I have a doubt of how the spring boot JDBC template works. I have read the documentation , but could not understand clearly :( When does the template opens connection , when does it gets closed . How does the transactions are handled . Does it gets opened and closed for every query execution ?
When does the template opens connection, when does it gets closed
For building JdbcTemplate you should specify the JDBC DataSource to obtain connections from:
public JdbcTemplate(DataSource dataSource)
Or:
public JdbcTemplate()
JdbcAccessor.setDataSource(javax.sql.DataSource)
Conclusively, JdbcTemplate works with this DataSource.
DataSource, depending on the implementation, may return new standard Connection objects that are not pooled or Connection objects that participate in connection pooling which can be an be recycled.
JdbcTemplate has pooled connections and releases them back to DataSource.
How does the transactions are handled
JdbcTemplate relies on database transactions.
If you want to operate transactions on service layer/business logic you need transaction management.
The simplest way is to annotate services with #Transactional or use org.springframework.transaction.support.TransactionTemplate.
Related
I want to create a one-shot database connection, based on spring classes.
To prevent spring loading the datasource on startup, I create it explicit when needed (only occasionally). I don't need any connection pooling, transactions and stuff like that.
DriverManagerDataSource ds = new DriverManagerDataSource(props.getUrl(), props.getUsername(), props.getPassword());
JdbcTemplate jdbc = new JdbcTemplate(ds);
jdbc.execute(...);
Question: how can I afterwards close/destroy the datasource and any open connections explicit?
I'm confused about the difference between DataSource and SessionFactory.
I think SessionFactory is a manager for retrieve Sessions (which are in fact connections to a database I guess).
DataSource has the method getConnection()
"Attempts to establish a connection with the data source that this DataSource object represents."
It means a DataSource object always works directly with the database?
If I have a pool of connections, DataSource will ask to the pool for a connection? Or will it try to get another connection to the database.
Are in fact DataSource and SessionFactory the same? Both try to give sessions/connections?
Datasource maintains the pool of connections, establishes the connection, knows how to connect etc.,
User configures data source either in the server(like websphere/weblogic) or in the spring/hibernate configuration file. Either way you give the handle of this data source to the sessionfactory during the app startup.
SessionFActory is an interface which hides all the details like opening the connection / closing the connections. Through out your development time you dont worry about these small things like loading driver/closing connection/opening etc., so you can concentrate on business logic/other important stuff.
How properly "lifecycle" of a Hibernate session under Spring should be done?
The SessionFactory is created automatically by Spring and is taking its DB connections from Glassfish connection pool. At the moment I am getting a Hibernate session via SessionFactory.getCurrentSession(). Then I start transaction, do the work and then commit() or rollback() at the end. Do I need to do any other actions like disconnect(), close(), flush() or any others at any time so connections would be properly returned back to the pool or is everything already automatically done by Spring?
With plenty of these methods it is a little confusing for me at the moment to understand when what should be done, maybe someone can point to right direction?
As SessionFactory is created automatically by Spring, Spring framework will take care of closing the connection.
Check out Spring Resource Management
If you want to check. You can check the log, if you are using logging for your app. It'll be like :
(main) INFO [AnnotationSessionFactoryBean] Closing Hibernate SessionFactory
I get following lines from this link
The main contract here is the creation of Session instances. Usually
an application has a single SessionFactory instance and threads
servicing client requests obtain Session instances from this factory.
The internal state of a SessionFactory is immutable. Once it is
created this internal state is set. This internal state includes all
of the metadata about Object/Relational Mapping.
Implementors must be threadsafe.
The policies about how the connection releases back to the connection pool have nothing to do with Spring .It is configured by Hibernate itself through the configuration parameter hibernate.connection.release_mode , which is identified by the enum in the org.hibernate.ConnectionReleaseMode
Start from version 3.1+ , the default value of the hibernate.connection.release_mode is auto which the corresponding ConnectionReleaseMode value depends on whether JTA or JDBC transaction is used. In case of JDBC transaction is used , it is set to ConnectionReleaseMode.AFTER_TRANSACTION (i.e after_transaction ).
The behaviour of ConnectionReleaseMode.AFTER_TRANSACTION is that : The connection will be returned to the connection pool after each transaction , that is by calling either transaction.commit() or transaction.rollback() , as well as calling session.close() and session.disconnect()
You can verify this behaviour in hibernate documentation Section 11.5.
Hope this link will guide you about session and transactions.
Then I start transaction, do the work and then commit() or rollback()
at the end. Do I need to do any other actions like disconnect(),
close(), flush() or any others at any time so connections would be
properly returned back to the pool or is everything already
automatically done by Spring?
As you call commit() on Transaction it will automatically closes the session, which ultimately calls close method on connection to return to it's pool.
When you are executing a hibernate query through SessionFactory.getCurrentSession() , Spring performs the necessary task of opening and closing the connection . The SessionFactory you are using in the spring config also calls the config.buildSessionFactory method internally .
Most of this happens in the implementations of the AbstractSessionFactoryBean. The closing of connecting is done by hibernate in the SessionFactoryImpl class using the statement settings.getConnectionProvider().close(); . In short , hibernate does everything for you . Spring just calls it's help when necessary.
How can I get the current Connection object for an Oracle database? I'm using the JDBC module in Spring 3.0.5.
Obtain the Connection from the DataSource bean.
You can access the dataSource by using Spring dependency injection to inject it into your bean, or by accessing ApplicationContext statically:
DataSource ds = (DataSource)ApplicationContextProvider.getApplicationContext().getBean("dataSource");
Connection c = ds.getConnection();
Just an Info :
I am using Spring JDBC Template, which holds the current connection object for me, which can be received as follows.
Connection con;
con = getJdbcTemplate().getDataSource().getConnection();
Use DataSourceUtils.getConnection().
It returns connection associated with the current transaction, if any.
I'm not sure if this method was available when this question was originally posted, however, it seems the preferred way to do it in the latest version of Spring is with JdbcTemplate and PreparedStatementCreator. See https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/jdbc/core/JdbcTemplate.html#query-org.springframework.jdbc.core.PreparedStatementCreator-org.springframework.jdbc.core.PreparedStatementSetter-org.springframework.jdbc.core.ResultSetExtractor- or any of the other query methods that take a PreparedStatementCreator as the first param:
jdbcTemplate.query(con -> {
// add required logic here
return con.prepareStatement("sql");
}, rs -> {
//process row
});
This has the advantage over the other provided answers (DataSourceUtils.getConnection() or jdbcTemplate.getDataSource().getConnection() as a new connection is not allocated, it uses the same connection management it would as calling any of the other jdbcTemplate querying methods. You also therefore do not need to worry about closing / releasing the connection, since spring will handle it.
if i create a new instance of JdbcTemplate like so;
JdbcTemplate jdbcTemplate = new JdbcTemplate(getDataSource());
by passing the datasource as a param (the datasource retrieves a connection from server connection pool) am i required to close the connection when im finished with it?
In other words, if i have a pool of connections will the previous code cause my application to create a new connection each time a request executes the code
No. That's the whole deal. Use the JdbcTemplate and it will manage the ressources (Connection, PreparedStatement, ResultSet). It is an implementation of the template method design pattern.
Javadoc:
It simplifies the use of JDBC and helps to avoid common errors. It
executes core JDBC workflow, leaving
application code to provide SQL and
extract results.
What I did, was to extend the JdbcTemplate and override the execute method to use the connection pool (a particular case).