JDBC in J2EE

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JDBC in J2EE

• Connection to Cloudscape database using JDBC
• J2EE Platform services and architecture
• Enterprise JavaBeans (EJB)
• Session Beans vs. Entity Beans
• EJB access to databases using JDBC
• Database connection
• Persistence management (Entity Bean e.g.)
• Transaction management (Session Bean e.g.)

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J2EE Services

• HTTP - enables Web browsers to access servlets
  and JavaServer PagesTM (JSP) files
• EJB - allows clients to invoke methods on
  enterprise beans
• Authentication - enforces security by requiring
  users to log in
• Naming and Directory - allows programs to locate
  services and components through the Java Naming
  and Directory InterfaceTM (JNDI) API

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J2EE Architecture
Ref. JavaTM 2 Enterprise Edition Developer's
Guide, Figure 1-2
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Enterprise JavaBeans (EJB)

• Server-side Java components
• Contain the business logic of enterprise
  application
• Support database access
• Transactional
• Multi-user secure
• Managed by the EJB container
• Prohibited from a set of operations

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Session Bean vs. Entity Bean
Ref. JavaTM 2 Enterprise Edition Developer's
Guide, Table 1-1
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EJB Access to Databases Using JDBC API
J2EE uses JDBC 2.0 (java.sql) and JDBC 2.0
Optional package (javax.sql)

• Making a connection to database
• Should not hardcode the actual name (URL) of the
  database in EJB
• Should refer to the database with a logical name
• Use a JNDI lookup when obtaining the database
  connection.
• Users and password not needed for the Cloudscape
  bundled with J2EE

• Driver and Data source properties
• set in J2EE default.properties file
• jdbc.driversCOM.cloudscape.core.RmiJdbcDriver
• jdbc.datasourcesjdbc/Cloudscapejdbccloudscaper
  miCloudscapeDB createtrue

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Making a connection to database example
1. Specify the logical database name. private
String dbName "javacomp/env/jdbc/AccountDB" 2
. Obtain the DataSource associated with the
logical name. InitialContext ic new
InitialContext() DataSource ds
(DataSource) ic.lookup(dbName) 3. Get the
Connection from the DataSource. Connection
con ds.getConnection()
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Specifying JNDI name for deployment Step 1 Enter
the code name
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Step 2 Map the coded name to the JNDI name
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Persistence Management

• Container-Managed Persistence
• Entity bean code does not contain database access
  calls.
• The EJB container generates the SQL statements.
• Bean-Managed Persistence
• Entity bean code contains the database access
  calls (SQLs) (i.e. you write the code!)

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Container Managed example Product entity bean
ProductEJB.java ProductHome.java Product.java Pro
ductClient.java
Bean Managed example Account entity bean
AccountEJB.java AccountHome.java Account.java Acc
ountClient.java
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Transaction Management
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Container-Managed Transactions

• Description
• Code does not include statements that begin and
  end the transaction
• Immediately before an EJB method starts -
  transaction begins
• Just before the method exits - commits
• Each method can be associated with a single
  transaction
• Prohibited methods, e.g.
• commit, setAutoCommit, and rollback methods of
  java.sql.Connection
• Limitation
• When a method is executing, it can be associated
  with either a single transaction or no
  transaction at all

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Bean Managed Transaction

• Description
• Session bean code invokes methods that mark the
  boundaries of the transaction - setAutoCommit()
  commit() rollback()
• An entity bean may not have bean-managed
  transactions

public void ship (String productId, String
orderId, int quantity) try
con.setAutoCommit(false)
updateOrderItem(productId, orderId)
updateInventory(productId, quantity)
con.commit() catch (Exception ex)
try con.rollback()
throw new EJBException("Transaction
failed " ex.getMessage()) catch
(SQLException sqx) throw new
EJBException("Rollback failed "
sqx.getMessage())
Ref. JavaTM 2 Enterprise Edition Developer's
Guide, JDBC Transaction
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Resouces

• JavaTM 2 SDK, Enterprise Edition Technical
  Documentation
• JavaTM 2 Enterprise Edition Developer's Guide
• http//java.sun.com/j2ee/j2sdkee/
• http//archives.java.sun.com/archives/j2ee-interes
  t.html
• Developing Enterprise Applications with the
  JavaTM 2 Platform Enterprise Edition
  http//java.sun.com/j2ee/blueprints/
• http//www.cloudscape.com