在线版简易计算器

package per.mjn._08_cal;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

// 在线版简易计算器
@WebServlet("/cal")
public class CalServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		req.setCharacterEncoding("UTF-8");
		resp.setContentType("text/html;charset=utf-8");
		PrintWriter out = resp.getWriter();
		// -----------------------------------
		// 2. 接收表单中的数据
		String sNum1 = req.getParameter("num1");
		String op = req.getParameter("op");
		String sNum2 = req.getParameter("num2");
		String result = "";
		if(hasLength(sNum1) && hasLength(sNum2)) {
			Integer num1 = Integer.valueOf(sNum1);
			Integer num2 = Integer.valueOf(sNum2);
			
			if("+".equals(op)) {
				result = num1 + num2 + "";
			}
			else if("-".equals(op)) {
				result = num1 - num2 + "";
			}
			else if("*".equals(op)) {
				result = num1 * num2 + "";
			}
			else if("/".equals(op)) {
				result = num1 / num2 + "";
			}
		}
//		System.out.println(sNum1);
//		System.out.println(op);
//		System.out.println(sNum2);

		// 1. 输出一个计算器的界面
		out.print("<form action=\'/day3/cal\' method=\'post\'>");
		out.print("<input type=\'number\' name=\'num1\' value=\'" + sNum1 + "\'/>");
		out.print("<select name=\'op\'>");
		out.print("<option>+</option>");
		out.print("<option>-</option>");
		out.print("<option>*</option>");
		out.print("<option>/</option>");
		out.print("</select>");
		out.print("<input type=\'number\' name=\'num2\' value=\'" + sNum2 + "\'/>");
		out.print("<input type=\'submit\' value=\' = \'/>");
		out.print("<input type=\'text\' value=\'" + result + "\' disabled/>");
	}
	
	private boolean hasLength(String str) {
		return str != null && !"".equals(str.trim());
	}
}

<!DOCTYPE html>
<html>
<head>
<meta charset=\'UTF-8\'>
<title>Insert title here</title>
</head>
<body>

	<form action=\'\' method=\'post\'>
		<input type=\'number\' name=\'num1\'/>
		<select name=\'op\'>
			<option>+</option>
			<option>-</option>
			<option>*</option>
			<option>/</option>
		</select>
		<input type=\'number\' name=\'num2\'/>
		<input type=\'submit\' value=\' = \'/>
		<input type=\'text\' value=\'\' disabled/>
	</form>
</body>
</html>