By default, MySQL Server will be installed with root superuser without any password. You can connect to MySQL server as root without requiring password or by keying in blank password. However, if you have set the password for root and forget or unable to recall the password, then you will need to reset the root password for MySQL.
MySQL Reference Manual has detail steps on how to reset password for root which are as below:
The procedure under Windows:
1. Log on to the Windows system where MySQL is running as Administrator.
2. Stop the MySQL server if it is running. For a server that is running as
a Windows service, go to the Services manager:
Start Menu -> Control Panel
-> Administrative Tools -> Services
Then find the MySQL service in the list, and stop it.
If your server is not running as a service, you may need to use the Task
Manager to force it to stop.
3. Create a text file and place the following command within it on a single line:
SET PASSWORD FOR ‘root’@'localhost’ = PASSWORD(‘MyNewPassword’);
Save the file with any name. For this example the file will be
C:\mysql-init.txt.
4. Open a console window to get to the DOS command prompt:
Start Menu -> Run -> cmd
5. If MySQL is installed in C:\mysql. If MySQL is installed in another location,
adjust the following commands accordingly.
At the DOS command prompt, execute this command:
C:\> C:\mysql\bin\mysqld-nt –init-file=C:\mysql-init.txt
The contents of the file named by the –init-file option are executed at
server startup, changing the root password. After the server has started
successfully, you should delete C:\mysql-init.txt.
If you installed MySQL using the MySQL Installation Wizard, you may need to
specify a –defaults-file option:
C:\> “C:\Program Files\MySQL\MySQL Server 5.0\bin\mysqld-nt.exe”
–defaults-file=”C:\Program Files\MySQL\MySQL Server 5.0\my.ini”
–init-file=C:\mysql-init.txt
The appropriate –defaults-file setting can be found using the Services
Manager:
Start Menu -> Control Panel -> Administrative Tools -> Services
Find the MySQL service in the list, right-click on it, and choose the
Properties option. The Path to executable field contains the –defaults-file setting. Be sure to supply the –init-file argument with the full system path to the file, regardless of your current working directory
6. Stop the MySQL server, then restart it in normal mode again. If the MySQL server is ran as a service, start it from the Windows Services window. If you start the server manually, use whatever command you normally use.
7. Connect to MySQL server by using the new password.
For Unix environment, the procedure for resetting the root password is as follows:
1. Log on to the Unix system as either the Unix root user or as the same user that the mysqld server runs as.
2. Locate the .pid file that contains the server’s process ID. The exact location and name of this file depend on your distribution, hostname, and configuration. Common locations are /var/lib/mysql/, /var/run/mysqld/, and /usr/local/mysql/data/. Generally, the filename has the extension of .pid and begins with either mysqld or the system’s hostname.
Stop the MySQL server by sending a normal kill (not kill -9) to the mysqld process, using the pathname of the .pid file in the following command:
shell> kill `cat /mysql-data-directory/host_name.pid`
Note the use of backticks rather than forward quotes with the cat command; these cause the output of cat to be substituted into the kill command.
3. Create a text file and place the following command within it on a single line:
SET PASSWORD FOR ‘root’@'localhost’ = PASSWORD(‘MyNewPassword’);
Save the file with any name. For this example the file will be ~/mysql-init.
4. Restart the MySQL server with the special –init-file=~/mysql-init option:
shell> mysqld_safe –init-file=~/mysql-init &
The contents of the init-file are executed at server startup, changing the root password. After the server has started successfully you should delete ~/mysql-init.
5. Connect to MySQL server by using the new password.
Alternatively, on any platform, mysql client can be used to set the new password, althought it’s less secure way of resetting the password (detailed instruction here):
1. Stop mysqld and restart it with the –skip-grant-tables –user=root options (Windows users omit the –user=root portion).
2. Connect to the mysqld server with this command:
shell> mysql -u root
3. Issue the following statements in the mysql client:
mysql> UPDATE mysql.user SET Password=PASSWORD(‘newpwd’)
-> WHERE User=’root’;
mysql> FLUSH PRIVILEGES;
Replace ‘newpwd’ with the actual root password that you want to use.
4. You should be able to connect using the new password.
Friday, January 29, 2010
Friday, January 8, 2010
Using the Singleton pattern in Java
The Java Singleton pattern belongs to the family of design patterns that governs the instantiation process. A Singleton is an object that cannot be instantiated.
This design pattern suggests that at any time there can only be one instance of a Singleton (object) created by the JVM. You implement the pattern by creating a class with a method that creates a new instance of the class if one does not exist. If an instance of the class exists, it simply returns a reference to that object.
How the Singleton pattern works
Here's a typical example of Singleton:
public class Singleton {
private final static Singleton INSTANCE = new Singleton();
// Private constructor suppresses generation of
// a (public) default constructor
private Singleton() {}
public static Singleton getInstance() {
return INSTANCE;
}
}
The classic Singleton does not use direct instantiation of a static variable with declaration -- it instantiates a static instance variable in the constructor without checking to see if it already exists:
public class ClassicSingleton {
private static ClassicSingleton INSTANCE = null;
private ClassicSingleton() {
// Exists only to defeat instantiation.
