(一)JSP注释
JSP注释用于标注程序开发过程中的开发演示。
JSP注释:<%-- comment--%> 它不会输出到客户端
HTML注释:<!--comment--> 它会输出到客户端
(二)JSP声明
JSP本质是Servlet,Servlet是特殊的JAVA类,所以JSP声明符合JAVA语法。
语法格式:<%!declaration%>
JSP声明用于声明变量和方法,可以放在JSP中的任何地方。JSP声明会转换成对应Servlet中的成员变量或成员方法。
<body>
<%!
public int count;
public String info(){
return "hello";
}
%>
<%out.print(count++ +" "+info()); %>
</body>
对应的Servlet代码为
package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.util.*; public final class test1_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { public int count; public String info(){ return "hello"; } 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 javax.el.ExpressionFactory _el_expressionfactory; private org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; } public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); } 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 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;charset=UTF-8"); 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 'test1.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("\t<link rel=\"stylesheet\" type=\"text/css\" href=\"styles.css\">\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(" "); out.write("\r\n"); out.write(" "); out.print(count++ +" "+info()); out.write("\r\n"); out.write(" </body>\r\n"); out.write("</html>\r\n"); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.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); } } }
1.JSP声明语法定义的变量和方法对应于Servlet类的成员变量和方法,所以JSP声明部分定义的变量和方法可以使用private,public等访问控制符修饰,也可以用static修饰,将其变成类属性和类方法,但是不能使用abstract修饰声明部分的方法,因为抽象方法将导致JSP对应Servlet编程抽象类,从而导致无法实例化。
2.打开多个浏览器,甚至可以在不同的机器上打开浏览器来刷新页面,将发现所有的客户端访问的count是连续的,及所有客户端共享了同一个count变量。这是因为JSP页面会编译成一个Servlet类,每个Servlet在容器中只有一个实例:在JSP中声明的变量是成员变量,成员变量只在创建实例时初始化,该变量的值一直保存,直到实例销毁。
(三)输出JSP表达式
语法:<%=expression%> ==<%out.println();%> 输出表达式等同于HTML页面的元素。
(四)JSP脚本 <% java code%>
通常来说,所有可执行java代码都可以通过JSP脚本嵌入HTML页面。
1.JSP页面中,可包含静态内容,指令,表达式,小脚本,声明,标准动作,注释。
2.expression,script(小脚本),declaration统称之为java脚本元素-------用来嵌入java代码
3.小脚本:在JSP页面中嵌入一段JAVA代码
注:脚本中嵌入的代码都是局部变量,定位于service方法中。实际上不仅JSP小脚本部分会转换成Service方法里的可执行代码,JSP页面里的所有静态类容都将由service方法里输出语句来输出,这就是JSP脚本可以控制JSP页面中静态内容的原因。由于JSP脚本将转换成Service方法里的可执行代码,而java语法不允许在方法里定义方法,所以JSP脚本里面不能定义方法。