Author: ybwen
The current enterprise application has been transferred from 2-Tier towards 3-Tier structures, and developers have many different ways to distribute applications and data to users. JSP API is part of J2EE, which provides a simple but powerful mechanism to create a variety of applications for Web and Java developers.
JSP provides two important capabilities to developers: 1. It provides mechanisms to access remote data such as EJB, RMI, JDBC. Second, it allows developers to achieve maximum code reuse and flexibility from the logic of the performance from the performance. Separation of logic and performance is a major advantage that transcends other web application structures.
In this article, I will have an overall description of JSP technology, of course, there will be some examples to demonstrate the advantages of JSP.
First, how JSP is executed
To support JSP, the web server must have a corresponding configuration. The popular web server supported by JSP is: WebSphere, JWEBServer, JSWDK, JRUN, TOMCAT, and more.
When the web server receives a request for the ".jsp" page, it triggers the JSP engine. The JSP engine first checks the JSP file is new or modified, and the file will be translated and compiled with the files. Translation is the core of how JSP works: The JSP engine takes a JSP file to convert it to Java servlet. Then use the standard JVA compiler to compile the servlet, and perform the Java Servlet using the standard API. This translation step is also a slow reason why JSP is slow.
Write a JSP
An example of a JSP is as follows:
<% @ page language = "java" info = "form processing page"%>
HTML
Body
<%! String cities [], month;%>
Pthe Cities SELECTED ARE:
/ P
<%
CITIES = Request.getParameterValues ("City");
Month = Request.getParameter ("MONTH");
IF (citive! = null) {
%>
UL
<%
For (int i = 0; i %> Li <% = CITIES%> <% } %> / UL <% } Else { %> Pnone selected. / P <% } %> Br Pand the successmed month is: B <% = MONTH%> / B / P / body / html The JSP tag allows the Java code to be embedded directly in HTML, as long as this page is requested. The JSP label has the following types: Label Description JSP 1.0 syntax Comment allows inline document comments HTML Comment: <- Comment -> JSP Comment: % - Comment -% Directive provides an instruction to the JSP engine when the page is translated Expression contains variables or constants, which will be calculated when the page is requested The Scriptlet contains a code snippet that will be executed when the page is requested. JSP executes JSP specific functions when the page is requested Comments. There are two types of comments in JSP. Standard HTML Comment --comment - it can be sent to the client browser. JSP comment % - Comment -% it does not appear in HTML. Directive: When the JSP page is translated into servlet, it indicates JSP engine processing. Declarations: Define variables in an expression or script segment. Expressions: Using an expression, you can dynamically calculate the value inserted into the JSP page. ScriptleTs: embed Java code blocks in the page. JSP: Based on normal label library syntax. Equal form of simple FORM processing Form.jsp is a simple JSP page that is used to process the request for the HTML table. Form.html is a typical HTML Form The source file of form.html is as follows: HTML Body
Shenzhen
Br
beijing
Br
Shanghai
Br
GuangzhouGdong
Br
Br
january
Br
june
Br
july
Br
September
Br
Br
/ form
/ body
/ html
The value of the control in the table can be accessed via the Request object, which is an instance of javax.servlet.ServletRequest (but usually using a more detailed javax.servlet.http.httpservletRequest). The JSP generated code is performed only a standard servlet's service () method, which has two parameters Request to the response object.
Use JavaBeans in JSP pages
Feedback.jsp is another example of processing for Form, except that JavaBean: Mailbean.java is used in JSP. If you are not familiar with JavaBeans, JavaBean is a Java component with properties, methods, events. Feedback.html is HTML for requesting feedback.jsp. The feedback.jsp source code is as follows:
HTML
Title
Results of sending the message
/ Title
Body
<%
Boolean Success = mail.sendMessage ();
IF (Success) {
%>
PYOUR Message Has Been Sent!
/ P
PTHANKS.
/ P
<%
}
Else {
%>
Pyour message was not Sent for Some REAASON.
/ P
Pplease Go Back and Try Again
/ P
<%
}
%>
/ body
/ html
The feedback.html source code is as follows:
HTML
HEAD
Titleemail Feedback Form
/ Title
/ HEAD
Body
