How to handle "null" value in CacheLoader.load(key) ?

[Sky]

hi, friends

I have a question about CacheLoader.load(key) method that what
should I do when I really can not find a value for the specific key,
for example, "no such record in database for the key".

Example code like this:

public class UserCacheLoader extends CacheLoader<String, User> {
public User load(String userId) throws Exception {
User user = userDao.find(userId);
if (user != null) {
return user;
} else {
//??
}
}
}

I know that in CacheLoader.load(key) method we should not return
a "null", the javadoc even told us "must not be null". And I had got a
"InvalidCacheLoadException" when I tried to return a null in test
case.

So, how to handle it in CacheLoader.load(key) in case the value is
not exist for the key ?

Any help will be great appreciated!

Best Regards
Sky Ao

[Louis Wasserman]

You could use Optional...

But it might be more appropriate here to write your own wrapper class that works like Optional but has more appropriate method names.

Louis Wasserman
wasserm...@gmail.com
http://profiles.google.com/wasserman.louis

--
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[Kevin Bourrillion]

Hang on; the first question to ask is whether you expect the null result to be cached or not.  If you do, Louis is right; if you don't, throw an exception.

--
Kevin Bourrillion @ Google

Java Core Libraries Team
http://guava-libraries.googlecode.com

[Ondrej Medek]

I suppose Sky Ao wants to cache null result, too.

BTW. Hibernate has a second level cache. Maybe better opition.
BTW2. Hibernate default 2nd level cache is a poor
HashtableCacheProvider. It would be great to have some well working
GuavaCacheProvider. EHCache is tricky to configure and IMHO overkill
for small projects.

On 6 ún, 23:25, Kevin Bourrillion <kev...@google.com> wrote:
> Hang on; the first question to ask is whether you expect the null result to

> be *cached* or not.  If you do, Louis is right; if you don't, throw an

> exception.
>
> On Mon, Feb 6, 2012 at 1:33 PM, Louis Wasserman

> <wasserman.lo...@gmail.com>wrote:

>
>
>
>
>
>
>
>
>
> > You could use Optional...
>
> > But it might be more appropriate here to write your own wrapper class that
> > works like Optional but has more appropriate method names.
>
> > Louis Wasserman

> > wasserman.lo...@gmail.com
> >http://profiles.google.com/wasserman.louis

> >> To get help:http://stackoverflow.com/questions/ask(use the tag "guava")

>
> >  --
> > guava-...@googlegroups.com
> > Project site:http://guava-libraries.googlecode.com
> > This group:http://groups.google.com/group/guava-discuss
>
> > This list is for general discussion.
> > To report an issue:http://code.google.com/p/guava-libraries/issues/entry

> > To get help:http://stackoverflow.com/questions/ask(use the tag "guava")

[oltranz...@gmail.com]

Hello, It is really late to respond but someone new may come and get a help form this.
So, in my case I did

User user = cashe.getIfPresent(userId);//userId as a used cache key

so, you will get Null if the key exist or some value if the there is a corresponding object valueEnter code here...
Note: I am using Guava-18.0 jar

[Sushrita Yerra]

Again, this is really late but just in case someone like me comes in looking, the getIfPresent seems to have a bug wherein a concurrent environment it returns null sometimes even if the value is present. So I think going with Kevin's ans would be suitable.

Ref: https://github.com/google/guava/issues/2131