java web--JSP（3）

JSP (3)

11. 和属性相关的方法:

1). 方法

void setAttribute(String name, Object o): 设置属性
Object getAttribute(String name): 获取指定的属性

Enumeration getAttributeNames(): 获取所有的属性的名字组成的 Enumeration 对象
removeAttribute(String name): 移除指定的属性

2). pageContext, request, session, application 对象都有这些方法!
这四个对象也称之为域对象.

pageContext: 属性的作用范围仅限于当前 JSP 页面
request: 属性的作用范围仅限于同一个请求.
session: 属性的作用范围限于一次会话: 浏览器打开直到关闭称之为一次会话(在此期间会话不失效)
application: 属性的作用范围限于当前 WEB 应用. 是范围最大的属性作用范围, 只要在一处设置属性, 在其他各处的 JSP 或 Servlet 中
都可以获取到.

12. JSP:

1). WHY:

JSP 是简 Servlet 编写的一种技术, 它将 Java 代码和 HTML 语句混合在同一个文件中编写,
只对网页中的要动态产生的内容采用 Java 代码来编写，而对固定不变的静态内容采用普通静态 HTML 页面的方式编写。

2). Java Server Page: Java 服务器端网页. 在 HTML 页面中编写 Java 代码的页面.

3). helloworld:

新建一个 JSP 页面, 在 body 节点内的 <% %> 即可编写 Java 代码.

<body>

<%
Date date = new Date();
System.out.print(date);
%>

</body>

4). JSP 可以放置在 WEB 应用程序中的除了 WEB-INF 及其子目录外的其他任何目录中,
JSP 页面的访问路径与普通 HTML 页面的访问路径形式也完全一样。

5). JSP的运行原理: JSP 本质上是一个 Servlet.

每个JSP 页面在第一次被访问时, JSP 引擎将它翻译成一个 Servlet 源程序, 接着再把这个 Servlet 源程序编译成 Servlet 的 class 类文件.
然后再由WEB容器（Servlet引擎）像调用普通Servlet程序一样的方式来装载和解释执行这个由JSP页面翻译成的Servlet程序。

6). JSP 页面的隐含变量: 没有声明就可以使用的对象. JSP页面一共有 9 个隐含对象.

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

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

//使用 <% %> 编写的代码在此位置. 可以用到 request, response, pageContext, session
//application, config, out, page 这 8 个隐含对象. (实际上还可以使用一个叫 exception 的隐含对象
}

①. request: HttpServletRequest 的一个对象. *
②. response: HttpServletResponse 的一个对象(在 JSP 页面中几乎不会调用 response 的任何方法.)

③. pageContext: 页面的上下文, 是 PageContext 的一个对象. 可以从该对象中获取到其他 8 个隐含对象. 也可以从中获取到当前
页面的其他信息. (学习自定义标签时使用它) *
④. session: 代表浏览器和服务器的一次会话, 是 HttpSession 的一个对象. 后面详细学习. *

⑤. application: 代表当前 WEB 应用. 是 ServletContext 对象. *
⑥. config: 当前 JSP 对应的 Servlet 的 ServletConfig 对象(几乎不使用). 若需要访问当前 JSP 配置的初始化参数,
需要通过映射的地址才可以.

映射 JSP:

<servlet>
<servlet-name>hellojsp</servlet-name>
<jsp-file>/hello.jsp</jsp-file>
<init-param>
<param-name>test</param-name>
<param-value>testValue</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>hellojsp</servlet-name>
<url-pattern>/hellojsp</url-pattern>
</servlet-mapping>

⑦. out: JspWriter 对象. 调用 out.println() 可以直接把字符串打印到浏览器上. *
⑧. page: 指向当前 JSP 对应的 Servlet 对象的引用, 但为 Object 类型, 只能调用 Object 类的方法(几乎不使用)

⑨. exception: 在声明了 page 指令的 isErrorPage="true" 时, 才可以使用. *

<%@ page isErrorPage="true" %>

pageContext, request, session, application(对属性的作用域的范围从小到大)
out, response, config, page 、 exception
6). JSP模版元素: JSP页面中的静态HTML内容称

7). JSP表达式（expression）提供了将一个 java 变量或表达式的计算结果输出到客户端的简化方式，
它将要输出的变量或表达式直接封装在<%= 和 %>之中。

<%
Date date = new Date();
out.print(date);
%>

<%= date %>

8). JSP脚本片断（scriptlet）是指嵌套在<% 和 %>之中的一条或多条Java程序代码。
多个脚本片断中的代码可以相互访问

<%
String ageStr = request.getParameter("age");
Integer age = Integer.parseInt(ageStr);
if(age >= 18){
%>
成人...
<%
}else{
%>
未成人...
<%
}
%>

9). JSP 声明: JSP 声明将 Java 代码封装在<%！和 %>之中，它里面的代码将被插入进 Servle t的 _jspService 方法的外面
(在 JSP 页面中几乎从不这样使用)

10). JSP注释的格式：<%-- JSP 注释 --%> 
区别: JSP 注释可以阻止 Java 代码的执行.

