简易servlet计算器

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<form action="jisuanqi" method="post">
<textarea id="text" name="textarea" style="width:200px; height:20px;"></textarea>
<br>
<input type="button" value="7" name="7" onclick="javascript:Insert('7')">
<input type="button" value="8" name="8" onclick="javascript:Insert('8')">
<input type="button" value="9" name="9" onclick="javascript:Insert('9')">
<input type="button" value=" +" name="jia" onclick="javascript:Insert('+')">
<br>
<input type="button" value="4" name="4" onclick="javascript:Insert('4')">
<input type="button" value="5" name="5" onclick="javascript:Insert('5')">
<input type="button" value="6" name="6" onclick="javascript:Insert('6')">
<input type="button" value=" -" name="jian" onclick="javascript:Insert('-')">
<br>
<input type="button" value="1" name="1" onclick="javascript:Insert('1')">
<input type="button" value="2" name="2" onclick="javascript:Insert('2')">
<input type="button" value="3" name="3" onclick="javascript:Insert('3')">
<input type="button" value=" ×" name="cheng" onclick="javascript:Insert('*')">
<br>
<input type="button" value="0" name="0" onclick="javascript:Insert('0')">
<input type="button" value=" ." name="." onclick="javascript:Insert('.')">
<input type="submit" value="=" name="deng">
<input type="button" value=" ÷" name="chu" onclick="javascript:Insert('/')">

</form>

</body>
<script language="javascript">

function Insert(str) {
var obj = document.getElementById('text');
if(document.selection) {
obj.focus();
var sel=document.selection.createRange();
document.selection.empty();
sel.text = str;
} else {
var prefix, main, suffix;
prefix = obj.value.substring(0, obj.selectionStart);
main = obj.value.substring(obj.selectionStart, obj.selectionEnd);
suffix = obj.value.substring(obj.selectionEnd);
obj.value = prefix + str + suffix;
}
obj.focus();
}         

</script>

</html>

package com.hanqi.web;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class jisuanqi extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public jisuanqi() {
        super();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String str=request.getParameter("textarea");

        try
        {
        if(str.length()!=str.replace("+", "").length())
        {

            String a=str.substring(0,1);

            String b=str.substring(1+1,str.length());
            response.getWriter().write(str+"="+( Double.parseDouble(a)+ Double.parseDouble(b)));
        }
        if(str.length()!=str.replace("-", "").length())
        {
            String c=str.substring(0,str.indexOf("-"));
            String d=str.substring(str.indexOf("-")+1,str.length());
            response.getWriter().write(str+"="+( Double.parseDouble(c)- Double.parseDouble(d)));
        }
        if(str.length()!=str.replace("*", "").length())
        {
            String e=str.substring(0,str.indexOf("*"));
            String f=str.substring(str.indexOf("*")+1,str.length());
            response.getWriter().write(str+"="+( Double.parseDouble(e)* Double.parseDouble(f)));
        }
        if(str.length()!=str.replace("/", "").length())
        {
            String g=str.substring(0,str.indexOf("/"));
            String h=str.substring(str.indexOf("/")+1,str.length());
            response.getWriter().write(str+"="+( Double.parseDouble(g)/ Double.parseDouble(h)));
        }

}catch(Exception e)
          {
                  response.getWriter().write("请正确使用计算器");
          }
}

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);
    }

}