JDBC+Servlet+JSP整合开发之23.JSP脚本元素-阿里云开发者社区

–脚本元素的类型
–JSP声明
? JSP声明中JSP/servlet之间的对应
? JSP声明：示例
–JSP表达式
? JSP表达式中JSP/servlet的对应
? JSP表达式：示例
–JSP scriptlet（代码块）
? JSP代码块中JSP/servlet的对应
–JSP声明和预定义变量
–JSP处理的两个阶段

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首先我们看下JAVA中如何申明变量、如何申明方法及方法与方法之间如何调用的哈~

看下结果

下面如果我们用JSP来写这个程序如何写哈~

? 脚本元素的类型
–声明
? 格式：<%! code %>
? 逐字地插入到servlet类的定义体中，不在任何方法之内
–表达式
? 格式：<%= expression %>
? 求值并插入到servlet的输出中
? 也就是会产生类似于out.print(expression)的语句
–scriptlet （代码块）
? 格式：<% code %>
? 逐字地插入到servlet的_jspService方法中(由service调用)

? JSP声明
–格式
? <%! Java Code %>
–结果
? 代码被逐字地插入到servlet类的定义中，在任何现有方法以外
–示例
<%! private int someField = 5; %>
<%! private void someMethod(...) {...} %>
–设计上的考虑
? 字段当然有用，但对于方法而言，通常在单独的Java类中定义更好一些
–XML兼容的语法
? <jsp:declaration>Java Code</jsp:declaration>
–JSP声明中JSP/servlet之间的对应
?原始的JSP

?生成的servlet代码

–JSP声明：示例

? JSP表达式
–格式
? <%= Java Expression %>
–结果
? 表达式被求值，转换成字符串，将按照它在JSP页面中出现的位置插入到HTML页面中。
? 即，表达式放置在out.print内
–示例
?当前时间：<%= new java.util.Date() %>
? 您的主机名：<%= request.getRemoteHost() %>
–XML兼容的语法
? <jsp:expression>Java Expression</jsp:expression>
?在单个页面中不能混合使用不同的版本。如果使用jsp:expression就必须整个页面都使用XML

–JSP表达式中JSP/servlet的对应
?原始的JSP

?所产生的具有代表性的servlet代码

–JSP表达式：示例

看下效果

JSP页面都会转换成Servlet,我们来看下

declaration_jsp.java

package org.apache.jsp;

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

public final class declaration_jsp extends org.apache.jasper.runtime.HttpJspBase
 implements org.apache.jasper.runtime.JspSourceDependent {

 private String name = "michael";
 private int age = 20;
 private String print(){
 return name+ ":"+age;
 }
 private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();

 private static java.util.List _jspx_dependants;

 private javax.el.ExpressionFactory _el_expressionfactory;
 private org.apache.AnnotationProcessor _jsp_annotationprocessor;

 public Object getDependants() {
 return _jspx_dependants;
 }

 public void _jspInit() {
 _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
 _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor. class.getName());
 }

 public void _jspDestroy() {
 }

 public void _jspService(HttpServletRequest request, HttpServletResponse response)
 throws java.io.IOException, ServletException {

 PageContext pageContext = null;
 HttpSession session = null;
 ServletContext application = null;
 ServletConfig config = null;
 JspWriter out = null;
 Object page = this;
 JspWriter _jspx_out = null;
 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( "\r\n");
 out.write( "\r\n");
 out.write( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n");
 out.write("<html>\r\n");
 out.write(" <head>\r\n");
 out.write(" \r\n");
 out.write(" <title>Test declarationJspPage...</title>\r\n");
 out.write(" \r\n");
 out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n");
 out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n");
 out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n");
 out.write("\t\r\n");
 out.write("\r\n");
 out.write(" </head>\r\n");
 out.write(" \r\n");
 out.write(" <body> \r\n");
 out.write(" \t\r\n");
 out.write(" ");
 out.write("\r\n");
 out.write(" \r\n");
 out.write(" Name:");
 out.print(name );
 out.write(" \r\n");
 out.write(" Age:");
 out.print(age );
 out.write(" \r\n");
 out.write(" Name and age:");
 out.print(print() );
 out.write("\r\n");
 out.write(" \r\n");
 out.write(" </body>\r\n");
 out.write("</html>\r\n");
 } catch (Throwable t) {
 if (!(t instanceof SkipPageException)){
 out = _jspx_out;
 if (out != null && out.getBufferSize() != 0)
 try { out.clearBuffer(); } catch (java.io.IOException e) {}
 if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
 }
 } finally {
 _jspxFactory.releasePageContext(_jspx_page_context);
 }
 }
}

