JSP Tutorial - JSP Actions

JSP actions controls the behavior of the underneath servlet engine.

With JSP actions we can dynamically insert a file, reuse JavaBeans components, or forward the user to another page.

The following code is the syntax for the Action element:

<jsp:action_name attribute="value" />

Example

We can use the following JSP actions.

Syntax	Purpose
jsp:include	Includes a file
jsp:useBean	Initialize a JavaBean
jsp:setProperty	Sets the property of a JavaBean
jsp:getProperty	Get the property from a JavaBean
jsp:forward	Forwards the request to another page
jsp:plugin	Generates an OBJECT or EMBED tag for the Java plugin
jsp:element	Defines XML elements dynamically.
jsp:attribute	Defines XML element's attribute.
jsp:body	Defines XML element's body.
jsp:text	Write template text in JSP pages and documents.

Common Attributes in JSP Actions

There are two common attributes for all Action elements: the id attribute and the scope attribute.

Id attribute uniquely identifies the Action element. We can use the id to reference the action in the JSP page.

Scope attribute identifies the lifecycle of the Action element. The scope attribute has four possible values:

page
request
session
application

jsp:include Action

jsp:include Action inserts files into the JSP pages. The syntax is listed as follows:

<jsp:include page="relative URL" flush="true" />

The include directive includes a file at the time the JSP page is translated into a servlet, while jsp:include action inserts the file at the time the page is requested.

The following table lists the attributes associated with include action.

Attribute	Description
page	The relative URL of the page to be included.
flush	The boolean attribute determines whether the included resource should have its buffer flushed before including.

The following code shows how to use include action.

Here is the data.jsp.

<p>
   Today's date: <%= (new java.util.Date()).toLocaleString()%>
</p>

Here is the content of main.jsp file:

<html>
<body>
<jsp:include page="date.jsp" flush="true" />
</body>
</html>

jsp:useBean Action

The useBean action first searches for an existing object using the id and scope attributes. If an object is not found, it then will create the specified object.

The simplest way to load a bean is as follows:

<jsp:useBean id="name" class="java.lang.String" />

<jsp:useBean id="yourName" class="com.yourCom.YourClassName" />

Once a bean is loaded, we can use jsp:setProperty and jsp:getProperty actions to modify and retrieve bean properties.

The following table list attributes associated with useBean action.

Attribute	Description
class	Defines the full package name of the bean.
type	Specifies the type of the variable.
beanName	Named the loaded bean.

jsp:setProperty Action

The setProperty action sets the properties of a Bean.

We can use jsp:setProperty after outside of a jsp:useBean element as follows.

<jsp:useBean id="myName" ... />
<jsp:setProperty name="myName" property="someProperty" .../>

Or we can include jsp:setProperty inside the body of a jsp:useBean element as follows.

<jsp:useBean id="myName" ... >
    ...
    <jsp:setProperty name="myName" property="someProperty" .../>
</jsp:useBean>

In the code above, the jsp:setProperty is executed only if a new object was instantiated, not if an existing one was found.

The following table lists the attributes associated with setProperty action.

Attribute	Description
name	The name of the bean whose property will be set.
property	Property to set. A value of "*" means that all request parameters whose names match bean property names will be passed to the appropriate setter methods.
value	Value to set to the property.
param	The param attribute is the name of the request parameter.

jsp:getProperty Action

The getProperty action retrieves the value of a given property and converts it to a string, and then inserts it into the output.

The getProperty action has two attributes listed as follows:

<jsp:useBean id="myName" ... />
...
<jsp:getProperty name="myName" property="someProperty" .../>

Following is the list of required attributes associated with getProperty action.

Attribute	Description
name	The name of the Bean which must have been previously defined.
property	The name of the Bean property.

Example for userBean, set/get Property

Create a JavaBean as follows.

package action;
 
public class TestBean {
   private String message = "No message specified";
 
   public String getMessage() {
      return(message);
   }
   public void setMessage(String message) {
      this.message = message;
   }
}

Compile above code to TestBean.class file and copy TestBean.class to C:\apache-tomcat\webapps\WEB-INF\classes\action folder.

Save the following code to hellow.jsp file.

<html>
<body>
<jsp:useBean id="test" class="action.TestBean" />
<jsp:setProperty name="test" 
                    property="message" 
                    value="Hello JSP..." />
<jsp:getProperty name="test" property="message" />
</body>
</html>

The jsp:forward Action

The forward action forwards the request to another a static page, or another JSP page, or a Java Servlet.

The simple syntax of this action is as follows:

<jsp:forward page="relativeURL | <%= expression %>" />

The following table lists the required attributes for forward action.

Attribute	Description
page	Relative URL for another resource.

The following code shows how to use the forward action.

The date.jsp file:

<p>
   Today's date: <%= (new java.util.Date()).toLocaleString()%>
</p>

Here is the main.jsp file:

<html>
<body>
<jsp:forward page="date.jsp" />
</body>
</html>

The jsp:plugin Action

The plugin action can insert Java applet, wrapped in the <object> or <embed> tags, into a JSP page.

The following code lists the typical syntax of using plugin action.

<jsp:plugin type="applet" codebase="dirname" code="MyApplet.class"
                           width="60" height="80">
   <jsp:param name="fontcolor" value="red" />
   <jsp:param name="background" value="black" />
 
   <jsp:fallback>
      Unable to initialize Java Plugin
   </jsp:fallback>
 
</jsp:plugin>

The jsp:body Action

The <jsp:element>, <jsp:attribute> and <jsp:body> actions defines XML elements dynamically.

The following code shows how to define XML elements dynamically.

<%@page language="java" contentType="text/html"%>
<html xmlns="http://www.w3c.org/1999/xhtml"
      xmlns:jsp="http://java.sun.com/JSP/Page">
<body>
    <jsp:element name="xmlElement">
    <jsp:attribute name="xmlElementAttr">
       Value
    </jsp:attribute>
    <jsp:body>
       Body
    </jsp:body>
    </jsp:element>
</body>
</html>