Optimizing fasterxml ObjectMapper for list of Objects

Question

I want to optimizes ObjectMapper for a list. The requirement is that I need to add a delimiter after each element of the list. My current code looks like :

    StringBuilder strBuilder = new StringBuilder();
    for (Event event : segregatedList) {
        String eventJson = mapper.writeValueAsString(event);
        strBuilder.append("\n");
        strBuilder.append(eventJson);

    }

This take a huge amount of time for a long list (~10000 events) .How can I optimize the code to do serializes the list in a single go ?

I think if you divide your task among multiple thread based on number of element in the `segregatedList`. for example if you are using 4 core cpu and you ~10000 list size, divide this list among 4 thread first thread process from `~ 0 - 2500`, second `~2500-5000` in the list and so on 4th thread. use countdown latch to ensure all thread gets completed. once all thread complete their task then combine result into one string. — Pandey Amit, Nov 02 '18 at 07:15

score 2 · Answer 1 · answered Nov 02 '18 at 07:13

mapper instances are thread-safe, so you can split the mapper.writeValueAsString to a parallel job. I guess something like this may help if you don't worry of the order in which they are appended!

segregatedList.parallelStream().map(event -> mapper.writeValueAsString(event)).collect(Collectors.joining("\n")))

Otherwise, I can see very minimum scope of improving here. Maybe you can optimize json by ignoring properties as mentioned by Dark Knight

score 0 · Answer 2 · answered Nov 02 '18 at 07:04

There are multiple ways to concatenate Strings in java.

concat() method from java.lang.String
Using + operator
Using StringBuffer
Using StringBuilder

From my personal analysis i can say + call on String gets translated into new StringBuilder().append( "" ). Since StringBuilder(String) constructor allocates a buffer with 16 char, appending more than 16 characters will require buffer reallocation. At last, StringBuffer.toString() calls create a new String object with a copy of StringBuilder buffer.

So if you don't want synchronization overhead StringBuilder stands best among others else i would advice you to use StringBuffer here. I see you are using StringBuilder already, so there is very little scope for improvement here. However you can optimize generated json by ignoring properties which are not useful.

Optimizing fasterxml ObjectMapper for list of Objects

2 Answers2