I want to insert the data at some positions in the text file without actually overwriting on the existing data.I tried RandomAccessFile ....but that also overwrites it.... I
You have to read your file and rewrite it. During this operation you have to find the place where you want to put your text and write it.
It is not possible (not with Java, and not with any other programming language) to "just" insert data in the middle of the file, without having to re-write the rest of the file. The problem is not the programming language, the problem is the way files work.