org.springframework.jdbc.datasource

Class LazyConnectionDataSourceProxy

  • All Implemented Interfaces:
    java.sql.Wrapper, javax.sql.CommonDataSource, javax.sql.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 and read-only mode 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.

    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.

    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.

    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 Java 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
    See Also:
    DataSourceTransactionManager
    • Constructor Detail

      • LazyConnectionDataSourceProxy

        public LazyConnectionDataSourceProxy(javax.sql.DataSource targetDataSource)
        Create a new LazyConnectionDataSourceProxy.
        Parameters:
        targetDataSource - the target DataSource
    • Method Detail

      • setDefaultAutoCommit

        public void setDefaultAutoCommit(boolean defaultAutoCommit)
        Set the default auto-commit mode to expose when no target Connection has been fetched yet (-> actual JDBC Connection default not known yet).

        If not specified, the default gets determined by checking a target Connection on startup. If that check fails, the default will be determined lazily on first access of a Connection.

        See Also:
        Connection.setAutoCommit(boolean)
      • setDefaultTransactionIsolation

        public void setDefaultTransactionIsolation(int defaultTransactionIsolation)
        Set the default transaction isolation level to expose when no target Connection has been fetched yet (-> actual JDBC Connection default not known yet).

        This property accepts the int constant value (e.g. 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 (e.g. "TRANSACTION_SERIALIZABLE").

        If not specified, the default gets determined by checking a target Connection on startup. If that check fails, the default will be determined lazily on first access of a Connection.

        See Also:
        setDefaultTransactionIsolationName(java.lang.String), Connection.setTransactionIsolation(int)
      • setDefaultTransactionIsolationName

        public void setDefaultTransactionIsolationName(java.lang.String constantName)
        Set the default transaction isolation level by the name of the corresponding constant in Connection, e.g. "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
      • afterPropertiesSet

        public void afterPropertiesSet()
        Description copied from interface: InitializingBean
        Invoked by the containing BeanFactory after it has set all bean properties and satisfied BeanFactoryAware, ApplicationContextAware etc.

        This method allows the bean instance to perform validation of its overall configuration and final initialization when all bean properties have been set.

        Specified by:
        afterPropertiesSet in interface InitializingBean
        Overrides:
        afterPropertiesSet in class DelegatingDataSource
      • checkDefaultConnectionProperties

        protected void checkDefaultConnectionProperties(java.sql.Connection con)
                                                 throws java.sql.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.

        This will be invoked once on startup, but also for each retrieval of a target Connection. If the check failed on startup (because the database was down), we'll lazily retrieve those settings.

        Parameters:
        con - the Connection to use for checking
        Throws:
        java.sql.SQLException - if thrown by Connection methods
      • defaultAutoCommit

        @Nullable
        protected java.lang.Boolean defaultAutoCommit()
        Expose the default auto-commit value.
      • defaultTransactionIsolation

        @Nullable
        protected java.lang.Integer defaultTransactionIsolation()
        Expose the default transaction isolation value.
      • getConnection

        public java.sql.Connection getConnection()
                                          throws java.sql.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 javax.sql.DataSource
        Overrides:
        getConnection in class DelegatingDataSource
        Returns:
        a lazy Connection handle
        Throws:
        java.sql.SQLException
        See Also:
        ConnectionProxy.getTargetConnection()
      • getConnection

        public java.sql.Connection getConnection(java.lang.String username,
                                                 java.lang.String password)
                                          throws java.sql.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 javax.sql.DataSource
        Overrides:
        getConnection in class DelegatingDataSource
        Parameters:
        username - the per-Connection username
        password - the per-Connection password
        Returns:
        a lazy Connection handle
        Throws:
        java.sql.SQLException
        See Also:
        ConnectionProxy.getTargetConnection()