13 请求的转发和重定向:

1). 本质区别: 请求的转发只发出了一次请求, 而重定向则发出了两次请求.

具体:

①. 请求的转发: 地址栏是初次发出请求的地址.
请求的重定向: 地址栏不再是初次发出的请求地址. 地址栏为最后响应的那个地址
②. 请求转发: 在最终的 Servlet 中, request 对象和中转的那个 request 是同一个对象.
请求的重定向: 在最终的 Servlet 中, request 对象和中转的那个 request 不是同一个对象.
③. 请求的转发: 只能转发给当前 WEB 应用的的资源
请求的重定向: 可以重定向到任何资源.
④. 请求的转发: / 代表的是当前 WEB 应用的根目录
请求的重定向: / 代表的是当前 WEB 站点的根目录.

14. HttpServlet:

1). 是一个 Servlet, 继承自 GenericServlet. 针对于 HTTP 协议所定制.

2). 在 service() 方法中直接把 ServletReuqest 和 ServletResponse 转为 HttpServletRequest 和 HttpServletResponse.
并调用了重载的 service(HttpServletRequest, HttpServletResponse)

在 service(HttpServletRequest, HttpServletResponse) 获取了请求方式: request.getMethod(). 根据请求方式有创建了
doXxx() 方法(xxx 为具体的请求方式, 比如 doGet, doPost)

@Override
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException {

HttpServletRequest request;
HttpServletResponse response;

try {
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
} catch (ClassCastException e) {
throw new ServletException("non-HTTP request or response");
}
service(request, response);
}

public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1. 获取请求方式.
String method = request.getMethod();
//2. 根据请求方式再调用对应的处理方法
if("GET".equalsIgnoreCase(method)){
doGet(request, response);
}else if("POST".equalsIgnoreCase(method)){
doPost(request, response);
}
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
// TODO Auto-generated method stub
}

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
}

3). 实际开发中, 直接继承 HttpServlet, 并根据请求方式复写 doXxx() 方法即可.

4). 好处: 直接由针对性的覆盖 doXxx() 方法; 直接使用 HttpServletRequest 和 HttpServletResponse, 不再需要强转.

15. GenericServlet:

1). 是一个 Serlvet. 是 Servlet 接口和 ServletConfig 接口的实现类. 但是一个抽象类. 其中的 service 方法为抽象方法

2). 如果新建的 Servlet 程序直接继承 GenericSerlvet 会使开发更简洁.

3). 具体实现:

①. 在 GenericServlet 中声明了一个 SerlvetConfig 类型的成员变量, 在 init(ServletConfig) 方法中对其进行了初始化
②. 利用 servletConfig 成员变量的方法实现了 ServletConfig 接口的方法
③. 还定义了一个 init() 方法, 在 init(SerlvetConfig) 方法中对其进行调用, 子类可以直接覆盖 init() 在其中实现对 Servlet 的初始化.
④. 不建议直接覆盖 init(ServletConfig), 因为如果忘记编写 super.init(config); 而还是用了 SerlvetConfig 接口的方法,
则会出现空指针异常.
⑤. 新建的 init(){} 并非 Serlvet 的生命周期方法. 而 init(ServletConfig) 是生命周期相关的方法.

public abstract class GenericServlet implements Servlet, ServletConfig {

/** 以下方法为 Servlet 接口的方法 **/

@Override
public void destroy() {}

@Override
public ServletConfig getServletConfig() {
return servletConfig;
}

@Override
public String getServletInfo() {
return null;
}

private ServletConfig servletConfig;
@Override
public void init(ServletConfig arg0) throws ServletException {
this.servletConfig = arg0;
init();
}

public void init() throws ServletException{}

@Override
public abstract void service(ServletRequest arg0, ServletResponse arg1)
throws ServletException, IOException;

/** 以下方法为 ServletConfig 接口的方法 **/
@Override
public String getInitParameter(String arg0) {
return servletConfig.getInitParameter(arg0);
}

@Override
public Enumeration getInitParameterNames() {
return servletConfig.getInitParameterNames();
}

