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JSP与Servlet的分工与联系
1、JSP与Servlet的分工
Servlet
负责处理业务并得到处理结果--------------------------------------厨师负责做菜，做好交给传菜员
JSP
不负责处理业务，主要负责将Servlet的处理结果写入到响应体中--------传菜员负责传菜给响应体
2、Servlet与JSP之间的关系
Servlet工作完毕后，通过Tomcat调用Jsp
request.getRequestDispatcher("/目标JSP文件").forward(request,response);
3、Servlet与Jsp二者之间如何实现数据共享？
Servlet将【处理结果】放到【请求作用域对象】中
request.setAttributes("处理结果");
Jsp在运行的时候从【请求作用域对象】得到处理结果并把它放到【响应体】中
request.getRequestDispatcher("/目标JSP文件").forward(request,response);
JSP文件运行原理
HTTP服务器调用JSP文件步骤
'servlet规范中说到'
'只有servlet接口的实现类，才能被浏览器调用，但是JSP文件是怎么调用的呢？'
1、Http服务器将JSP文件内容编辑为一个'Servlet接口实现类(.java)'
2、Http服务器将Servlet接口实现类【编译】为一个class文件(.class)
3、Http服务器负责创建这个class文件的实例对象————即Servlet实例对象
4、HTTP服务器通过该Servlet实例对象调用'_jspServices方法'，将jsp文件内容写入到响应体中
Http服务器【编辑】和【编译】JSP文件的位置
在
C:\Users\尽欢.IntelliJIdea2018.3\system\tomcat\Unnamed_JSP教程\work\Catalina\localhost\myWeb\org\apache\jsp
这个文件夹中
实例
<%--
Created by IntelliJ IDEA.
User: 尽欢
Date: 2021/11/18
Time: 17:08
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%--
第一部分
纯文本
--%>
Hello world
<br>
<%--
第二部分
含有java命令
--%>
<%
int num1 = 10;
int num2 = 20;
%>
num1 + num2的值是：<%=num1+num2%><br>
<%--
第三部分
拆分的java语句（检验是否一个JSP文件中所有的<%%>中的语句是一个整体
--%>
<%
for(int i = 0;i < 10;i++){
%>
<br>
<font size="12">i的值是<%=i%></font><br>
<%
}
%>
编译后的代码
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/9.0.30
* Generated at: 2021-11-18 09:20:19 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 check_jsp extends org.apache.jasper.runtime.HttpJspBase
//这个java类check_jsp继承了org.apache.jasper.runtime.HttpJspBase
//而org.apache.jasper.runtime.HttpJspBase的父类实现了Servlet接口，所以是一个货真价实的Servlet接口实现类
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() {
}
/*
重点
_jspServices方法
*/
public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
//这个方法中的参数，就是Servlet在调用JSP文件的时候传进来的response和request
//request.getRequestDispatcher("/目标JSP文件").forward(request,response);
throws java.io.IOException, javax.servlet.ServletException {
//判断请求方式
if (!javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
final java.lang.String _jspx_method = request.getMethod();
if ("OPTIONS".equals(_jspx_method)) {
response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
return;
}
if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method)) {
response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
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;charset=UTF-8");
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;
//对应的文本信息
out.write("\r\n");
out.write("\r\n");
out.write("\r\n");
out.write("Hello world\r\n");
out.write("<br>\r\n");
out.write('\r');
out.write('\n');
//java代码
int num1 = 10;
int num2 = 20;
out.write("\r\n");
out.write("num1 + num2的值是：");
out.print(num1+num2);
out.write("<br>\r\n");
out.write("\r\n");
out.write('\r');
out.write('\n');
//检验完整性，都是通过out.write()和out.print()来写的
for(int i = 0;i < 10;i++){
out.write("\r\n");
out.write("<br>\r\n");
out.write("<font size="12">i的值是");
out.print(i);
out.write("</font><br>\r\n");
}
} 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);
}
}
}
