Servlet(2):通过servletContext对象实现数据共享
阅读原文时间:2023年07月12日阅读:1
  • 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

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

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");

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

       //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>;
}

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