JSP Tutorial Objective
- Learn the importance and reason for JSPs.
- Understand the advantages of JSPs over servlets.
- Examine the basics of a JSP file and what the container does with it.
- Explore JSP implicit objects.
- Learn JSP scripting element syntax.
- Understand why JSP comments should be used in place of standard HTML comments.
- Understand the purpose of JSP directives.
- Explore the include and page directives.
JSP is an easier way, compared to servlets, of generating dynamic content for the Web. A JSP provides a more HTML-centric way of creating a Web application. Unlike servlet technology a JSP doesn’t require a Web developer to put HTML code into a Java program. Furthermore, JSP writers don’t need to create or work with XML mappings. Thus, JSPs become an easier way to create a Web page and JSPs are typically used for the presentation layer of a Web application. While JSPs are simpler to create than servlets, they do introduce the developer to a new syntax.
In this chapter, you learn the basic principles of JSPs and how they relate to the underlying servlet architecture. You also become familiar with the JSP scripting elements.
Servlets had advantages over other dynamic Web technology. Servlets are compiled code so they run faster than scripting languages. Servlets stay in memory, as opposed to loading the script for each request, again providing faster execution. A single servlet object is used by many requests as the container threads multiple requests through the object. This allows servlet Web sites to scale very well. Servlets run in a virtual machine and can be added to just about any Web server running on any platform (platform independence). Because servlets run in the virtual machine, they are more secure. A collapse of a servlet does not affect the entire Web site. Servlets, as Java code, allow access to the massive set of Java code libraries.
But servlets also present some challenges. Do you like to code HTML inside of out.println()’s? Can you imagine a graphic artist or HTML expert jumping to be a hardcore Java servlet expert? Working through servlets presents difficulties in development shops where front end developers are not server-side, middleware developers. Do you like configuring web.xml for every new servlet? Most IDE’s help with web. xml changes, but when small quick changes need to be affected in production, this creates problems.
JavaServer Pages (JSP) is a very successful approach to making servlet development easier. JSP was extracted from a very similar technology called JHTML that was part of ATG Dynamo. JSP is like ASP (not only in name) because ASP proved a very easy server-side language for HTMLers to learn. JSP is like ColdFusion because ColdFusion created extra tags that hid the server-side programming from HTML coders.
TEXT NOTE: You may note, up to this point, references to both HTML and XHTML have been used to refer to standard Web pages. XHTML, is a markup language that offers HTML functionality, but also conforms to XML syntax. XHTML is particularly useful today in Web sites that offer more rich inteactive user experiences; such as those using Ajax. Going forward, the text will only refer to HTML for simplicity. Substitute HTML/XHTML whenever the term HTML is used. In fact, the code examples adhere to XHTML standards.
What is a JSP?
JavaServer Pages are an extension to the Java servlet API. To create a JSP just make an HTML file and save it with the .jsp extension. JSPs are stored with the HTML pages of your Web site. JSPs are a mix of HTML and Java code. They allow you to add Java processing to standard HTML Web pages. The Web container takes a JSP and turns it into a servlet, generating and compiling the Java code for you.
What are the advantages of JSPs? JSPs allow layout (HTML) professionals to ignore the compilation, and even the Java code. HTML developers (and Java coders) can utilize Web page development tools to build the pages. JSP provides server-side developers with the full power of the Java programming language in HTML. This Java is not a subset of Java or new scripting language. JSP is built directly on top of the servlet API. So essentially, every time a JSP is run, a servlet is actually executing behind the scenes. Unlike servlets, no configuration of JSPs is required. JSPs are not registered or mapped in the web.xml file.
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