jsp运行原理：
根据jsp文件创建java文件（servlet），并编译运行
第一次访问时会被翻译成servlet后执行
jsp三个指令：
1.page指令：页面翻译运行的属性的配置(通常使用默认)
language="java" 可以嵌入的语言
contentType="text/html; charset=UTF-8" 设置servlet的response.setContentType内容
pageEncoding="UTF-8" 当前jsp文件的编码
session="true" 默认session可以直接使用
import="java.util.*" 导入java包
errorPage="xxx.jsp" 如果java代码有错，跳转到某个新页面
注意这里的错误不是404错误，而是代码错误，如果要配置404错误跳转的页面，需要在web.xml中配置
isErrorPage="true" 是否是由于错误跳转后的页面
2.include指令：可以将其他的jsp页面包含到另一个jsp页面中
<%@ include file ="地址" %>
3.taglib指令：在jsp页面中引入标签库
<%@taglib uri="标签库地址" prefix="前缀"%>
jsp内置对象：
需要特别强调的2个对象
1.out对象：作用：在客户端页面输出内容
三种方法：
1.<% out.write("hello world");%>
2.<% response.getWriter().write("hello world");%>
3.<%="hello world"%>
本质上后两者都是转化成out对象
1,3写入out缓冲区，2写入response缓冲区
由于tomcat会从response缓冲区获得内容，所以out缓冲区内容会被刷到response缓冲区
于是先输出的是2，但是设置缓冲区（默认8kb）buffer=0kb，则按顺序输出
2.pageContext对象：页面上下文对象
是一个域对象，范围是当前页面
域对象方法setAttribute等和request，session域类似
范围可以设置
???????//使用pageContext向request域存数据 ???????//request.setAttribute("name", "zhangsan"); ???????//pageContext.setAttribute("name", "sunba"); ???????//pageContext.setAttribute("name", "lisi", PageContext.REQUEST_SCOPE);//request域 ???????//pageContext.setAttribute("name", "wangwu", PageContext.SESSION_SCOPE);//session域 ???????//pageContext.setAttribute("name", "tianqi", PageContext.APPLICATION_SCOPE);//application域取出
<%=request.getAttribute("name") %><%=pageContext.getAttribute("name", PageContext.REQUEST_SCOPE)%>特有的方法：findAttribute
<!-- findAttribute会从小到大搜索域的范围中的name --><!-- page域<request域<session域<application域 --><%=pageContext.findAttribute("name") %>获得其他对象
???<% ???????pageContext.getRequest(); ???????pageContext.getOut(); ???%>
静态包含和动态包含：
静态：<%@include file="地址" %>
合成一个页面，再进行翻译成java文件
动态：<jsp:include page="地址"/>
两个jsp文件翻译成java文件，编译运行
运行阶段调用方法include
请求转发：
<jsp:forward page="资源"/>
转发后地址不变
接下来做一个案例：
动态显示商品列表
数据库准备：
CREATE DATABASE web;USE web;CREATE TABLE `product` ( ?`pid` VARCHAR(50) NOT NULL, ?`pname` VARCHAR(50) DEFAULT NULL, ?`market_price` DOUBLE DEFAULT NULL, ?`shop_price` DOUBLE DEFAULT NULL, ?`pimage` VARCHAR(200) DEFAULT NULL, ?`pdate` DATE DEFAULT NULL, ?`is_hot` INT(11) DEFAULT NULL, ?`pdesc` VARCHAR(255) DEFAULT NULL, ?`pflag` INT(11) DEFAULT NULL, ?`cid` VARCHAR(32) DEFAULT NULL, ?PRIMARY KEY (`pid`))
添加多条数据，这里略
对应类：
package domain;public class Product { ???private String pid; ???private String pname; ???private double market_price; ???private double shop_price; ???private String pimage; ???private String pdate; ???private int is_hot; ???private String pdesc; ???private int pflag; ???private String cid; ???public String getPid() { ???????return pid; ???} ???public void setPid(String pid) { ???????this.pid = pid; ???} ???public String getPname() { ???????return pname; ???} ???public void setPname(String pname) { ???????this.pname = pname; ???} ???public double getMarket_price() { ???????return market_price; ???} ???public void setMarket_price(double market_price) { ???????this.market_price = market_price; ???} ???public double getShop_price() { ???????return shop_price; ???} ???public void setShop_price(double shop_price) { ???????this.shop_price = shop_price; ???} ???public String getPimage() { ???????return pimage; ???} ???public void setPimage(String pimage) { ???????this.pimage = pimage; ???} ???public String getPdate() { ???????return pdate; ???} ???public void setPdate(String pdate) { ???????this.pdate = pdate; ???} ???public int getIs_hot() { ???????return is_hot; ???} ???public void setIs_hot(int is_hot) { ???????this.is_hot = is_hot; ???} ???public String getPdesc() { ???????return pdesc; ???} ???public void setPdesc(String pdesc) { ???????this.pdesc = pdesc; ???} ???public int getPflag() { ???????return pflag; ???} ???public void setPflag(int pflag) { ???????this.pflag = pflag; ???} ???public String getCid() { ???????return cid; ???} ???public void setCid(String cid) { ???????this.cid = cid; ???}}servlet：
