THE COMPLETE REFERENCE JSP 2.0 PDF
JSP: The Complete Reference 2 Evolution of the Web Application 5. 3 Overview of the Hypertext Transfer Protocol (HTTP) JSP complete ecogenenergy.info - Ebook download as PDF File .pdf), Text File .txt) or read book 2 and and 1. respectively.2 and JSP ecogenenergy.info2 specifications We want to thank the community that implemented the reference implementation, and .. files that contain complete JSP pages, or included segments of pages.
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Luckily, when using the EL in template text, these quoting issues rarely raise their head.
Section 4 Introducing Scoped Variables Fixed values are all well and good, but the true strength of the EL lies in expressing dynamic values. These values can be generated from a number of sources, but are always represented by scoped variables. The concept of a variable should be familiar: a named element that represents a dynamic value that can be assigned to it.
But the concept of the JSP scopes may be new. These scopes define the order in which variable names are resolved, the lifetime of the variable, and its purview.
The scopes, in their default search order, are: page, request, session and application. In Java code, these scoped variables are created by the setAttribute method of their respective Java classes. Lifetime of the application context. Scoped variables can be created in many places, but a very common scenario is for the page controller servlet to create scoped variables in request scope, then forward to a JSP page in order to display that data. For example: This statement creates a request-scoped variable named greeting with the string value Hi there!.
Now let's see how we can use that variable in a JSP.
Application scope is a very handy place to store information that needs to be made available to all resources within a web application. It's easy to establish such data whenever a web application starts up by doing so in context listener. A context listener is simply a Java class that implements the javax.
ServletContextListener interface, and is declared as a listener in the deployment descriptor web. Methods in such a class are invoked whenever a web application is put into and taken out of service, making it an ideal choice for application setup and tear down. And best of all, any scoped variables placed in application scope are available to any EL expression in any JSP in the application!
Section 5 Referencing Simple Values The example code in the previous section created a scoped variable named greeting that contains a simple text value. Regardless of what kind of value a scoped variable contains, it can be referenced in an EL expression simply by naming it.
Scoped variables can be referenced anywhere in an EL expression. Let's say that the scoped variables a and b contain numeric values.
Regardless of what type of values are referenced, the final evaluated result is always converted to its string equivalent before being emitted. So if the result is a Java object whose class has no explicit toString method defined, you might end with goop like the following in the output: org. MyBean afd This can be rectified by making sure that the class in this case, MyBean has an appropriate toString method defined.
Section 6 Grabbing JavaBean Properties While strings and numbers are useful for representing scalar values, more frequently, complex objects in the form of JavaBeans are what we have to deal with, so the EL is specifically designed to make it easy to access the properties of JavaBeans.
For example, imagine a JavaBean of class Person that has properties such as: firstName, lastName, address, and title.
Java Server-Side Programming
These would be represented in the Java class respectively with the accessor methods: getFirstName , getLastName , getAddress and getTitle. If an instance of this class were to be created as a scoped variable named person, we could use the EL's property operator to reference the property values. This operator has two forms; the simplest and most commonly-used form is the dot period character.
This operator can be chained. Imagine that the address property is itself a JavaBean whose class defines a number of properties, one of which is city. Scoped variables that represent classes which do not conform to the JavaBean rules are generally much less useful as EL targets. Servlet servlet, javax. ServletRequest request, javax. ServletResponse response, java. In a servlet, you need to use out.
Pieces of Java codes written by programmer are embedded into the HTML file to perform the business logic. The presentation and business logic can be cleanly separated. This example displays a form with checkboxes, and echos your selections. The default "action" is the current page i. The JSP scriptlet checks if the query parameter "author" exists. For the first request, "author" parameter is absent.
JSP Tutorial & Learning materials
Once the user fills in and submits the form, "author" will be present in the HTTP request. The values are echoed back to the client in an unordered list. The Java expression will be placed inside a out. Hence, the expression will be evaluated and resultant value printed out as part of the response message.
Any valid Java expression can be used. There is no semi-colon at the end of the expression.
Date ; out. The Java codes must be syntactically correct, with Java statements terminated by a semi-colon. That is, scriptlets are safe and secure!
JSP 2.0: The Complete Reference
These information will be written to the response message's header. The default is "true". Setting to "false" could reduce the server's load, if session tracking is not needed in your application. You can use include directive to include navigation bar, copyright statement, logo, etc. You can use the taglib directive to tell Tomcat what libraries to load and where they are.
A JSP action may contain sub-action. The syntax is as follows.
JavaServer Pages (JSP) (1.2 and 2.0)
Tomcat clears the output buffer upon executing a forward action. It does not have public variables.
It is defined in a named package. It can not be kept in the default no-name package.
For a private variable xxx, there is a public getter getXxx or isXxx for boolean and a public setter setXxx. It implements Serializable interface, so that its state can be stored and retrieved to and from external storage, for persistent.
The attribute scope specifies the scope of this bean: page: default, stored in PageContext, available to this page only. Simple type conversion from String will be carried out. UserBean called "user". UserBean to the value of the request parameter "username" i. UserBean i.Then the first scriptlet is simply copied to the servlet: Enumeration Returns an Enumeration of the getAttributeNames names of all attributes in this request. Client-side browser applications applets have encountered limitations in three areas: The chapter presents several examples of Web browsers and servers using this language to communicate.
This distinction is important to understand because it affects the context in which the code operates. To maintain a reference to the servlet context.
The value 1 means reload every second. String getProtocol Returns the name and version of the protocol used by this request. Where the include directive was similar to the C language include preprocessor directive. We'll start by looking at the arithmetic operators.