This is a simple program that converts a Classic 0.25_05 SURVIVAL TEST Minecraft level to be playable in Classic 0.27 SURVIVAL TEST. Earlier versions convert to 0.27 successfully and 0.25_05 will convert to later versions successfully, it is only this one update that encounters an unavoidable error.
The problem is that the Player$1 class did not have its serialVersionUID set to 0 in 0.25_05 like most other classes. Therefore, the serialVersionUID defaulted to -5141891085410515807 in 0.25_05. Notch set the serialVersionUID to 0 by Classic 0.27 which caused an error when reading files from 0.25_05 that prevents it from being read. By Classic 0.28_01 and later, Notch made a specialized class that extends ObjectInputStream just so either serialVersionUID from 0.25_05 or 0.27 could be accepted allowing all levels to upgrade. This most likely applies to other versions as well but as of 26 March, 2023 these are the only archived versions this program works to fix.
This program only edits the serialVersionUID of Player$1 in the file from -5141891085410515807 to 0. This value is only used by Java's deserializer to identify the classes it is reading in and has no effect in game. Important note: if you spawn a sign in Classic 0.25_05 SURVIVAL TEST it won't be able to update to any future versions, this tool does not fix that issue given it's separate and avoidable.
Ensure Java 8 or later is installed in order to use this program. You can either run the JAR file by double-clicking it or using the command line.
The JAR file (download on the Releases tab) can be used to simply correct the file.
- Put JAR file in the same folder as the level file with the name "level.dat"
- Double-click the JAR file to run it and the program will output the new, corrected file to "output.dat" in that same folder
- Move the "output.dat" file in your instance's directory and rename back to "level.dat" in order to be played by your launcher
The main method of this program can be ran with zero or two parameters. With no parameters, the program defaults to read from level.dat and write to
output.dat (java -jar Classic25to27Converter.jar).
If two parameters are given, the first should be the path to the input file and the second should be the path to the output file. The two paths cannot be the same. (java -jar Classic25to27Converter.jar My025Level.dat Corrected027Level.dat)