[置顶] jsp和servlet之间的关系+示例入门

作者：王奎我的博客：www.marksaas.com

首先先对jsp和servlet概念做一个讲解。

Jsp（Java server page）是运行在服务器上的脚本程序，是以java语言作为脚本语言的，Jsp网页为整个服务器端的Java库单元提供了一个接口来服务区Http服务器，

JSP使Java代码和特定的预定义动作可以嵌入到静态页面中。JSP句法增加了被称为JSP动作的XML标签，它们用来调用内建功能。另外，可以创建JSP标签库，然后像使用标准HTML或XML标签一样使用它们。标签库提供了一种和平台无关的扩展服务器性能的方法。

JSP被JSP编译器编译成Java Servlets。一个JSP编译器可以把JSP编译成JAVA代码写的servlet然后再由JAVA编译器来编译成机器码，也可以直接编译成二进制码。

下面我们来写一个简单的jsp来看一下吧，我们先用Myeclipse建立一个web项目，名称为JspDemo，创建好后，我们打开index.jsp，如下：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">

    <title>jsp,demo</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>
    hello,jsp.
  </body>
</html>

然后启动服务器，把项目部署到服务器，再浏览器中输出http://localhost:8080/JspDemo

我们将会看到 hello，jsp字样输出。

其实我们看到的输出不是Jsp直接输出在浏览器的，而是服务器把jsp编译为servlet后由out对象输出到浏览器的。来看一下Jsp编译后的代码吧。

package org.apache.jsp;

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

public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {

  private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();

  private static java.util.List _jspx_dependants;

  private javax.el.ExpressionFactory _el_expressionfactory;
  private org.apache.AnnotationProcessor _jsp_annotationprocessor;

  public Object getDependants() {
    return _jspx_dependants;
  }

  public void _jspInit() {
    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
    _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());
  }

  public void _jspDestroy() {
  }

  public void _jspService(HttpServletRequest request, HttpServletResponse response)
        throws java.io.IOException, ServletException {

    PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;
    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');
      out.write('\n');

String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

      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(basePath);
      out.write("\">\r\n");
      out.write("    \r\n");
      out.write("    <title>jsp,demo</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("  </head>\r\n");
      out.write("  \r\n");
      out.write("  <body>\r\n");
      out.write("    hello,jsp.\r\n");
      out.write("  </body>\r\n");
      out.write("</html>\r\n");
    } catch (Throwable t) {
      if (!(t instanceof 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);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

这就是编译后的Jsp，说白了，jsp就是Servlet，所以要想学好Jsp，还是先学好Servlet为好。

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[置顶] jsp和servlet之间的关系+示例入门

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