@Override
public ServletContext getServletContext() {
return servletConfig.getServletContext();
}

@Override

public String getServletName() {
return servletConfig.getServletName();
}

}

16.代码区

package com.atguigu.javaweb;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ForwardServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ForwardServlet's doGet");
        
        request.setAttribute("name", "abcde");
        System.out.println("ForwardServlet's name: " + request.getAttribute("name"));
        
        //请求的转发.
        //1. 调用 HttpServletRequest 的 getRequestDispatcher() 方法获取  RequestDispatcher 对象
        //调用 getRequestDispatcher() 需要传入要转发的地址
        String path = "testServlet";
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/" + path);
        
        //2. 调用 HttpServletRequest 的 forward(request, response) 进行请求的转发. 
        requestDispatcher.forward(request, response); 
    }

}

ForwardServlet

package com.atguigu.javaweb;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class LoginServlet extends GenericServlet {

    //对当前的 Servlet 进行初始化: 覆盖 init 方法
    @Override
    public void init(javax.servlet.ServletConfig config) throws ServletException {
        super.init(config);
    }
    
    @Override
    public void service(ServletRequest request, ServletResponse response)
            throws ServletException, IOException {
        
        //获取请求方式是 GET 还是 POST
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        String method = httpServletRequest.getMethod();
        System.out.println(method); 
        
        //1. 获取请求参数: username, password
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        //2. 获取当前 WEB 应用的初始化参数: user, password.
        //需要使用 ServletContext 对象. 
        String initUser = getServletContext().getInitParameter("user");
        String initPassword = getServletContext().getInitParameter("password");

        PrintWriter out = response.getWriter();
        
        //3. 比对
        //4. 打印响应字符串. 
        if(initUser.equals(username) && initPassword.equals(password)){
            out.print("Hello: " + username);
        }else{
            out.print("Sorry: " + username);
        }
        
        
    }

}

LoginServlet

package com.atguigu.javaweb;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet2 extends HttpServlet {
    /**
     * 
     */
    private static final long serialVersionUID = 1L; 

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws IOException {

        // 获取请求方式是 GET 还是 POST
        String method = request.getMethod();
        System.out.println(method);

        // 1. 获取请求参数: username, password
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // 2. 获取当前 WEB 应用的初始化参数: user, password.
        // 需要使用 ServletContext 对象.
        String initUser = getServletContext().getInitParameter("user");
        String initPassword = getServletContext().getInitParameter("password");

        PrintWriter out = response.getWriter();

        // 3. 比对
        // 4. 打印响应字符串.
        if (initUser.equals(username) && initPassword.equals(password)) {
            out.print("Hello: " + username);
        } else {
            out.print("Sorry: " + username);
        }

    }

}

LoginServlet2

package com.atguigu.javaweb;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet3 extends HttpServlet{
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        
        PrintWriter out = resp.getWriter();
        
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql:///atguigu";
            String user = "root";
            String password2 = "1230";
            connection = DriverManager.getConnection(url, user, password2);
            
            String sql = "SELECT count(id) FROM users WHERE username = ? " +
                    "AND password = ?";
            
            statement = connection.prepareStatement(sql);
            statement.setString(1, username);
            statement.setString(2, password);
            
            resultSet = statement.executeQuery();

            StringBuilder result = new StringBuilder();
            result.append("<html>")
                  .append(" <head>")
                  .append(" </head>") 
                  .append("</html>");
            
            if(resultSet.next()){
                int count = resultSet.getInt(1);
                
                if(count > 0){
                    out.print(result.toString());
                    
                }else{
                    out.print("Sorry: " + username);
                }
            }
            
            
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            try {
                if(resultSet != null){
                    resultSet.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }

            try {
                if(statement != null){
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            
            try {
                if(connection != null){
                    connection.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            
        }
        
        
        
    }

}

LoginServlet3

package com.atguigu.javaweb;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * 自定义的一个 Servlet 接口的实现类: 让开发的任何 Servlet 都继承该类. 以简化开发
 */
public abstract class MyGenericServlet implements Servlet, ServletConfig {

    /** 以下方法为 Servlet 接口的方法 **/
    @Override
    public void destroy() {}

    @Override
    public ServletConfig getServletConfig() {
        return servletConfig;
    }

    @Override
    public String getServletInfo() {
        return null;
    }

    private ServletConfig servletConfig;
    
    @Override
    public void init(ServletConfig arg0) throws ServletException {
        this.servletConfig = arg0;
        init();
    }

    public void init() throws ServletException{}

    @Override
    public abstract void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException;

