【Servlet】根据用户输入的圆半径，输出圆面积

1、创建Servlet类

import java.io.*;
import javax.servlet.ServletException;
import javax.servlet.http.*;

public class CircleServlet extends HttpServlet{
	public void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException,IOException{
		response.setContentType("text/html; charset=bg2312" );
		PrintWriter out = response.getWriter();
		double  r = Double.parseDouble(request.getParameter("r"));
		out.println(" 面积 = " + Math.PI*r*r);
		out.close();
	}
}

2、改写配置文件web.xml

<servlet>
		<servlet-name>CircleServlet</servlet-name>
		<servlet-class>myDemo.CircleServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>CircleServlet</servlet-name>
		<url-pattern>/calcu</url-pattern>
	</servlet-mapping>

3、编写jsp调用servlet 

<form action="calcu" method ="get"> <%--clacu对应的是servlet的URL,调用CircleServlet --%>
		圆的半径:<input type="text" name="r"><br/>
		<input type="submit" value="计算">
	</form>