会话技术！

会话技术

实现会话跟踪技术方式：

• 客户端会话跟踪技术：Cookie
• 服务端会话跟踪技术：Session

两者之间的区别：
cookie是存储在浏览器中的
session是存储在服务器中的

对于cookie的操作主要分为两大类，分别是发送cookie和获取cookie

• 发送cookie

1. 创建cookie对象并设置数据

Cookie cookie = new Cookie(“key”,“value”);

2. 发送cookie到客户端：使用response对象

response.addCookie(cookie)
案例：
(1)创建Maven项目cookie-demo，并在pom.xml添加依赖

<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>

javax.servlet javax.servlet-api 3.1.0 provided javax.servlet.jsp jsp-api 2.2 provided jstl jstl 1.2 taglibs standard 1.1.2 org.apache.tomcat.maven tomcat7-maven-plugin 2.2

(2)编写Servlet类，名称为AServlet

@WebServlet(“/aServlet”)
public class AServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    this.doGet(request, response);
}

}

(3)在Servlet中创建Cookie对象，存入数据，发送给前端

@WebServlet(“/aServlet”)
public class AServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//发送Cookie
//1. 创建Cookie对象
Cookie cookie = new Cookie(“username”,“zs”);
//2. 发送Cookie，response
response.addCookie(cookie);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    this.doGet(request, response);
}

}

4）启动测试，在浏览器查看Cookie对象中的值

访问http://localhost:8080/cookie-demo/aServlet

chrome浏览器查看Cookie的值
选中打开开发者工具或者 使用快捷键F12 或者 Ctrl+Shift+I

• 获取Cookie

• 获取客户端携带的所有Cookie，使用request对象

Cookie[] cookies = request.getCookies();

• 遍历数组，获取每一个Cookie对象：for
• 使用Cookie对象方法获取数据

cookie.getName();
cookie.getValue();

在BServlet中使用request对象获取Cookie数组，遍历数组，从数据中获取指定名称对应的值

@WebServlet("/bServlet")
public class BServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        //获取Cookie
        //1. 获取Cookie数组
        Cookie[] cookies = request.getCookies();
        //2. 遍历数组
        for (Cookie cookie : cookies) {
    
            //3. 获取数据
            String name = cookie.getName();
            if("username".equals(name)){
    
                String value = cookie.getValue();
                System.out.println(name+":"+value);
                break;
            }
        }

    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        this.doGet(request, response);
    }
}

启动测试，在控制台打印出获取的值

访问`http://localhost:8080/cookie-demo/bServlet