Re: Still need help with layered Map iteration in JSP
I guess the first thing to make sure you understand is that, when iterating over
a Map, the object exposed by JSTL via the var attribute is of type Map.Entry.
It's equivalent to doing a map.entrySet().iterator(). As for getting the size
of an array, Collection, or Map, use the bean:size tag.
Quoting Erik Weber [EMAIL PROTECTED]:
OK, I'll take ANY WAY TO DO THIS AT ALL.
I have a c:forEach over a Map. The value for each key in the Map can be
an array of objects, or I can make it a List. I don't care at this point.
All I want to do is get the length of this array or List, before I start
iterating over *it*, during the current iteration of the Map. I am told
that I access the array or List like this:
1) Given this Map iteration:
c:forEach items=myMap
var=currentMapEntryWhichIsBothAKeyAndAValueTogether
2) access the value of the current Map entry (which will be either an
array or a List) like this:
${currentMapEntryWhichIsBothAKeyAndAValueTogether.value}
But I have tried all of these, none of them work:
c:when
test=${currentMapEntryWhichIsBothAKeyAndAValueTogether.value.length
0}!-- where the value of the Map entry is an array --
c:when
test=${currentMapEntryWhichIsBothAKeyAndAValueTogether.value.size
0}!-- where the value of the Map entry is a List --
c-rt:when
test=${fn:length(currentMapEntryWhichIsBothAKeyAndAValueTogether.value)
0}!-- where the value of the Map entry is either an array or a
List --
Not that they would have worked, because I was merely guessing in every
case.
This is the type of thing that makes me sorry I ever got involved with
tag libraries.
I have a Map of Lists. I didn't invent this. This is a common structure
to use in Java. So someone please show me a single document that tells
you how to work with JSTL tags (or any other tags) to do such a simple
thing as to do a nested iteration of a Map of Lists or a Map of arrays!
Here is the Java equivalent of what I need to do:
//Map, stored as request attribute, has String keys, MyClass[] values
Map map = getMapWhichIsARequestAttribute();
Iterator i = map.keySet().iterator();
while (i.hasNext()) {
String key = (String) i.next();
MyClass[] values = (MyClass[]) map.get(key);
int size = values.length; // *HOW DO I GET THIS VALUE USING TAGS?*
if (size 0) { // *HOW DO I IMPLEMENT THIS TEST USING TAGS?*
if (size 5) {
//do setup for a big array
for (int x = 0; x size; x++) {
//do output for each item in array
}
}
else {
//do setup for a small array
for (int x = 0; x size; x++) {
//do output for each item in array
}
}
}
else {
//no records found for this key
}
}
Failing that, I would appreciate it if someone could show me how to do
this using Struts tags. If I had used scriptlets, I would have been done
hours ago.
Thanks,
Erik
Erik Weber wrote:
I have a c:forEach where items refers to a Map, and var refers to
the current Map entry.
c:forEach items=myMap var=currentEntry
The value for each Map entry is an array. How do I switch on the
length of this array? I tried this:
c:when test=${currentEntry.value.length 5}
But I get a syntax error; it says I supplied the . operator with an
index value of type java.lang.String to be applied to an array, but
that the value cannot be converted to an integer.
Is there some sort of way I can use items.length or items.size or
something similar? More importantly, WHERE IS THIS DOCUMENTED?
I have searched the Internet for decent documents on JSTL and cannot
find a simple complete guide to tag usage -- something similar to what
Struts has for its tags. For example, where is a document that
explains what you can do with var, varStatus, items, etc. on a
c:forEach tag, and covers all the tags? The Sun web services tutorial
does not do this, it only gives examples.
Thank you,
Erik
Erik Weber wrote:
Thanks again.
Erik
Kris Schneider wrote:
c:forEach supports a varStatus attribute. The value of that
atrribute is a
String that names an instance of
javax.servlet.jsp.jstl.core.LoopTagStatus. The
LoopTagStatus instance has nested visibility so that it's only
available within
the enclosing c:forEach tag. LoopTagStatus exposes a number of
properties,
but the one you're probably interested in is index:
..
c:forEach var=bean varStatus=status items=${entry.value}
%-- ${status.index} is the current index --%
...
/c:forEach
..
Quoting Erik Weber [EMAIL PROTECTED]:
How can I refer to the index of the current iteration with
c:forEach (analogous to the indexId attribute to logic:iterate)?
Thanks,
Erik
Kris Schneider wrote:
%@ taglib
Re: Still need help with layered Map iteration in JSP
Kris, once again you have helped me get my work done. bean:size did the
trick. I was looking over and over again for a JSTL tag or expression to
do this; I probably never would have thought of bean:size.
To complete the post for any other reader who is as suicidal as I am
after trying to figure this out:
c:forEach items=myMap var=currentEntry!-- where Map has String
keys and array or List values --
bean-el:size collection=${currentEntry.value} id=size/!-- page
scope variable size (of type java.lang.Integer) will now contain the
size of the array or list associated with the current Map key --
. . .
c:when test=${size 5}!-- how to test how big the current array
or List is --
. . .
c:forEach items=currentEntry.value var=currentItemInArrayOrList
varStatus=iteratorStatus!--- how to iterate the current array or
List --
. . .
c:out value=${currentItemInArrayOrList.someProperty}/!-- how to
print some property of the current item in the current array or List --
. . .
c:when test=${iteratorStatus.index % 2 == 0}!-- how to tell if
you are on an even-numbered row in your iteration --
and so on . . .
Thank you,
Erik
P.S. I would love to know how you learned all this (I suppose I must buy
a JSTL book).
