Jsp是什麼
Jsp本質上是一個Servlet- 在
HTML文檔中嵌入Java代碼，來生成動態網頁
運行流程
- 在web應用內編寫Jsp源文件
- 部署到Tomcat
- 在瀏覽器輸入相應URL來訪問這個Jsp文件
- 查找與Jsp文件對應的Servlet，如果已經存在，就調用它的服務方法
- 如果Jsp已經更新或者還不存在Servlet，就解析文件系統中的Jsp文件，翻譯爲Servlet並編譯此Servlet，然後初始化並運行此Servlet
Jsp翻譯爲Servlet，一般只發生在客戶端首次訪問和Jsp文件有更新時
Jsp對應的Servlet Jsp文件：hello.jsp
<%@ page language="java" import="java.io.File" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>lifeJSP</title>
</head>
<body>
<%!
int initVar = 0;
int serivceVar = 0;
int destryVar = 0;
%>
<%!
public void jspInit() {
++initVar;
System.out.println("JspInit()被初始化 " + initVar +" 次");
}
public void jspDestory() {
++destryVar;
System.out.println("JspDestory()被銷燬 " + destryVar + "次");
}
%>
<%
++serivceVar;
System.out.println("JspSerivce()響應了" + serivceVar + "次");
String initTime = "JspInit()被初始化 " + initVar +" 次";
String destoryTime = "JspDestory()被銷燬 " + destryVar + "次";
String sericetime = "JspSerivce()響應了" + serivceVar + "次";
File temp = (File)application.getAttribute("javax.servlet.context.tempdir");
String workdir = "工作目錄：" + temp.getPath();
%>
<h1><%= workdir %></h1>
<h1><%= initTime %></h1>
<h1><%= destoryTime %></h1>
<h1><%= sericetime %></h1>
</body>
</html>對應的Servlet
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class hello_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent,
org.apache.jasper.runtime.JspSourceImports {
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=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\n");
out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">\r\n");
out.write("<title>Insert title here</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\t");
out.print( "HelloWorld" );
out.write("\r\n");
out.write("</body>\r\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);
}
}
}- 由於原Servlet文件內容太多，這裏就只保留了了一部分
- 與Jsp文件對應的Servlet類繼承org.apache.jasper.runtime.HttpJspBase,HttpJspBase由Tomcat提供，它實現了Servlet API中的javax.servlet.jsp.HttpJspPage接口，該接口繼承了javax.servlet.jsp.JspPage接口，而JspPage又繼承了javax.servlet.Servlet接口
- 方法
_jspInit()爲Jsp對應Servlet的初始化方法 - 方法
_jspDestory()爲Jsp對應Servlet的銷燬方法 - 方法
_jspService()爲Jsp對應Servlet的服務方法 - Jsp對應的Servlet把Jsp文件中的HTML標記都作爲打印流的內容輸出到客戶端