The JDBC documentation from Oracle says that driver provider should implement DataSource interface, but in real project source file, I always see the DataSource come from 3rd, such as DBCP connection pool.
I wonder if MySQL driver in itself implements DataSource interface?
If you are talking about Connector/J, it provides:
com.mysql.jdbc.jdbc2.optional.MysqlDataSource (which implements DataSource),
com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource (which implements ConnectionPoolDataSource)
com.mysql.jdbc.jdbc2.optional.MysqlXADataSource (which implements XADataSource)
So, as far as your question goes. Yes Connector/J provides implementations to the DataSource interface and conforms with JDBC specs.
But, as you are aware by your question and #Piotr's answer, most applications will never deal with those implementations directly. At least in ten years as a Java Developer I have never done that. Let the Java EE App Server handle connections for you, or install a third party connection pool if you are down to standalone applications.
You can use native DataSource provided by JDBC driver, but what you usually do is you use a connection pool like DBCP, C3P0 or BoneCP.
Related
As far as I understand there are two types of DataSource connections, javax.sql.DataSource and javax.sql.XADataSource, this tutorial explains that javax.sql.DataSource give the connection the ability to be pooled and javax.sql.XADataSource give the connection distributed transactional behavior.
I understand most XADataSource will implement connection pooling as well as distributed transactions so I don't see the point to use a DataSource when you could use a XADataSource and have both.
Are there any tradeoff when choosing a XADataSource over a DataSource?
I understand is not mandatory for a XADataSource to use pooled connections, is it there a way to find out if a XADataSource uses pooled connections or only relying on the XADataSource provider's documentation?
EDIT:
I am refering to javax.sql.DataSource and javax.sql.XADataSource because those are the types Tomcat 8 factory gives you:
Type should always be javax.sql.DataSource or javax.sql.XADataSource
Depending on the type a org.apache.tomcat.jdbc.pool.DataSource or a
org.apache.tomcat.jdbc.pool.XADataSource will be created.
I do understand that in the end I would be using a DataSource on my code as an API, abstracting the underlying implementation... my question is more related on the decision making process I have to go through when I am configuring Tomcat 8 (or any other server as well).
I want to have pooled connections and there are many XADataSource implementations that will give transactional and pooled connections, so why not always use XADataSource if I will get more? (this of course doesn't applies for a XADataSource that doesn't implements pooled connections)
When to configure XADataSource
As explained in the second section, your code will always use the DataSource interface (which might use a XADataSource). If the question is when should you use a XADataSource (eg configure it in your application server), then the answer is simple:
You use an XADataSource if you need to have distributed transactions: that is ensure a transaction succeeds or fails across multiple resources (eg different databases).
If you don't need distributed transactions, then you can still configure an XADataSource, but this might have some overhead in terms of memory and processing, for example extra objects (eg XAResource) that go unused, and maybe in terms of the 'bookkeeping' done by the data source. This overhead is probably negligible though.
Some data source (eg the Tomcat pool as mentioned in your question), can either use a DataSource or an XADataSource as a factory to create connections (according to the JDBC spec a ConnectionPoolDataSource should also be available as a factory, but it looks like Tomcat ignores that option). This doesn't change the way you decide what to use:
Don't need distributed transactions:
Program --uses--> Tomcat connection pool DataSource --uses--> JDBC driver DataSource
Need distributed transactions:
Program --uses--> Tomcat connection pool DataSource --uses--> JDBC driver XADataSource
In both cases the connection pool is provided by the Tomcat connection pool DataSource, not by the JDBC driver (XA)DataSource. A correct* implementation of XADataSource will not implement connection pooling: that would be the (optional) responsibility of the DataSource implementation that uses the XADataSource as its factory. So that is not a reason to choose (or not choose) an XADataSource.
Your question might stem from the confusing terminology that a XADataSource creates XAConnection which extends PooledConnection. The name PooledConnection doesn't mean it comes from a connection pool, it means that after creation these can be held in a connection pool (which would be inside the DataSource that called XADataSource.getXAConnection).
