JSP编程--基本语法

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1、Declaration 声明
<%！ %>–成员变量、成员方法
<% %>–局部变量（不能用于声明方法）

<html><head><title>JSP Declaration</title></head><body><H1>JSP Declaration</H1><%! int accessCount=0;%><% int accessCount1=0;%><H2>Accesses to page since server reboot:<%=++accessCount%></H2><br /><%=++accessCount1%></body></html>

不断刷新页面，发现变量accessCount不断递增，而accessCount1的值不变。这是因为JSP要想运行需要先转换为Servlet，而servlet要求就只能有一个对象。在JSP_005fDeclarations_jsp.java文件（JSP转换为Servlet后的程序）中accessCount为成员变量，而accessCount1为局部变量。每次刷新后_jspService函数就会被调用一次。成员函数accessCount增一。

/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/8.0.35 * Generated at: 2016-05-28 02:32:40 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 JSP_005fDeclarations_jsp extends org.apache.jasper.runtime.HttpJspBase    implements org.apache.jasper.runtime.JspSourceDependent,                 org.apache.jasper.runtime.JspSourceImports { int accessCount=0;  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.jsp");    _jspx_imports_packages.add("javax.servlet.http");    _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><title>JSP Declaration</title></head>\r\n");      out.write("<body>\r\n");      out.write("<H1>JSP Declaration</H1>\r\n");      out.write('\r');      out.write('\n'); int accessCount1=0;      out.write("\r\n");      out.write("<H2>Accesses to page since server reboot:\r\n");      out.print(++accessCount);      out.write("</H2>\r\n");      out.write("<br />\r\n");      out.write(" \r\n");      out.print(++accessCount1);      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);    }  }}

2、Scriptlet 小程序段
<%程序代码区%>
3、Comment 注释 html注释
<%– –%>
<%// %>
<%/* */%>

<%@ page contentType="text/html; charset=utf-8" language="java" import="java.sql.*" errorPage="" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>JSp-Scriptlet&Comment</title></head><!--html注释--> //页面上可见<%--注释1 aaaa--%><%//注释2/*注释3    aaaaaaaaa*/String bgColor=request.getParameter("bgColor");boolean hasExplicitColor;if(bgColor!=null){    hasExplicitColor=true;}else{    hasExplicitColor=false;    bgColor="WHITE";}%><body bgcolor="<%=bgColor %>"><H2 Align="CENTER">Color Testing</H2><%if(hasExplicitColor){    out.println("You supplied an explicit background color of"+bgColor+".");}else{    out.println("Using default background color of WHITE "+                "Supply the bgColor request attribute to try"+                "a standard color, an RRGGBB value,or to see"+                "if your browser suports XLL color names.");}%></body></html>

地址栏输入http://localhost:8889/test/JSP_Scriptlet_Comment.jsp的运行结果

地址栏输入http://localhost:8889/test/JSP_Scriptlet_Comment.jsp?bgColor=red的运行结果
这里写图片描述
Expression 表达式
<%= %>–原封不动打印出来

Directives–编译期间的指令
<%@Directive 属性=“属性值”>
常见的Directive
page–指明页面特点如：language exdends import(引入包、类) buffer session autoFlush isThreadSafe info errorPage isErrorPage ContentType
<%@page import=“java.util.*”%>
<%@page contentType=”text/html;chatset=gb2312”>
include–将JSP程序或者HTML文件包含进来
<%@ include file=”fileURL”%>

taglib

Action–动作
运行期间的命令
jsp:useBean
jsp:setProperty
jsp:getProperty
jsp:include 用于动态包含JSP程序或HTML文件等
除非这个指令会被执行到，否则它是不会被Tomcat等JSP Engine编译

jsp:forward   jsp:paramjsp:plugin

内置对象

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