关于JSP学习中一些记录

【JSP探究】

一、JSP转换后的源文件的位置

• 由于不同版本的IDEA的默认路径不同，所以我们无法统一按照网上所给路径进行查找
• 我们可以创建一个JavaWeb项目并运行，查看日志就能找到运行时文件所放位置

然后就可以找到了！

二、JSP声明变量的位置

在JSP中用两种声明变量的方法，一种是在

    $Title$

  Welcome! You are visitor number

  Welcome! You are visitor number

刷新页面运行结果：

package org.apache.jsp;

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

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

 int count = 0; //声明在中的变量
  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map _jspx_dependants;

  private static final java.util.Set _jspx_imports_packages;

  private static final java.util.Set _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("javax.servlet");
    _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 getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set getPackageImports() {
    return _jspx_imports_packages;
  }

  public java.util.Set 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 {

    if (!javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      final java.lang.String _jspx_method = request.getMethod();
      if ("OPTIONS".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        return;
      }
      if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
        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("\n");
      out.write("\n");
      out.write("\n");
      out.write("  \n");
      out.write("    $Title$\n");
      out.write("  \n");
      out.write("  \n");
      out.write('\n');
      out.write('\n');

      out.write(' ');
      out.write(' ');
 count++;
      out.write("\n");
      out.write("  Welcome! You are visitor number\n");
      out.write("  ");
      out.print( count );
      out.write("\n");
      out.write("  \n");
      out.write("\n");
      out.write("  \n");
      out.write("  ");
 int i = 0; //声明在中的变量
      out.write('\n');
      out.write(' ');
      out.write(' ');
 i++;
      out.write("\n");
      out.write("  Welcome! You are visitor number\n");
      out.write("  ");
      out.print( i );
      out.write("\n");
      out.write("  \n");
      out.write("\n");
      out.write("\n");
      out.write("\n");
      out.write("\n");
      out.write("\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);
    }
  }
}

通过观察代码后我们发现，原先声明在

我们学习JAVA的时候就知道成员变量会被多个对象共享，而局部变量单独对象访问。所以count会自动增加，i不递增。

在这里还有个问题需要说明，如果在

Original: https://www.cnblogs.com/HuihuiGoforIt/p/16200333.html
Author: 小hui同学
Title: 关于JSP学习中一些记录