在Struts2标签中检查请求参数值

Question

我的JSP中有以下代码：

<s:property value="#parameters['test']"/>
<br/><s:property value="'1'.equals(#parameters['test'])"/>

现在，如果我这样访问此操作：test.action？test = 1

我得到以下内容：

1
false

想知道，为什么1不等于1？

Answer 1

编辑：之间有区别 "" （双引号）和 '' （单引号）在OGNL中。

双引号评估单个字符的字符串，而单引号将单个字符评估为字符类型。你可以放 多 单个引号中的字符，并将其作为字符串评估。

进一步的请求范围不是

Map<String, String> 

但

Map<String, String[]> 

如下所示，在JSP的最后5行中可以看出。

JSP

<%@taglib prefix="s" uri="/struts-tags"%>
<!-- values from action where letters = "abcd" -->
<s:property value="letters"/><br/> <!-- Displays: abcd -->
<s:property value="letters.equals('abcd')"/><br/> <!-- Displays: true -->
<s:property value="'abcd'.compareTo('abcd')"/><br/> <!-- Displays: 0 -->
<s:property value="'abcd'.compareTo('abcd') == 0"/><br/> <!-- Displays: true -->
<s:property value="'abcd'.equals('abcd')"/><br/> <!-- Displays: true -->
<s:property value="'abcd'.equals(letters)"/><br/> <!-- Displays: true -->
<br/>
<!-- RUN with ?test=a&test2=abc appended to the url -->
<!-- Time for the numbers from action where number = 1-->
<s:property value="number"/><br/><!-- Displays: 1 -->
<s:property value="number.toString()"/><br/><!-- Displays: 1 -->
<!-- OGNL strings in certain cases must be double quoted -->
<s:property value='"1".equals(number.toString())'/><br/><!-- Displays: true -->
<!-- As we can see single quotes does automatic type conversion to Character which is then evaluates false-->
<s:property value="'1'.equals(number.toString())"/><br/><!-- Displays: false -->
<!-- here a string is compared to an integer which is false-->
<s:property value='"1".equals(number)'/><br/><!-- Displays: false -->
<br/><!-- Request Variables -->
<s:property value="#parameters['test']"/><br/><!-- Displays: a -->
<!-- a is single quoted so automatic type conversion probably converted it to a Character, which is not equal to string "a" -->
<s:property value="'a'.equals(#parameters['test'])"/><br/><!-- Displays: false -->
<!-- both are strings so equality works as expected -->
<s:property value='#parameters["test"]'/><br/><!-- Displays: a -->
<s:property value='"a".equals(#parameters["test"])'/><br/><!-- Displays: false because #parameters["test"] is a string[] and calling toString on string[] does not work -->
<!-- #parameters['test2'] now is 'abc' automatic type conversion of OGNL swill convert 'abc' to a string and so both are equal -->
<s:property value='#parameters["test2"]'/><br/>
<!-- Double quotes must be a string -->
<s:property value='"abc".compareTo(#parameters["test2"]) == 0'/><br/><!-- Displays: true -->
<!-- Single quote so automatic type conversion... string of chars is converted to String -->
<s:property value="'abc'.compareTo(#parameters['test2']) == 0"/><br/><!-- Displays: true -->
<!-- Out of curiosity I'd like to know if '1' is an Integer or a Byte -->
<s:property value="'1'.toString()"/><br/><!-- Answer: Neither it prints "class java.lang.Character" -->
<!-- 'a' is a Character however equals calls toString() -->
<!-- But the request object (and session too) is not <string, string> but <string, string[]> -->
1: <s:property value='"1".class'/><br/> <!-- class java.lang.String -->
2: <s:property value='#parameters["test"].class'/><br/> <!-- Array of string: class [Ljava.lang.String; -->
3: <s:property value='#parameters["test"][0].class'/><br/> <!-- This is what we need: class java.lang.String -->
<s:property value='#parameters["test"][0].equals("a")'/><br/> <!-- Now this works -->
<s:property value="#parameters['test'][0].equals('a'.toString())"/><br/> <!-- this is another way, leaving off the .toString results in false -->

test.jsp（动作）

包装杆2;导入com.opensymphony.xwork2.actionsupport;

public class test extends ActionSupport{
    public String letters = "abcd";
    public int number = 1;
}

Answer 2

我刚刚发现#parameters ['test']返回字符串数组。所以当你说

<s:property value="'1'.equals(#parameters['test'])"/>

实际上，您将字符串'1'与数组{'1'}进行比较，因此它返回false。也许这是因为有两个参数具有相同的名称

正确的事情将是

<s:property value="'1'.equals(#parameters['test'][0])"/>