How to I read and edit txt in a serialised file?

Question

I have an object which is serialised and written to a file.

Before de serialising the file back into an object instance, I want to maliciously edit the txt in the file.

//Before
¨Ìsr&Snippets.Parsed.EmployeeSerialization0I
bankBalanceLnametLjava/lang/String;xp•Åt
Henry Crappe

//After
ÔøΩÔøΩsr&Snippets.Parsed.EmployeeSerialization0I
bankBalanceLnametLjava/lang/String;xpÔøΩÔøΩt
Fsekc Dhdhfie

However the edited file isn't correct and has some unusual characters.

 //Before ¨Ìsr&Snippets.Parsed.EmployeeSerialization0I bankBalanceLnametLjava/lang/String;xp•Åt Henry Crappe //After ÔøΩÔøΩsr&Snippets.Parsed.EmployeeSerialization0I bankBalanceLnametLjava/lang/String;xpÔøΩÔøΩt Fsekc Dhdhfie 

I'm guessing there is some sort of non readable character issue or something?

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Answer continued in a new question is here

Answer 1

A file which contains a serialized object instance is a binary file: you should not edit it with a BufferedWriter. Edit it with a RandomAccessFile, for example.

If you are wondering of why, the charset used in a Writer could not map one-to-one with a byte. Saving all the file would change also unexpected positions.