# JavaWeb笔记（五）---- ServletContext

本人个人学习笔记 未经授权不允许转发

1. 共享数据
2. 获取初始化参数
3. 请求转发
4. 读取资源文件

Web容器在启动时会为每个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用。他可以起到共享数据的作用。在一个servlet中保存的数据可以被另一个servlet拿到

在java目录下创建两个类一个叫 GetServletContext 另一个叫 SetServletContext

GetServletContext：

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //设置显示的页面类型和字符集utf-8
    resp.setContentType("text/html;charset=utf-8");
    ServletContext context = this.getServletContext();
    String username = (String) context.getAttribute("username");
    resp.getWriter().print("名字："+username); 
}

SetServletContext：

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
	ServletContext context = this.getServletContext();
    String username = "张三";
    context.setAttribute("username",username); //将一个数据保存在了ServletContext中
}

在xml文件中添加初始化参数

  
    url
    www.baidu.com
  

使用getInitParameter获取初始化参数

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    resp.setContentType("text/html;charset=utf-8");
    ServletContext context = this.getServletContext();
    String text = (String) context.getInitParameter("url");
    resp.getWriter().print(text);
}

网页显示路径不会变化 但是内容会改变

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    
    context.getRequestDispatcher("/getp").forward(req,resp);
}

Properties:

• 在java目录下创建aa.properties
• 在resource目录下创建db.properties
  内容：

username=Admin
password=123456

两个properties都被打包到了 classes （类路径下）

 
        
            
                src/main/resources
                
                    ****.xml
                
                true
            
            
                src/main/java
                
                    ****.xml
                
                true
            
        

对应程序读取properties

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        ServletContext context = this.getServletContext();
        InputStream is = context.getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties prop = new Properties();
        prop.load(is);
        String username = (String) prop.getProperty("username");
        String pwd = (String) prop.getProperty("password");
        resp.getWriter().print(username+":"+pwd);
    }