import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class HelloServlet extends HttpServlet {@Overridepublic void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("get请求将执行");}@Overridepublic void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("post请求将执行");}
}

<!-- demo01 servlet hello start
\3. 浏览器访问
在浏览器地址栏输入：http://localhost:8080/hello
l 浏览器显示空白页面
l 控制打印信息* <servlet> 注册servlet<servlet-name> servlet名称，当前xml中唯一<servlet-class> servlet实现类的全限定类名* <servlet-mapping> 给注册的servlet添加映射路径<servlet-name> 已经注册的servlet名称。注意：必须与注册的名称一致。<url-pattern> 访问路径。要求：必须/开头
-->
<servlet><servlet-name>helloServlet</servlet-name><servlet-class>cn.itcast.demo01.a_servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping><servlet-name>helloServlet</servlet-name><url-pattern>/hello</url-pattern>
</servlet-mapping>
<!-- demo01 servlet hello end -->

<form action="./demo01ParamServlet" method="post">用户名：<input type="text" name="username" value="jack" /> <br/>密码：<input type="text" name="password" value="1234" /> <br/>爱好：<input type="checkbox" name="hobby" value="抽烟" checked="checked"/> 抽烟<input type="checkbox" name="hobby" value="喝酒" checked="checked" /> 喝酒<input type="checkbox" name="hobby" value="烫头" /> 烫头  <br/><input type="submit" value="post提交" />
</form>

public class Demo01ParamServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//0请求参数中文乱码request.setCharacterEncoding("UTF-8");//1 使用参数名获得一个值//1.1 获得用户名String username = request.getParameter("username");//1.2 获得密码String password = request.getParameter("password");System.out.println(username  + " : " + password);//2 使用参数名获得一组值String[] hobbies = request.getParameterValues("hobby");System.out.println(Arrays.toString(hobbies));//3 获得所有数据，遍历MapSystem.out.println("---------------");Map<String,String[]> allData = request.getParameterMap();for (Map.Entry<String, String[]> entry : allData.entrySet()) {System.out.print(entry.getKey());System.out.print( " --> ");System.out.println(Arrays.toString(entry.getValue()));}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {/* 开发中我们发现，doPost和doGet两个方法编写的内容相同* 所以常使用一个调用另一个，此处我们使用doPost调用doGet* 所有的内容之后都编写doGet方法中*/doGet(request, response);}

<servlet><servlet-name>Demo01ParamServlet</servlet-name><servlet-class>cn.itcast.demo01.b_request.Demo01ParamServlet</servlet-class>
</servlet>
<servlet-mapping><servlet-name>Demo01ParamServlet</servlet-name><url-pattern>/demo01ParamServlet</url-pattern>
</servlet-mapping>

<servlet><servlet-name>helloServlet</servlet-name><servlet-class>cn.itcast.demo01.a_servlet.HelloServlet</servlet-class><load-on-startup>2</load-on-startup>
</servlet>

例如:  /ServletDemo4 , /aaa/ServletDemo5 , /aaa/bbb/ServletDemo6

例如: /* （所有） ,/aaa/* （aaa目录下的所有） ,/aaa/bbb/*

例如: *.do , .action 、.jsp 、*.jpg
* 错误的写法  ： /*.do

tomcat获得匹配路径时，优先级顺序：1 > 2 > 3 > 4

<servlet><servlet-name>ServletDemo4</servlet-name><servlet-class>com.itheima.a_servlet.ServletDemo4</servlet-class>
</servlet>
<servlet-mapping><servlet-name>ServletDemo4</servlet-name><url-pattern>/ServletDemo4</url-pattern>
</servlet-mapping>
<servlet><servlet-name>ServletDemo5</servlet-name><servlet-class>com.itheima.a_servlet.ServletDemo5</servlet-class>
</servlet>
<servlet-mapping><servlet-name>ServletDemo5</servlet-name><url-pattern>/*</url-pattern>
</servlet-mapping>
<servlet><servlet-name>ServletDemo6</servlet-name><servlet-class>com.itheima.a_servlet.ServletDemo6</servlet-class>
</servlet>
<servlet-mapping><servlet-name>ServletDemo6</servlet-name><url-pattern>*.do</url-pattern>
</servlet-mapping>

 <servlet><servlet-name>hello</servlet-name><servlet-class>HelloServlet</servlet-class><init-param><param-name>key</param-name><param-value>value</param-value></init-param></servlet>

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//name = "HelloServlet"：servlet名称，相当于web.xml中的<servlet-name>
//urlPatterns = "/hello"：servlet的访问路径，相当于<url-pattern>
@WebServlet(name = "HelloServlet",urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) {System.out.println("get 请求执行");
}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) {System.out.println("post 请求执行");}
}