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JSP学习1-概述

2017-12-07 21:12 183 查看

1、为什么需要使用jsp

JSP是简化Servlet编写的一种技术，它将 Java代码和 HTML代码混合在同一个文件中编写，只对网页中的要动态产生的内容采用Java代码来编写，而对固定不变的静态内容采用普通静态 HTML页面的方式编写。

2、JSP-hello world

新建一个JSP页面，在body节点内的<% %>即可编写Java代码。

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ page import="java.util.*" %>//导入包
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<%
Date date = new Date();
System.out.println(date);
%>
</body>
</html>

JSP可以放置在WEB应用程序中的除了web-inf及其子目录外的其他任何目录中，JSP页面的访问路径与普通HTML页面的访问路径形式也完全一样。

3、JSP的运行原理：JSP本质上是一个servlet

每个jsp页面在第一次被访问时，jsp引擎将它翻译成一个servlet源程序，接着再把这个servlet源程序编译成servlet的class类文件，然后再由web容器（servlet引擎）像调用普通servlet程序一样的方式来装载和解释执行这个由jsp页面翻译成的servlet程序。

-------如何找到被引擎解释成的servlet的java文件，在Windows电脑工程目录下大致为这个路径
D:\project\javaee\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\work\Catalina\localhost\JSPlearn\org\apache\jsp

----hello_jsp.java

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.*;

public final class hello_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("java.util");
_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; 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;

out.write("\r\n");
out.write("\r\n");
out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">\r\n");
out.write("<title>Insert title here</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\r\n");
out.write("\t");

Date date = new Date();
System.out.println(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);
}
}
}

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标签： servlet jsp

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