Servlet(2)：通过servletContext对象实现数据共享

一，ServletContext介绍

• web容器在启动时，它会为每一个web应用程序都创建一个ServletContext对象，它代表当前web应用
• 多个Servlet通过ServletContext对象实现数据共享
• 获取web应用的初始化参数
• 用ServletContext实现请求转发
• 使用ServletContext对象读取资源文件

二，通过servletContext对象实现数据共享

1，通过this获得ServletContext，实现数据的共享

//存入数据
        response.setCharacterEncoding("UTF-8");
  ServletContext context = this.getServletContext();
        String username="清水河";
        context.setAttribute("name",username);
        response.getWriter().print("设置name成功："+username);

//读取数据
       response.setCharacterEncoding("UTF-8");
ServletContext context = this.getServletContext();
        String name = (String) context.getAttribute("name");      
        response.getWriter().print("我们获取的信息为："+name);

2，运行结果

三，通过servletContext对象读取网站配置文件

1，新建一个properties文件

driver=com.mysql.jdbc.Driver
username=root
password=123456
url=jdbc:mysql://localhost:3306/smbms

2，编写servlet类

//获取配置文件的路径
String realPath = this.getServletContext().getRealPath(
        "WEB-INF/classes/resources/database.properties");
System.out.println("获取的路径："+realPath);
Properties properties = new Properties();

FileInputStream is = new FileInputStream(realPath);
//把文件流加载到配置文件对象中

properties.load(is);
String driver = properties.getProperty("driver");

String username = properties.getProperty("username");

String password = properties.getProperty("password");

String url = properties.getProperty("url");
//响应到网页

response.getWriter().print(driver);

response.getWriter().print(username);

response.getWriter().print(password);

response.getWriter().print(url);

3，配置web.xml

<servlet>
    <servlet-name>ServletTest03</servlet-name>
    <servlet-class>com.kuang.servlet.ServletTest03</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ServletTest03</servlet-name>
    <url-pattern>/s3</url-pattern>
</servlet-mapping>

4，访问查看

localhost：8080/demo02/s3

四，简单验证码

       //自动刷新网页
        response.setHeader("refresh","2");
    <span class="hljs-comment">//验证码是一个图片 ， 我们需要制作一个图片</span>
    BufferedImage image = <span class="hljs-keyword">new</span> BufferedImage(<span class="hljs-number">100</span>,<span class="hljs-number">30</span>,BufferedImage.TYPE_3BYTE_BGR);

    <span class="hljs-comment">//图片写入一些东西</span>
    Graphics2D graphics = image.createGraphics();
    graphics.setColor(Color.red);
    <span class="hljs-built_in">String</span> <span class="hljs-built_in">num</span> = <span class="hljs-built_in">String</span>.valueOf(newRandom());
    graphics.drawString(<span class="hljs-built_in">num</span>,<span class="hljs-number">10</span>,<span class="hljs-number">10</span>);

    <span class="hljs-comment">//想办法让浏览器知道我们给的是一张图片</span>
    response.setContentType(<span class="hljs-string">"image/jpg"</span>);

    <span class="hljs-comment">//让网站去打开图片</span>
    ImageIO.write(image,<span class="hljs-string">"jpg"</span>,response.getOutputStream());
}

<span class="hljs-comment">//生成随机数</span>
public <span class="hljs-built_in">int</span> newRandom(){
    <span class="hljs-built_in">int</span> <span class="hljs-built_in">num</span> = (<span class="hljs-built_in">int</span>)(Math.random()*<span class="hljs-number">9</span>+<span class="hljs-number">1</span>)*<span class="hljs-number">100000</span>;
    <span class="hljs-keyword">return</span> <span class="hljs-built_in">num</span>;
}