【Servlet】根据用户输入的圆半径,输出圆面积

本文介绍了如何使用Servlet实现计算圆面积的功能,并通过JSP页面调用Servlet进行演示。

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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>



在Java Web开发中,如果你想输出用户输入半径,然后计算并显示其周长和面积,你可以创建一个简单的HTML页面配合后台Java Servlet或者JSP来进行操作。下面是一个简化的例子: 首先,创建一个HTML表单让用户输入半径: ```html <!DOCTYPE html> <html> <head> <title>Circle Calculator</title> </head> <body> <form action="circle_calculator" method="post"> <label for="radius">Enter the radius:</label> <input type="number" id="radius" name="radius"><br><br> <input type="submit" value="Calculate"> </form> </body> </html> ``` 然后,在Servlet (`CircleCalculator.java`)或JSP文件中处理请求,获取用户输入半径计算周长(C = 2 * π * r)和面积(A = π * r²),并将结果展示出来。这里假设π取3.14159: ```java (servlet) // CircleCalculator.java (Java Servlet) import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class CircleCalculator extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { double radius = Double.parseDouble(request.getParameter("radius")); double circumference = 2 * 3.14159 * radius; double area = 3.14159 * Math.pow(radius, 2); PrintWriter out = response.getWriter(); out.println("<h1>Results:</h1>"); out.println("Circumference: " + circumference); out.println("Area: " + area); } } ``` 在JSP中,你可以使用EL表达式(Expression Language)来简化代码: ```jsp <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> ... <body> ... <% double radius = Double.parseDouble(request.getParameter("radius")); %> <% double circumference = 2 * 3.14159 * radius; double area = 3.14159 * radius * radius; out.println("<p>Circumference: " + circumference + "</p>"); out.println("<p>Area: " + area + "</p>"); %> ... </body> </html> ```
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