🥼JavaWeb~(叁)Cookie/Session验证,JSP开篇

笔记代码
Servlet
- HttpServletRequest
Cookie、Session
- Cookie
- Session
JSP

笔记代码

Servlet

HttpServletRequest

例子: 在 index.jsp 提交表单信息给 /login,此 Servlet 后端读取发送来的表单信息并在页面输出显示.

删掉并用 idea 重建 index.jsp,会补齐一些编码信息.

<%@ page
    contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>登录页面</title>
</head>
<body>
<h1>登录</h1>

<div style="text-align: center">
  <form action="/login" method="post">
    <label>
      用户名:
      <input type="text" name="username" placeholder="无"/><br>
    </label>
    <label>
      密码:
      <input type="password" name="password" placeholder=""/><br>
    </label>

    爱好:
    <label><input type="checkbox" name="hobbys" value="女孩"/>女孩</label>
    <label><input type="checkbox" name="hobbys" value="代码"/>代码</label>
    <label><input type="checkbox" name="hobbys" value="动漫"/>动漫</label>
    <label><input type="checkbox" name="hobbys" value="美食"/>美食</label><br>
    <input type="submit">
  </form>
</div>
</body>
</html>

src/main/java/servlet/Login.java

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;

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

public class Login extends HttpServlet {
  /**
  *
  */
  private static final long serialVersionUID = -7958099474557186407L;

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf8");
    resp.setContentType("text/html");
    resp.setCharacterEncoding("utf8");
    PrintWriter writer = resp.getWriter();

    String username = req.getParameter("username");
    String password = req.getParameter("password");
    String[] hobbys = req.getParameterValues("hobbys");

    writer.println("username: " + username);
    writer.println("password: " + password);
    writer.println("爱好: " + Arrays.toString(hobbys));
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doGet(req, resp);
  }
}

web.xml

<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>login</servlet-name>
    <servlet-class>servlet.Login</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

Cookie 是服务端在客户端上做的标记,用请求和响应进行传递,用来记录用户的访问信息 (客户端技术)
session 是在服务端上保存用户的访问信息 (服务端技术)

例子: 访问 /cookie 时,会显示上一次访问此 URL 的时间 (这个时间通过服务端传给客户端 Cookie 来记录)

src/main/java/servlet/HelloCookie.java

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

public class HelloCookie extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf-8");
    resp.setCharacterEncoding("utf-8");
    resp.setContentType("text/html");
    PrintWriter writer = resp.getWriter();

    // 获取客户端请求中携带的cookie
    Cookie[] cookies = req.getCookies();
    boolean isFirst = true; // 标志是否是第一次访问

    writer.println("你上一次访问时间是: ");
    for (Cookie cookie : cookies) {
      if (cookie.getName().equals("LastLoginTime")) {
        isFirst = false;
        writer.println(cookie.getValue());
      }
    }
    if (isFirst) {
      writer.println("这次是第一次访问.");
    }

    // 响应携带cookie返回给客户端
    Cookie lastLoginTime = new Cookie("LastLoginTime", System.currentTimeMillis() + "");// 非字符串+"" = 字符串
    resp.addCookie(lastLoginTime);
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doGet(req, resp);
  }
}

web.xml

<!DOCTYPE web-app PUBLIC
    "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>cookie</servlet-name>
    <servlet-class>servlet.HelloCookie</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>cookie</servlet-name>
    <url-pattern>/cookie</url-pattern>
  </servlet-mapping>
</web-app>

常用方法

Cookie[] cookies = req.getCookies(); //获得Cookie
cookie.getName(); //获得cookie中的key
cookie.getValue(); //获得cookie中的vlaue
new Cookie("lastLoginTime", System.currentTimeMillis()+""); //新建一个cookie
cookie.setMaxAge(24*60*60); //设置cookie的有效期
resp.addCookie(cookie); //响应给客户端一个cookie

一些细节
- cookie 大小和数量
  - 不同浏览器支持的大小和数量不一样,大小都是 4K 左右,数量为每域名几十到无数个不等.
  cookie 大小限制
- 设置存活期:
  - 不设置: 关闭浏览器自动失效
  - 设置为 0,立即失效.
- 遇到传输的中文乱码问题,可以用 URLEncoder 编码
  URLEncoder.encode("齐下无贰","utf-8")
  URLDecoder.decode(cookie.getValue(),"UTF-8")

Session

cookie 用来传输一些字符串验证信息,并存放在客户端中.
而 session 可以存放更宽泛的数据(对象,文件等等),其数据存放在服务端.
- 服务端传给客户端一个名为 JSESSIONID 的 cookie 用来验证 session
- 一个 Seesion 对象独占一个浏览器,不同浏览器有不同的 session

例子: 开启服务器并访问第一个页面 localhost:8080 时,session 就被创建了,然后访问 /setSession设置 person 信息,再访问 /getSession会显示 person 信息.

src/main/java/servlet/SetSession.java

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;

public class SetSession extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    //解决乱码问题
    req.setCharacterEncoding("UTF-8");
    resp.setCharacterEncoding("UTF-8");
    resp.setContentType("text/html");