}
public static ClassicSingleton getInstance() {
if(INSTANCE == null) {
INSTANCE = new ClassicSingleton();
}
return INSTANCE;
}
}
The Singleton class's default constructor is made private, which prevents the direct instantiation of the object by other classes using the new keyword. A static modifier is applied to the instance method that returns the Singleton object; it makes this a class level method that can be accessed without creating an object.
When you need Singleton
Singletons are truly useful when you need only one instance of a class, and it is undesirable to have more than one instance of a class.
When designing a system, you usually want to control how an object is used and prevent users (including yourself) from making copies of it or creating new instances. For example, you can use it to create a connection pool. It's not wise to create a new connection every time a program needs to write something to a database; instead, a connection or a set of connections that are already a pool can be instantiated using the Singleton pattern.
The Singleton pattern is often used in conjunction with the factory method pattern to create a systemwide resource whose specific type is not known to the code that uses it. An example of using these two patterns together is the Abstract Windowing Toolkit (AWT). In GUI applications, you often need only one instance of a graphical element per application instance, like the Print dialog box or the OK button.
Watch out for potential problems
Although the Singleton design pattern is one of the simplest design patterns, it presents a number of pitfalls.
Construct in multi-threaded applications
You must carefully construct the Singleton pattern in multi-threaded applications. If two threads are to execute the creation method at the same time when a Singleton does not exist, both must check for an instance of the Singleton, but only one thread should create the new object. The classic solution to this problem is to use mutual exclusion on the class that indicates that the object is being instantiated. This is a thread-safe version of a Singleton:
public class Singleton
{
// Private constructor suppresses generation
// of a (public) default constructor
private Singleton() {}
private static class SingletonHolder
{
private final static Singleton INSTANCE = new Singleton();
}
public static Singleton getInstance()
{
return SingletonHolder.INSTANCE;
}
}
For an alternative solution, you can add the synchronized keyword to the getInstance() method declaration:
public static synchronized Singleton getInstance()
Think ahead about cloning prevention
You can still create a copy of the Singleton object by cloning it using the Object's clone() method. To forbid this, you need to override the Object's clone method, which throws a CloneNotSupportedException exception:
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
Consider making the singleton class final
You may want to make the Singleton class final to avoid sub classing of Singletons that may cause other problems.
Remember about garbage collection
Depending on your implementation, your Singleton class and all of its data might be garbage collected. This is why you must ensure that there must be a live reference to the Singleton class when the application is running.
Conclusion
The Singleton pattern is widely used and has proved its usability in designing software. Although the pattern is not specific to Java, it has become a classic in Java programming. Despite its simplicity, remember the limitations of the Singleton pattern that I describe in this article.
This design pattern suggests that at any time there can only be one instance of a Singleton (object) created by the JVM. You implement the pattern by creating a class with a method that creates a new instance of the class if one does not exist. If an instance of the class exists, it simply returns a reference to that object.
How the Singleton pattern works
Here's a typical example of Singleton:
public class Singleton {
private final static Singleton INSTANCE = new Singleton();
// Private constructor suppresses generation of
// a (public) default constructor
private Singleton() {}
public static Singleton getInstance() {
return INSTANCE;
}
}
The classic Singleton does not use direct instantiation of a static variable with declaration -- it instantiates a static instance variable in the constructor without checking to see if it already exists:
public class ClassicSingleton {
private static ClassicSingleton INSTANCE = null;
private ClassicSingleton() {
// Exists only to defeat instantiation.
}
public static ClassicSingleton getInstance() {
if(INSTANCE == null) {
INSTANCE = new ClassicSingleton();
}
return INSTANCE;
}
}
The Singleton class's default constructor is made private, which prevents the direct instantiation of the object by other classes using the new keyword. A static modifier is applied to the instance method that returns the Singleton object; it makes this a class level method that can be accessed without creating an object.
When you need Singleton
Singletons are truly useful when you need only one instance of a class, and it is undesirable to have more than one instance of a class.
When designing a system, you usually want to control how an object is used and prevent users (including yourself) from making copies of it or creating new instances. For example, you can use it to create a connection pool. It's not wise to create a new connection every time a program needs to write something to a database; instead, a connection or a set of connections that are already a pool can be instantiated using the Singleton pattern.
The Singleton pattern is often used in conjunction with the factory method pattern to create a systemwide resource whose specific type is not known to the code that uses it. An example of using these two patterns together is the Abstract Windowing Toolkit (AWT). In GUI applications, you often need only one instance of a graphical element per application instance, like the Print dialog box or the OK button.
Watch out for potential problems
Although the Singleton design pattern is one of the simplest design patterns, it presents a number of pitfalls.
