JSP相關

jsp是運行在server上的

當客戶端訪問一個jsp網頁時,tomcat瞭解到用戶訪問的是一個jsp,會把訪問的jsp翻譯成一個servlet,用來相應用戶的請求,因此可以吧jsp理解爲servlet,然後調用servlet的service方法提供服務,其處理過程和我們學習servlet的時候一樣,

一下是tomcat翻譯後的servlet的部分代碼,tomcat給定義好的屬性和service方法

//service方法,我們打開一個jsp網址時,tomcat就會訪問這個Servlet,調用對應的service方法

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

//定義的屬性,這也是爲什麼我們可以在jsp中直接使用這些屬性的原因
    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");
      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;

//這些就是我們在jsp中寫的html代碼

其中的out相當於respond.getWriter得到的PrintWriter對象,用來向客戶端輸出網頁內容,

out.write("\n");
      out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">\n");
      out.write("<html>\n");
      out.write(" <head>\n");
      out.write(" <title>401 Unauthorized</title>\n");
      out.write(" <style type=\"text/css\">\n");
      out.write("    \n");
      out.write(" </style>\n");
      out.write(" </head>\n");
      out.write(" <body>\n");
      out.write("   <h1>401 Unauthorized</h1>\n");
      out.write("   <p>\n");
      out.write("    You are not authorized to view this page. If you have not changed\n");
      out.write("    any configuration files, please examine the file\n");
      out.write("    <tt>conf/tomcat-users.xml</tt> in your installation. That\n");
      out.write("    file must contain the credentials to let you use this webapp.\n");
      out.write("   </p>\n");
      out.write("   <p>\n");
      out.write("    For example, to add the <tt>manager-gui</tt> role to a user named\n");
      out.write("    <tt>tomcat</tt> with a password of <tt>s3cret</tt>, add the following to the\n");
      out.write("    config file listed above.\n");
      out.write("   </p>\n");
      out.write("<pre>\n");
      out.write("<role rolename=\"manager-gui\"/>\n");
      out.write("<user username=\"tomcat\" password=\"s3cret\" roles=\"manager-gui\"/>\n");
      out.write("</pre>\n");
      out.write("   <p>\n");
      out.write("    Note that for Tomcat 7 onwards, the roles required to use the manager\n");
      out.write("    application were changed from the single <tt>manager</tt> role to the\n");
      out.write("    following four roles. You will need to assign the role(s) required for\n");
      out.write("    the functionality you wish to access.\n");
      out.write("   </p>\n");
      out.write("    <ul>\n");
      out.write("      <li><tt>manager-gui</tt> - allows access to the HTML GUI and the status\n");
      out.write("          pages</li>\n");
      out.write("      <li><tt>manager-script</tt> - allows access to the text interface and the\n");
      out.write("          status pages</li>\n");
      out.write("      <li><tt>manager-jmx</tt> - allows access to the JMX proxy and the status\n");
      out.write("          pages</li>\n");
      out.write("      <li><tt>manager-status</tt> - allows access to the status pages only</li>\n");
      out.write("    </ul>\n");
      out.write("   <p>\n");
      out.write("    The HTML interface is protected against CSRF but the text and JMX interfaces\n");
      out.write("    are not. To maintain the CSRF protection:\n");
      out.write("   </p>\n");
      out.write("   <ul>\n");
      out.write("    <li>Users with the <tt>manager-gui</tt> role should not be granted either\n");
      out.write("        the <tt>manager-script</tt> or <tt>manager-jmx</tt> roles.</li>\n");
      out.write("    <li>If the text or jmx interfaces are accessed through a browser (e.g. for\n");
      out.write("        testing since these interfaces are intended for tools not humans) then\n");
      out.write("        the browser must be closed afterwards to terminate the session.</li>\n");
      out.write("   </ul>\n");
      out.write("   <p>\n");
      out.write("    For more information - please see the\n");
      out.write("    <a href=\"/docs/manager-howto.html\">Manager App HOW-TO</a>.\n");
      out.write("   </p>\n");
      out.write(" </body>\n");
      out.write("\n");
      out.write("</html>\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);
    }
}