检测浏览器是否能成功加载Java小程序-Firefox上的意外行为

我有一个加载Java小程序的ASP.NET页面。我首先检查客户端计算机是否能够运行applet（Java版本等），方法是给标记一个ID“AppletID”-然后调用该applet的一个函数，该函数始终返回“true”

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

因此，以下代码行：var isRunning=document.getElementById（'AppletID'）。如果成功调用小程序中的方法“appletRunning”（表示客户端可以正确加载小程序），则appletRunning（）将返回“true”

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

直到最近，这种方法一直有效。然而，最近，Firefox浏览器给了我一个交互式对话框，显示“您没有所需的Java最低版本…”消息。（其他情况下，它会正确检测到小程序可以加载）。然后小程序继续正确加载，但首先不应显示对话框。我想知道为什么会发生这种情况-可能是该文档。检查getElementById（'AppletID'）时，它是空的，因此导致“checkAppletRunning”方法的“catch”部分？IE始终正常，从不返回此对话框

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

下面是.aspx页面的代码

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

window.onload=函数（）
{
var appletCheck=checkAppletRunning（）；
如果（appletCheck==1）
{
警报（“服务器已关闭…请稍后再试。”）；
window.location.href=“Default.htm”；
}
否则如果（appletCheck==2）
{
警报（“您没有启用或安装所需的Java最低版本。必须从以下位置启用或下载Java:http://www.java.com");
window.location.href=“Default.htm”；
}
}
函数checkAppletRunning（）
{
var-OK=0；
var-serverDown=1；
var appletNotSupported=2；
尝试
{
var isRunning=document.getElementById（'AppletID'）.appletRunning（）；
如果（正在运行）
{
返回OK；
}
其他的
{
返回appletNotSupported；
}
} 
捕获（e）
{
返回appletNotSupported；
}
}

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

我非常感谢你在这件事上的帮助

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

提前感谢,，

---

Timothy可能是因为小程序尚未完成启动

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

---

尝试为异常返回不同的结果（或记录异常），以更好地了解其失败的原因。

更简单的方法是，如果Java不可用，则不会解释小程序标记

<script type="text/javascript" language="javascript">
    window.onload = function()
    {
        var appletCheck = checkAppletRunning();

        if (appletCheck == 1)
        {
            alert("Server is down...please try again later.");
            window.location.href = "Default.htm";
        }
        else if (appletCheck == 2)
        {
            alert("You do not have the required minimum version of Java enabled or installed. Java must be enabled or downloaded from http://www.java.com");
            window.location.href = "Default.htm";
        }
    }

    function checkAppletRunning()
    {
        var OK = 0;
        var serverDown = 1;
        var appletNotSupported = 2;

        try 
        {
            var isRunning = document.getElementById('AppletID').appletRunning();
            if (isRunning)
            {
                return OK;
            }
            else
            {
                return appletNotSupported;
            }
        } 
        catch (e)
        {
            return appletNotSupported;
        }
    }
</script>

<HTML><HEAD></HEAD><BODY>
<APPLET CODE="MyApplet.class"
        NAME="myApplet"
        HEIGHT=400 WIDTH=400>

    <A HREF="nojava.html">Oups! You don't have JAVA enabled, click here.</A>

</APPLET>
</BODY></HTML>

您好，谢谢您的回复。我已经创建了该页面的另一个版本，以便在“var isRunning=document.getElementById（'AppletID'）.appletRunning（）；”之前打印document.getElementById（'AppletID'）的值。我注意到，当检测到Java时，警报显示小程序的entry类的实例。单击“运行”取消Java对话框后，将显示此警报。但是，当Java未被检测到时，在Java对话框出现之前，警报将显示[object HTMLAppletElement]。所以，我认为Java还没有启动？有什么想法吗？谢谢您可以使用的一种方法是让Javaapplet调用javascript。需要javascript端的计时器告诉它停止等待小程序调用（即未安装java）