JSP编程--基本语法

最新推荐文章于 2024-06-17 16:29:49 发布

mingqiong_4

最新推荐文章于 2024-06-17 16:29:49 发布

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分类专栏： JSP 文章标签：编程 jsp

本文链接：https://blog.youkuaiyun.com/u013165156/article/details/51523987

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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”%>