CODEWITHSUNDEEP
javajsonjackson
N.F.
N.F.

Reputation: 4182

Jackson writeValueAsString too slow

I want to create JSON string from object.

ObjectMapper om = new ObjectMapper();
String str = om.writeValueAsString(obj);

Some objects are large, and it takes long time to create JSON string. To create 8MB JSON string, it needs about 15secs.

How can I improve this?

Upvotes: 2

Views: 11884

Answers (1)

StaxMan
StaxMan

Reputation: 116572

Make sure you have enough memory: Java String for storing 8 MB of serialized JSON needs about 16 megabytes of contiguous memory in heap.

But more importantly: why are you creating a java.lang.String in memory? What possible use is there for such a huge String?

If you need to write JSON content to a file, there are different methods for that; similarly for writing to a network socket. At very least you could write output as a byte[] (takes 50% less memory), but in most cases incremental writing to an external stream requires very little memory.

15 seconds is definitely very slow. Without GC problems, after initial warmup, Jackson should write 8 megs in fraction of a second, something like 10-20 milliseconds for simple object consisting of standard Java types.

EDIT:

Just realized that during construction of the result String, temporary memory usage will be doubled as well, since buffered content is not yet cleared when String is constructed. So 8 MB would need at least 32 MB to construct String. With default heap of 64 MB this would not work well.

Upvotes: 5

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