Construct in multi-threaded applications
You must carefully construct the Singleton pattern in multi-threaded applications. If two threads are to execute the creation method at the same time when a Singleton does not exist, both must check for an instance of the Singleton, but only one thread should create the new object. The classic solution to this problem is to use mutual exclusion on the class that indicates that the object is being instantiated. This is a thread-safe version of a Singleton:
public class Singleton
{
// Private constructor suppresses generation
// of a (public) default constructor
private Singleton() {}
private static class SingletonHolder
{
private final static Singleton INSTANCE = new Singleton();
}
public static Singleton getInstance()
{
return SingletonHolder.INSTANCE;
}
}
For an alternative solution, you can add the synchronized keyword to the getInstance() method declaration:
public static synchronized Singleton getInstance()
Think ahead about cloning prevention
You can still create a copy of the Singleton object by cloning it using the Object's clone() method. To forbid this, you need to override the Object's clone method, which throws a CloneNotSupportedException exception:
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
Consider making the singleton class final
You may want to make the Singleton class final to avoid sub classing of Singletons that may cause other problems.
Remember about garbage collection
Depending on your implementation, your Singleton class and all of its data might be garbage collected. This is why you must ensure that there must be a live reference to the Singleton class when the application is running.
Conclusion
The Singleton pattern is widely used and has proved its usability in designing software. Although the pattern is not specific to Java, it has become a classic in Java programming. Despite its simplicity, remember the limitations of the Singleton pattern that I describe in this article.
Friday, November 6, 2009
Configuring JDBC in Oracle JDeveloper
The Java Database Connectivity (JDBC) API is used to access a SQL database from a Java application. JDBC also supports tabular data sources, such as a spreadsheet.
Oracle JDeveloper is a free Integrated Development Environment (IDE) for modeling, developing, debugging, optimizing, and deploying Java applications. JDeveloper 10g is used to develop J2EE applications comprising the JSPs, EJBs, struts, servlets, and Java classes that may require accessing a database table in an Oracle 10g Database or a third-party database. In this extract from the book JDBC 4.0 and Oracle JDeveloper for J2EE Development (Packt Publishing), we will see how to configure JDBC in the JDeveloper IDE.
Unlike the Eclipse IDE, which requires a plug-in, JDeveloper has a built-in provision to establish a JDBC connection with a database. JDeveloper is the only Java IDE with an embedded application server, Oracle Containers for J2EE (OC4J) or WebLogic Server in JDeveloper 11g. Thus a database-based Web application may run in JDeveloper without a third-party application server. However, JDeveloper also supports third-party application servers. Starting with JDeveloper 11, application developers can point the IDE to an application server instance, including third-party application servers, that you want to use for testing during development. JDeveloper provides connection pooling for the efficient use of database connections. A database connection may be used in an ADF BC (Business Components) application or in a Java EE application.
A database connection in JDeveloper may be configured in the Connections Navigator. A Connections Navigator connection is available as a DataSource registered with a JNDI naming service. The database connection in JDeveloper is a reusable named connection that developers configure once and then use in as many of their projects as they want. Depending on the nature of the project and the database connection, the connection is configured in the bc4j.xcfg file or a Java EE data source. Here, it is necessary to distinguish between data source and DataSource. A data source is a source of data; for example, an RDBMS database is a data source. A DataSource is an interface that represents a factory for JDBC Connection objects.
JDeveloper uses the term Data Source or data source to refer to a factory for connections. We will also use the term Data Source or data source to refer to a factory for connections, which in the javax.sql package is represented by the DataSource interface. A DataSource object may be created from a data source registered with the JNDI (Java Naming and Directory) naming service using JNDI lookup. A JDBC Connection object may be obtained from a DataSource object using the getConnection method. As an alternative to configuring a connection in the Connections Navigator, a data source may also be specified directly in the data source configuration file data-sources.xml.
In this article we will discuss the procedure to configure a JDBC connection and a JDBC data source in JDeveloper 10g IDE. We will use the MySQL 5.0 database server and MySQL Connector/J 5.1 JDBC driver, which support the JDBC 4.0 specification. In this article you will learn the following:
* Creating a database connection in JDeveloper Connections Navigator.
* Configuring the Data Source and Connection Pool associated with the connection configured in the Connections Navigator.
* The common JDBC Connection Errors.
Before we create a JDBC connection and a data source we will discuss connection pooling and DataSource.
Connection Pooling and DataSource
The javax.sql package provides the API for server-side database access. The main interfaces in the javax.sql package are DataSource, ConnectionPoolDataSource, and PooledConnection. The DataSource interface represents a factory for connections to a database. DataSource is a preferred method of obtaining a JDBC connection. An object that implements the DataSource interface is typically registered with a Java Naming and Directory API-based naming service. DataSource interface implementation is driver-vendor specific. The DataSource interface has three types of implementations:
* Basic implementation: In a basic implementation there is a 1:1 correspondence between a client`s Connection object and the connection with the database. This implies that for every Connection object, there is a connection with the database. With the basic implementation, the overhead of opening, initiating, and closing a connection is incurred for each client session.
* Connection pooling implementation: A pool of Connection objects is available from which connections are assigned to the different client sessions. A connection pooling manager implements the connection pooling. When a client session does not require a connection, the connection is returned to the connection pool and becomes available to other clients. Thus, the overheads of opening, initiating, and closing connections are reduced.
