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【Head First Servlets and JSP】笔记24：include指令与include动作 & param动作 & foward动作

2017-06-22 17:48 676 查看

include指令与include动作

1、样例代码

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page import = "java.io.*,java.util.*" %>

<html>
<head>
<title>Auto Refresh Header Example</title>
</head>

<body>
<%-- 在这里插入页眉文件 --%>
<%@ include file="Header.jsp"%>

<center>
<h2>Auto Refresh Header Example</h2>
<%
// Set refresh, autoload time as 5 seconds
response.setIntHeader("Refresh", 60);

// Get current time
Calendar calendar = new GregorianCalendar();
String am_pm;

int hour = calendar.get(Calendar.HOUR);
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);

if(calendar.get(Calendar.AM_PM) == 0)
am_pm = "AM";
else
am_pm = "PM";
String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
out.println("Crrent Time: " + CT + "\n");
%>
</center>

<%-- 在这里插入页脚文件 --%>
<jsp:include page="Footer.jsp" />

</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<img src="images/header.jpg"  alt="上海鲜花港 - 郁金香" />
<p>我是页眉</p>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<img src="images/header.jpg"  alt="上海鲜花港 - 郁金香" />
<p>我是页眉</p>

2、源码分析

web项目结构

把这些文件打包成war，部署到本地tomcat的webapps下，启动tomcat。

在第一次访问index.jsp之后，将生成如下文件

我们观察到，并没生成Header_jsp，原因可想而知，因为使用了include指令而不是include动作。

接着查看index_jsp源码：

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("\n");
out.write("\n");
out.write("\n");
out.write("<html>\n");
out.write("<head>\n");
out.write("  <title>Auto Refresh Header Example</title>\n");
out.write("</head>\n");
out.write("\n");
out.write("<body>\n");
out.write('\n');
out.write("\r\n");
out.write("\r\n");
out.write("<img src=\"images/header.jpg\"  alt=\"上海鲜花港 - 郁金香\" />\r\n");
out.write("<p>我是页眉</p>\r\n");
      out.write("\r\n");
out.write("\n");
out.write("\n");
out.write("<center>\n");
out.write("  <h2>Auto Refresh Header Example</h2>\n");
out.write("  ");

// Set refresh, autoload time as 5 seconds
response.setIntHeader("Refresh", 60);

// Get current time
Calendar calendar = new GregorianCalendar();
String am_pm;

int hour = calendar.get(Calendar.HOUR);
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);

if(calendar.get(Calendar.AM_PM) == 0)
am_pm = "AM";
else
am_pm = "PM";
String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
out.println("Crrent Time: " + CT + "\n");

out.write("\n");
out.write("</center>\n");
out.write("\n");
out.write('\n');
org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "Footer.jsp", out, false);
out.write("\n");
out.write("\n");
out.write("</body>\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);
}

加粗的分别是include指令和include动作的转换代码。

param动作

修改上面的index.jsp代码：

<%-- 在这里插入页脚文件 --%>
<jsp:include page="Footer.jsp">
<jsp:param name="subTitle" value="we take the string out of SOAP." />
</jsp:include>

修改Footer.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<a href="index.jsp">home page 我是页脚！</a>
<h3>${param.subTitle}</h3>

效果截图

foward动作

乱码问题没解决，只能输入中文。

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<p>欢迎来到我的页面！</p>
   <% if (request.getParameter("userName")== null) { %>
<jsp:forward page="HandleIt.jsp" />
<% } %>
<p>你好！${param.userName}</p>
</body>
</html>

HandleIt.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<%
request.setCharacterEncoding("utf-8");
%>
<p>很抱歉，你需要重新登陆。</p>
<form action="Hello.jsp">
<p>用户名：<input type="text" name="userName"></p>
<p><input type="submit"></p>
</form>
</body>
</html>

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