1. Overview of JSP
Disadvantages of Servlet:1. HTML tags appear in the form of strings, and it is very cumbersome to process HTTP response messages;
2. All text and HTML are hard-coded, and minor changes in the presentation layer need to be recompiled;
personal opinion: 1. It is difficult to observe the realization of complex pages;
2. The entire interaction logic is complicated;
3. Changes need to be recompiled.
The emergence of JSP (JavaServer Pages) solves the above two problems
Note : Jsp: Essentially a Servlet
Servlet/jsp container translates jsp into Servlet.
2. JSP annotation
JSP comment: <%-- -->HTML comment: <!- --> : Send to browser for processing
3. JSP implicit object
request javax.servlet.http.HttpServletRequestresponse javax.servlet.http.HttpDervletResponse
out javax.sevlet.jsp.JspWriter
session javax.servlet.http.Httpsession
application javax.servlet.ServletContext
config
pageContext
page
exception
例：request:
<%
String username=request.getParameter("username");
%>
out:
<%
out.println("Buffer size:"+response.getBufferSize());
out.println("Servlet name:"+session.getId());
out.println("Serlvet info:"+application.getServerInfo());
%>
4. Instructions
page:
The <%@page attribute="value1" attribute="value2"%>page directive is a little bit similar to the attribute setting value attribute="value"
page directive common attribute setting:
import : define one or more import and The java type used
session: A value of true will import session management. A
value of false will be the opposite
. info: Returns the result of calling the getServletInfo method of the Servlet class generated by the container.
isErrorPage: identifies this page as an error handling page
contentType : defines the content type of the implicit object response of this page, the default text/html
pageEncoding : defines the character encoding of this page, the default is: ISO-8859-1
language: defines in this page The scripting language type
isELIgnored: Whether to ignore EL expressions when configuring. EL:Expression Language
include command: Include the contents of other files into the current JSP page. A page can contain multiple include directives
<%@include file="*.jspf">
Application: divide the page into modular design
Example: import
5. Script elements
Basic elements:<% %> Java code blocks start with <% and end with %>
Expressions:
<%=expression %>
Expression example: <%=Calendar.getInstance().getTimeInMillis() %>
Declaration:You can declare variables or methods that are used in JSP pages.
<%! %>
example:
<%!
public String getTodayDate(){return new Date().toGMTString();
}
public void jspInit(){
System.out.println("nsjk");
}
public void jspDestroy(){
System.out.println("hcsn");
}
%>注：禁用脚本元素：
<jsp-property-group>
<url-pattren>*.jsp<url-pattern>
<scripting-invalid>true</scripting-invalid>
</jsp-property-group>
6. Action
useBean创建实例：
<jsp:useBean id="name" class="*">
实例赋值setProperty
<jsp:setProperty name="*" property="attributeName" value="SttributeValue">
输出实例值
<jsp:getProperty name="" property="attributeName">
include
<jsp:include page="*.jsp">
<jsp:param name="text" value="how are you?">
</jsp:include>
include directive and include action:
Include directive: Resource introduction occurs when the page is converted (jsp--->servlet), that is, when the jsp container converts the page into a servlet.The action of include: Resource introduction occurs when the page is requested.
Summary: The include action can pass parameters, but the include command cannot pass parameters.
When applying the include command to include a file, because the included file will eventually generate a file, the include file and the included file cannot have variables or methods with the same name.
When applying <jsp:include> include files, since each file is compiled separately, variable and method names do not conflict.
forward: transfer the current page to another page
<jsp:forward page="*.jsp">
<jsp:param name="text" value="Please login"/>
</jsp:forward>
7. Error handling
The page directive isErrorPage attributeidentifies a JSP page as an error handling page
<%@page isErrorPage="true"%>