DAO

DAO(Data Access Object)- main aim is to interact with data machines

• Do persistence operations
• Interact with rdbms, ldap, nosql or xml
• Interface between Business & data machine for simple data access operations
• We can implement DAO using
• jdbc from sun
• jax-b, jax-p parsers for xml files
• ORM tools to access data from rdbms database
• EJB
• JPA
• Hybernate
• ibates
• OGM to interact with nosql
• Spring-jdbc for rdbms machines
• Spring-orm for rdbms machines
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For implementing DAOs we should follow interface implementation pattern

• Standard way of creating DAO
• Create a modal with fields/structure same as DB table. Add getters/setters
• Create DAO interface with all the required methods(signatures and return values). eg: update, delete, findByName, findAll
• Create DAOImpl1 implementing all the methods of DAO interface in previous step using JDBC 
• in side the method, get the connection from pool, do operation, and release the connection to pool
• 
  

DataSource is interface given by Sun, for implementing connection pool. Similarly DriverManagerDataSource is given by Spring
WeblogicDataSource by Weblogic
BasicDataSource by Apache

Sample code to create connection pool:
BasicDataSource bds=new BasicDataSource();  //pool reference.
bds.setDriverClassName(driver);
bds.url(dburl);
bds.setUsername(user);
bds.setPassword(pass);
bds.setMaxActiveConnections(20);
bds.setMinIdle(5);
bds.setWaitTime(1000*5);

bds.getConnection() -> To get a connection object


Pool is maintained using map objects(freeMap and consumed map). When user closes a connection, it is moved from consumed map to freemap


http://theblasfrompas.blogspot.in/2007/10/using-dao-j2ee-design-pattern-with-adf.html