A program of this type is usually embedded into the application server and run automatically the first time a JSP is accessed, but pages may also be precompiled for better performance, or compiled as a part of the build process to test for errors. For example, the common directive may instead be written as a tag, and tag libraries are imported using XML namespaces, instead of the usual tag.Ī JavaServer Pages compiler is a program that parses JSPs, and transforms them into executable Java Servlets. Since the usual JSP syntax is not valid in XML, a developer must use alternative tags provided by JSP. jspx file extension, which usually causes the application server to validate the XML syntax. Such JSP files commonly use the alternative. JSP pages may also be written in fully valid XML syntax. One such library is the JSTL, with support for common tasks such as iteration and conditionals (the equivalent of "for" and "if" statements in Java). Additionally, the technology allows for the creation of custom JSP tag libraries that act as extensions to the standard JSP syntax. The JSP syntax add additional tags, called JSP actions, to invoke built-in functionality. The value of "variable" in the object "javabean" is $. In JSP 2.1, it was folded into the Unified Expression Language, which is also used in JavaServer Faces. Version 2.0 of the JSP specification added support for the Expression Language (EL), used to access data and functions in Java objects. The output displayed in the user's web browser would be: The following would be a valid for loop in a JSP page:Ĭounting to three: This number is. Likewise, content inside a loop construct may appear multiple times in the output, depending upon how many times the loop body runs. Content inside an if block will only appear in the output when the if condition evaluates to true.
This allows code to be intermingled and can result in poor programming practices.Ĭontent that falls inside a split block of Java code (spanning multiple scriptlets) is subject to that code. For example, any Java if/for/while blocks opened in one scriptlet must be correctly closed in a later scriptlet for the page to successfully compile. It can straddle markup content, provided that the page as a whole is syntactically correct. Java code is not required to be complete or self-contained within a single scriptlet block. Other common delimiters include for expressions, where the scriptlet and delimiters are replaced with the result of evaluating the expression, and directives, denoted with. A scriptlet is a fragment of Java code that runs when the user requests the page. The most basic is, which encloses a JSP scriptlet. JSP pages use several delimiters for scripting functions. Wikibooks has a book on the topic of: J2EE Programming/JavaServer Pages
JSP Engine creates these objects during translation phase. The Web container creates JSP implicit objects like request, response, session, application, config, page, pageContext, out and exception. JSPs are usually used to deliver HTML and XML documents, but through the use of OutputStream, they can deliver other types of data as well.
jar or Java program, code must be executed within a Java virtual machine (JVM) that interacts with the server's host operating system to provide an abstract, platform-neutral environment. The compiled pages, as well as any dependent Java libraries, contain Java bytecode rather than machine code. The resulting page is compiled and executed on the server to deliver a document. JSP allows Java code and certain predefined actions to be interleaved with static web markup content, such as HTML. Jakarta Server Pages can be used independently or as the view component of a server-side model–view–controller design, normally with JavaBeans as the model and Java servlets (or a framework such as Apache Struts) as the controller. JSPs are translated into servlets at runtime, therefore JSP is a Servlet each JSP servlet is cached and re-used until the original JSP is modified. Architecturally, JSP may be viewed as a high-level abstraction of Java servlets.