* Distributed transaction implementation: Distributed transaction implementation produces a Connection object that is mostly used for distributed transactions and is always connection-pooled. A transaction manager implements the distributed transactions.
An advantage to using a data source is that code accessing a data source does not have to be modified when an application is migrated to a different application server. Only the data source properties need to be modified. A JDBC driver that is accessed with a DataSource does not register itself with a DriverManager. A DataSource object is created using a JNDI lookup and subsequently a Connection object is created from the DataSource object. For example, if a data source JNDI name is jdbc/OracleDS, a DataSource object may be created using JNDI lookup. First, create an InitialContext object and subsequently create a DataSource object using the InitialContext lookup method. From the DataSource object create a Connection object using the getConnection() method:
InitialContext ctx=new InitialContext();
DataSource ds=ctx.lookup("jdbc/OracleDS");
Connection conn=ds.getConnection();
The JNDI naming service, which we used to create a DataSource object, is provided by J2EE application servers such as the Oracle Application Server Containers for J2EE (OC4J) embedded in the JDeveloper IDE.
A connection in a pool of connections is represented by the PooledConnection interface, not the Connection interface. The connection pool manager, typically the application server, maintains a pool of PooledConnection objects. When an application requests a connection using the DataSource.getConnection() method, as we did using the jdbc/OracleDS data source example, the connection pool manager returns a Connection object, which is actually a handle to an object that implements the PooledConnection interface.
A ConnectionPoolDataSource object, which is typically registered with a JNDI naming service, represents a collection of PooledConnection objects. The JDBC driver provides an implementation of the ConnectionPoolDataSource, which is used by the application server to build and manage a connection pool. When an application requests a connection, if a suitable PooledConnection object is available in the connection pool, the connection pool manager returns a handle to the PooledConnection object as a Connection object. If a suitable PooledConnection object is not available, the connection pool manager invokes the getPooledConnection() method of the ConnectionPoolDataSource to create a new PooledConnection object. For example, if connectionPoolDataSource is a ConnectionPoolDataSource object, a new PooledConnection gets created as follows:
PooledConnection
pooledConnection=connectionPoolDataSource.getPooledConnection();
The application does not have to invoke the getPooledConnection() method though; the connection pool manager invokes the getPooledConnection() method and the JDBC driver implementing the ConnectionPoolDataSource creates a new PooledConnection and returns a handle to it. The connection pool manager returns a Connection object, which is a handle to a PooledConnection object, to the application requesting a connection. When an application closes a Connection object using the close() method, as follows, the connection does not actually get closed.
conn.close();
The connection handle gets deactivated when an application closes a Connection object with the close() method. The connection pool manager does the deactivation. When an application closes a Connection object with the close() method, any client info properties that were set using the setClientInfo method are cleared.
The connection pool manager is registered with a PooledConnection object using the addConnectionEventListener() method. When a connection is closed, the connection pool manager is notified and the connection pool manager deactivates the handle to the PooledConnection object and returns the PooledConnection object to the connection pool to be used by another application.
The connection pool manager is also notified if a connection has an error. A PooledConnection object is not closed until the connection pool is being reinitialized, the server is shutdown, or a connection becomes unusable.
In addition to connections being pooled, PreparedStatement objects are also pooled by default if the database supports statement pooling. It can be discovered if a database supports statement pooling using the supportsStatementPooling() method of the DatabaseMetaData interface. The PreparedStatement pooling is also managed by the connection pool manager. To be notified of PreparedStatement events such as a PreparedStatement getting closed or a PreparedStatement becoming unusable, a connection pool manager is registered with a PooledConnection manager using the addStatementEventListener() method. A connection pool manager deregisters a PooledConnection object using the removeStatementEventListener() method. Methods addStatementEventListener and removeStatementEventListener are new methods in the PooledConnection interface in JDBC 4.0. Pooling of Statement objects is another new feature in JDBC 4.0. The Statement interface has two new methods in JDBC 4.0 for Statement pooling: isPoolable() and setPoolable().
The isPoolable method checks if a Statement object is poolable and the setPoolable method sets the Statement object to poolable. When an application closes a PreparedStatement object using the close() method, the PreparedStatement object is not actually closed. The PreparedStatement object is returned to the pool of PreparedStatements. When the connection pool manager closes a PooledConnection object by invoking the close() method of PooledConnection, all the associated statements also get closed. Pooling of PreparedStatements provides significant optimization, but if a large number of statements are left open, it may not be an optimal use of resources. Thus, the following procedure is followed to obtain a connection in an application server using a data source:
1. Create a data source with a JNDI name binding to the JNDI naming service.
2. Create an InitialContext object and look up the JNDI name of the data source using the lookup method to create a DataSource object. If the JDBC driver implements the DataSource as a connection pool, a connection pool becomes available.
3. Request a connection from the connection pool. The connection pool manager checks if a suitable PooledConnection object is available. If a suitable PooledConnection object is available, the connection pool manager returns a handle to the PooledConnection object as a Connection object to the application requesting a connection.
