一.JSP基础
1.JSP概述
JSP（Java Server Pages）是JavaWeb服务器端的动态资源。它与html页面的作用是相同的，显示数据和获取数据。
JSP = html + Jsp脚本（代码片段） + JSP动态标签
2.JSP语法
- <%=…%>：输出！打到这里内容等同与打到response.getWriter().print(…)中了。
<%=”hello”%>，可以
<%=System.out.println(“hello”);%>，不可以！
<%= Math.min(10,20)%>，可以
- <%...%>：代码片段！打到这里内容等同与打到方法中。注：每次访问不会在原值上加加，因为是局部变量。并且多个代码片段之间是互通的！
<%int i = 10;i = 100;%>，可以。
<%System.out.print(“hello”);%>，可以
<%private int a = 10;%>，不可以
<%public volid fun1() {}%>，不可以
- <%!...%>：定义（声明）！打到这里的内容等同与打到类体中。class A {…} 注：每次访问时会在原值上加加，因为是全局变量。
<%! int a;%>：可以；
<%! public void fun2() {..}%>：可以
<%!private class A {}%>：可以
注：在声明中，不能使用9大内置对象，因为查看JSP真身发现9大内置对象都在_jspservice下方，而声明实在_jspservice上方的，所以不能使用九大内置对象，只有java代码段和表达式可以使用这九大内置对象。
JSP内置对象：不用创建即可直接使用！
l application：SevletContext
l request：HttpServletRequest
l response：HttpServletResponse
l session：HttpSession
l out：JspWriter，等同与response.getWriter()
l config：ServletConfig
l exception：异常对象，它是Throwable
l page：Object，它表示this。例如：Object page = this;
l pageContext：页面上下文！PageContext
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>JSP演示</title>
</head>
<body>
<h1>JSP演示</h1>
<%
// Java语句
String s1 = "hello jsp";
// 不会输出到客户端，而是在服务器端的控制台打印
System.out.println(s1);
%>
<!-- 输出到客户端浏览器上 -->
输出变量：<%=s1 %><br/>
输出int类型常量：<%=100 %><br/>
输出String类型常量：<%="你好" %><br/>
<br/>
使用表达式输出常量是很傻的一件事，因为可以直接使用html即可，下面是输出上面的常量：<br/>
100<br/>
你好
</body>
</html>
输出三种形式：
1.直接打字
2.out.print("你好")
3.response.getwriter(),print("你好")
3.JSP原理
- jsp就是servlet!
- tomcat会把jsp转换成html，其实是把jsp变成.java
- 然后把.java编译成.class，其实这个类就是一个servlet!
- 而这个servlet中存在大量out.write(“<html>”)，这就是最终的输出结果，即html
4.jsp注释
我们现在已经知道JSP是需要先编译成.java，再编译成.class的。其中<%-- ... --%>中的内容在JSP编译成.java时会被忽略的，即JSP注释。
也可以在JSP页面中使用html注释：<!-- … -->，但这个注释在JSP编译成的.java中是存在的，它不会被忽略，而且会被发送到客户端浏览器。但是在浏览器显示服务器发送过来的html时，因为<!-- … -->是html的注释，所以浏览器是不会显示它的。
附:jsp真身代码
package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.util.*; public final class regist_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; static { _jspx_dependants = new java.util.HashMap<java.lang.String,java.lang.Long>(2); _jspx_dependants.put("jar:file:/F:/tomcat/webapps/day11_30/WEB-INF/lib/jstl-1.2.jar!/META-INF/c.tld", Long.valueOf(1153356282000L)); _jspx_dependants.put("/WEB-INF/lib/jstl-1.2.jar", Long.valueOf(1480475931708L)); } 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.jsp"); _jspx_imports_packages.add("javax.servlet.http"); _jspx_imports_classes = null; } private org.apache.jasper.runtime.TagHandlerPool _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody; 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() { _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody = org.apache.jasper.runtime.TagHandlerPool.getTagHandlerPool(getServletConfig()); } public void _jspDestroy() { _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.release(); } 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(" "); out.write(" "); String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; out.write(" "); out.write(" "); out.write("<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> "); out.write("<html> "); out.write(" <head> "); out.write(" <base href=""); out.print(basePath); out.write(""> "); out.write(" "); out.write(" <title>My JSP 'regist.jsp' starting page</title> "); out.write(" "); out.write(" <meta http-equiv="pragma" content="no-cache"> "); out.write(" <meta http-equiv="cache-control" content="no-cache"> "); out.write(" <meta http-equiv="expires" content="0"> "); out.write(" <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> "); out.write(" <meta http-equiv="description" content="This is my page"> "); out.write(" <!-- "); out.write(" <link rel="stylesheet" type="text/css" href="styles.css"> "); out.write(" --> "); out.write("<script type="text/javascript"> "); out.write(" function _change(){ "); out.write(" var imgEle = document.getElementById("imgEle"); "); out.write(" imgEle.src = ""); if (_jspx_meth_c_005furl_005f0(_jspx_page_context)) return; out.write("?"+ new Date().getTime(); "); out.write(" } "); out.write("</script> "); out.write(" </head> "); out.write(" "); out.write(" <body> "); out.write("<h1>注册页面</h1> "); out.write("<!-- "); out.write("1.显示表单页面 "); out.write("2.显示服务器端的输入校验错误信息 "); out.write("3.显示后台校验错误信息 "); out.write("4.校验失败时回显数据 "); out.write("--> "); out.write("<p style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${msg}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</p> "); out.write("<form action=""); if (_jspx_meth_c_005furl_005f1(_jspx_page_context)) return; out.write("" method="post"> "); out.write("用户名：<input type="text" name="username" value=""); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${form.username}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write(""/> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.username}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write("性 别：<input type="text" name="gender" value=""); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${form.gender}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write(""/> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.gender}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write("年 