In the code review for JDK-8257733, there were expressed wishes that charsetmapping recieves additional love. For instance, parts of make/modules/jdk.charsets/Gensrc.gmk should perhaps move to java.base, and src/java.base/share/data/charsetmapping/Single/DoubleByte-X.java.template should probably move out of data and move in with the other *.java.template files.