ServletContext功能获取MIME类型和域对象和获取文件服务器路径

ServletContext功能

1.获取MIME类型

MIME类型：在互联网通信过程中定义的一种文件数据类型

　　格式：大类型/小类型　　text/html　　image/jpeg

获取：String getMimeType(String file)

@WebServlet("/servletContextD2")
public class ServletContextD2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //2.通过HTTPServlet获取
        ServletContext context = this.getServletContext();
        //定义文件名称
        String str = "a.jpg";
        //获取MIME类型
        String mimeType = context.getMimeType(str);
        System.out.println(mimeType);
    }

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

获取出来的为image/jpeg

 

 

2.域对象：共享数据

1.setAttribute(String name,Object value)通过名称设置值

2.getAttribute(String name)通过名称获取值

3.removeAttribute(String name)通过名称移除对应的值键

 

ServletContext对象范围：所有用户所有请求的数据

ServletContextD3 ：

@WebServlet("/servletContextD3")
public class ServletContextD3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //2.通过HTTPServlet获取
        ServletContext context = this.getServletContext();
        //设置数据
        context.setAttribute("msg","haha");
    }

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

ServletContextD4：

@WebServlet("/servletContextD4")
public class ServletContextD4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //2.通过HTTPServlet获取
        ServletContext context = this.getServletContext();
        //获取数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);
    }

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

先去访问3进行存入进数据

可以在换个浏览器访问4就可以获取到3的数据

3.获取文件服务器路径

获取文件的真实(服务器)路径

1.方法：String getRealPath(String path)

@WebServlet("/servletContextD5")
public class ServletContextD5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //2.通过HTTPServlet获取
        ServletContext context = this.getServletContext();
        //获取文件的服务器路径
        String realPath = context.getRealPath("/b.txt");//web目录下的资源访问
        System.out.println(realPath);

        String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录资源访问
        System.out.println(c);

        String a = context.getRealPath("/WEB-INF/classes/a.txt");//获取src下的a.txt的资源访问
        System.out.println(a);
        
    }

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

 

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