With the large amount of online business expected, the owner will definitely need connection pooling. Opening and closing connections involves a great deal of overhead, and the owner anticipates that this online ordering system will necessitate a sizable number of queries and updates.
With connection pooling, a pool of connections can be used over and over again, avoiding the expense of creating a new connection for every database access. In addition, the owner now has a second DBMS that contains data for the recently acquired coffee roasting company.
This means that the owner will want to be able to write distributed transactions that use both the old DBMS server and the new one. The chain owner has reconfigured the computer system to serve the new, larger customer base.
The owner has purchased the most recent JDBC driver and an EJB application server that works with it to be able to use distributed transactions and get the increased performance that comes with connection pooling. Client computers making requests are the first tier. The system administrator needs to deploy DataSource objects so that The Coffee Break's programming team can start using them. Deploying a DataSource object consists of three tasks:.
First, consider the most basic case, which is to use a basic implementation of the DataSource interface, that is, one that does not support connection pooling or distributed transactions.
In this case there is only one DataSource object that needs to be deployed. A basic implementation of DataSource produces the same kind of connections that the DriverManager class produces.
This driver includes the class com. BasicDataSource that implements the DataSource interface. The following code excerpt creates an instance of the class BasicDataSource and sets its properties. First, the system administrator creates the BasicDataSource object ds using the default constructor.
The system administrator then sets three properties. Note that the following code is typically be executed by a deployment tool:. The particular naming service that is used is usually determined by a system property, which is not shown here. The first line creates an InitialContext object, which serves as the starting point for a name, similar to root directory in a file system.
In the next code excerpt, you give the naming service this logical name, and it returns the BasicDataSource object. The logical name can be any string. In the previous example, jdbc is a subcontext under the initial context, just as a directory under the root directory is a subdirectory.
The subcontext jdbc is reserved for logical names to be bound to DataSource objects, so jdbc will always be the first part of a logical name for a data source.
After a basic DataSource implementation is deployed by a system administrator, it is ready for a programmer to use. This means that a programmer can give the logical data source name that was bound to an instance of a DataSource class, and the JNDI naming service will return an instance of that DataSource class. The method getConnection can then be called on that DataSource object to get a connection to the data source it represents. The first line of code gets an initial context as the starting point for retrieving a DataSource object.
Because the return value of the method lookup is a Java Object , we must cast it to the more specific DataSource type before assigning it to the variable ds.
The variable ds is an instance of the class com. Calling the method ds. Because of its properties, a DataSource object is a better alternative than the DriverManager class for getting a connection. Also, DataSource properties make maintaining code much simpler. If there is a change, the system administrator can update data source properties and not be concerned about changing every application that makes a connection to the data source. For example, if the data source were moved to a different server, all the system administrator would have to do is set the serverName property to the new server name.
Aside from portability and ease of maintenance, using a DataSource object to get connections can offer other advantages. When the DataSource interface is implemented to work with a ConnectionPoolDataSource implementation, all of the connections produced by instances of that DataSource class will automatically be pooled connections. 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.
The next section shows how to deploy these types of DataSource implementations. A system administrator or another person working in that capacity can deploy a DataSource object so that the connections it produces are pooled connections. To do this, he or she first deploys a ConnectionPoolDataSource object and then deploys a DataSource object implemented to work with it. The properties of the ConnectionPoolDataSource object are set so that it represents the data source to which connections will be produced.
Generally only two properties must be set for the DataSource object: description and dataSourceName. The value given to the dataSourceName property is the logical name identifying the ConnectionPoolDataSource object previously deployed, which is the object containing the properties needed to make the connection. This connection will be to the data source specified in the ConnectionPoolDataSource object's properties.
The following example describes how a system administrator for The Coffee Break would deploy a DataSource object implemented to provide pooled connections.
The system administrator would typically use a deployment tool, so the code fragments shown in this section are the code that a deployment tool would execute. The system administrator creates an instance of this class, sets its properties, and registers it with a JNDI naming service.
The Coffee Break has bought its DataSource class, com. The class com. PooledDataSource implements connection pooling by using the underlying support provided by the ConnectionPoolDataSource class com. However, the return value for the method lookup is a reference to a Java Object , the most generic of objects, so it must be cast to the more narrow DataSource before it can be assigned to the DataSource variable ds. Therefore, in the third line of code, calling the method DataSource.