Responsibilities of DataSource and XADataSource
In JDBC the responsibility of a DataSource is to create connections that can be used by your application. This means that it can be a very basic implementation that does nothing more than go directly to DriverManager, but also an implementation that provides connection pooling, and support for distributed transactions.
The idea is that you can swap one implementation for the other, while your code would be untouched.
So, the code consuming connections should always use a javax.sql.DataSource implementation. The javax.sql.XADataSource (and javax.sql.ConnectionPoolDataSource for that matter) are intended to be used by javax.sql.DataSource implementations that provided advanced features like connection pooling and/or distributed transactions. They should not be used directly in your own program. As the tutorial you link says:
Similarly, when the DataSource implementation is implemented to work with an XADataSource class, all of the connections it produces will automatically be connections that can be used in a distributed transaction.
In other words DataSource is the API you use to obtain a connection, and a XADataSource is used by a data source library that provides distributed transaction support. It obtains the XAConnection, registers it with a distributed transaction manager, and then gives you the logical connection obtained from XAConnection.getConnection().
This is also a described in the JDBC 4.2 specification, section 12.1:
Distributed transactions require an infrastructure that provides these
roles:
Transaction manager — controls transaction boundaries and manages the two-phase commit protocol. This typically will be an
implementation of JTA.
JDBC drivers that implement the XADataSource, XAConnection, and XAResource interfaces. These are described in the next section.
An application-visible implementation of DataSource to “sit on top of” each XADataSource object and interact with the transaction
manager. The DataSource implementation is typically provided by an
application server.
Resource manager(s) to manage the underlying data. In the context of the JDBC API, a resource manager is a DBMS server. The term
“resource manager” is borrowed from JTA to emphasize the point that
distributed transactions using the JDBC API follow the architecture
specified in that document.
TL;DR: You --use--> DataSource --(potentially) uses--> XADataSource
*: Historically there has been some confusion in various JDBC implementations regarding responsibilities, and in some cases connection pools have implemented all three interfaces at the same time.
I was connecting to DB2 systems using org.apache.commons.dbcp.BasicDataSource and I have
found that com.ibm.db2.jcc.DB2DataSource is more extensive as it allows me to generate traces.
Now I would like to know the difference more accurately and which is preferable as I believe that BasicDataSource is light as compared to DB2DataSource.
org.apache.commons.dbcp.BasicDataSource is actually a connection pool, from which you can borrow/return connections to any flavour of database: Oracle, Sybase, DB2, etc.
com.ibm.db2.jcc.DB2DataSource is a DB2 data source.
So, you could have a DBCP pool of perhaps 100 DB2 connections. The pool will return you a pretty generic datasource for use in your code - unless you cast it explicitly to a DB2 one e.g. in order to get access to its fuller API. Edit following comment below: you shouldn't really need to do this, normal idiom of use is to go with the regular DataSource interface.
Read more about DBCP and its configuration options at:
http://commons.apache.org/proper/commons-dbcp/index.html
http://commons.apache.org/proper/commons-dbcp/configuration.html
What is the difference between Spring DriverManagerDataSource and apache BasicDataSource?
Which of them is preferable and in which situations?
Thank you.
As per the Spring documentation
This class is not an actual connection pool; it does not actually pool Connections. It just serves as simple replacement for a full-blown connection pool, implementing the same standard interface, but creating new Connections on every call.
If you need a "real" connection pool outside of a J2EE container, consider Apache's Jakarta Commons DBCP or C3P0. Commons DBCP's BasicDataSource and C3P0's ComboPooledDataSource are full connection pool beans, supporting the same basic properties as this class plus specific settings (such as minimal/maximal pool size etc).