package servlet;import java.io.IOException;import java.sql.SQLException;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanListHandler;import domain.Product;import utils.DataSourceUtils;public class ProductListServlet extends HttpServlet { ???public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????//准备所有商品数据，存入List ???????QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource()); ???????List<Product> productList = null; ???????String sql = "select * from product"; ???????try { ???????????productList = runner.query(sql, new BeanListHandler<Product>(Product.class)); ???????} catch (SQLException e) { ???????????e.printStackTrace(); ???????} ???????//将数据存到request域，转发给jsp文件 ???????request.setAttribute("productList", productList); ???????request.getRequestDispatcher("/product_list.jsp").forward(request, response); ???????????} ???public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????doGet(request, response); ???}}用到的连接池工具类（注意c3p0-config.xml的配置）：
package utils;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import javax.sql.DataSource;import com.mchange.v2.c3p0.ComboPooledDataSource;public class DataSourceUtils { ???private static DataSource dataSource = new ComboPooledDataSource(); ???private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); ???// 直接可以获取一个连接池 ???public static DataSource getDataSource() { ???????return dataSource; ???} ???// 获取连接对象 ???public static Connection getConnection() throws SQLException { ???????Connection con = tl.get(); ???????if (con == null) { ???????????con = dataSource.getConnection(); ???????????tl.set(con); ???????} ???????return con; ???} ???// 开启事务 ???public static void startTransaction() throws SQLException { ???????Connection con = getConnection(); ???????if (con != null) { ???????????con.setAutoCommit(false); ???????} ???} ???// 事务回滚 ???public static void rollback() throws SQLException { ???????Connection con = getConnection(); ???????if (con != null) { ???????????con.rollback(); ???????} ???} ???// 提交并且 关闭资源及从ThreadLocall中释放 ???public static void commitAndRelease() throws SQLException { ???????Connection con = getConnection(); ???????if (con != null) { ???????????con.commit(); // 事务提交 ???????????con.close();// 关闭资源 ???????????tl.remove();// 从线程绑定中移除 ???????} ???} ???// 关闭资源方法 ???public static void closeConnection() throws SQLException { ???????Connection con = getConnection(); ???????if (con != null) { ???????????con.close(); ???????} ???} ???public static void closeStatement(Statement st) throws SQLException { ???????if (st != null) { ???????????st.close(); ???????} ???} ???public static void closeResultSet(ResultSet rs) throws SQLException { ???????if (rs != null) { ???????????rs.close(); ???????} ???}}jsp页面中的内容：
<%@ page language="java" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%><%@ page import="java.util.*" %><%@ page import="domain.*" %>............ ???????<% ???????????????????????????????//获得集合List<Product> ???????????List<Product> productList = (List<Product>)request.getAttribute("productList"); ???????????if(productList!=null){ ???????????????for(Product product : productList){ ???????????????????out.write("<div class=‘col-md-2‘ style=‘height:250px‘>"); ???????????????????out.write("<a href=‘product_info.htm‘>"); ???????????????????out.write("<img src=‘"+product.getPimage()+"‘ width=‘170‘ height=‘170‘ style=‘display: inline-block;‘>"); ???????????????????out.write("</a>"); ???????????????????out.write("<p><a href=‘product_info.html‘ style=‘color: green‘>"+product.getPname()+"</a></p>"); ???????????????????out.write("<p><font color=‘#FF0000‘>商城价：¥"+product.getShop_price()+"</font></p>"); ???????????????????out.write("</div>"); ???????????????} ???????????} ???????????????????????%>web.xml:
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5"> ?<display-name>WEB7</display-name> ?<welcome-file-list> ???<welcome-file>index.html</welcome-file> ???<welcome-file>index.htm</welcome-file> ???<welcome-file>index.jsp</welcome-file> ???<welcome-file>default.html</welcome-file> ???<welcome-file>default.htm</welcome-file> ???<welcome-file>default.jsp</welcome-file> ?</welcome-file-list> ?<servlet> ???<description></description> ???<display-name>ProductListServlet</display-name> ???<servlet-name>ProductListServlet</servlet-name> ???<servlet-class>servlet.ProductListServlet</servlet-class> ?</servlet> ?<servlet-mapping> ???<servlet-name>ProductListServlet</servlet-name> ???<url-pattern>/productList</url-pattern> ?</servlet-mapping></web-app>
这里运用了简单的MVC三层架构
注意：访问/product_list.jsp将会没有内容
访问/productList查询数据库转发后才会有内容
Servlet案例7：jsp技术及案例
原文地址：https://www.cnblogs.com/xuyiqing/p/8421256.html