Update only the new content in a file all five minutes

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...

`System.err.println("Error in FileWrite: " + e.getMessage());` - this will lose the stack trace, and your program shouldn't really be carrying on. Better to rethrow it as `RuntimeException`. — artbristol, Oct 08 '12 at 09:07
@artbristol: thanks, but first i want to run the code, after that i catch the faults... — Michael Schmidt, Oct 08 '12 at 09:10
@dTDesing yeah, but your code will make it *harder* to catch the faults while you're debugging. — artbristol, Oct 08 '12 at 09:11
@dTDesign : How large is the file? Is it MB or a few KB? Also are the changes only at the Bigining/End or anywhere? What is the format of the file? — Pushkar, Oct 08 '12 at 09:11

score 2 · Accepted Answer · answered Oct 08 '12 at 09:44

2

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.

answered Oct 08 '12 at 09:44

artbristol

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+1 for this great answer. But it's easy to work with HashMap. How should i save the Map to use it again? I'm not sure the file would be so small over the time... – Michael Schmidt Oct 08 '12 at 09:50
@dTDesign Just write out the whole thing again. Don't worry about performance until you need to. Test your program with large amounts of data and see what happens. – artbristol Oct 08 '12 at 09:53
ok thanks. i do it so. but for the learning effect, i want also try the other version, when i've time for that. i accept the answer. As soon as i found a solution for my method, i post it in my answer. thank you for your help! – Michael Schmidt Oct 08 '12 at 11:25

Unni Kris · Answer 2 · 2012-10-08T09:29:03.550

0

You can call the updateFile method in a loop and then call sleep for 5 minutes (5*60*1000 ms).

Thread.Sleep(300000); // sleep for 5 minutes

To append to your already existing file you can use :

FileOutputStream fooStream = new FileOutputStream(file, true);

edited Oct 08 '12 at 09:29

answered Oct 08 '12 at 09:15

Unni Kris

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yeah found it already, but thanks. The big question is the update of the file... – Michael Schmidt Oct 08 '12 at 09:21
If you are just adding to the end of the content, then append will always be the best option.. – Unni Kris Oct 08 '12 at 09:26
Then overwriting would be best. See this question : http://stackoverflow.com/questions/11253843/is-there-a-better-way-to-overwrite-file-contents – Unni Kris Oct 08 '12 at 09:33

score 0 · Answer 3 · answered Oct 08 '12 at 09:27

0

Use the constructor FileOutputStream(File file, boolean append), set the boolean append to true. It will append the text in the existing file.

answered Oct 08 '12 at 09:27

Pr38y

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i think not that append is the right method. Take a look to my EDIT. – Michael Schmidt Oct 08 '12 at 09:34
You can use two option the one is to set `append false` so that it will overwrite the changes. The other option is - if the file already exist than read the content parse it as `String` or use `Regex` than replace the changes. – Pr38y Oct 08 '12 at 09:43

Update only the new content in a file all five minutes

3 Answers3