java.lang.NumberFormatException：jsp 和 tomcat 为空

Question

我正在尝试打开我的 battle.jsp，但出现此错误

这是我第一个 jsp 页面的部分：

<link rel="stylesheet" href="firstPage.css">

<div class="container">
    
    <div class="header">
    <h1>RPG</h1>
    </div>
    

    <div class="left">
        <img src="images/hero.png" width="300" height="300" class="hero">
        <input type="number" class="heroNumber" min="1" max="3" value="1" name="heroes"> 
    </div>


    
    <div class="middle">
        <p class="VS">VS.</p>
            <form action="battle.jsp" method="post" name="form1">
                <input type="submit" value="Fight" class="submitFight">
            </form>
    </div>

    
    
    <div class="right2">
        <img src="images/wolf.png" width="152" height="150" class="wolf">
        <input type="number" class="wolfNumber" min="1" max="5" value="1" name="wolfs"> 
    </div>
    
    
    <div class="right2">
        <img src="images/orc.png" width="150" height="150" class="orc">
        <input type="number" class="orcNumber" min="1"max="3" value="1" name="orcs">
    </div>

这是第二部分（为什么会出现错误）：

<%
int amountOrc = Integer.parseInt(request.getParameter("orcs"));
int amountWolf = Integer.parseInt(request.getParameter("wolfs"));
int amountHero = Integer.parseInt(request.getParameter("heroes"));

之前一切正常，但现在出现此错误

Answer 1

您的数据必须通过 <form> 提交。所有在表单外提交的数据都不会被 servlet 接收。

因此您的代码应该是：

<div class="container">
    <form action="/path" method="POST">
    <div class="header">
    <h1>RPG</h1>
    </div>
    

    <div class="left">
        <img src="images/hero.png" width="300" height="300" class="hero">
        <input type="number" class="heroNumber" min="1" max="3" value="1" name="heroes"> 
    </div>


    
    <div class="middle">
        <p class="VS">VS.</p>
            <form action="battle.jsp" method="post" name="form1">
                <input type="submit" value="Fight" class="submitFight">
            </form>
    </div>

    
    
    <div class="right2">
        <img src="images/wolf.png" width="152" height="150" class="wolf">
        <input type="number" class="wolfNumber" min="1" max="5" value="1" name="wolfs"> 
    </div>
    
    
    <div class="right2">
        <img src="images/orc.png" width="150" height="150" class="orc">
        <input type="number" class="orcNumber" min="1"max="3" value="1" name="orcs">
    </div>
</form>
</div>

另外，我建议不要使用这个：

int amountOrc = Integer.parseInt(request.getParameter("orcs"));
int amountWolf = Integer.parseInt(request.getParameter("wolfs"));
int amountHero = Integer.parseInt(request.getParameter("heroes"));

但是使用这个：

String orcs = request.getParameter("orcs");
String wolfs = request.getParameter("wolfs");
String heroes = request.getParameter("heroes");
if(orcs!=null&&wolfs!=null&&heroes!=null){
    int amountOrc = Integer.parseInt(orcs);
    int amountWolf = Integer.parseInt(wolfs);
    int amountHero = Integer.parseInt(heroes);
}

无论如何，为了避免 NullPointerExceptions 或用户尝试抛出一个。

java.lang.NumberFormatException：jsp 和 tomcat 为空

java.lang.NumberFormatException: null with jsp and tomcat

html

jsp

tomcat

exception

numberformatexception