来看下计算器的实例

看下结果

字段当然有用，但对于方法而言，通常在单独的Java类中定义更好一些

Calculator.java

declaration.jsp

看下效果

再看一个页面被访问的次数

看下效果：

exception.jsp

看下结果

exception_jsp.java

package org.apache.jsp;

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

public final class exception_jsp extends org.apache.jasper.runtime.HttpJspBase
 implements org.apache.jasper.runtime.JspSourceDependent {

 String name = "michael";
 public String getTime(){
 return new Date().toLocaleString();
 }
 private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();

 private static java.util.List _jspx_dependants;

 private javax.el.ExpressionFactory _el_expressionfactory;
 private org.apache.AnnotationProcessor _jsp_annotationprocessor;

 public Object getDependants() {
 return _jspx_dependants;
 }

 public void _jspInit() {
 _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
 _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor. class.getName());
 }

 public void _jspDestroy() {
 }

 public void _jspService(HttpServletRequest request, HttpServletResponse response)
 throws java.io.IOException, ServletException {

 PageContext pageContext = null;
 HttpSession session = null;
 ServletContext application = null;
 ServletConfig config = null;
 JspWriter out = null;
 Object page = this;
 JspWriter _jspx_out = null;
 PageContext _jspx_page_context = null;

 try {
 response.setContentType( "text/html;charset=ISO-8859-1");
 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');
 out.write('\n');

String path = request.getContextPath();
String basePath = request.getScheme()+ "://"+request.getServerName()+":"+request.getServerPort()+path+"/";

 out.write("\r\n");
 out.write("\r\n");
 out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n");
 out.write("<html>\r\n");
 out.write(" <head>\r\n");
 out.write(" <base href=\"");
 out.print(basePath);
 out.write("\">\r\n");
 out.write(" \r\n");
 out.write(" <title>My JSP 'exception.jsp' starting page</title>\r\n");
 out.write(" \r\n");
 out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n");
 out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n");
 out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n");
 out.write("\t\r\n");
 out.write("\r\n");
 out.write(" </head>\r\n");
 out.write(" \r\n");
 out.write(" <body>\r\n");
 out.write(" Time1:");
 out.print(new Date().toLocaleString() );
 out.write(" \r\n");
 out.write(" \r\n");
 out.write(" ");
 out.write("\r\n");
 out.write(" Name:");
 out.print(name );
 out.write(" \r\n");
 out.write(" Time2:");
 out.print(getTime() );
 out.write(" \r\n");
 out.write(" </body>\r\n");
 out.write("</html>\r\n");
 } catch (Throwable t) {
 if (!(t instanceof SkipPageException)){
 out = _jspx_out;
 if (out != null && out.getBufferSize() != 0)
 try { out.clearBuffer(); } catch (java.io.IOException e) {}
 if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
 }
 } finally {
 _jspxFactory.releasePageContext(_jspx_page_context);
 }
 }
}

? JSP scriptlet（代码块）
–格式
? <% Java Code %>
–结果
? 代码被逐字地插入到servlet的_jspService方法中
–示例
<%
String queryData = request.getQueryString();
out.println("Attached GET data: " + queryData);
%>
<% response.setContentType("text/plain"); %>
–XML兼容的语法
? <jsp:scriptlet>Java Code</jsp:scriptlet>

