Patterns: Implementing Self-Service in an SOA Environment

152 Patterns: Implementing Self-Service in an SOA Environment

򐂰 Promotes the ability to drop common information on multiple pages, such as

displaying the current weather information and current stock price on all the

pages of the Web application.

A disadvantage of formatter beans is that some of the display page functionality

that is best expressed in a JSP is now moved into Java code.

7.2.5 Command bean design pattern

The business logic part of a Web application must address a wide range of

potential requirements, including transactional integrity, application data access,

workflow support, and integration of new and legacy applications. To achieve

this, business logic components may use various protocols, including JDBC,

JNDI, IIOP, RMI, Web services, JCA, JMS, and so on to communicate with

enterprise applications, enterprise data sources, and external applications. The

Model is not only responsible for implementing the business logic, but also for

hiding the details of the data and application access protocols. To simplify the

implementation of the Model, we can implement one business logic bean per

task. We call such beans

command beans.

Command beans can be defined as JavaBeans that provide a standard way to

invoke business logic. The following are the key characteristics of command

beans:

򐂰 Each command bean corresponds to a single business logic task, such as a

query or an update task.

򐂰 All command beans inherit from a single command interface. In essence, they

implement the command interface.

򐂰 The inherited command bean defines business domain-specific properties

such as account numbers.

򐂰 Command execution results are stored as properties of a command bean.

Therefore, command beans also act as result beans.

򐂰 Commands have a simple, uniform usage pattern:

a. Create an instance of the command bean.

b. Initialize the bean by setting its properties.

c. Cause the bean to execute its action by calling one of its methods.

d. Access the results of command execution by inspecting its properties.

e. Discard the command object.

򐂰 Commands can be serialized.

Figure 7-5 on page 153 shows how such a command bean interacts with the

other components of the Web application.