龄：<input type="text" name="age" value=""); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${form.age}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write(""/> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.age}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write("密 码：<input type="password" name="password"/> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.password}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write("确认密码：<input type="password" name="repassword"/> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.repassword}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write("验证码：<input type="text" name="verifyCode" size="3" value=""); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${form.verifyCode}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write(""/> "); out.write(" <img src=""); if (_jspx_meth_c_005furl_005f2(_jspx_page_context)) return; out.write("" id="imgEle"/> "); out.write(" <a href="javascript:_change()">换一张</a> "); out.write(" <span style="color:red;font-size:10pt;font-weight:900">"); out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${errors.verifyCode}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null)); out.write("</span> "); out.write(" <br/> "); out.write(" <input type="submit" value="注册"/> "); out.write("</form> "); out.write(" </body> "); 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); } } private boolean _jspx_meth_c_005furl_005f0(javax.servlet.jsp.PageContext _jspx_page_context) throws java.lang.Throwable { javax.servlet.jsp.PageContext pageContext = _jspx_page_context; javax.servlet.jsp.JspWriter out = _jspx_page_context.getOut(); // c:url org.apache.taglibs.standard.tag.rt.core.UrlTag _jspx_th_c_005furl_005f0 = (org.apache.taglibs.standard.tag.rt.core.UrlTag) _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.get(org.apache.taglibs.standard.tag.rt.core.UrlTag.class); _jspx_th_c_005furl_005f0.setPageContext(_jspx_page_context); _jspx_th_c_005furl_005f0.setParent(null); // /regist.jsp(26,16) name = value type = null reqTime = true required = false fragment = false deferredValue = false expectedTypeName = null deferredMethod = false methodSignature = null _jspx_th_c_005furl_005f0.setValue("/VerifyCodeServlet"); int _jspx_eval_c_005furl_005f0 = _jspx_th_c_005furl_005f0.doStartTag(); if (_jspx_th_c_005furl_005f0.doEndTag() == javax.servlet.jsp.tagext.Tag.SKIP_PAGE) { _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f0); return true; } _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f0); return false; } private boolean _jspx_meth_c_005furl_005f1(javax.servlet.jsp.PageContext _jspx_page_context) throws java.lang.Throwable { javax.servlet.jsp.PageContext pageContext = _jspx_page_context; javax.servlet.jsp.JspWriter out = _jspx_page_context.getOut(); // c:url org.apache.taglibs.standard.tag.rt.core.UrlTag _jspx_th_c_005furl_005f1 = (org.apache.taglibs.standard.tag.rt.core.UrlTag) _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.get(org.apache.taglibs.standard.tag.rt.core.UrlTag.class); _jspx_th_c_005furl_005f1.setPageContext(_jspx_page_context); _jspx_th_c_005furl_005f1.setParent(null); // /regist.jsp(40,14) name = value type = null reqTime = true required = false fragment = false deferredValue = false expectedTypeName = null deferredMethod = false methodSignature = null _jspx_th_c_005furl_005f1.setValue("RegistServlet"); int _jspx_eval_c_005furl_005f1 = _jspx_th_c_005furl_005f1.doStartTag(); if (_jspx_th_c_005furl_005f1.doEndTag() == javax.servlet.jsp.tagext.Tag.SKIP_PAGE) { _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f1); return true; } _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f1); return false; } private boolean _jspx_meth_c_005furl_005f2(javax.servlet.jsp.PageContext _jspx_page_context) throws java.lang.Throwable { javax.servlet.jsp.PageContext pageContext = _jspx_page_context; javax.servlet.jsp.JspWriter out = _jspx_page_context.getOut(); // c:url org.apache.taglibs.standard.tag.rt.core.UrlTag _jspx_th_c_005furl_005f2 = (org.apache.taglibs.standard.tag.rt.core.UrlTag) _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.get(org.apache.taglibs.standard.tag.rt.core.UrlTag.class); _jspx_th_c_005furl_005f2.setPageContext(_jspx_page_context); _jspx_th_c_005furl_005f2.setParent(null); // /regist.jsp(57,13) name = value type = null reqTime = true required = false fragment = false deferredValue = false expectedTypeName = null deferredMethod = false methodSignature = null _jspx_th_c_005furl_005f2.setValue("/VerifyCodeServlet"); int _jspx_eval_c_005furl_005f2 = _jspx_th_c_005furl_005f2.doStartTag(); if (_jspx_th_c_005furl_005f2.doEndTag() == javax.servlet.jsp.tagext.Tag.SKIP_PAGE) { _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f2); return true; } _005fjspx_005ftagPool_005fc_005furl_0026_005fvalue_005fnobody.reuse(_jspx_th_c_005furl_005f2); return false; } }