–JSP scriptlet（代码块）中JSP/servlet的对应
?原始的JSP

?所产生的具有代表性的servlet代码

Scriptlet.jsp

看下效果：

Scriptlet_jsp.java

package org.apache.jsp;

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

public final class Scriptlet_jsp extends org.apache.jasper.runtime.HttpJspBase
 implements org.apache.jasper.runtime.JspSourceDependent {

 private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();

 private static java.util.List _jspx_dependants;

 private javax.el.ExpressionFactory _el_expressionfactory;
 private org.apache.AnnotationProcessor _jsp_annotationprocessor;

 public Object getDependants() {
 return _jspx_dependants;
 }

 public void _jspInit() {
 _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
 _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor. class.getName());
 }

 public void _jspDestroy() {
 }

 public void _jspService(HttpServletRequest request, HttpServletResponse response)
 throws java.io.IOException, ServletException {

 PageContext pageContext = null;
 HttpSession session = null;
 ServletContext application = null;
 ServletConfig config = null;
 JspWriter out = null;
 Object page = this;
 JspWriter _jspx_out = null;
 PageContext _jspx_page_context = null;

 try {
 response.setContentType( "text/html;charset=ISO-8859-1");
 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');
 out.write('\n');

String path = request.getContextPath();
String basePath = request.getScheme()+ "://"+request.getServerName()+":"+request.getServerPort()+path+"/";

 out.write("\r\n");
 out.write("\r\n");
 out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n");
 out.write("<html>\r\n");
 out.write(" <head>\r\n");
 out.write(" <base href=\"");
 out.print(basePath);
 out.write("\">\r\n");
 out.write(" \r\n");
 out.write(" <title>My JSP 'Scriptlet.jsp' starting page</title>\r\n");
 out.write(" \r\n");
 out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n");
 out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n");
 out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n");
 out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n");
 out.write("\t\r\n");
 out.write("\r\n");
 out.write(" </head>\r\n");
 out.write(" \r\n");
 out.write(" <body>\r\n");
 out.write(" ");

 if(Calendar.AM_PM==Calendar.AM){
 out.println("Good morning!");
 }else{
 out.println("Good afternoon!");
 }
 out.println("<hr/>");
 String queryString = request.getQueryString();
 out.println(queryString);
 out.println("<hr/>");
 String name = request.getParameter("name");
 out.println(name);
 out.println(" ");
 String age = request.getParameter("age");
 out.println(age);
 out.println(" ");
 String blog = request.getParameter("blog");
 out.println(blog);
 out.write("\r\n");
 out.write(" </body>\r\n");
 out.write("</html>\r\n");
 } catch (Throwable t) {
 if (!(t instanceof SkipPageException)){
 out = _jspx_out;
 if (out != null && out.getBufferSize() != 0)
 try { out.clearBuffer(); } catch (java.io.IOException e) {}
 if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
 }
 } finally {
 _jspxFactory.releasePageContext(_jspx_page_context);
 }
 }
}

? JSP声明和预定义变量
–问题
? 预定义变量(request, response, out, session, 等)是jspService方法中的局部变量。因而，由JSP声明定义的方法或辅助类中的方法都不能使用它们。怎么处理这种情况呢？
–解决方案：将它们作为参数传递，例如 <%!
private void someMethod(HttpSession s) {
doSomethingWith(s);
}
%>
<% someMethod(session); %>
–要注意：JspWriter的println方法抛出IOException异常
? 使用println的方法要使用“throws IOException”

? JSP处理的两个阶段
–JSP页面转换阶段
?页面被编译成Java类，所有的HTML标签和JSP标签被处理，来生成一个Servlet类，然而，脚本和表达式不被执行。
–请求处理阶段
?当客户端请求服务器时，处于请求处理阶段
?在该阶段脚本和表达式被执行

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附件：http://down.51cto.com/data/2355528

本文转自redking51CTO博客，原文链接：http://blog.51cto.com/redking/294129，如需转载请自行联系原作者

JDBC+Servlet+JSP整合开发之23.JSP脚本元素

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