java的jsp文件

首先在没有jsp文件的情况下，是以下方式写页面：

package com.oracle.index;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class indexServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().write("<!DOCTYPE html>");
        response.getWriter().write("<html>");
        response.getWriter().write("<head>");    
        response.getWriter().write("<meta http-equiv='Content-Type' content='text/html; charset=UTF-8'>");
        response.getWriter().write("<title>Insert title here</title>");        
        response.getWriter().write("</head>");
        response.getWriter().write("<body>");
        response.getWriter().write("1234567890");
        response.getWriter().write("</body>");
        response.getWriter().write("</html>");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

效果如下：

1、jsp

(实质上就是一个servlet)

（1）jsp脚本：
1）<% java代码 %>--相当于写在方法里；所以不能定义方法；
2）<%= java变量或表达式%>---相当于写在out.print()里面
3）<%!java代码%>---相当于成员变量；所以能定义方法；
（2）jsp注释：
1）//java单行注释 jsp源码、翻译后的servlet、
2）/*java多行注释*/ jsp源码、翻译后的servlet、
3）<!--html注释--> jsp源码、翻译后的servlet、html源代码
4）<%--jsp注释--%> jsp源码、

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" session="false"  errorPage="error.jsp"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>

<body>
    <!-- html注释 -->
    <%--jsp注释 --%>
   <%int i = 0;
   System.out.println(i);
    //java单行注释
   %>
   <%= i %>
   <%! String str = "ni hao java";      
    /*java多行注释*/
   %>
   <%=str %>
</body>
</html>

具体表现如下：

网页显示为：

 控制台显示为：

具体显示的java文件可以发现具体的注释位置和变量

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/7.0.52
 * Generated at: 2018-11-16 03:11:37 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
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 {

 String str = "ni hao java";      
    /*java多行注释*/
   
  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

  private javax.el.ExpressionFactory _el_expressionfactory;
  private org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
    return _jspx_dependants;
  }

  public void _jspInit() {
    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
    _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
  }

  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 javax.servlet.jsp.PageContext pageContext;
    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,
                  "error.jsp", false, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("
");
      out.write("<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
");
      out.write("<html>
");
      out.write("<head>
");
      out.write("<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
");
      out.write("<title>Insert title here</title>
");
      out.write("</head>
");
      out.write("
");
      out.write("<body>
");
      out.write("	<!-- html注释 -->
");
      out.write("	");
      out.write("
");
      out.write("   ");
int i = 0;
   System.out.println(i);
    //java单行注释
   
      out.write("
");
      out.write("   ");
      out.print( i );
      out.write("
");
      out.write("   ");
      out.write("
");
      out.write("   ");
      out.print(str );
      out.write("
");
      out.write("</body>
");
      out.write("</html>");
    } catch (java.lang.Throwable t) {
      if (!(t instanceof javax.servlet.jsp.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);
        else throw new ServletException(t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

以及页面源代码：


（3）jsp运行原理
第一次访问index.jsp --> index_jsp.java [Tomcat下的work目录下] --> 编译运行;

当访问完index.jsp后如图：

（4）jsp三大指令
1）page指令：
language：jsp脚本可以嵌套的代码，但是只能是java；


pageEncoding：当前jsp脚本的编码


contentType："text/html; charset=UTF-8"相当于响应的中文乱码问题解决；


session："true","false"；

是否使用session对象


import：导包；

一个一个的导入：

<%@ page import="java.sql.*" %>
<%@ page import="java.util.regex.*"%>

一块导入：

<%@ page import="java.sql.*,java.util.regex.*" %>中间用逗号隔开，后面不加逗号！

errorPage：当前页面出错跳转到其他页面；


isErrorPage：当前页面是一个处理错误的页面；


2）include指令：
静态：<%@ include file="被包含的文件地址"%>；

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
         <h1>这是头部！</h1>
</body>
</html>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
      <%@ include file="header.jsp"%>
      <h3>这是内容！</h3>
      <%@ include file="footer.jsp"%>
</body>
</html>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
          <h1>这是尾部！</h1>
</body>
</html>

效果如下：

动态：<jsp:include page="被包含的页面"/>；

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
        <h1>这是include1</h1>
</body>
</html>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
        <jsp:include page="/include.jsp"></jsp:include>
        <h2>这是include的h2标签</h2>
</body>
</html>

效果如下：

静态包含：被包含文件不编译，直接以Html进入文件；动态包含：被包含文件编译，指向被包含文件地址，进行编译；


3）taglib指令；
（5）九大内置对象：out、request、response、config、session、application、page、pagecontext、exception、
（6）out对象：out缓冲区的内容添加到response缓冲区、默认为buffer="8kb"，设置"0kb"时直接进入response缓冲区；

最后注意打印顺序：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" buffer="8kb"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
        <% 
           out.write("bbbbbbbbbbbbbbb");
           response.getWriter().write("ccccccccccccccccc");
        %>
        <%="gggggggggggggggg" %>
</body>
</html>

具体表现如下：

原因如下：

1、首先介绍write()和print()方法的区别：
(1)、write()：仅支持输出字符类型数据，字符、字符数组、字符串等
(2)、print()：可以将各种类型（包括Object）的数据通过默认编码转换成bytes字节形式，这些字节都通过write(int c)方法被输出
2、介绍response.getWriter()和out的区别：
(1)、out和response.getWriter的类不一样，一个是JspWriter，另一个是java.io.PrintWriter。
(2)、执行原理不同:JspWriter相当于一个带缓存功能的printWriter，它不是直接将数据输出到页面，而是将数据刷新到response的缓冲区后再输出，
response.getWriter直接输出数据（response.print()），所以（out.print）只能在其后输出。
(3)、out为jsp的内置对象，刷新jsp页面，自动初始化获得out对象，所以使用out对象是需要刷新页面的，
而response.getWriter()响应信息通过out对象输出到网页上，当响应结束时它自动被关闭，与jsp页面无关，无需刷新页面
形象的比喻：当我们调用response.getWriter()这个对象同时获得了网页的画笔，这时你就可以通过这个画笔在网页上画任何你想要显示的东西。
(4)、out的print()方法和println()方法在缓冲区溢出并且没有自动刷新时候会产生ioexception，
而response.getWrite()方法的print和println中都是抑制ioexception异常的，不会有ioexception


（7）pageContext对象：pageContext可以向指定的其他域中存取数据；
findAttribute(String name)依次从pageContext域，request域，session域，application域中获取属性，
在某个域中获取后将不在向后寻找
pageContext.getRequest()；可以获得其他8大隐式对象

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <% pageContext.setAttribute("name", "zhangsan"); %>
    <!-- 向request域中设置值 -->
    <% pageContext.setAttribute("name", "lisi",pageContext.REQUEST_SCOPE); %>
    <% pageContext.setAttribute("name", "wangwu",pageContext.APPLICATION_SCOPE); %>
    <% pageContext.setAttribute("name", "xiaohongmao",pageContext.SESSION_SCOPE); %>
    <%= pageContext.getAttribute("name") %>
    <%= pageContext.getAttribute("name",pageContext.REQUEST_SCOPE) %>
    <%= pageContext.getAttribute("name",pageContext.SESSION_SCOPE) %>
</body>
</html>

（8）jsp标签（动作）：
1）页面包含（动态包含）：<jsp:include page="被包含的页面"/>
2）请求转发：<jsp:forward page="要转发的资源" />

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原文地址：https://www.cnblogs.com/scw123/p/9968519.html