Also read Controlling database connections
When using Spring's JDBC layer, you obtain a data source from JNDI or you configure your own with a connection pool implementation provided by a third party. Popular implementations are Apache Jakarta Commons DBCP and C3P0. Implementations in the Spring distribution are meant only for testing purposes and do not provide pooling.
From Spring DriverManagerDataSource API:
This class is not an actual connection pool; it does not actually
pool Connections. It just serves as simple replacement for a full-blown
connection pool, implementing the same standard interface, but creating new
Connections on every call.
In other words, it may be OK for tests but in real application use Apache DBCP
I am reading about Connections vs DataSources in Java and I have some questions. Is a DataSource really just a manager and an abstraction of a Connection (or multiple connections)?
From docs:
A factory for connections to the physical data source that this DataSource object represents. An alternative to the DriverManager facility, a DataSource object is the preferred means of getting a connection.
Actually, a DataSource is a provider of Connections and it has a variety of implementations which operate in different manners. Such as:
Basic implementation -- produces a standard Connection object
Connection pooling implementation -- produces a Connection object that will automatically participate in connection pooling. This
implementation works with a middle-tier connection pooling manager.
Distributed transaction implementation -- produces a Connection object that may be used for distributed transactions and almost always
participates in connection pooling. This implementation works with a
middle-tier transaction manager and almost always with a connection
pooling manager.
Connection is the connection :) DataSource is a manager of connections (pool of connections).
Data source is the source of your data, the connection is the driver.
DataSource is ill concept in its existing form as if it was meant to abstract interactions it should not return some SQL connection to interact with in the first place. Also it is overkill and XA is fantasy concept that some paid dearly for lack of reliable implementation in the world (I mean all enterprise commercial implementers simply fail and expose business... someone got hurt because of it in finance, but I will not mention names). In general, regardless if Sun or Oracle recommends it, it results in over-engineering and some technical dirt in code (dealing with contexts, extra steps to get to data, some external configurations... and in the end it is still specific to vendor implementations anyway). Some developed coroporate solutions that deal with pooling, connection recovery e.t.c much better based on plain connections and DriverManager than DataSource implemtations provided by enterprise DBMS vendors.
For the record I worked with both and I base it on facts encountered in different places. And if you doubt it then ask why you can see plain JDBC URL in Hibernate configuration all over the place in businesses. Many simply dump the heavyweigtt idea of J2EE and go lightweight... also using plain connections based on DriverManager.
You want to get your career on line then go ahead with XA DataSources and recovery of failed transactions where poor XA implemetation failed badly.
I am creating a JDBC connection pool resource for GlassFish, using the server's Admin Console.
One of the fields on the page to create the pool is labeled 'Resource Type'. This field has four possible values: javax.sql.DataSource, javax.sql.XADataSource, javax.sql.ConnectionPoolDataSource and javax.sql.Driver, but the help text for the Create JDBC connection pool 'wizard' does not have much info about the advantages and disadvantages of these choices.
When prompted to pick a resource type which should I choose?
I am going to connect to a local MySQL server. It would be nice to get an explanation of the differences between the choices in the drop-down as well.
Below are the scenarios where you would need each of the resource types listed. Hope this helps.
DataSource
DataSource A DataSource object is a factory for Connection objects. When using simple DataSource, appserver uses its own pooling instead of native.
ConnectionPoolDataSource
A ConnectionPoolDataSource object is a factory for PooledConnection objects. ConnectionPoolDataSource is used to give access to PooledConnection which implements native pooling by JDBC driver. In this case application server can implement connections pooling using this native interface. Please refer to Java API to know what a PooledConnection is...A ConnectionPoolDataSource can use a third party implementation for pooling - as far as I know for Tomcat, for instance, DBCP connection pooling is used.
XADataSource
You need an XADataSource if you want to execute a Distributed Transaction. You should use XADataSource instead of DataSource if the application
Uses the Java Transaction API (JTA)
Includes multiple database updates within a single transaction
Accesses multiple resources, such as a database and the Java Messaging Service (JMS), during a transaction