Chapter 7: Making JavaBeans

1
Chapter 7Making JavaBeans
Reference Building J2EE Apps with WebSphere
2
Objectives

• Understand JavaBeans basics
• Properties
• Methods
• Events
• Bean Types
• Building JavaBeans in WSAD

3
What Are JavaBeans?

• Javas software component model specification
• Written in Java platform neutral
• JavaBean Conventions
• Must have a zero-argument constructor
• Used when restoring JavaBean from a file
• Must be serializable
• Implements java.io.Serializable
• Can save JavaBean to a file
• Private instance variables
• Public features (methods, properties, events)

4
JavaBean Property Types

• Reference Page 131 - 133
• Simple
• Use standard getter/setter signatures
• E.g., public String getName()
• Boolean
• Use isltPropertyNamegt for getter method
• E.g., public boolean isValid()
• Indexed
• Represents an array of values
• Use java.util.ArrayList for dynamic arrays

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Simple JavaBean Sample

• WSAD 5.1 can generate getter/setter methods for
  you.
• public class User implements java.io.Serializable
  
• private String name
• public User()
• super()
• public String getName()
• return name
• public void setName(String string)
• name string

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Indexed JavaBean Sample

• public class UserList implements
  java.io.Serializable
• java.util.ArrayList userList
• public UserList()
• super()
• // generated methods
• // get/set entire ArrayList
• public java.util.ArrayList getUserList()
• return userList
• public void setUserList(java.util.ArrayList
  list)
• userList list
• // manually added methods
• // get/set an element of an ArrayList
• public User getUserList(int index)
• return (User) userList.get(index)
• public void setUserList(User aUser, int index)

7
JavaBean Types

• Reference Pages 131 - 140
• GUI Beans
• E.g., Button, TextField, JFrame
• Not the focus of this course
• Invisible Beans
• Used mainly as data holders
• May contain application logic (e.g., validation)
• WSAD Support Can add JavaBeans to JSP

8
Building JavaBeans

• Reference Pages 142 151
• WSAD 5.1 has wizards to build JavaBeans
• Class Wizard
• Remember to implement java.io.Serializable
• Generate Getter/Setter methods
• Refactoring
• Lazy Initialization
• Always return a valid object and not a null
  reference.