JSP研究（一）

用jsp开发了程序好些时间了，但感觉对jsp的掌握还是不够。现在先分析一下*.jsp文件编译后的*_jsp.java 文件。
先写一个简单的my.jsp文件如下：

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<!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=gb2312">
<title>baiming</title>
</head>

<body>
hello
</body>
</html>
****************************************************************
把改文件放到 tomcat根目录/webapps/ROOT 下。
运行tomcat，在地址栏里输入http://localhost:8080/my.jsp
在 tomcat根目录/work/Catalina/localhost/_/org/apache/jsp 下就会生成my_jsp.java文件。
我们现在来看看这个文件：
package org.apache.jsp;

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

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

  private static java.util.Vector _jspx_dependants;

  public java.util.List getDependants() {
    return _jspx_dependants;
  }

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

    JspFactory _jspxFactory = null;
    PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;

    try {
      _jspxFactory = JspFactory.getDefaultFactory();
      response.setContentType("text/html; charset=gb2312");
      pageContext = _jspxFactory.getPageContext(this, request, response,
         "", true, 8192, true);
      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=gb2312/">/r/n");
      out.write("<title>baiming</title>/r/n");
      out.write("</head>/r/n");
      out.write("/r/n");
      out.write("<body>/r/n");
      out.write("hello/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)
          out.clearBuffer();
        if (pageContext != null) pageContext.handlePageException(t);
      }
    } finally {
      if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext);
    }
  }
}

你会发现jsp里使用的8个隐含的对象。

out.write( )用于输出html流，也就是客户端收到的html内容。