java JSP中如何控制显示位数？
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How to control of display the number of digit in JSP?
提问by Questions
I want to ask a question about the JSP and Java. I am writing the JSP page and has a bean class. In the class, i have a getter function which will return a double var in the jsp page. I used the following code to display the number.
我想问一个关于JSP和Java的问题。我正在编写 JSP 页面并且有一个 bean 类。在课堂上，我有一个 getter 函数，它将在 jsp 页面中返回一个双变量。我使用以下代码来显示数字。
<p> the value of AB is <%=obj.getValue() %> <p>
I expect that display will like the following
我希望显示器会喜欢以下内容
the value of AB is 0.45
However, the real display is the following
但是，真正的显示如下
the value of AB is 0.4569877987
I only want to display the last two digit. What should I do in order to display what I want. Should I modify the JSP page or the Java class variable? thank you.
我只想显示最后两位数。我该怎么做才能显示我想要的东西。我应该修改 JSP 页面还是 Java 类变量？谢谢。
采纳答案by Grodriguez
You can use a DecimalFormatto format the value as a string, e.g.:
您可以使用 aDecimalFormat将值格式化为字符串，例如：
DecimalFormat df = new DecimalFormat("#0.00");
(the pattern assumes you always want two digits in the fractional part, even if the fractional part is zero. Otherwise, use #0.##)
（该模式假设您总是希望小数部分中有两位数字，即使小数部分为零。否则，使用#0.##）
However in general it is recommended not to call the DecimalFormatconstructors directly. Instead, the recommended practice is to call one of the factory methods of NumberFormat, then customize the pattern as needed, e.g.:
但是一般情况下建议不要DecimalFormat直接调用构造函数。相反，推荐的做法是调用 的工厂方法之一NumberFormat，然后根据需要自定义模式，例如：
NumberFormat nf = NumberFormat.getInstance();
nf.setMaximumFractionDigits(2);
nf.setMinimumFractionDigits(2);
Javadoc including examples:
Javadoc 包括示例：
- http://download-llnw.oracle.com/javase/6/docs/api/java/text/NumberFormat.html
- http://download-llnw.oracle.com/javase/6/docs/api/java/text/DecimalFormat.html
- http://download-llnw.oracle.com/javase/6/docs/api/java/text/NumberFormat.html
- http://download-llnw.oracle.com/javase/6/docs/api/java/text/DecimalFormat.html
This should work in your JSP page:
这应该适用于您的 JSP 页面：
<%@ page import="java.text.NumberFormat" %>
<%
NumberFormat nf = NumberFormat.getInstance();
nf.setMaximumFractionDigits(2);
nf.setMinimumFractionDigits(2);
%>
[...]
<p> the value of AB is <%= nf.format(obj.getValue()) %> <p>
Also see Bozho's answer for a way to achieve the same result using JSTL.
另请参阅 Bozho 的回答，了解使用 JSTL 实现相同结果的方法。
回答by Bozho
In JSP you can do this using the JSTL tag <fmt:formatNumber>. You can set either a pettern(#0.##) or maxFractionDigits="2"
在 JSP 中，您可以使用 JSTL 标记来做到这一点<fmt:formatNumber>。您可以设置pettern( #0.##) 或maxFractionDigits="2"
Avoid using Java code in JSPs - use JSTL instead. See this tutorial. And see this question
回答by Andrzej Doyle
To answer your last question first - you should modify the JSP page, since you want to change how the number is displayed, not what the number actually is.
首先回答您的最后一个问题 - 您应该修改 JSP 页面，因为您想要更改数字的显示方式，而不是数字实际是什么。
To do this, instead of invoking the number's default toString method, you could use a DecimalFormatobject to convert the number to text in whatever format you want. In this case, you probably want to use:
为此，您可以使用DecimalFormat对象将数字转换为您想要的任何格式的文本，而不是调用数字的默认 toString 方法。在这种情况下，您可能想要使用：
new DecimalFormat("#0.##")
as the format string.
作为格式字符串。
However, as per Bozho's answerthere is a JSTL tag to achieve this, which is a better way to solve your problem.
但是，根据 Bozho 的回答，有一个 JSTL 标签可以实现这一点，这是解决问题的更好方法。
