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Java Forum / General / March 2008Is there a easy way to get complete info about JSTL and EL?
How do I get to know that : <c:forEach var="cookieVal" items="${cookie}"> <c:if test="${cookieVal.key == 'abc'}"> <c:out value="${cookieVal.value.value}"></c:out> </c:if> </c:forEach> only ${cookieVal.value.value} can output the right value of that single cookie,but ${cookieVal.value} can not? btw: it really sucks... I saw some stuff on java.sun.com (http://java.sun.com/products/jsp/ syntax/2.0/syntaxref207.html#1010522)，but it did not tell me the thing above. Must I search these tips on the planet or see the jsr??? I just need a manual,a chm for example,to deal with all the mess... > How do I get to know that : > [quoted text clipped - 14 lines] > > I just need a manual,a chm for example,to deal with all the mess... In general there isn't such a manual, although for JSTL generally the Sun tutorial is a good start: <http://java.sun.com/javaee/5/docs/tutorial/doc/bnakc.html> The reason there isn't a general manual is that your problem depended on specifics of your code, namely the types of 'cookieVal' and 'cookieVal.value'. Apparently 'cookieVal.value' is itself of a holder type. What are those two types?  SignatureLew > Apparently 'cookieVal.value' is itself of a holder type. What are those two > types? In fact, ${cookie} is provided by EL,not me, I've no idea what type it is when I iterate the ${cookie}. >> Apparently 'cookieVal.value' is itself of a holder type. What are those two >> types? > > In fact, ${cookie} is provided by EL,not me, I've no idea what type it > is when I iterate the ${cookie}. If you don't know the type of 'cookie', how do you know that you can iterate through it? SignatureLew >>> Apparently 'cookieVal.value' is itself of a holder type. What are >>> those two [quoted text clipped - 5 lines] > If you don't know the type of 'cookie', how do you know that you can > iterate through it? This is, of course, the heart of your problem. As explained in <http://www.informit.com/articles/article.aspx?p=30946&seqNum=7> cookies is a Map. When you iterate over the Map, each iteration yields a Map.Entry. Your code extract (do NOT use TAB characters to indent Usenet listings): > <c:forEach var="cookieVal" items="${cookie}"> > <c:if test="${cookieVal.key == 'abc'}"> [quoted text clipped - 4 lines] > single cookie,but ${cookieVal.value} can not? > btw: it really sucks... It sucks because you didn't check the data type first, so you failed to understand what you needed to do. The Entry has a value - that's ${cookieVal.value} - that's the Map.Entry value right there. The value has a type - since ${cookies} is a Map from String to javax.servlet.http.Cookie, that's the type of the value. <http://java.sun.com/javaee/5/docs/api/javax/servlet/http/Cookie.html> You want the value of the Cookie, which is the value of the value of the Map.Entry: ${cookieVal.value.value} Gee, that doesn't suck at all, not really, not in any way. Q.E.D. SignatureLew >>>> Apparently 'cookieVal.value' is itself of a holder type. What are >>>> those two [quoted text clipped - 38 lines] > > Q.E.D. Good explanation of those points. On a different note, why iterate over a map if you are actually interested only in the value corresponding to one key? A map implementation lets you test for the existence of a key. I am not sure of the exact syntax here but I think it's something like <c:if test="${not empty cookie["cookieName"]}">... Don't hold me to it, but I think the above is close ('empty' apparently does an empty test on collections but also does a null test). In any case, the point is that it will be doable to test to see if the key ("abc") exists, and then act on that, rather than iterate over all entries in the map. AHS > Good explanation of those points. On a different note, why iterate over a > map if you are actually interested only in the value corresponding to one [quoted text clipped - 5 lines] > Don't hold me to it, but I think the above is close ('empty' apparently does > an empty test on collections but also does a null test). In any case, the You're correct, and more than that, 'empty' subsumes the idiom for Strings (x == null || x.length() == 0) Basically, 'empty' matches the obvious interpretations of the word. It's as if it had a series of reasonable tests for each valid expression type that it can handle. > point is that it will be doable to test to see if the key ("abc") exists, > and then act on that, rather than iterate over all entries in the map. SignatureLew >> Apparently 'cookieVal.value' is itself of a holder type. What are those two >> types? > > In fact, ${cookie} is provided by EL,not me, I've no idea what type it > is when I iterate the ${cookie}. Incidentally, the point in asking you what the type was, since it was already obvious that you didn't know, was to have you look it up, not just toss your hands in the air and give up. It took me less than ten minutes of googling to find the answer - you should have invested that time yourself. If you get in the habit of finding out these answers, it'll become possible for you to write code. SignatureLew Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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