4. If a PooledConnection object is not available, the connection pool manager invokes the getPooledConnection() method of the ConnectionPoolDataSource, which is implemented by the JDBC driver.
5. The JDBC driver implementing the ConnectionPoolDataSource creates a PooledConnection object and returns a handle to it.
6. The connection pool manager returns a handle to the PooledConnection object as a Connection object to the application requesting a connection.
7. When an application closes a connection, the connection pool manager deactivates the handle to the PooledConnection object and returns the PooledConnection object to the connection pool.
ConnectionPoolDataSource provides some configuration properties to configure a connection pool. The configuration pool properties are not set by the JDBC client, but are implemented or augmented by the connection pool. The properties can be set in a data source configuration. Therefore, it is not for the application itself to change the settings, but for the administrator of the pool, who also sometimes happens to be the developer, to do so.
Oracle JDeveloper is a free Integrated Development Environment (IDE) for modeling, developing, debugging, optimizing, and deploying Java applications. JDeveloper 10g is used to develop J2EE applications comprising the JSPs, EJBs, struts, servlets, and Java classes that may require accessing a database table in an Oracle 10g Database or a third-party database. In this extract from the book JDBC 4.0 and Oracle JDeveloper for J2EE Development (Packt Publishing), we will see how to configure JDBC in the JDeveloper IDE.
Unlike the Eclipse IDE, which requires a plug-in, JDeveloper has a built-in provision to establish a JDBC connection with a database. JDeveloper is the only Java IDE with an embedded application server, Oracle Containers for J2EE (OC4J) or WebLogic Server in JDeveloper 11g. Thus a database-based Web application may run in JDeveloper without a third-party application server. However, JDeveloper also supports third-party application servers. Starting with JDeveloper 11, application developers can point the IDE to an application server instance, including third-party application servers, that you want to use for testing during development. JDeveloper provides connection pooling for the efficient use of database connections. A database connection may be used in an ADF BC (Business Components) application or in a Java EE application.
A database connection in JDeveloper may be configured in the Connections Navigator. A Connections Navigator connection is available as a DataSource registered with a JNDI naming service. The database connection in JDeveloper is a reusable named connection that developers configure once and then use in as many of their projects as they want. Depending on the nature of the project and the database connection, the connection is configured in the bc4j.xcfg file or a Java EE data source. Here, it is necessary to distinguish between data source and DataSource. A data source is a source of data; for example, an RDBMS database is a data source. A DataSource is an interface that represents a factory for JDBC Connection objects.
JDeveloper uses the term Data Source or data source to refer to a factory for connections. We will also use the term Data Source or data source to refer to a factory for connections, which in the javax.sql package is represented by the DataSource interface. A DataSource object may be created from a data source registered with the JNDI (Java Naming and Directory) naming service using JNDI lookup. A JDBC Connection object may be obtained from a DataSource object using the getConnection method. As an alternative to configuring a connection in the Connections Navigator, a data source may also be specified directly in the data source configuration file data-sources.xml.
In this article we will discuss the procedure to configure a JDBC connection and a JDBC data source in JDeveloper 10g IDE. We will use the MySQL 5.0 database server and MySQL Connector/J 5.1 JDBC driver, which support the JDBC 4.0 specification. In this article you will learn the following:
* Creating a database connection in JDeveloper Connections Navigator.
* Configuring the Data Source and Connection Pool associated with the connection configured in the Connections Navigator.
* The common JDBC Connection Errors.
Before we create a JDBC connection and a data source we will discuss connection pooling and DataSource.
Connection Pooling and DataSource
The javax.sql package provides the API for server-side database access. The main interfaces in the javax.sql package are DataSource, ConnectionPoolDataSource, and PooledConnection. The DataSource interface represents a factory for connections to a database. DataSource is a preferred method of obtaining a JDBC connection. An object that implements the DataSource interface is typically registered with a Java Naming and Directory API-based naming service. DataSource interface implementation is driver-vendor specific. The DataSource interface has three types of implementations:
* Basic implementation: In a basic implementation there is a 1:1 correspondence between a client`s Connection object and the connection with the database. This implies that for every Connection object, there is a connection with the database. With the basic implementation, the overhead of opening, initiating, and closing a connection is incurred for each client session.
* Connection pooling implementation: A pool of Connection objects is available from which connections are assigned to the different client sessions. A connection pooling manager implements the connection pooling. When a client session does not require a connection, the connection is returned to the connection pool and becomes available to other clients. Thus, the overheads of opening, initiating, and closing connections are reduced.
* Distributed transaction implementation: Distributed transaction implementation produces a Connection object that is mostly used for distributed transactions and is always connection-pooled. A transaction manager implements the distributed transactions.