    /** 以下方法为 ServletConfig 接口的方法 **/
    @Override
    public String getInitParameter(String arg0) {
        return servletConfig.getInitParameter(arg0);
    }

    @Override
    public Enumeration getInitParameterNames() {
        return servletConfig.getInitParameterNames();
    }

    @Override
    public ServletContext getServletContext() {
        return servletConfig.getServletContext();
    }

    @Override
    public String getServletName() {
        return servletConfig.getServletName();
    }

}

MyGenericServlet

package com.atguigu.javaweb;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 针对于 HTTP 协议定义的一个 Servlet 基类
 */
public class MyHttpServlet extends MyGenericServlet {

    @Override
    public void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException {
        
        if(arg0 instanceof HttpServletRequest){
            HttpServletRequest request = (HttpServletRequest)arg0;
            
            if(arg1 instanceof HttpServletResponse){
                HttpServletResponse response = (HttpServletResponse)arg1;
                
                service(request, response);
            }
        }
        
    }
    
    public void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1. 获取请求方式.
        String method = request.getMethod();
        
        //2. 根据请求方式再调用对应的处理方法
        if("GET".equalsIgnoreCase(method)){
            doGet(request, response);
        }else if("POST".equalsIgnoreCase(method)){
            doPost(request, response);
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException{
        // TODO Auto-generated method stub
        
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        
    }


}

MyHttpServlet

package com.atguigu.javaweb;

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 RedirectServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("RedirectServlet's doGet");
        
        request.setAttribute("name", "xyzmn");
        System.out.println("RedirectServlet's name: " + request.getAttribute("name"));
        
        
        //执行请求的重定向, 直接调用 response.sendRedirect(path) 方法,
        //path 为要重定向的地址
        String path = "testServlet";
        response.sendRedirect(path);
    }

}

RedirectServlet

package com.atguigu.javaweb;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestAttr
 */
public class TestAttr extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        PrintWriter out = response.getWriter();
        
        //1. 在 Servlet 中无法得到 pageContext 对象
        
        //2. request
        Object requestAttr = request.getAttribute("requestAttr");
        out.print("requestAttr: " + requestAttr);
        out.print("<br><br>");
        
        //3. session
        Object sessionAttr = request.getSession().getAttribute("sessionAttr");
        out.print("sessionAttr: " + sessionAttr);
        out.print("<br><br>");
        
        //4. application
        Object applicationAttr = getServletContext().getAttribute("applicationAttr");
        out.print("applicationAttr: " + applicationAttr);
        out.print("<br><br>");
                
    }

}

TestAttr

package com.atguigu.javaweb;

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 TestServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("TestServlet's doGet 方法. ");
        
        System.out.println("TestServlet's name: " + request.getAttribute("name"));
        
    }

}

TestServlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  
  <context-param>
    <param-name>user</param-name>
    <param-value>atguigu</param-value>
  </context-param>
  <context-param>
    <param-name>password</param-name>
    <param-value>123567</param-value>
  </context-param>
  
  <servlet>
    <servlet-name>loginServlet</servlet-name>
    <servlet-class>com.atguigu.javaweb.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>loginServlet</servlet-name>
    <url-pattern>/loginServlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <description></description>
    <display-name>ForwardServlet</display-name>
    <servlet-name>ForwardServlet</servlet-name>
    <servlet-class>com.atguigu.javaweb.ForwardServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ForwardServlet</servlet-name>
    <url-pattern>/forwardServlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <description></description>
    <display-name>TestServlet</display-name>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>com.atguigu.javaweb.TestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/testServlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <description></description>
    <display-name>RedirectServlet</display-name>
    <servlet-name>RedirectServlet</servlet-name>
    <servlet-class>com.atguigu.javaweb.RedirectServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RedirectServlet</servlet-name>
    <url-pattern>/redirectServlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>hellojsp</servlet-name>
    <jsp-file>/hello.jsp</jsp-file>
    <init-param>
      <param-name>test</param-name>
      <param-value>testValue</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>hellojsp</servlet-name>
    <url-pattern>/hellojsp</url-pattern>
  </servlet-mapping>
    
  <servlet>
    <description></description>
    <display-name>TestAttr</display-name>
    <servlet-name>TestAttr</servlet-name>
    <servlet-class>com.atguigu.javaweb.TestAttr</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestAttr</servlet-name>
    <url-pattern>/testAttr</url-pattern>
  </servlet-mapping>
  
