问题
Consider the following where availableExclusions is an array of Date objects.
<s:select listValue="(new java.text.SimpleDateFormat('MM/dd/yyyy')).format(new java.util.Date(#this[0].time))" size="25" id="inputExclusionDates" name="available" list="availableExclusions" multiple="true" cssClass="multi-select" />
I created the above in response to this question How would I format a list of dates within a struts 2 select tag? (and I also recommended that the other solution may be the better way to go). Regardless if using such long OGNL expression is a good idea or not, I can't see the need for: new java.util.Date(#this[0].time) despite creating that fragment out of frustration and to my surprise found it worked where the seemingly equivalent #this[0] did not (produced no output).
If we substitute in listValue="#this[0].class" we see what we would expect: class java.util.Date
Creating a new Date behaves as expected, and calling the deprecated properties of Date such as listValue="#this[0].day" produces the expected output.
Why must I use the redundant expression new java.util.Date(#this[0].time) instead of #this[0] in this select statement?
Using Struts 2.3.1.2
回答1:
Because #this[0] is automatically converted to String. If you turn log level to debug you can see an exception message that's normally suppressed.
来源：https://stackoverflow.com/questions/10474967/strange-ognl-behaviour-when-using-this-in-sselect