JAVAWEB:JSP Technology Foundation

Javaweb:jsp Technology Quick Start Introduction

• JSP full name Java Server pages, is a Dynamic Web development technology . It uses JSP tags to insert Java code into the HTML Web page. labels usually end with <% beginning with%> .
• JSP is a Java servlet that is primarily used to implement the user interface portion of a Java Web application . Web developers write JSPs by combining HTML code, XHTML code, XML elements, and embedded JSP operations and commands.
• JSPs get user input data, Access databases, and other data sources through Web Forms, and then dynamically create Web pages .
• JSP tags have a variety of functions, such as access to the database, record user selection information, access to JavaBeans components, etc., but also in different Web pages to pass control information and share information .
• JSP technology is in the Java language as a scripting language, JSP Web page for the entire server-side Java Library unit provides an interface to serve the HTTP application.
• The jsp file suffix is named *.jsp.
• JSP-developed Web applications can be used across platforms and can run on Linux and on Windows.

First JSP page

JSP processing JSP creation process
The following steps show how a Web server uses JSPs to create a Web page:

 
 

  
  
 
   
Just like other normal web pages, your browser sends an HTTP request to the server.
 
   
The WEB server recognizes that this is a request to a JSP Web page and passes the request to the JSP engine. Complete by using a URL or a. jsp file.
 
   
The JSP engine loads the JSP files from the disk and translates them into servlets. This conversion simply transforms all template text into a println () statement and translates all of the JSP elements into Java code.
 
   
The JSP engine compiles the servlet into an executable class and passes the original request to the servlet engine.
 
   
a component of the WEB server invokes the servlet engine and then loads and executes the servlet class. during execution, the Servlet produces an HTML-formatted output that is embedded in the HTTP response and handed over to the WEB server.
 
   
The WEB server returns HTTP response to your browser in the form of a static HTML Web page.
 
   
Eventually, the Web browser handles the dynamically generated HTML page in the HTTP response as if it were working on a static web page.
 
  
 
 
Legend
　　
In a word, JSP and servlet relationship:JSP Web page is another way to write a Servlet without becoming a Java programmer. In addition to the interpretation phase, JSP Web pages can be treated almost as a common Servlet .
JSP life cycle
The key to understanding the underlying functionality of the JSP is to understand the life cycle that they follow. The JSP lifecycle is the entire process from creation to destruction, similar to the servlet life cycle, except that the JSP life cycle also includes compiling the JSP file into a servlet.
Here are a few stages of the JSP life cycle:
Compile phase
When the browser requests a JSP page, the JSP engine first checks to see if the file needs to be compiled. If the file has not been compiled, or has been changed since the last compilation, compile the JSP file.
The compilation process consists of three steps:

 
 

  
  
 
   
Parse the JSP file.
 
   
Convert the JSP file to a servlet.
 
   
Compile the servlet.
 
  
 
 
Initialization phase
After the container loads the JSP file, it calls the Jspinit () method before providing any services for the request. If you need to perform a custom JSP initialization task, the Jspinit () method is OK, just like this:
public void Jspinit () {  //Initialize code}
In general, the program is initialized only once, and so is the servlet. Typically, you can initialize a database connection, open a file, and create a query table in the Jspinit () method.
Implementation phase
This phase describes all the interaction of requests in the JSP lifecycle until it is destroyed.
Destruction phase
The destruction phase of the SP life cycle describes everything that happens when a JSP page is removed from the container
JSP Development Basic Syntax
JSP directives
JSP directives are used to set properties related to the entire JSP page, such as the encoding of the Web page and the scripting language .
The syntax format is as follows:
<%@ directive attribute= "value"%>
Directives can have many properties, which exist as key-value pairs and are separated by commas.
Three types of directive tags in JSPs:

 
 
 
  
  
 
   
 
    
instruction
 
    
 Description
 
   
 
   
 
    
<%@ page ...%>
 
    
Define Web page dependency properties such as scripting language, error page, caching requirements, and more
 
   
 
   
 
    
<%@ include ...%>
 
    
Include other files
 
   
 
   
 
    
<%@ taglib ...%>
 
    
Introducing the definition of a tag library
 
   
 
  
 
 
 
JSP Action Element Description
Unlike JSP directive elements,JSP action elements work in the request processing phase . JSP action elements are written in XML syntax. JSP actions can be used to dynamically insert files, reuse JavaBean components, redirect users to additional pages, and generate HTML code for Java plugins. The action element has only one syntax, which conforms to the XML standard:
<jsp:action_name attribute= "Value"/>
Action elements are basically predefined functions, the JSP specification defines a series of standard actions, which are prefixed with JSP, and the standard action elements available are as follows:

 
 
 
  
  
 
   
 
    
Grammar
 
    
Description
 
   
 
   
 
    
Jsp:include
 
    
A file is introduced when the page is requested.
 
   
 
   
 
    
Jsp:usebean
 
    
Find or instantiate a JavaBean.
 
   
 
   
 
    
Jsp:setproperty
 
    
Sets the properties of the JavaBean.
 
   
 
   
 
    
Jsp:getproperty
 
    
Outputs the properties of a JavaBean.
 
   
 
   
 
    
Jsp:forward
 
    
Move the request to a new page.
 
   
 
   
 
    
Jsp:plugin
 
    
Generates an object or embed tag for the Java plug-in based on the browser type.
 
   
 
   
 
    
Jsp:element
 
    
Defining dynamic XML Elements
 
   
 
   
 
    
Jsp:attribute
 
    
Sets the dynamically defined XML element properties.
 
   
 
   
 
    
Jsp:body
 
    
Sets the content of a dynamically defined XML element.
 
   
 
   
 
    
Jsp:text
 
    
Using templates that write text in JSP pages and documents
 
   
 
  
 
 
 
Demonstrate
JSP simple Application Page refresh automatically
This example uses the Setintheader () method to set the flush header to simulate a digital clock:
<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "    pageencoding=" UTF-8 "%><%@ page import=" java.io.*,java.util.* "%>
Click Volume Statistics
<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "    pageencoding=" UTF-8 "%><%@ page import=" java.io.*,java.util.* "%>
Page redirection
<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "    pageencoding=" UTF-8 "%><%@ page import=" java.io.*,java.util.* "%>
　
JAVAWEB:JSP Technology Foundation