servlet中的初始化与获取上下文对象的方法

￡神魔★判官ぃ 2022-06-01 00:45 150阅读 0赞

@Override
    	public void init(ServletConfig config) throws ServletException {
    		//加载初始化配置
    		//获取到当前servlet的配置信息
    		String charset = config.getInitParameter("charset");
    		String value  = config.getInitParameter("key");
    		
    		//获取到所有的配置信息
    		Enumeration<String> num = config.getInitParameterNames();
    		while(num.hasMoreElements()) {
    			String name = num.nextElement();
    			System.out.print(name+":");
    			System.out.println(config.getInitParameter(name));
    		}
    		
    		String username = config.getInitParameter("username");
    		System.out.println("username:"+username);
    		
    		//获取到servlet的名称
    		String values = config.getServletName();
    		System.out.println(values);
    	}

//获取上下文对象方式1
    	private ServletContext context;
    	
    	@Override
    	public void init(ServletConfig config) throws ServletException {
    
    		context = config.getServletContext();
    	
    	}
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		//获取已经配置的上下文对象
    		String contextVla=  context.getInitParameter("abc");
    		System.out.println("配置的全局信息为："+contextVla);		
    		
    		//将数据保存到上下文对象
    		context.setAttribute("username", "xiaowang");
    		//获取上下文对象
    		String str = (String) context.getAttribute("username");
    		System.out.println(str);
    		
    
    	}

/**
    	 * 重写了init方法就必须通过init方法里面的config对象获取到上下文对象
    	 */
    		//获取到上下文对象方式2
    	@Override
    	protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
    		ServletContext context = this.getServletContext();
    		String value = (String) context.getAttribute("username");
    		System.out.println(value);
    		
    		String contextVla=  context.getInitParameter("abc");
    		System.out.println("配置的全局信息为："+contextVla);
    	}

//上下文对象应用---获取到网站访问的次数
    public class TestServlet4 extends HttpServlet{
    	
    	private ServletContext context;
    	
    	@Override
    	public void init(ServletConfig config) throws ServletException {
    		context = config.getServletContext();
    	}
    	
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		
    		resp.setCharacterEncoding("utf-8");
    		resp.setContentType("text/html;charset=utf-8");
    		
    		PrintWriter out = resp.getWriter();
    		Object obj = context.getAttribute("num");
    		
    		if(obj==null) {
    			context.setAttribute("num", "1");
    			out.print("访问次数为：1");
    		}else {
    			int res = Integer.parseInt(obj.toString());
    			res++;
    			context.setAttribute("num", res+"");
    			out.print("访问次数为："+res);
    		}
    	}
    }