We recently surveyed Java developers about their preferences for our 2021 Spring Framework User Survey. One of the questions we asked was: Which library would you consider to be the most useful for your day-to-day working life? Of the 450 people who took the survey, 146 answered this free-response question with their top choice.

According to the survey results, here is a list of the top 6 most useful libraries for Java developers in 2021:

#1: HTTP library

With 23 mentions out of 146, this was the top response 

#2: PDF library

PDF Library got 21 responses, putting it in second place.

#3: Excel reading library

This came in third, with 9 calling it out by name.

#4: Collection libraries

8 respondents said collection libraries was their top choice.

#5: Messaging libraries

Messaging libraries came in 5th place, with 6 responses.

#6: Bytecode libraries and Scala library

Both of these responses came in at 6th place with 5 responses.

Other libraries that were mentioned fewer than 5 times are: XML parsing libraries, Email APIs, Logging libraries, AssertJ, Hibernate, Mootools, Clojure, Jackson, Mignon, Apache, Lagback, and General Purpose Libraries. Honorable mentions also include the Library of Congress and the Technology for Everyday Life courses at Watertown Library in Massachusetts.

To read the responses to the rest of our survey questions, check out the new report.