如何在< script>中访问用户定义对象的数组在JSP？ [英] How to access array of user defined objects within <script> in JSP?

问题描述

我有一组用户定义的对象，我从servlet传递给JSP。现在，我需要在JSP中的脚本标记内访问此数组。我该怎么办？

I have an array of user defined objects which I'm passing from a servlet to a JSP. Now, I need to access this array within the script tag in my JSP. How do I do it?

现在，我在脚本标签中有以下内容：

For now, I have the following within script tag:

var dCount = '${chart}';

var index;
   for(index=0; index<dCount.length;index++){
        alert(dCount);
    }

当我这样做时，我将输出视为未定义。我认为这是因为 $ {chart} 返回一个对象？如果是这样，我该如何将其转换为用户定义的类？或者这里有其他问题吗？

When I do this, I get the output as undefined. I assume this is bcause the ${chart} returns an Object? If so, how do I convert it to my user defined class? Or is something else the problem here?

谢谢。

推荐答案

您需要意识到JSP基本上是一个HTML代码生成器，而CSS / JS是生成的HTML输出的一部分。您需要以生成有效HTML / JS代码的方式编写JSP代码。一个有3个对象的有效JS数组，每个属性 foo 和 bar 看起来像这样：

You need to realize that JSP is basically a HTML code generator and that CSS/JS is part of the generated HTML output. You need to write JSP code in such way that valid HTML/JS code is generated. A valid JS array of 3 objects with each the properties foo and bar look like this:

var chart = [{
    foo: "foo1",
    bar: "bar1"
},{
    foo: "foo2",
    bar: "bar2"
},{
    foo: "foo3",
    bar: "bar3"
}];

var index;
for(index = 0; index < chart.length; index++) {
    var item = chart[index];
    alert(item.foo + ", " + item.bar);
}

现在，您需要确保以这样的方式编写JSP代码： 完全生成此有效的HTML / JS代码（您可以通过右键单击并在webbrowser中查看源进行验证）。

Now, you need to make sure that you write JSP code in such way that exactly this valid HTML/JS code is generated (as you can verify by rightclick and View Source in webbrowser).

如果 $ {chart} 是列表< Item> 或 Item [] ，最天真的方法之一是使用< c：forEach> 来循环它，打印所需的JS代码输出：

Provided that ${chart} is a List<Item> or Item[], one of most naive ways is using <c:forEach> to loop over it, printing the desired JS code output:

var chart = [<c:forEach items="${chart}" var="item" varStatus="loop">
    { foo: "${item.foo}", bar: "${item.bar}" }${loop.last ? '' : ','}
</c:forEach>];

最简单的形式，它应该可以正常工作。但是，一旦你将特殊字符作为属性值，例如甚至换行符，就会出现麻烦。你需要逃避它。更好的是使用现有的 JSON库，例如 Google Gson 为了转换复杂的Java对象，例如列表< Item> 或项目[] ，到一个有效的JSON字符串。例如，在servlet中如下：

In its simplest form, it should work fine. However, trouble starts once you get "special characters" as property values, such as " or even a newline. You'd need to escape it. Much better is to use an existing JSON library, such as Google Gson in order to convert a complex Java object, such as a List<Item> or Item[], to a valid JSON string. E.g. as follows in the servlet:

List<Item> chart = createItSomehow();
request.setAttribute("chart", new Gson().toJson(chart));
// ...

然后你可以这样做：

var chart = ${chart};

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