An advantage to using a data source is that code accessing a data source does not have to be modified when an application is migrated to a different application server. Only the data source properties need to be modified. A JDBC driver that is accessed with a DataSource does not register itself with a DriverManager. A DataSource object is created using a JNDI lookup and subsequently a Connection object is created from the DataSource object. For example, if a data source JNDI name is jdbc/OracleDS, a DataSource object may be created using JNDI lookup. First, create an InitialContext object and subsequently create a DataSource object using the InitialContext lookup method. From the DataSource object create a Connection object using the getConnection() method:
InitialContext ctx=new InitialContext();
DataSource ds=ctx.lookup("jdbc/OracleDS");
Connection conn=ds.getConnection();
The JNDI naming service, which we used to create a DataSource object, is provided by J2EE application servers such as the Oracle Application Server Containers for J2EE (OC4J) embedded in the JDeveloper IDE.
A connection in a pool of connections is represented by the PooledConnection interface, not the Connection interface. The connection pool manager, typically the application server, maintains a pool of PooledConnection objects. When an application requests a connection using the DataSource.getConnection() method, as we did using the jdbc/OracleDS data source example, the connection pool manager returns a Connection object, which is actually a handle to an object that implements the PooledConnection interface.
A ConnectionPoolDataSource object, which is typically registered with a JNDI naming service, represents a collection of PooledConnection objects. The JDBC driver provides an implementation of the ConnectionPoolDataSource, which is used by the application server to build and manage a connection pool. When an application requests a connection, if a suitable PooledConnection object is available in the connection pool, the connection pool manager returns a handle to the PooledConnection object as a Connection object. If a suitable PooledConnection object is not available, the connection pool manager invokes the getPooledConnection() method of the ConnectionPoolDataSource to create a new PooledConnection object. For example, if connectionPoolDataSource is a ConnectionPoolDataSource object, a new PooledConnection gets created as follows:
PooledConnection
pooledConnection=connectionPoolDataSource.getPooledConnection();
The application does not have to invoke the getPooledConnection() method though; the connection pool manager invokes the getPooledConnection() method and the JDBC driver implementing the ConnectionPoolDataSource creates a new PooledConnection and returns a handle to it. The connection pool manager returns a Connection object, which is a handle to a PooledConnection object, to the application requesting a connection. When an application closes a Connection object using the close() method, as follows, the connection does not actually get closed.
conn.close();
The connection handle gets deactivated when an application closes a Connection object with the close() method. The connection pool manager does the deactivation. When an application closes a Connection object with the close() method, any client info properties that were set using the setClientInfo method are cleared.
The connection pool manager is registered with a PooledConnection object using the addConnectionEventListener() method. When a connection is closed, the connection pool manager is notified and the connection pool manager deactivates the handle to the PooledConnection object and returns the PooledConnection object to the connection pool to be used by another application.
The connection pool manager is also notified if a connection has an error. A PooledConnection object is not closed until the connection pool is being reinitialized, the server is shutdown, or a connection becomes unusable.
In addition to connections being pooled, PreparedStatement objects are also pooled by default if the database supports statement pooling. It can be discovered if a database supports statement pooling using the supportsStatementPooling() method of the DatabaseMetaData interface. The PreparedStatement pooling is also managed by the connection pool manager. To be notified of PreparedStatement events such as a PreparedStatement getting closed or a PreparedStatement becoming unusable, a connection pool manager is registered with a PooledConnection manager using the addStatementEventListener() method. A connection pool manager deregisters a PooledConnection object using the removeStatementEventListener() method. Methods addStatementEventListener and removeStatementEventListener are new methods in the PooledConnection interface in JDBC 4.0. Pooling of Statement objects is another new feature in JDBC 4.0. The Statement interface has two new methods in JDBC 4.0 for Statement pooling: isPoolable() and setPoolable().
The isPoolable method checks if a Statement object is poolable and the setPoolable method sets the Statement object to poolable. When an application closes a PreparedStatement object using the close() method, the PreparedStatement object is not actually closed. The PreparedStatement object is returned to the pool of PreparedStatements. When the connection pool manager closes a PooledConnection object by invoking the close() method of PooledConnection, all the associated statements also get closed. Pooling of PreparedStatements provides significant optimization, but if a large number of statements are left open, it may not be an optimal use of resources. Thus, the following procedure is followed to obtain a connection in an application server using a data source:
1. Create a data source with a JNDI name binding to the JNDI naming service.
2. Create an InitialContext object and look up the JNDI name of the data source using the lookup method to create a DataSource object. If the JDBC driver implements the DataSource as a connection pool, a connection pool becomes available.
3. Request a connection from the connection pool. The connection pool manager checks if a suitable PooledConnection object is available. If a suitable PooledConnection object is available, the connection pool manager returns a handle to the PooledConnection object as a Connection object to the application requesting a connection.
4. If a PooledConnection object is not available, the connection pool manager invokes the getPooledConnection() method of the ConnectionPoolDataSource, which is implemented by the JDBC driver.
5. The JDBC driver implementing the ConnectionPoolDataSource creates a PooledConnection object and returns a handle to it.
6. The connection pool manager returns a handle to the PooledConnection object as a Connection object to the application requesting a connection.
7. When an application closes a connection, the connection pool manager deactivates the handle to the PooledConnection object and returns the PooledConnection object to the connection pool.
