context的简单应用

数据上传

context.setAttribute

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username="吴梓超";
        context.setAttribute("username",username);
    }

数据请求

context.getAttribute

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username =(String) context.getAttribute("username");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字："+username);
    }

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

参数获取

context.getInitParameter

context-param>
	<param-name>url</param-name>
	<param-value>jdbc:mysql://localhost:3306</param-value>
</context-param>

 @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);
    }

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

请求转发

context.getRequestDispatcher("/s3").forward(req,resp);

 @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        context.getRequestDispatcher("/s3").forward(req,resp);

    }

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

读取资源文件

需要一个文件流

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
    Properties prop=new Properties();
    prop.load(is);
    String name = prop.getProperty("username");
    String password = prop.getProperty("password");
    resp.getWriter().print(name+"+"+password);
}

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