Writing Java objects or a List into a text file is ok. But I want to know how I can update or rewrite a object which was written previously without writing objects again. For example, let s assume there is a java.util.List has a set of Objects. and then that list is written to a text file. Then later that file will be read again and get all objects from list and then change one object's value at run time by a java application. Then I don't need to write entire list back to the text file. Instead only the updated object in the list is required to be rewritten or updated in the text file without rewriting the whole list again. Any suggestion, or helpful source with sample codes please.
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You are using a text file as a database. Things will get messy, you could separate elements on different lines based on index; but I would go the database route. – Alberto Zaccagni Aug 04 '13 at 12:57
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Take a look at RandomAccessFile. This will let you seek to the place in the file you want, and only update the part that you want to update.
Also take a look at this question on stackoverflow.
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Ankur Shanbhag
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Without some fairly complex logic, you won't usually be able to update an object without rewriting the entire file. For example, if one of the objects on your list contains a string "shortstring", and you need to update it with string "muchmuchlongerstring", there will be no space in the file for the longer string without rewriting all the following content in the file.
If you want to persist large object trees to a file and still have the ability to update them, your code will be less buggy and life will be simplified by using one of the many file-based DBs out there, like:
- SQLite (see Java and SQLite)
- Derby
- H2 (disk-based tables)
