2021-3-31[Web注解]

WEB3.0版本之后出现了注解，为了替代web.xml配置

@WebServlet

1.使用注解的方式访问Servlet

  自己写一个类Servlet，类继承HttpServlet （extends HttpServlet）<br />      类重写方法<br />      方法参数    抛出异常<br />      配置 在类上 添加一个注解<br />      @WebServlet()<br />                urlPatterns={"/test","/test2"}<br />                如果请求url只有一个的话  大括号是可以省略的<br />                value信息   等价于urlPatterns  <br />                建议用value如果只有value是可以生路的  <br />                loadOnStartUp信息    控制servlet对象的加载的(立即)<br />                initParams   为了携带信息<br />                   里面需要{@WebInitParam(name="",value="")}

package controller;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Enumeration;
@WebServlet(
//        name = "test",
//        description = "类似注释",
//        displayName = "显示请求名",
//        asyncSupported = true,
//        value = "",
        urlPatterns = {"/test",""},
        loadOnStartup = 0,
        initParams = {
                @WebInitParam(name = "zhangsan",value = "333"),
                @WebInitParam(name = "lisi",value = "444"),
                @WebInitParam(name = "wangwu",value = "555"),
        }
)
public class TestController extends HttpServlet {
    public void init(ServletConfig config) throws ServletException {
        System.out.println("testController对象加载ing...");
        Enumeration en = config.getInitParameterNames();
        while (en.hasMoreElements()){
            String key = (String) en.nextElement();
            String value = config.getInitParameter(key);
            System.out.println(key+"--"+value);
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("This is a TestController,执行ing...");
        String name = request.getParameter("name");
        String pass = request.getParameter("pass");
        System.out.println(name+"--"+pass);
    }
}

@WebFilter

2.使用注解的方式访问Filter

  自己写一个类，类继承HttpFilter（ extends HttpFilter ）<br />      重写方法doFilter<br />      方法参数 request respons chain  抛异常<br />      配置   类上添加注解<br />      @WebFilter<br />                urlPatterns<br />                value<br />                initParams   为了携带信息<br />                    里面需要{@WebInitParam(name="",value="")}

package filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.http.HttpFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Enumeration;
@WebFilter(
//        description = "",
//        displayName = "",
//        value = {"","",""};
        urlPatterns = {"/*",""},
        initParams = {
                @WebInitParam(name = "key1",value = "value1"),
                @WebInitParam(name = "key2",value = "value2")
        }
)
//@WebFilter("/*")
public class TestFilter extends HttpFilter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("This is a Filter，真正init方法加载ing```");
        Enumeration en = filterConfig.getInitParameterNames();
        while (en.hasMoreElements()){
            String key = (String) en.nextElement();
            String value = filterConfig.getInitParameter(key);
            System.out.println(key+"--"+value);
        }
    }
    protected void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("This is a Filter,真正doFilter方法执行ing...");
        chain.doFilter(request,response);
    }
}

@WebListener

3.使用注解的方式让Listener执行

  自己写一个类，实现接口 （impliments ServletRequestListener）<br />      方法必须重写<br />      配置    类上添加注解<br />      @WebListener

package listener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
@WebListener()
public class TestRequestListener implements ServletRequestListener {
    public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println("request对象销毁了");
    }
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("request对象创建了");
    }
}