ConnectionPoolDataSource provides some configuration properties to configure a connection pool. The configuration pool properties are not set by the JDBC client, but are implemented or augmented by the connection pool. The properties can be set in a data source configuration. Therefore, it is not for the application itself to change the settings, but for the administrator of the pool, who also sometimes happens to be the developer, to do so.
Monday, August 24, 2009
Struts 2 Hello World Example
I had seen many new deveopers struggling against struts2 hello world example. So I decided to write a small example.
Below are the required libraries to run this example which are easily availabel
struts2-core-2.0.11
xwork-2.0.4
commons-logging-1.0.4
commons-logging-api-1.1
freemarker-2.3.8
ognl-2.6.11
The structure of the applictaion which I am following is (Eclipse IDE)
Struts2Demo
|---src
| |----org
| | |----vinod
| | | |----action
| | | | |----HelloWorld।java
|---struts.xml
|---WebContent
| |---jsp
| |---HelloWorld।jsp
|---index.jsp
|---WEB-INF
| |---lib
| |---web.xml
It is true that different IDE's use different structure, but at last when war is build they follow same structure.
Lets start...
HelloWorld.java
package org.vinod.action;
import com.opensymphony.xwork2.ActionSupport;
public class HelloWorld extends ActionSupport{
String greetings = null;
public String execute() throws Exception {
setGreetings("Hello World");
return SUCCESS;
}
/**
* @return the greetings
*/
public String getGreetings() {
return greetings;
}
/**
* @param greetings the greetings to set
*/
public void setGreetings(String greetings) {
this.greetings = greetings;
}
}
HelloWorld.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
Struts 2 Example
index.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
Struts 2 Example
struts.xml
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
/jsp/HelloWorld.jsp
web.xml
struts2
org.apache.struts2.dispatcher.FilterDispatcher
struts2
/*
index.jsp
Below are the required libraries to run this example which are easily availabel
struts2-core-2.0.11
xwork-2.0.4
commons-logging-1.0.4
commons-logging-api-1.1
freemarker-2.3.8
ognl-2.6.11
The structure of the applictaion which I am following is (Eclipse IDE)
Struts2Demo
|---src
| |----org
| | |----vinod
| | | |----action
| | | | |----HelloWorld।java
|---struts.xml
|---WebContent
| |---jsp
| |---HelloWorld।jsp
|---index.jsp
|---WEB-INF
| |---lib
| |---web.xml
It is true that different IDE's use different structure, but at last when war is build they follow same structure.
Lets start...
HelloWorld.java
package org.vinod.action;
import com.opensymphony.xwork2.ActionSupport;
public class HelloWorld extends ActionSupport{
String greetings = null;
public String execute() throws Exception {
setGreetings("Hello World");
return SUCCESS;
}
/**
* @return the greetings
*/
public String getGreetings() {
return greetings;
}
/**
* @param greetings the greetings to set
*/
public void setGreetings(String greetings) {
this.greetings = greetings;
}
}
HelloWorld.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
index.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
struts.xml
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
web.xml
Friday, August 14, 2009
Spring Properties File Based Data Injection
File: helloworld-context.properties
source.(class)=SimpleMessageData
destination.(class)=StdoutMessageReporter
service.(class)=DefaultMessageService
service.source(ref)=source
service.destination(ref)=destination
File: Main.java
import org.springframework.beans.factory.support.BeanDefinitionReader;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.PropertiesBeanDefinitionReader;
import org.springframework.core.io.ClassPathResource;
public class Main {
public static void main(String[] a) {
DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
BeanDefinitionReader reader = new PropertiesBeanDefinitionReader(bf);
reader.loadBeanDefinitions(new ClassPathResource("helloworld-context.properties"));
MessageService service = (MessageService) bf.getBean("service");
service.execute();
}
}
interface MessageService {
void execute();
}
class DefaultMessageService implements MessageService {
private MessageData source;
private MessageReporter destination;
public void execute() {
this.destination.write(this.source.getMessage());
}
public void setSource(MessageData source) {
this.source = source;
}
public void setDestination(MessageReporter destination) {
this.destination = destination;
}
}
interface MessageReporter {
void write(String message);
}
interface MessageData {
String getMessage();
}
class StdoutMessageReporter implements MessageReporter {
public void write(String message) {
System.out.println(message);
}
}
class SimpleMessageData implements MessageData {
private final String message;
public SimpleMessageData() {
this("Hello, world");
}
public SimpleMessageData(String message) {
this.message = message;
}
public String getMessage() {
return this.message;
}
}
click here
source.(class)=SimpleMessageData
destination.(class)=StdoutMessageReporter
service.(class)=DefaultMessageService
service.source(ref)=source
service.destination(ref)=destination
File: Main.java
import org.springframework.beans.factory.support.BeanDefinitionReader;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.PropertiesBeanDefinitionReader;
import org.springframework.core.io.ClassPathResource;
public class Main {
public static void main(String[] a) {
DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
BeanDefinitionReader reader = new PropertiesBeanDefinitionReader(bf);
reader.loadBeanDefinitions(new ClassPathResource("helloworld-context.properties"));
MessageService service = (MessageService) bf.getBean("service");
service.execute();
}
}
interface MessageService {
void execute();
}
class DefaultMessageService implements MessageService {
