拥有servlet的特性和优点(本身就是一个servlet)
直接在HTML中内嵌jsp代码
jsp程序由JSP Engine先将其转换成Servlet代码,接着将他编译成类文件载入执行
只有当客户端第一次请求JSP时,才需要将其转换、编译
优点:
优良的性能
平台无关性:与操作系统、web服务器无关
可扩展性:tag的扩展机制、简化页面开发
三种基本语法:JSP传统语法、JSTL、JSF、其他taglib(如struts)
JSP传统语法:
<%程序代码区 %>
注释:<%-- --%><%// %> <%/* */ %>
4、Directive:编译指令:相当于在编译期间执行的命令
<%@Directive 属性=“属性值” %>
常见Directive:page:指明与JSP的沟通方式举例:errorPage:相当于import语句 ;
<%@page contentType="text/html; charset=UTF-8"%>
<%@page errorPage=“XXX.jsp”%>如果当前页面出错,则显示XXX.jsp页面
<%@page isErrorPage="true/false"%>XXX.jsp要写true
include:将特定的JSP或HTML包含进来再编译运行 <%@include file=“fileURL”%>
限制:不能向fileURL里面传参数
常见的命令:
JSP:include:用于动态包含JSP程序或HTML文件等,除非这个指令被执行到,否则他是不会被Tomcat等JSP Engine编译。
格式:
<jsp:include page="URLSpec" flush="true" />
<jsp:include page="URLSpec" flush="true" >
<jsp:param name="ParamName" value="paramValue"/>
</jsp:include>
jsp:param用来设定include文件时的参数和对应的值
和include编译指令的区别:include编译指令是在jsp程序的转换时期就将file属性指定的程序内容嵌入,然后再编译执行;而include指令在转换期间不会被编译,只有在客户端请求时期如果被执行到才会被动态编译嵌入。include不能带参数,而<jsp:include可以
JSP:forward:用于将一个jsp直接跳转到page所指定的jsp程序或者servlet中处理。
格式:
<jsp:forward page="urlSpec" flush="true"/>
<jsp:forward page="urlSpec">
<jsp:param name="paramName" value="paramValue"/>
</jsp:forward>
jsp:param用来设定参数和对应的值
jsp:useBean:用它可以在JSP中使用定义好的Bean。
Bean的基本要求:必须要有一个不带参数的构造函数,Bean类不允许直接访问实例变量,变量名称必须小写,通过getter和setter来读写变量,并且将对应的变量首字母大写。不要使用裸体类,放到包里面。
<jsp:useBean id="beanName scope="page|request|session|application" class="package.BeanClass type="typeName"/>
<jsp:useBean>
<jsp:setProperty...>
<jsp:getProperty...>
</jsp:useBean>
<jsp:useBean id="aaa" class="bean.CounterBean">
</jsp:useBean>
相当于
<% CounterBean aaa = new CounterBean();
%>
useBean各项参数:
id:对象实例名称
scope:bean的作用范围,默认为page,对整个jsp页面有效
class:bean类名称
type:bean实例类型,可以是本类,父类,或实现的接口,默认本类
scope各项参数的意义:
page:默认,仅涵盖使用JavaBean的页面
request:有效范围限于使用JavaBean的请求
session:有效范围在用户整个连接过程中
application:有效范围涵盖整个程序(网站)
jsp:setProperty
jsp:getProperty
hello world示例:D:\Tomcat 9.0\webapps\LeonTest
<html>
<head>
<title>HelloWorldJSP</title>
</head>
<body>
<%
out.println("HelloWorld!<br/>");
out.println(new java.util.Date());
%>
</body>
</html>
对应生成的servlet:D:\Tomcat 9.0\work\Catalina\localhost\LeonTest\org\apache\jsp
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/9.0.0.M20
* Generated at: 2017-07-31 07:28:59 UTC
* Note: The last modified time of this file was set to
* the last modified time of the source file after
* generation to assist with modification tracking.
*/
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class helloworld_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent,
org.apache.jasper.runtime.JspSourceImports {
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;
private static final java.util.Set<java.lang.String> _jspx_imports_packages;
private static final java.util.Set<java.lang.String> _jspx_imports_classes;
static {
_jspx_imports_packages = new java.util.HashSet<>();
_jspx_imports_packages.add("javax.servlet");
_jspx_imports_packages.add("javax.servlet.http");
_jspx_imports_packages.add("javax.servlet.jsp");
_jspx_imports_classes = null;
}
private volatile javax.el.ExpressionFactory _el_expressionfactory;
private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
return _jspx_dependants;
}
public java.util.Set<java.lang.String> getPackageImports() {
return _jspx_imports_packages;
}
public java.util.Set<java.lang.String> getClassImports() {
return _jspx_imports_classes;
}
public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
if (_el_expressionfactory == null) {
synchronized (this) {
if (_el_expressionfactory == null) {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
}
}
}
return _el_expressionfactory;
}
public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
if (_jsp_instancemanager == null) {
synchronized (this) {
if (_jsp_instancemanager == null) {
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
}
}
return _jsp_instancemanager;
}
public void _jspInit() {
}
public void _jspDestroy() {
}
public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
throws java.io.IOException, javax.servlet.ServletException {
final java.lang.String _jspx_method = request.getMethod();
if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD");
return;
}
final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;
final javax.servlet.ServletContext application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.PageContext _jspx_page_context = null;
try {
response.setContentType("text/html");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("<html>\r\n");
out.write(" <head>\r\n");
out.write(" <title>HelloWorldJSP</title>\r\n");
out.write(" </head>\r\n");
out.write(" <body>\r\n");
out.write(" ");
out.println("HelloWorld!<br/>");
out.println(new java.util.Date());
out.write("\r\n");
out.write(" </body>\r\n");
out.write("</html>");
} catch (java.lang.Throwable t) {
if (!(t instanceof javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
try {
if (response.isCommitted()) {
out.flush();
} else {
out.clearBuffer();
}
} catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}