource(@Nullable DataSource readOnlyDataSource)

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.

Since:

6.1.2

See Also:

• DelegatingDataSource.setTargetDataSource(DataSource)
• setDefaultAutoCommit(boolean)
• setDefaultTransactionIsolation(int)
• TransactionDefinition.isReadOnly()

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:

• Connection.setAutoCommit(boolean)

setDefaultTransactionIsolationName

public void setDefaultTransactionIsolationName(String constantName)

Set the default transaction isolation level by the name of the corresponding constant in Connection — for example, "TRANSACTION_SERIALIZABLE".

Parameters:

constantName - name of the constant

See Also:

• setDefaultTransactionIsolation(int)
• Connection.TRANSACTION_READ_UNCOMMITTED
• Connection.TRANSACTION_READ_COMMITTED
• Connection.TRANSACTION_REPEATABLE_READ
• Connection.TRANSACTION_SERIALIZABLE

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.

See Also:

• setDefaultTransactionIsolationName(String)
• Connection.setTransactionIsolation(int)

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(Connection)

checkDefaultConnectionProperties

protected void checkDefaultConnectionProperties(Connection con)
                                         throws SQLException

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

protected @Nullable Boolean defaultAutoCommit()

Expose the default auto-commit value.

defaultTransactionIsolation

protected @Nullable Integer defaultTransactionIsolation()

Expose the default transaction isolation value.

getConnection

public Connection getConnection()
                         throws SQLException

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 interface DataSource

Overrides:

getConnection in class DelegatingDataSource

Returns:

a lazy Connection handle

Throws:

SQLException

See Also:

• ConnectionProxy.getTargetConnection()

getConnection

public Connection getConnection(String username,
 String password)
                         throws SQLException

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 interface DataSource

Overrides:

getConnection in class DelegatingDataSource

Parameters:

username - the per-Connection username

password - the per-Connection password

Returns:

a lazy Connection handle

Throws:

SQLException

See Also:

• ConnectionProxy.getTargetConnection()