The rest of the code fragment uses a single transaction to execute two queries and print the results of each query. If the DataSource class had been implemented to work with an XADataSource class, and the preceding code example was executed in the context of a distributed transaction, the code could not have called the method Connection. It also would not have set the auto-commit mode to false because that would have been unnecessary.
The default for newly-created connections that can participate in distributed transactions is to have auto-commit mode turned off. The next section will discuss the three broad categories of DataSource implementations. In addition to the version of getConnection that takes a user name and password, the DataSource interface provides a version of the method DataSource. It is available for situations where a data source does not require a user name and password because it uses a different security mechanism or where a data source does not restrict access.
The DataSource interface may be implemented to provide three different kinds of connections. As a result of DataSource objects working with a JNDI service provider, all connections produced by a DataSource object offer the advantages of portability and easy maintenance, which are explained later in this chapter.
Implementations of DataSource that work with implementations of the more specialized ConnectionPoolDataSource and XADataSource interfaces produce connections that are pooled or that can be used in distributed transactions. The following list summarizes the three general categories of classes that implement the DataSource interface:. An instance of a class that implements the DataSource interface represents one particular data source. Every connection produced by that instance will reference the same data source.
In a basic DataSource implementation, a call to the method DataSource. DataSource objects that implement connection pooling likewise produce a connection to the particular data source that the DataSource class represents.
The Connection object that the method DataSource. An application uses the Connection object just as it usually does and is generally unaware that it is in any way different.
Connection pooling has no effect whatever on application code except that a pooled connection, as is true with all connections, should always be explicitly closed. When an application closes a connection that is pooled, the connection joins a pool of reusable connections. The next time DataSource. Because connection pooling avoids creating a new physical connection every time one is requested, it can help to make applications run significantly faster. Connection pooling is generally used, for example, by a web server that supports servlets and JavaServertm Pages.
A DataSource class can likewise be implemented to work with a distributed transaction environment. An EJB server, for example, supports distributed transactions and requires a DataSource class that is implemented to interact with it.
In this case, the DataSource. As a rule, EJB servers provide a DataSource class that supports connection pooling as well as distributed transactions. Like connection pooling, transaction management is handled internally, so using distributed transactions is easy.
The only requirement is that when a transaction is distributed involves two or more data sources , the application cannot call the methods commit or rollback. It also cannot put the connection in auto-commit mode. The reason for these restrictions is that a transaction manager begins and ends a distributed transaction under the covers, so an application cannot do anything that would affect when a transaction begins or ends. The DataSource interface provides methods that allow a user to get and set the character stream to which tracing and error logging will be written.
A user can trace a specific data source on a given stream, or multiple data sources can write log messages to the same stream provided that the stream is set for each data source.
Log messages that are written to a log stream specific to a DataSource object are not written to the log stream maintained by the DriverManager. Can you please specify the path where i need to keep db. How are you running the program? The file should be in the classpath. If running through Eclipse, put it in the project root directory. When we call connection.
Here connection is Connection pool object. Can you show other features of org. That would be really useful. Your tutorials are really great. Thank you. MysqlDataSource c8 java. Following line converts PooledConnection to OracleConnection. Getting this error …. Also check if you are able to connect using mysql command line.
Could you please tell me why I am getting that type of exception when I run the program. Exception given below.
Seems like your Database connection is not working properly. Please check user, password settings. Which one is better method? Best option is to use server for creating connection pool and then use it in our application by getting connection from pool using JNDI.
I am looking at exackly that, can you please explain how I can do that. How do lookup for this datasource in my application. Hi I am using apache common dbcp 1. OracleDriver 2. I am not sure what is wrong by looking at your code snippet, if you can share that with me then I might have a look at it.
I want crate a table in oracle using remote desktop connection then I want write java code for import that data from oracle to mysql in my system. Please help me to write a code for this issue. Kindly, request you to help me in this code. I have not worked on anything like this, please use Google. I am sure you will find something to get started.
OracleDriver in props file. We are not using it anywhere in our code? This is to keep it configurable. But have error while connecting to database. Vendor code 0. Only driver and sqldeveloper installed. In testcase result it coming data source is null. There is no data base. If yes please help me..
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