Erik
Kris Schneider wrote:
I guess the first thing to make sure you understand is that, when iterating over
a Map, the object exposed by JSTL via the var attribute is of type Map.Entry.
It's equivalent to doing a map.entrySet().iterator(). As for getting the size
of an array, Collection, or Map, use the bean:size tag.
Quoting Erik Weber [EMAIL PROTECTED]:
OK, I'll take ANY WAY TO DO THIS AT ALL.
I have a c:forEach over a Map. The value for each key in the Map can be
an array of objects, or I can make it a List. I don't care at this point.
All I want to do is get the length of this array or List, before I start
iterating over *it*, during the current iteration of the Map. I am told
that I access the array or List like this:
1) Given this Map iteration:
c:forEach items=myMap
var=currentMapEntryWhichIsBothAKeyAndAValueTogether
2) access the value of the current Map entry (which will be either an
array or a List) like this:
${currentMapEntryWhichIsBothAKeyAndAValueTogether.value}
But I have tried all of these, none of them work:
c:when
test=${currentMapEntryWhichIsBothAKeyAndAValueTogether.value.length
0}!-- where the value of the Map entry is an array --
c:when
test=${currentMapEntryWhichIsBothAKeyAndAValueTogether.value.size
0}!-- where the value of the Map entry is a List --
c-rt:when
test=${fn:length(currentMapEntryWhichIsBothAKeyAndAValueTogether.value)
0}!-- where the value of the Map entry is either an array or a
List --
Not that they would have worked, because I was merely guessing in every
case.
This is the type of thing that makes me sorry I ever got involved with
tag libraries.
I have a Map of Lists. I didn't invent this. This is a common structure
to use in Java. So someone please show me a single document that tells
you how to work with JSTL tags (or any other tags) to do such a simple
thing as to do a nested iteration of a Map of Lists or a Map of arrays!
Here is the Java equivalent of what I need to do:
//Map, stored as request attribute, has String keys, MyClass[] values
Map map = getMapWhichIsARequestAttribute();
Iterator i = map.keySet().iterator();
while (i.hasNext()) {
String key = (String) i.next();
MyClass[] values = (MyClass[]) map.get(key);
int size = values.length; // *HOW DO I GET THIS VALUE USING TAGS?*
if (size 0) { // *HOW DO I IMPLEMENT THIS TEST USING TAGS?*
if (size 5) {
//do setup for a big array
for (int x = 0; x size; x++) {
//do output for each item in array
}
}
else {
//do setup for a small array
for (int x = 0; x size; x++) {
//do output for each item in array
}
}
}
else {
//no records found for this key
}
}
Failing that, I would appreciate it if someone could show me how to do
this using Struts tags. If I had used scriptlets, I would have been done
hours ago.
Thanks,
Erik
Erik Weber wrote:
I have a c:forEach where items refers to a Map, and var refers to
the current Map entry.
c:forEach items=myMap var=currentEntry
The value for each Map entry is an array. How do I switch on the
length of this array? I tried this:
c:when test=${currentEntry.value.length 5}
But I get a syntax error; it says I supplied the . operator with an
index value of type java.lang.String to be applied to an array, but
that the value cannot be converted to an integer.
Is there some sort of way I can use items.length or items.size or
something similar? More importantly, WHERE IS THIS DOCUMENTED?
I have searched the Internet for decent documents on JSTL and cannot
find a simple complete guide to tag usage -- something similar to what
Re: Still need help with layered Map iteration in JSP
It's certainly not a bad idea to grab a JSTL book, but the spec itself is quite
readable and full of good information:
http://jcp.org/aboutJava/communityprocess/final/jsr052/
The only JSTL book I've even partially read is JSTL in Action by Shawn Bayern
and I have no reservations recommending it. There are also plenty of web
resources available:
http://www.javaworld.com/javaworld/jw-02-2003/jw-0228-jstl.html
http://www.onjava.com/pub/a/onjava/2002/08/14/jstl1.html
http://www.onjava.com/pub/a/onjava/2002/09/11/jstl2.html
http://www.onjava.com/pub/a/onjava/2002/03/13/jsp.html
http://www.onjava.com/pub/a/pub/a/onjava/2002/05/08/jstl.html
http://java.sun.com/developer/technicalArticles/javaserverpages/faster/
http://java.sun.com/developer/technicalArticles/Intl/MultilingualJSP/
etc.
Quoting Erik Weber [EMAIL PROTECTED]:
Kris, once again you have helped me get my work done. bean:size did the
trick. I was looking over and over again for a JSTL tag or expression to
do this; I probably never would have thought of bean:size.
To complete the post for any other reader who is as suicidal as I am
after trying to figure this out:
c:forEach items=myMap var=currentEntry!-- where Map has String
keys and array or List values --
bean-el:size collection=${currentEntry.value} id=size/!-- page
scope variable size (of type java.lang.Integer) will now contain the
size of the array or list associated with the current Map key --
. . .
c:when test=${size 5}!-- how to test how big the current array
or List is --
. . .
c:forEach items=currentEntry.value var=currentItemInArrayOrList
varStatus=iteratorStatus!--- how to iterate the current array or
List --
. . .
c:out value=${currentItemInArrayOrList.someProperty}/!-- how to
print some property of the current item in the current array or List --
. . .
c:when test=${iteratorStatus.index % 2 == 0}!-- how to tell if
you are on an even-numbered row in your iteration --
and so on . . .
Thank you,
Erik
P.S. I would love to know how you learned all this (I suppose I must buy
a JSTL book).
Erik
--
Kris Schneider mailto:[EMAIL PROTECTED]
D.O.Tech http://www.dotech.com/
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