JSP指令碼元素和注釋複習總結樣本

最後更新：2017-02-28 來源：互聯網

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今天複習了JSP指令碼元素和注釋部分，案例寫出來，大家自己調試下，整體總結如下，
1、JSP申明語句：
<%！申明語句 %>
使用申明語句的變數為全域變數，多個使用者執行此JSP頁面，將共用該變數。
如：

複製代碼代碼如下:
<html>
<head>
<title>JSP Demo</title>
</head>
<body>
<%! int a = 1 ;%>
<%
out.println("a="+a);
a++;
%>
</body>
</html>

結果如下：

再次重新整理，會發現如下a的值加一了，因為變數a是全域變數，a++運算多次累計，多用客服端共用：

2、JSP Scriptlets：
<% Java代碼%>
在JSP Scriptlets中可包含多個語句，如：方法，變數，運算式等；
如：

複製代碼代碼如下:
<html>
<head>
<title>test demo</title>
</head>
<body>
<%
String str = "Hello,xiaomo!";
out.println(str);
%>
</body>
</html>

結果如下：

3、JSP運算式：
<%= Java代碼 %>
一種簡單的輸出形式，必須有一個可以輸出的值，運算式中的代碼會首先執行，然後轉換成字串顯示到頁面。
如：

複製代碼代碼如下:
<html>
<head>
<title>test demo</title>
</head>
<body>
<% String str = "Hello,xiaomo!"; %>
<%= str %>
</body>
</html>

結果如下：

4、JSP注釋：
 HTML注釋，會顯示於用戶端；
<%-- --%>JSP注釋，不會顯示於用戶端；
如：

複製代碼代碼如下:
<html>
<head>
<title>test demo</title>
</head>
<body>

<%-- 這是一個JSP注釋 --%>
</body>
</html>

結果如下：

大家發現都沒有什麼顯示，點擊瀏覽器右鍵查看源碼可以看到網頁注釋是在的，JSP注釋沒有，這個只有在JSP源碼才能看到：

複製代碼代碼如下:
<html>
<head>
<title>test demo</title>
</head>
<body>

</body>
</html>

應該很多人都知道，JSP頁面是轉譯成Servlet後在通過伺服器轉換成html代碼發送到用戶端顯示的，下面給大家看下本案例的JSP頁面轉換成Servlet後的源碼（其中紅色標註為轉換成前台的html代碼）：

複製代碼代碼如下:

/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/7.0.34
* Generated at: 2013-07-03 01:27:37 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 HelloXiaoMo_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
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("rn");
out.write("<html>rn");
out.write("t<head>rn");
out.write("tt<title>test demo</title>rn");
out.write("t</head>rn");
out.write("t<body>rn");
out.write("ttrn");
out.write("tt");
out.write("rn");
out.write("t</body>rn");
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 { 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);
}
}
}

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