Filter过滤器

Fileter可以实现：

1）客户端的请求访问servlet之前拦截这些请求，对用户请求进行预处理

2）对HttpServletResponse进行后处理；

注意

多个Filter的执行顺序在web.xml配置文件中的配置顺序一致，一般把feilter配置在servlet之前

代码示例

public class MyFilter implements Filter {

	@Override

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

			throws IOException, ServletException {

	System.out.println("过滤器拦截成功");

		request.setCharacterEncoding("UTF-8");

		response.setCharacterEncoding("GBK");

		//放行请求

		chain.doFilter(request, response);

	}

}

web.xml配置Filter

 <!-- 配置filter过滤器 -->

  <filter>

   <!-- 别名 -->

  	<filter-name>my</filter-name>

  	 <!-- 地址 -->

  	<filter-class>code.filter.MyFilter</filter-class>

  </filter>

   <!-- 配置filter映射关系 -->

  <filter-mapping>

  	<filter-name>my</filter-name>

  	 <!-- 设置拦截路径 ，路径为/* 为拦截所有路径-->

  	<url-pattern>/m</url-pattern>

  </filter-mapping>

执行顺序

在web.xml设置初始化参数

getInitParameter（）方法可以获取在web.xml配置文件中配置的init-param参数

//在MyFilter内的init方法验证

@Override

	public void init(FilterConfig filterConfig) throws ServletException {

		System.out.println("filter-init");

		String site = filterConfig.getInitParameter("Site");

		System.out.println(site);

	}

listener监听器

定义

用于监听web项目的常见对象

HttpServletRequest/HttpSession/ServltContext/HttpServletResponse

作用

1）监听web对象的创建与销毁

2）监听web对象属性的变化

3）监听session绑定javabean的操作（Java类）

代码

package code.listener;

import javax.servlet.ServletRequestEvent;

import javax.servlet.ServletRequestListener;

public class ReqListener implements ServletRequestListener{

	@Override

	public void requestDestroyed(ServletRequestEvent sre) {

		System.out.println("listener-req-destroy");

	}

	@Override

	public void requestInitialized(ServletRequestEvent sre) {

		System.out.println("listener-req-init");

	}

}

web.xml配置Listener

运行顺序

filter过滤器和listener监听器的区别

WEB-INF目录

利用反射创建BaseServlet实现调用自定义业务方法

BaseServlet不需要再配置web.xml，因为只需要其提供doGet（）doPost（）方法



public class BaseServlet extends HttpServlet{

	@Override

	protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

		//获取请求中的method参数，该参数的值，表示业务方法的名字

		String mName = req.getParameter("method");//在路径后加？method=xxx

		//this当前类对象，创建反射的Class类对象

		Class c = this.getClass();

		try {

                        //创建反射method对象

			Method method = c.getDeclaredMethod(mName, HttpServletRequest.class,HttpServletResponse.class);

			//执行方法

			method.invoke(this, req, res);

		} catch (Exception e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

	@Override

	protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

		doGet(req, res);

	}

	public void test(HttpServletRequest req, HttpServletResponse res) throws IOException{

		PrintWriter out = res.getWriter();

		out.write("baseservlet-function-test()");

		out.flush();

		if(out!=null) out.close();

	}

	public void test2(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException{

		req.getRequestDispatcher("page/demo.jsp").forward(req, res);

	}

}

可以将BaseServlet设置doGet（）方法，然后其他的servlet类都可以继承这个类实现调用自定义业务方法

public class BaseServlet extends HttpServlet{

	@Override

	protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

		//获取请求中的method参数，该参数的值，表示业务方法的名字

		String mName = req.getParameter("method");

		//this当前类对象，创建反射的Class类对象

		Class c = this.getClass();

		//创建反射method对象

		try {

			Method method = c.getDeclaredMethod(mName, HttpServletRequest.class,HttpServletResponse.class);

			//执行方法

			method.invoke(this, req, res);

		} catch (Exception e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

	@Override

	protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

		doGet(req, res);//如果post方法接收的话，也跳转到doGet方法

	}

}

//

//因为 MyServlet 继承 BaseServlet，所以继承了baseservlet的doget方法，所以在运行时BaseServlet内的this关键字相当于指代MyServlet类对象

public class MyServlet extends BaseServlet{

	public void run(HttpServletRequest req, HttpServletResponse res){

		PrintWriter out = res.getWriter();

		out.write("MyServlet-function test()");

		out.flush();

		if(out != null) out.close();

	}

}

巴特西

day33 过滤器filter & 监听器listener & 利用反射创建BaseServlet实现调用自定义业务方法