javaweb之jsp標簽
阿新 • • 發佈：2018-10-21
sch gap obj end port ron pre extend 頁面
1.JSP標簽簡介
JSP標簽也稱之為Jsp Action(JSP動作)元素，它用於在Jsp頁面中提供業務邏輯功能，避免在JSP頁面中直接編寫java代碼，造成jsp頁面難以維護。
2.JSP常用標簽
- <jsp:include>標簽
- <jsp:forward>標簽
- <jsp:param>標簽
2.1 <jsp:include>標簽
<jsp:include>標簽用於把另外一個資源的輸出內容插入進當前jsp頁面的輸出內容之中，這種在jsp頁面執行時的引入方式稱之為動態引入。即jsp:include指令為動態包含。如果被包含的頁面是JSP，則先處理之後再將結果包含，而如果包含的是非*.jsp文件，則只是把文件內容靜態包含進來，功能與@include類似。
語法：<jsp:include page="relativeURL | <%=expression%>" flush="true|false" </jsp:include>
page屬性用於指定被引入資源的相對路徑，它可以通過執行一個表達式來獲得；flush屬性則指定在插入其他資源的輸出內容時，是否將當前的jsp頁面已經輸出的內容刷新到客戶端。
如下所示的includeTest3.jsp代碼：
<%@ 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代碼，將@include指令改為<jsp:include page="includeTest3.jsp"></jsp:include>，運行結果同上，但是生成的新的includeTest1_jsp類的源碼為：
/*
* 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);
}
}
}
從源碼可以看出，includeTest1.jsp使用org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "includeTest3.jsp", out, false);將includeTest3.jsp的動態內容包含進來，includeTest3.jsp的靜態內容並沒有包含進來。動態引入並不像@include一樣生成一個Servlet源文件，而是生成兩個Servlet源文件，然後通過org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "includeTest3.jsp", out, false);方式將另一個Servlet的目標頁面包含進來。
很顯然，jsp：include標簽是在當前jsp頁面的執行期間插入被引入資源的輸出內容，被動態引入的資源必須是一個能獨立被WEB容器調用和執行的資源。動態包含就是指先將各個頁面分別處理，處理之後再將處理之後的結果包含進來。而include指令的靜態引入只能引入遵循jsp格式的文件，被引入文件與當前jsp文件共同被翻譯成一個Servlet的源文件。靜態包含就是將全部內容包含進來之後再進行處理，屬於先包含後處理。
2.2 <jsp:forward>標簽
<jsp:forward>標簽用於把請求轉發給另外一個資源。
語法：<jsp:forward page="relativeURL | <%=expression%>" <jsp:forward/>
page屬性用於指定請求轉發到的資源的相對路徑，它也可以通過執行一個表達式來獲得。
使用<jsp:forward>標簽跳轉頁面，例如在includeTest1.jsp中，添加如下代碼，
<jsp:forward page="/jspTest/includeTest2.jsp"></jsp:forward>
運行後輸出的includeTest2.jsp輸出的內容：
它的效果和下面的代碼效果是一樣的，
<%
request.getRequestDispatcher("/jspTest/includeTest2.jsp").forward(request,response);
%>
但是用jsp：forward可以使用jsp：param子標簽向includeTest2.jsp傳入一些參數，同樣jsp：include也可以使用jsp：param子標簽。
例如：
<jsp:forward page="/jspTest/includeTest2.jsp">
<jsp:param value="koala" name="username"/>
</jsp:forward>
這樣在includeTest2.jsp中就可以通過request.getParameter("username")獲取到傳入的參數，
2.3 <jsp:param>標簽
當使用<jsp:include>和<jsp:forward>標簽引入或將請求轉發給其它資源時，可以使用<jsp:param>標簽向這個資源傳遞參數。
語法1：
<jsp:include page="relativeURL | <%=expression%>">
<jsp:param name="parameterName" value="parameterValue|<%= expression %>" />
</jsp:include>
語法2：
<jsp:forward page="relativeURL | <%=expression%>">
<jsp:param name="parameterName" value="parameterValue|<%= expression %>" />
</jsp:forward>
<jsp:param>標簽的name屬性用於指定參數名，value屬性用於指定參數值。在<jsp:include>和<jsp:forward>標簽中能使用多個<jsp:param>標簽來傳遞多個參數。
javaweb之jsp標簽