private MessageData source;
private MessageReporter destination;
public void execute() {
this.destination.write(this.source.getMessage());
}
public void setSource(MessageData source) {
this.source = source;
}
public void setDestination(MessageReporter destination) {
this.destination = destination;
}
}
interface MessageReporter {
void write(String message);
}
interface MessageData {
String getMessage();
}
class StdoutMessageReporter implements MessageReporter {
public void write(String message) {
System.out.println(message);
}
}
class SimpleMessageData implements MessageData {
private final String message;
public SimpleMessageData() {
this("Hello, world");
}
public SimpleMessageData(String message) {
this.message = message;
}
public String getMessage() {
return this.message;
}
}
click here
Saturday, August 8, 2009
Stereotype Annotations Cut Down XML Configuration in Spring
getname.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
"http://www.w3.org/TR/html4/loose.dtd">
Greeting Request
---------------------------------------------------
HelloWorldController.java
package com.intertech.mvc;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
@Controller
public class HelloWorldController {
@ModelAttribute("name")
public String populateName(
@RequestParam(value = "name", required = false) String name) {
return name;
}
@RequestMapping(value = "/greeting.request", method = RequestMethod.POST)
protected String sayHello() {
return "greet";
}
@RequestMapping(value = "/greeting.request", method = RequestMethod.GET)
protected String showForm() {
return "getname";
}
}
---------------------------------------------------
web.xml
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
HelloWorldAnnotated
dispatcher
org.springframework.web.servlet.DispatcherServlet
contextConfigLocation
/WEB-INF/mvc-beans.xml
dispatcher
*.request
*.xls
index.html
---------------------------------------------------
mvc-beans.xml
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
---------------------------------------------------
greet.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
"http://www.w3.org/TR/html4/loose.dtd">
Greeting
---------------------------------------------------
Note :
Add the commons-logging.jar, spring.jar and spring-webmvc.jar (Spring 2.5 or better) to the
/WEB-INF/lib folder.
To run HelloWorld, deploy the application to a Web Container, then request getname.jsp with the
following URL:
http://localhost:8080/HelloWorldAnnotated/getname.jsp
Because the controller has RequestMapping for both POST and GET HTTP methods, you can also
run HelloWorld by requesting the following URL:
http://localhost:8080/HelloWorldAnnotated/greeting.request
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
"http://www.w3.org/TR/html4/loose.dtd">
---------------------------------------------------
HelloWorldController.java
package com.intertech.mvc;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
@Controller
public class HelloWorldController {
@ModelAttribute("name")
public String populateName(
@RequestParam(value = "name", required = false) String name) {
return name;
}
@RequestMapping(value = "/greeting.request", method = RequestMethod.POST)
protected String sayHello() {
return "greet";
}
@RequestMapping(value = "/greeting.request", method = RequestMethod.GET)
protected String showForm() {
return "getname";
}
}
---------------------------------------------------
web.xml
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
---------------------------------------------------
mvc-beans.xml
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
---------------------------------------------------
greet.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
"http://www.w3.org/TR/html4/loose.dtd">
Hello ${name}
---------------------------------------------------
Note :
Add the commons-logging.jar, spring.jar and spring-webmvc.jar (Spring 2.5 or better) to the
/WEB-INF/lib folder.
To run HelloWorld, deploy the application to a Web Container, then request getname.jsp with the
following URL:
http://localhost:8080/HelloWorldAnnotated/getname.jsp
Because the controller has RequestMapping for both POST and GET HTTP methods, you can also
run HelloWorld by requesting the following URL:
http://localhost:8080/HelloWorldAnnotated/greeting.request
In Eclipse, is there a way to run the Javadoc tool against my code?
The answer is yes! While I knew this was possible, I wasn’t exactly sure of how this is done. It turns out using Javadoc from within Eclipse is a piece of cake. Given your Eclipse IDE is already configured to use the tools from a JDK, chances are good that it is already setup to generate Javadocs for your code with a simple menu selection. In Eclipse, look for the Project menu option on the Eclipse menu bar. Select Generate Javadoc… from the Project pull-down menu.
This should cause the Generate Javadoc window to open where you can specify what members should be included (private up to public) and where the documents generated should be put. If the JDK’s bin folder and/or the javadoc.exe tool can’t be found, the same window allows you to point Eclipse to a valid Javadoc generating tool and configure it per your needs.
Once the Javadocs are created, the documents are used by Eclipse to produce hovers over the classes, methods, variables, etc.
This should cause the Generate Javadoc window to open where you can specify what members should be included (private up to public) and where the documents generated should be put. If the JDK’s bin folder and/or the javadoc.exe tool can’t be found, the same window allows you to point Eclipse to a valid Javadoc generating tool and configure it per your needs.
Once the Javadocs are created, the documents are used by Eclipse to produce hovers over the classes, methods, variables, etc.
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