jsp技术1.jsp:java server pages,是sun公司定义的一种用来开发动态web资源的技术。servlet也是用于开发动态web资源的技术。jsp和servlet都是用于开发动态web:1.在servlet中对数据进行美化展示比较麻烦,但是适合编写大量的java代码。2.在jsp页面中不适合编写大量的java代码,但是做数据美化比较方便,写jsp类似写html代码。所以:jsp:页面的展示。servlet:数据的处理。jsp中的两门技术:EL表达式。JSTL标签两种技术是解决jsp中不写java代码的技术。jsp的调用和运行原理:当我们访问一个jsp页面时候,其实是访问servlet,因为容器会将这个jsp页面翻译成servlet.
在servlet中:
RequestDispatcher requestDispatcher = req.getRequestDispatcher("/WEB-INF/jsp/1.jsp");requestDispatcher.forward(req, resp);
显示1jsp页面,在tomcat容器中,容器将这个1.jsp翻译成:
package org.apache.jsp.WEB_002dINF.jsp;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;import java.util.*;public final class _1_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(" </head>\r\n"); out.write(" \r\n"); out.write(" <body>\r\n"); out.write(" This is my JSP page. <br>\r\n"); out.write(" \r\n"); out.write(" \r\n"); out.write(" "); Date date = new Date(); out.write(date.toLocaleString()); 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); } }}
继承的这个类(org.apache.jasper.runtime.HttpJspBase)的源码是:/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.apache.jasper.runtime;import java.io.IOException;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.jsp.HttpJspPage;import javax.servlet.jsp.JspFactory;import org.apache.jasper.compiler.Localizer;/** * This is the super class of all JSP-generated servlets. * * @author Anil K. Vijendran */public abstract class HttpJspBase extends HttpServlet implements HttpJspPage { protected HttpJspBase() { } public final void init(ServletConfig config) throws ServletException { super.init(config);jspInit(); _jspInit(); } public String getServletInfo() {return Localizer.getMessage("jsp.engine.info"); } public final void destroy() {jspDestroy();_jspDestroy(); } /** * Entry point into service. */ public final void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { _jspService(request, response); } public void jspInit() { } public void _jspInit() { } public void jspDestroy() { } protected void _jspDestroy() { } public abstract void _jspService(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;}
这个类继承了HttpServlet,可见容器是将jsp页面翻译成了servlet,然后进行展示。
服务器给客户端返回的数据是:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="http://localhost:8080/Servlet/"> </head> <body> This is my JSP page. <br> 2013-9-10 14:58:43 </body></html>
原理是在1_jsp.java中调用out流对象输出(编写的java代码原封输出): 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(" </head>\r\n"); out.write(" \r\n"); out.write(" <body>\r\n"); out.write(" This is my JSP page. <br>\r\n"); out.write(" \r\n"); out.write(" \r\n"); out.write(" "); Date date = new Date(); out.write(date.toLocaleString()); out.write("\r\n"); out.write(" </body>\r\n"); out.write("</html>\r\n");在jsp页面中我们可以调用out流对象,还有: request response 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;
JSP语法:eclipse中修改jsp模板(在eclipse中搜索Servlet.java,然后在同目录中的jsp中修改模板)1.jsp模板元素jsp页面中的html内容称之为jsp的模板元素。jsp模板元素定义了网页的基本骨架,即定义了jsp页面的结构和外观。2.jsp脚本表达式。<%= %>:作用是用于向浏览器输出内容。翻译成:out.print();3.脚本片段<% %> :嵌入代码,将代码原封不动的输出。4.jsp声明:<%! %:定义的方法、属性,变量,是在service方法的外面。5.jsp注释<%-- --%>:jsp注释不会把内容打给浏览器,而html的注释会把内容打给浏览器。6.jsp指令(告诉tomcat如何处理这个jsp页面)page指令include指令taglib指令jsp中的九大隐式对象:request HttpServletRequestresponse HttpServletResponseconfig ServletConfigapplication ServletContextexception Throwablesession HttpSessionpage this(翻译完的Servlet对象)out JspWriter pageContext PageContextpageContext对象是JSP技术中最重要的一个对象,它代表JSP页面的运行环境,该对象提供了三个功能获得其他8个隐式对象作为域对象存储数据,被称为page域提供了一些常用操作,forward请求转发、include包含web开发接触到了4个域对象:(之所以他们是域对象,原因就是他们都内置了map集合,都有setAttribute getAttribute方法。)pageContext(称之为page域) PageContextrequest(称之为request域)HttpServletRequestsession(称之为session域)HttpSessionapplication(称之为application域)ServletContext代表各个域的常量APPLICATION_SCOPE、SESSION_SCOPE、REQUEST_SCOPE、PAGE_SCOPE Web开发中的四个域对象: 由范围小到大:page(jsp有效) request(一次请求) session(一次会话) application(当前web应用) page域指的是pageContext. request域指的是request HttpServletRequest session 域指的是 session HTTPSession application 域指的是 application ServletContext 之所以他们是域对象,原因就是他们都内置了map集合,都有setAttribute getAttribute方法。 他们都有自己固定的生命周期和作用域。 这4个对象的生命周期:page:jsp页面被执行,生命周期开始,jsp页面执行完毕,声明周期结束 request:用户发送一个请求,开始,服务器返回响应,请求结束,生命周期结束 session:用户打开浏览器访问,创建session(开始),session超时或被声明失效,该对象生命周期结束 application:web应用加载的时候创建。Web应用被移除或服务器关闭,对象销毁。[结束]。 Page只在当前jsp有效,每次请求风别对应不同的request. Request,只在当前请求有效,每次请求分别对应不同的request域 Session只在一次会话中有效,会话结束就无法取到数据了。 四个域对象在选择的时候,能用范围小的绝不用范围大的 page:数据只是暂时存在集合,在jsp页面的其他地方要用,用page(页面中自定义的map) (什么时候需要用map了,就用page) Request:数据只是做显示的,看完了就没用了。就存request域,请求转发,Servlet产生的处理结果(数据)交给jsp显示。 数据转发可以带数据。 Session:数据给用户看完了,一定还要用,会话结束了就没用了 用户登录,用户信息发给客户端看,看完了,一会访问别的页面还要看用户信息。 购物车,购物车成功了,给用户看购物车,待会随时间可以查看购物车 请求重定向,因为是两次请求,每一次请求的数据,第二次请求还要看。 application:数据给一个用户用完了,别人还要用 聊天室,聊天记录,需要给所有的用户看 统计网站在线人数,所有看到的应该是一个数 总结:需要定义Map不如用page,请求转发Servlet,带给jsp的数据存request请求重定向带过去的数据存Session,全局的数据存application。 在自定义标签中,只要将pageContext传出去,这样在自定义标签中就可以或得其他的八大隐式对象。而不需要将所有的对象传过去。