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Using object mapper in spring web application

Posted on 2016-08-11
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Last Modified: 2016-09-02
HI,
In my main controller code in many function i am using ObjectMapper (import org.codehaus.jackson.map.ObjectMapper;
) like :
ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(urlJsonMap);

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        ObjectMapper mapper = new ObjectMapper();
            Bun bun = mapper.readValue(event, Bun.class);

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I am thinking of moving it out on top of controller like :
ObjectMapper mapper = new ObjectMapper();

This way i can avoid unnecessary calls to creation of this object.
Please suggest if the above appraoch will be fine... Or alternatively is there any spring way annotation etc... i can achieve the same ?

Thanks
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Question by:Rohit Bajaj
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by:gurpsbassi
gurpsbassi earned 150 total points
ID: 41753609
Why can't you auto wire in the object mapper?
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mccarl earned 350 total points
ID: 41753627
The approach will be fine, that object is thread safe so even if multiple threads are executing your controller code, it will be ok. I even make it final static constant of the class most of the time in my code.
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Author Comment

by:Rohit Bajaj
ID: 41754835
HI,
Just to elaborate the above points and some questions also :
1) Autowiring Object Mapper as i understand is will require some entry into the xml bean config file or either i do it using @Bean Annotation inside a java class...
I was thinking of avoiding this because looks like for a simple object instatiaion which is probably needed in one class i could avoid that.
If this object was required in many classes then probably putting it into container and autowiring it would be better.

2) Can you please let me know how did you find out that ObjectMapper is thread safe in the above scenarios.

3) Regarding making it private final static

(i) I understand the final part because i will never change the object once created. But whats the need for static in this case ?
    Only reason i see is if some other class wanted to access ObjectMapper then it could do so.

Thanks
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Assisted Solution

by:mccarl
mccarl earned 350 total points
ID: 41755861
In response...

1) Yes, I agree

2) It was on the Jackson wiki, but that seems to be down at the moment.

3) the "static" part just means that one instance of the ObjectMapper will be shared regardless of how many objects your controller class get instantiated. It is unlikely that Spring would created more than one instance of the controller anyway, but using static just ensures that only one ObjectMapper would be created.
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Author Comment

by:Rohit Bajaj
ID: 41755866
thanks..
is there any way one can discover himself that something like object mapper is thread safe....may be i can post that as another question if that requires discussion...
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by:mccarl
mccarl earned 350 total points
ID: 41755882
There's no concrete way to know, it's up to the developer to communicate it in some way, generally through the Javadoc or otherwise via some other documentation, such as user guide, wiki, etc.
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Author Comment

by:Rohit Bajaj
ID: 41756003
Hi,
One more thing i found that there is an object mapper class :
com.fasterxml.jackson.databind.ObjectMapper
Whereas the class which i am using is org.codehaus.jackson.map.ObjectMapper

Which class were you referring to.. Or probably both of them are Thread Safe.
I found that fasterxml is the newer one. probably i should replace the older one with this new one.
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by:gurpsbassi
gurpsbassi earned 150 total points
ID: 41756032
use whichever one your spring application comes with. You shouldn't have both on your path.
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