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javaweb之jsp标签

时间:2018-10-21 13:33:57      阅读:174      评论:0      收藏:0      [点我收藏+]

标签:功能   UNC   after   set   static   Servle   servlet   scom   map   

1.JSP标签简介

JSP标签也称之为Jsp Action(JSP动作)元素,它用于在Jsp页面中提供业务逻辑功能,避免在JSP页面中直接编写java代码,造成jsp页面难以维护。

2.JSP常用标签

  • <jsp:include>标签  
  • <jsp:forward>标签  
  • <jsp:param>标签

2.1 <jsp:include>标签

<jsp:include>标签用于把另外一个资源的输出内容插入进当前jsp页面的输出内容之中,这种在jsp页面执行时的引入方式称之为动态引入。即jsp:include指令为动态包含。如果被包含的页面是JSP,则先处理之后再将结果包含,而如果包含的是非*.jsp文件,则只是把文件内容静态包含进来,功能与@include类似。

语法:<jsp:include page="relativeURL | <%=expression%>" flush="true|false" </jsp:include>

page属性用于指定被引入资源的相对路径,它可以通过执行一个表达式来获得;flush属性则指定在插入其他资源的输出内容时,是否将当前的jsp页面已经输出的内容刷新到客户端。

如下所示的includeTest3.jsp代码:

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path3 = request.getContextPath();
String basePath3 = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path3+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath3%>">
    
    <title>My JSP ‘includeTest3.jsp‘ starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
    <h2>"includeTest3.jsp‘s content"</h2>
  </body>
</html>

 修改上篇中includeTest1.jsp代码,将@include指令改为<jsp:include page="includeTest3.jsp"></jsp:include>,运行结果同上,但是生成的新的includeTest1_jsp类的源码为:

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/8.5.9
 * Generated at: 2018-10-20 13:53:54 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.jspTest;

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

public final class includeTest1_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {

  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 static final java.util.Set<java.lang.String> _jspx_imports_packages;

  private static final java.util.Set<java.lang.String> _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("javax.servlet");
    _jspx_imports_packages.add("java.util");
    _jspx_imports_packages.add("javax.servlet.http");
    _jspx_imports_packages.add("javax.servlet.jsp");
    _jspx_imports_classes = null;
  }

  private volatile javax.el.ExpressionFactory _el_expressionfactory;
  private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set<java.lang.String> getPackageImports() {
    return _jspx_imports_packages;
  }

  public java.util.Set<java.lang.String> getClassImports() {
    return _jspx_imports_classes;
  }

  public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
    if (_el_expressionfactory == null) {
      synchronized (this) {
        if (_el_expressionfactory == null) {
          _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
        }
      }
    }
    return _el_expressionfactory;
  }

  public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
    if (_jsp_instancemanager == null) {
      synchronized (this) {
        if (_jsp_instancemanager == null) {
          _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
        }
      }
    }
    return _jsp_instancemanager;
  }

  public void _jspInit() {
  }

  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 java.lang.String _jspx_method = request.getMethod();
    if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD");
      return;
    }

    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=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 path1 = request.getContextPath();
String basePath1 = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path1+"/";

      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(basePath1);
      out.write("\">\r\n");
      out.write("    \r\n");
      out.write("    <title>My JSP ‘includeTest.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("  <script>\"undefined\"==typeof CODE_LIVE&&(!function(e){var t={nonSecure:\"51550\",secure:\"51555\"},c={nonSecure:\"http://\",secure:\"https://\"},r={nonSecure:\"127.0.0.1\",secure:\"gapdebug.local.genuitec.com\"},n=\"https:\"===window.location.protocol?\"secure\":\"nonSecure\";script=e.createElement(\"script\"),script.type=\"text/javascript\",script.async=!0,script.src=c[n]+r[n]+\":\"+t[n]+\"/codelive-assets/bundle.js\",e.getElementsByTagName(\"head\")[0].appendChild(script)}(document),CODE_LIVE=!0);</script></head>\r\n");
      out.write("  \r\n");
      out.write("  <body data-genuitec-lp-enabled=\"false\" data-genuitec-file-id=\"wc1-8\" data-genuitec-path=\"/MyWebProject/WebRoot/jspTest/includeTest1.jsp\">\r\n");
      out.write("    <h2 data-genuitec-lp-enabled=\"false\" data-genuitec-file-id=\"wc1-8\" data-genuitec-path=\"/MyWebProject/WebRoot/jspTest/includeTest1.jsp\">\"includeTest1.jsp‘s content\"</h2>\r\n");
      out.write("    ");
      org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "includeTest3.jsp", out, false);
      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 {
            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);
    }
  }
}

 从源码可以看出,includeTest1.jsp使用org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "includeTest3.jsp", out, false);将includeTest3.jsp的动态内容包含进来,includeTest3.jsp的静态内容并没有包含进来。动态引入并不像@include一样生成一个Servlet源文件,而是生成两个Servlet源文件,然后通过org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "includeTest3.jsp", out, false);方式将另一个Servlet的目标页面包含进来。

很显然,jsp:include标签是在当前jsp页面的执行期间插入被引入资源的输出内容,被动态引入的资源必须是一个能独立被WEB容器调用和执行的资源。动态包含就是指先将各个页面分别处理,处理之后再将处理之后的结果包含进来。而include指令的静态引入只能引入遵循jsp格式的文件,被引入文件与当前jsp文件共同被翻译成一个Servlet的源文件。静态包含就是将全部内容包含进来之后再进行处理,属于先包含后处理。

2.2 <jsp:forward>标签

<jsp:forward>标签用于把请求转发给另外一个资源。
语法:<jsp:forward page="relativeURL | <%=expression%>" <jsp:forward/>
page属性用于指定请求转发到的资源的相对路径,它也可以通过执行一个表达式来获得。

使用<jsp:forward>标签跳转页面,例如在includeTest1.jsp中,添加如下代码,

<jsp:forward page="/jspTest/includeTest2.jsp"></jsp:forward>

 运行后输出的includeTest2.jsp输出的内容:

技术分享图片

它的效果和下面的代码效果是一样的,

<%
request.getRequestDispatcher("/jspTest/includeTest2.jsp").forward(request,response);
%>

但是用jsp:forward可以使用jsp:param子标签向includeTest2.jsp传入一些参数,同样jsp:include也可以使用jsp:param子标签。

例如:

<jsp:forward page="/jspTest/includeTest2.jsp">
    <jsp:param value="koala" name="username"/>
</jsp:forward>

这样在includeTest2.jsp中就可以通过request.getParameter("username")获取到传入的参数,

技术分享图片

2.3 <jsp:param>标签

当使用<jsp:include>和<jsp:forward>标签引入或将请求转发给其它资源时,可以使用<jsp:param>标签向这个资源传递参数。

语法1:

<jsp:include page="relativeURL | <%=expression%>">
        <jsp:param name="parameterName" value="parameterValue|<%= expression %>" />
</jsp:include>

语法2:

<jsp:forward page="relativeURL | <%=expression%>">
        <jsp:param name="parameterName" value="parameterValue|<%= expression %>" />
</jsp:forward>

<jsp:param>标签的name属性用于指定参数名,value属性用于指定参数值。在<jsp:include>和<jsp:forward>标签中能使用多个<jsp:param>标签来传递多个参数。

 

 

javaweb之jsp标签

标签:功能   UNC   after   set   static   Servle   servlet   scom   map   

原文地址:https://www.cnblogs.com/naihuangbao/p/9824677.html

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