    //得到Session和writer
    HttpSession session = req.getSession();
    PrintWriter writer = resp.getWriter();

    //给Session中存东西
    session.setAttribute("person", new Person("齐下无贰", 100));

    //获取Session的ID
    String sessionId = session.getId();

    //判断Session是不是新创建
    if (session.isNew()) {
      writer.println("session创建成功,ID: " + sessionId);
    } else {
      writer.println("session已经在服务器中存在了,ID: " + sessionId);
    }
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doGet(req, resp);
  }
}

class Person {
  private String name;
  private int age;

  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }

  public void setName(String name) {
    this.name = name;
  }

  public void setAge(int age) {
    this.age = age;
  }

  @Override
  public String toString() {
    return "Person{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }
}

src/main/java/servlet/GetSession.java

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

public class GetSession extends HttpServlet {
  /**
   *
   */
  private static final long serialVersionUID = -4606977948300644893L;

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //解决乱码问题
    req.setCharacterEncoding("UTF-8");
    resp.setCharacterEncoding("UTF-8");
    resp.setContentType("text/html");

    //得到Session和writer
    HttpSession session = req.getSession();
    PrintWriter writer = resp.getWriter();

    // 获取属性并输出
    Person person = (Person) session.getAttribute("person");
    writer.println(person);

    // 移除属性
    session.removeAttribute("name");

    //手动注销Session
    session.invalidate();
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doGet(req, resp);
  }
}

web.xml

<!DOCTYPE web-app PUBLIC
    "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>setSession</servlet-name>
    <servlet-class>servlet.SetSession</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>getSession</servlet-name>
    <servlet-class>servlet.GetSession</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>setSession</servlet-name>
    <url-pattern>/setSession</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>getSession</servlet-name>
    <url-pattern>/getSession</url-pattern>
  </servlet-mapping>
</web-app>

session 有效期问题
- 默认失效时间是 30 分钟
- 是从 session 断开连接(浏览器关闭开始计算的),而不是从 session 连接开始计算
- 可以在 web.xml 中设置
  <session-config>
  <session-timeout>1</session-timeout>
  </session-config>
关于 session 的失效时间和过期

JSP

介绍

JSP (Java Server Pages),写法类似 HTML 的动态 Java 页面
最终 JSP 会被转换为一个 Java 类,实际上本质就是 Servlet 的简化实现.
- *.jsp -> *.java -> *.class

jsp 转换为的 java 文件核心部分:

//初始化
public void _jspInit() {
}

//销毁
public void _jspDestroy() {
}

//JSPService
public void _jspService(HttpServletRequest request,HttpServletResponse response)

JSPService 内初始化的对象

final javax.servlet.jsp.PageContext pageContext;  //页面上下文
javax.servlet.http.HttpSession session = null;    //session
final javax.servlet.ServletContext application;   //Context->application
final javax.servlet.ServletConfig config;         //config
javax.servlet.jsp.JspWriter out = null;           //writer->out
final java.lang.Object page = this;               //当前页面->page
HttpServletRequest request                        //请求
HttpServletResponse response                      //响应

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;

JSP 中可以写 Java 代码,Java 代码会原封不动的正常执行
- HTML 代码在 JSP->Java 时会被转换成 out.write("<html>\r\n"); 这种形式.

依赖导入

<!-- servlet依赖 -->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>4.0.1</version>
  <scope>provided</scope>
</dependency>
<!-- JSP依赖 -->
<dependency>
  <groupId>javax.servlet.jsp</groupId>
  <artifactId>javax.servlet.jsp-api</artifactId>
  <version>2.3.3</version>
  <scope>provided</scope>
</dependency>
<!-- JSTL表达式依赖 -->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>jstl</artifactId>
  <version>1.2</version>
</dependency>
<!-- Standard标签库 -->
<dependency>
  <groupId>taglibs</groupId>
  <artifactId>standard</artifactId>
  <version>1.1.2</version>
</dependency>

基本语法

<%@ page import="java.util.Date" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>测试</title>
  </head>
  <body>
    <!-- 这是HTML的注释,会在客户端显示 -->
    <%-- 这是JSP注释,不会在客户端显示 --%>

    <!--
      JSP表达式: 用来将程序输出到客户端
      <%= "变量或者表达式"%>
    -->
    <%= new Date()%>

    <!--
      JSP脚本片段
      <% jsp脚本片段 %>
    -->
    <%
      int sum = 0;
      for (int i = 1; i <=100 ; i++) { sum+=i; }
      out.println("<h1>Sum="+sum+"</h1>");
    %>

    <!--
      JSP声明
      会被编译到JSP生成Java的类中！其他的，就会被生成到_jspService方法中！
    -->
    <%!
      static {
        System.out.println("Loading Servlet!");
      }

      private int globalVar = 0;

      public void kuang(){
        System.out.println("进入了方法Kuang！");
      }
    %>
  </body>
</html>