I want to display the payload with line breaks for better readability on Splunk Web.
Splunk receives the payload as a stream of data with no line breaks which results in a continuous text. So we included a unique string at the end of the line before sending to Splunk. We are trying to replace the unique string     
with line breaks so that it will helps the with the readability. Will LINE_BREAKER work for this?
Current:
    Exception in thread "main" java.lang.NullPointerException     at com.example.myproject.Book.getTitle(Book.java:16)     at com.example.myproject.Author.getBookTitles(Author.java:25)     at com.example.myproject.Bootstrap.main(Bootstrap.java:14)          
Expected:
Exception in thread "main" java.lang.NullPointerException
at com.example.myproject.Book.getTitle(Book.java:16)
at com.example.myproject.Author.getBookTitles(Author.java:25)
at com.example.myproject.Bootstrap.main(Bootstrap.java:14)
This works for me.
| rex mode=sed "s/ /\n/g"
Rex mode command works and I am assuming SEDCMD will also work. I am worried about the performance. Will there be any impacts on the performance if SEDCMD command is used?
rex mode=sed "s/
/\n/g"
SEDCMD-breaklinekpaths=s/
/\n/g
Should be too bad, but this seem to be your only option.
LINE_BREAKER is intended to create new events which I doubt you want each line to be a separate Splunk event. Why is your log inserting characters as HTML entities? I think the best way would be to use sed to convert all the html entities or build a Splunk command.