Question

I get a file personHashMap.ser with a HashMap in it. Here’s the code how i create it:

String file_path = ("//releasearea/ToolReleaseArea/user/personHashMap.ser");
public void createFile(Map<String, String> newContent) {
    try{
        File file = new File(file_path);

        FileOutputStream fos=new FileOutputStream(file);
        ObjectOutputStream oos=new ObjectOutputStream(fos);

        oos.writeObject(newContent);
        oos.flush();
        oos.close();
        fos.close();

    }catch (Exception e){
        System.err.println("Error in FileWrite: " + e.getMessage());
    }

}

Now i want, when the program is running, that all five minutes update the file personHashMap.ser only with the content which changed. So the method i called:

public void updateFile(Map<String, String> newContent) {
    Map<String, String> oldLdapContent = readFile();
    if(!oldLdapContent.equals(ldapContent)){ // they arent the same, 
                                             // so i must update the file

    }   

}

But now i haven’t any ideas how i can realise that.
And is it better for the performance to update only the new content or should i clean the full file and insert the new list again?

Hope you can Help me..

EDIT:

The HashMap includes i.e street=Example Street.
But now, the new street called New Example Street. Now i must update the HashMap in the File. So i can’t just append the new content…

Answer 1

Firstly HashMap isn’t really an appropriate choice. It’s designed for in-memory usage, not serialization (though of course it can be serialized in the standard way). But if it’s just 2kb, then go ahead and write the whole thing rather than the updated data.

Second, you seem to be overly worried about performance of this rather trivial method (for 2kb the write will take mere milliseconds). I would be worried more about consistency and concurrency issues. I suggest you look into using a lightweight database such as JavaDB or h2.