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JSP编程--基本语法

2016-05-28 11:14 501 查看

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

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:param
jsp:plugin

内置对象

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标签： 编程 jsp

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