</web-app>

web.xml

<%@ 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>    
    <h4>AAA PAGE</h4>    
    <a href="b.jsp">TO B PAGE</a>    
</body>
</html>

a.jsp

<%@page import="java.util.Date"%>
<%@ 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("pageContextAttr", "pageContextValue");
        request.setAttribute("requestAttr", "requestValue");
        session.setAttribute("sessionAttr", "sessionValue");
        application.setAttribute("applicationAttr", "applicationValue");
    %>
    
    <h2>Attr 111 Page: <%= new Date() %></h2>
    
    <br><br>
    pageContextAttr: <%= pageContext.getAttribute("pageContextAttr") %>
    
    <br><br>
    requestAttr: <%= request.getAttribute("requestAttr") %>

    <br><br>
    sessionAttr: <%= session.getAttribute("sessionAttr") %>    
    
    <br><br>
    applicationAttr: <%= application.getAttribute("applicationAttr") %>
    
    <br><br>
    <a href="attr_2.jsp">To Attr2 Page</a>

    <br><br>
    <a href="testAttr">To Attr Servlet</a>
    
    <% 
        request.getRequestDispatcher("/attr_2.jsp").forward(request, response);
    %>
        
    
</body>
</html>

attr_1.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.util.Date"%>
<!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>
    
    <h2>Attr 222 Page: <%= new Date() %></h2>
    
    <br><br>
    pageContextAttr: <%= pageContext.getAttribute("pageContextAttr") %>
    
    <br><br>
    requestAttr: <%= request.getAttribute("requestAttr") %>

    <br><br>
    sessionAttr: <%= session.getAttribute("sessionAttr") %>    
    
    <br><br>
    applicationAttr: <%= application.getAttribute("applicationAttr") %>
    
</body>
</html>

attr_2.jsp

<%@ 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>

    <h4>BBB PAGE</h4>
    
    <% 
        //1. 请求转发的代码:
        //request.getRequestDispatcher("/c.jsp").forward(request, response);
        //request.getRequestDispatcher("http://www.atguigu.com").forward(request, response);
    
        //2. 请求的重定向
        response.sendRedirect(request.getContextPath()+"/c.jsp");
        //response.sendRedirect("http://www.atguigu.com");
    %>
    
</body>
</html>

b.jsp

<%@ 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>

    <h4>CCC PAGE</h4>

</body>
</html>

c.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ page isErrorPage="true" %>

<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    
    
    
</body>
</html>

error.jsp

<%@page import="java.util.Date"%>
<%@ 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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>

    <% 
        Date date = new Date();
        //System.out.print("-->" + date); 
    %>
    
    <% 
        String str = date.toString();    
        //没有声明就可以使用的对象
        String name = request.getParameter("name");
        System.out.println(name);
        
        //
        System.out.println(response instanceof HttpServletResponse);
        
        ServletRequest req = pageContext.getRequest();
        System.out.print(req == request); 
        
        System.out.println(session.getId());
        
        System.out.println(application.getInitParameter("password"));
        
        System.out.println(config.getInitParameter("test"));
        
        out.println(request.getParameter("name")); 
        out.println("<br><br>");
        out.println(application.getInitParameter("password"));
        out.println("<br><br>");
        out.println(this);
        out.println("<br><br>");
        out.println(page);
        
    /*null
true
true50F1C99C85D6821D43A1CA2DC23787E4
123567
null
*/    
    %>

</body>
</html>

hello.jsp

<%@page import="java.util.Date"%>
<%@ 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>
    
    <% 
        Date date = new Date();
        out.print(date);
    %>
    
    <br><br>
    
    <!-- JSP 表达式 -->
    <%= date %>
    
    <% 
        String ageStr = request.getParameter("age");
        Integer age = Integer.parseInt(ageStr);
        
        if(age >= 18){
    %>
            成人...
    <%
        }else{
    %>
            未成人...
    <%
        }
    %>
    
    <%! 
        void test(){}
    %>
    
    <%-- JSP 注释 --%><!-- HTML 注释 -->
    
    <!-- 
    <% 
        System.out.println("打印信息...");
    %>
    -->
    
</body>
</html>

hello2.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>
    
    <form action="loginServlet" method="post">
        
        user: <input type="text" name="username"/>
        password: <input type="password" name="password"/>
        
        <input type="submit" value="Submit"/>
    
    </form>
    
</body>
</html>

<!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>
    
    <a href="loginServlet">Test</a>
    
    <br><br>
    
    <a href="forwardServlet">Forward</a>
    
    <br><br>
    
    <a href="redirectServlet">Redirect</a>
</body>
</html>

test.html