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JSP Action
tags/Standard Actions
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and 5
Scope4
Using 3
Java Beans2
Standard Action Tags1
Contents
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Know
Standard Action Tags
What Java Beans are
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Be able to
Implement Standard Action Tags and JavaBeans
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Standard Action Tags
Actions may affect the current out stream anduse, modify and/or create objects.
These tags translate into to certain predefined
java code.They are used so that the JSP filedoesn't have too much embedded java code.
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Standard Action Tags The JSP specification includes some actions
that are standardand must be implemented byall conforming JSP containers;
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Java Beans
A Java Bean is a reusable software componentthat can be visually manipulated in builder tools
A java bean is simply a java class that meet thefollowing criteria:
1. The class must be public.
2. The class must have a no-arguments constructor.
3. The class must provide set and get methods toaccess variables.
4. The class should be serializable.
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public class Employee implementsjava.io.Serializable {
private String empno;private String name;public Employee(){}public void setEmpno(String empno){
this.empno=empno;}public void setName(String name){this.name=name;}
public String getEmpno(){return empno;}public String getName(){return name;}}
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Bean -Simple properties
Simple property is a bean property with a single
value whose changes are independent of
changes in any other property.
To add simple properties to a bean, addappropriate getXXXand setXXXmethods (or
isXXXand setXXXmethods for a boolean
property).
Note that for boolean to specify accessor
public boolean isRetired(){ return this.r; }
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Bean-indexed property
An indexed property is an array of properties Individual values
PropertyElementgetPropertyName(int index)
public void setPropertyName(intindex,PropertyElement element)
Entire array
public PropertyElement[]getPropertyName()public voidsetPropertyName(PropertyElement
element[])
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Used to instantiate or create a reference to a Java Class
(Bean) inside a JSP page.
The basic semantic tries to find an existing object usingid and scope.
If the object is not found it will attempt to create theobject using the other attributes.
body
typeSpc :
class=className |
class=className type=typeName |
type=typeName
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id: The name used to identify the object instance in
the specified scopes namespace
The scripting variable name declared andinitialized with that object reference
Is case sensitive and should conform to thecurrent scripting language variable-naming
conventions
The id attribute of a useBean tag is mandatoryand can be an arbitrary string, but must be
unique within any one page
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scope: page, request, session and application
Default is page.
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class: The fully qualified name of the class that defines
the implementation of the object
Name is case sensitive
If the class and beanName attributes are not
specified, the object must be present in the givenscope.
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beanName: The name of a Bean, as expected by the
instantiate() method of the java.beans.Beansclass.
This attribute can accept a request-time attributeexpression as a value.
The beanName attribute can be used to point toa file that contains a serialized bean (theextension .ser is used to indicate a serializedobject). However when using beanName with a
serialized file the .ser extension is not included. A useBean tag can use either class or
beanName but not both. A beanName attributemust always be accompanied by a type attribute.
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type: If specified, it defines the type of the scripting variable
defined. The type is required to be either the class itself, a
superclass of the class, or an interface implementedby the class specified.
The object referenced is required to be of this type,
otherwise a java.lang.ClassCastException occurs atrequest time when the assignment of the objectreferenced to the scripting variable is attempted.
If unspecified, the value is the same as the value ofthe class attribute.
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Using
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Same as the as 1 but returns an Object class.
Translates into:
java.lang.Objectlist=session.getAttribute("list");
if(list==null)
list= new java.util.Vector();
session.setAttribute("list,list);
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Scope
page scope:
the object is available only to this page.
request scope:
the object is now associated with the request.
If the request is forwarded (using
or tag ) to another
JSP, the object is available. This object canbe accessed by invoking getAttribute()
method on request object.
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Scope
session scope:
the object will be available to all JSPs in the
current session.
It is a fatal translation error to attempt to use
session scope when the JSP page so
attempting has declared, via the directive (see later) that it does notparticipate in a session.
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Scope
application scope:
the object will be available in any JSP page in
the same web application. This object can beaccessed by invoking getAttribute() method
on application object.
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tag is used along with tag, to set values of thebean property.
prop_expr
property=property value=value
property=property
property=property param =paramproperty=*
property: name of the bean property. It can also be *. If so, if requestparameters have the same name as the bean property, then the value of therequest parameter is automatically set to the bean property.
value: Value to be set to the property.
param:The name of the request parameter whose value the bean propertywill be set to.
name: is the name of the bean instance which has been created using the tag.
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Places the value of a Bean instance property,converted to a String, into the implicit out object,from which you can display the value as output.
Student java
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..
sr.Student
-name
-reg
+String getName()
+String getReg()
Student.java
+void setReg(String reg)
+void setName(String nm)
stud.setName(request.getParameter(name)
Displays value of reg
stud.setName(request.getParameter(nm)
Student java stud jsp
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Student.java stud.jsp
stud.html
On submitting the form the name
and reg property of the stud beanis automatically set to the values
entered by the user.
If there is no matching request parameter
for a bean property then it remains unset.
You should always make sure that your
beans default constructor sets appropriate
default values.
sr.Student
-name
-reg
+String getName()
+String getReg()
+void setName(String nm)
+void setReg(String reg)
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where c.Cust is a java bean which implementsSerializable interface.
beanName attribute example
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The Web containerwill automatically attempt to converttheString into the type of the bean parameter. This conversionwill work for the following types:
byte or Byte As indicated in java.lang.Byte.valueOf(String) boolean or Boolean As indicated in
java.lang.Boolean.valueOf(String)
char or CharacterAs indicated in String.charAt(0)
double or Double As indicated injava.lang.Double.valueOf(String)
int or IntegerAs indicated in java.lang.Integer.valueOf(String)
float or Float As indicated in java.lang.Float.valueOf(String)
long or Long As indicated in java.lang.Long.valueOf(String)
short of Short As indicated in java.lang.Short.valueOf(String)
Object As if new String(string-literal)
Valid Value Assignments
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Used to provide other tags with additional
information in the form of the name-value pairs.
Used in conjunction with the &
Allows the JSP to transfer the control to another
JSP, servlet or static HTML page. The jsp that forwards the request should not use the
output stream that is used to communicate to theclient prior to forwarding the request.
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Allows static or dynamic resource to be included in the
current JSP page at the request processing time.
Similar to RequestDispatchers include() method.
The argument can be extracted by using
request.getParameter(p1) in servlet/jsp.
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and
1. 1.
2. Done at the request processing
time 2. Done at the translation time.(That is,
the contents of the included file will beincluded in the JSP source at the point
where the tag is defined and therefore
processed by the JSP page
compilation procedure.
3. Both static and dynamic contentcan be included.
3. The included file may contain both
static content and other JSP tags.
E l
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Example:
Forward action test page
Forward action test page
Please enter your username:
and password:input type=submit value=Log in>
forward.html
jsp/4.forward
forward.jsp
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forward.jsp
Forward action test: Loginsuccessful!
(h1>Forward action test: Loginsuccessful!
Welcome,
forward2.jsp
