How many connection will hold for a single hibernate session where there is only one DB?
there is one connection per session.
the connection is opened only if the session needs to send JDBC queries
you should avoid using the underlying connection. The connection() method has been deprecated. If you need to perform raw jdbc operations, use the doWork(..) method (if your hibernate version is the latest)
At a given time given session will only hold one connection
which you can access with the connect() method.
The connection used can be changed though using the reconnect() method.
Related
I have a session object as shown below
Session session = HibernateUtil.currentSession();
Would it be possible to to create prepared statement with that for a query
in Java instead of the normal method using connection?
org.hibernate Interface Session does not allow to work directly with JDBC, that means use prepared statements and so on.
org.hibernate Interface Session allows to work with Criteria API, HQL and Native queries.
https://docs.jboss.org/hibernate/orm/3.5/javadocs/org/hibernate/Session.html
But the doWork method of the org.hibernate Interface Session gives access to the Connection object managed by this Session and there you can make usual JDBC stuff - prepared statements and so on.
Examples are here:
https://www.javatips.net/api/org.hibernate.jdbc.work
that's a question which has confuse me a lot.
for example:
when I design the Dao layer,sometimes,I must do some insert operation,and than
I should do some query such as select the data's id by auto-generate in db.
my question was that:
when I use spring to help manage datasource,
when I do more than two sql operation one by one,
how many times the java client connect to the db?? only one ? or more?
code,such as fellows:
getSimpleJdbcTemplate().update(some params...);
getSimpleJdbcTemplate().query(some params...);
It depends on your Transactional settings.
Spring-transactions in local mode, work on a thread-local connection for all the db activities within single transaction.
If you have not configured transactions, then basically each DB call will retrieve connection from datasource using Datasource.getConnection()
In terms client connecting to DB, if you are using datasource with connection pooling capability, then connections are returned from the pool.
But if datasource is not backed by pool, then it will instantiate connection to DB server on demand ( on getConnection() ) call
I'm working with spring jdbc, In my case I have to execute a query and refresh cache only when data base is up running for this I'm not finding any method appropriate to call on Connection object.
If you're using Spring JdbcTemplate you could perhaps use:
public <T> T execute(ConnectionCallback<T> action) throws DataAccessException
Execute a JDBC data access operation, implemented as callback action
working on a JDBC Connection. This allows for implementing arbitrary
data access operations, within Spring's managed JDBC environment: that
is, participating in Spring-managed transactions and converting JDBC
SQLExceptions into Spring's DataAccessException hierarchy.
The callback action can return a result object, for example a domain object or a collection of domain objects.
jdbcTemplate.
You could execute an action once the connection is established such a simple query perhaps.
Let me know if that helps.
I'm using org.apache.commons.dbcp.BasicDataSource as my datasource implementation, my code geting connection and closing the connection like this:
Connection conn = dataSource.getConnection();
when I finished the connection work I will close it
conn.close();
My question is: the conn.close() is really close, so when the connection be closed like conn.close(), how is datasource doing. I heard that the datasource connection close is not really close, just is release, but I can't find the release API from datasource class. I want to know how does datasource manage the creation, close and release of database connection.
By the way a little question: how does datasource refresh the connection, I mean if the connections of the datasource haven't been used for one year, how does datasource keep the connections available?
DataSource (javax.sql.DataSource) represents an abstract concept of something you can get database connections from.
So, DataSource itself doesn't define any details of how connections are managed, and different implementations of DataSource may manage connections in different ways:
A naive implementation (such as Spring's DriverManagerDataSource) may create a new connection each time you request it, and in this case close() actually closes connections.
An implementation backed by a connection pool (such as Apache DBCP or c3p0) returns existing connections from the pool. Connection object returned by such an implementation is a proxy, and its close() method is overriden to return connection to the pool instead of closing it.
If you want to know how exactly your connection pool manages connections, check documentation of your connection pool implementation.
The close() call on a connection from a datasource doesn't necessarily close the database connection. It would merely return the connection to the pool for reuse. The way this is done is, the actual connection to the database is decorated with a PooledConnection sort of class and the close() method on this PooledConnection is overridden to just mark the connection as available.
I am pretty new on the ORM's. I just start to read books and documents about Java Persistence API with Hibernate.
I just wondered, closing EntityManagerFactory is similar with jdbc database connection closing?
Should we close it after every persist/update/delete or not? If we don't close it, will the database connection stay opened?
I just wondered, closing EntityManagerFactory is similar with jdbc database connection closing?
This is not exactly true but closing an EntityManagerFactory would be closer to destroying a whole connection pool. If you want to think JDBC connection, you should think EntityManager.
Should we close it after every persist/update/delete or not?
Creating an EntityManagerFactory is a pretty expensive operation and should be done once for the lifetime of the application (you close it at the end of the application). So, no, you should not close it for each persist/update/delete operation.
The EntityManagerFactory is created once for all and you usually get an EntityManager per request, which is closed at the end of the request (EntityManager per request is the most common pattern for a multi-user client/server application).
If we don't close it, will the database connection stay opened?
As hinted, it's the EntityManager that is actually associated to a database connection and closing the EntityManager will actually release the JDBC connection (most often, return it to a pool).