• JSP其实底层就是一个servlet
  

• out：字符输出流对象，可以将数据输出到页面上。和response.getwriter()类似
• 在tomcat服务器真正给客户端做出响应之前，会先找response缓冲区数据，再找out缓冲区数据。
• response.getWriter()数据输出永远在out.write()之前
• 为了格式统一，建议都用out

<%--
  Created by IntelliJ IDEA.
  User: djy
  Date: 2022/5/5
  Time: 11:28
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    





<%
    int i = 5;
    String contextPath = request.getContextPath();
    
    out.print(contextPath);
%>


<%!int i = 3;%>

<%= "表达式hello" %>


System.out.print("hello jsp");


Hi ~jsp


response对象即使在最后，也会先于out对象输出，为了格式统一，建议都用out输出


<%response.getWriter().write("response对象输出");%>

• <% 代码 %> ：在service方法中可以定义什么，该脚本就定义什么
• <%! 代码 %> ：在java类的成员位置可以定义什么，该脚本就定义什么
• <%= 代码 %> ：会输出到页面，输出语句可以定义什么，该脚本就定义什么

package org.apache.jsp.jstl;

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

public final class jstl5_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {

int i = 3;
  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 {

    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("rn");
      out.write("rn");
      out.write("rn");
      out.write("rn");
      out.write("    rn");
      out.write("rn");
      out.write("rn");
      out.write("rn");
      out.write("
rn");

    int i = 5;
    String contextPath = request.getContextPath();
    
    out.print(contextPath);

      out.write("rn");
      out.write("
rn");
      out.write("rn");
      out.write("rn");
      out.print( "表达式hello" );
      out.write("rn");
      out.write("
rn");
      out.write("System.out.print("hello jsp");rn");
      out.write("
rn");
      out.write("Hi ~jsprn");
      out.write("
rn");
      out.write("response对象即使在最后，也会先于out对象输出，为了格式统一，建议都用out输出rn");
      out.write("
rn");
response.getWriter().write("response对象输出");
      out.write("rn");
      out.write("rn");
      out.write("rn");
    } 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);
    }
  }
}