LDIFReader.java:
Extracted methods findFirstNonSpaceCharPosition(), base64Decode() and decodeDN().
In readAttribute(), moved common code out of if/else branches.
Used early exits.
Removed useless parenthesis.
Condensed code and comments on one line where possible.

LDIFWriter.java:
Extracted methods writeDN(), writeAttribute().
In writeEntries(), simplified the code.
In writeModifyChangeRecord(), removed useless switch statement.
In appendLDIFSeparatorAndValue(), removed duplicate code.
Removed useless parenthesis.
Comments => javadocs
Condensed code and comments on one line where possible.