change String.replaceAll() to replace() to improve performance.

Location:

(1) pluto-container/src/main/java/org/apache/pluto/container/impl/RenderResponseImpl.java

(2) pluto-taglib/src/main/java/org/apache/pluto/tags/BaseURLTag.java

Since the string to be replaced is simple string literal that does not need to be compiled, i.e., not regular expression. Another API String.replace() should be used and recommended for better performance.