Log file auto monitoring in java which is incrimenting every time and always want to monitor new line

Question

I have a log file which is increasing always due to logging for different logging event in my application. Now i want to check some patterns in the log file and if I find any match for the patterns I will print it some where else. The log file is not static file it is always increasing and I my program should not check the old line again. It should always checks the new line which have not been checked yet.

["_incriminating_"](https://dictionary.cambridge.org/dictionary/learner-english/incriminating) who? Or is it whom? — Boris the Spider, Sep 24 '16 at 12:08
It is increasing by the different places of the application where I used to log an event. — ARUP BAROI, Sep 24 '16 at 12:12
Is it totally necessary to do this in Java? If you command a command like you could do this easily with `tail` and `grep` — tddmonkey, Sep 24 '16 at 12:26
Have a look at logstash https://www.elastic.co/products/logstash — Michel Feldheim, Sep 24 '16 at 12:46

score 0 · Accepted Answer · edited May 23 '17 at 12:00

0

Store the position of what you have checked up to in some kind of integer or file. now when you look for a pattern look for a regular expression and then print it to whatever output stream.

First read the file into an array like so, call the getWordsFromFile() method.

/**
 *
 * @param fileName is the path to the file or just the name if it is local
 * @return the number of lines in fileName
 */
public static int getLengthOfFile(String fileName) {
    int length = 0;
    try {
        File textFile = new File(fileName);
        Scanner sc = new Scanner(textFile);
        while (sc.hasNextLine()) {
            sc.nextLine();
            length++;
        }
    } catch (Exception e) {

    }
    return length;
}

/**
 *
 * @param fileName is the path to the file or just the name if it is local
 * @return an array of Strings where each string is one line from the file
 * fileName.
 */
public static String[] getWordsFromFile(String fileName) {
            int lengthOfFile = getLengthOfFile(fileName);
    String[] wordBank=new String[lengthOfFile];
    int i = 0;
    try {
        File textFile = new File(fileName);
        Scanner sc = new Scanner(textFile);
        for (i = 0; i < lengthOfFile; i++) {
        wordBank[i] = sc.nextLine();
        }
        return wordBank;
    } catch (Exception e) {
                System.err.println(e);
        System.exit(55);
    }
    return null;
}

For larger files see this question Then once you load your String[], you can iterate through like so.

for(int i=0;i<arr.length;i++) 
doSomething(arr[i]);

to something like

for(int i= start;i<arr.length;i++)
doSomething(arr[i]);

edited May 23 '17 at 12:00

Community

1
1

answered Sep 24 '16 at 12:15

Rohan Jhunjhunwala

416
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But how can i avoid rechecking the previously check lines? Line number I can save but it have to check each line then only can find the last read line which is not what i want. – ARUP BAROI Sep 24 '16 at 12:17
@ARUPBAROI I need to see your code, but assuming you know how to read a file into an array. modify it from for(int i=0;i – Rohan Jhunjhunwala Sep 24 '16 at 12:18
I think normal file reading will not work. I think you are telling me using a buffer reader and check for each line. But I want when next time I start reading the file It should start counting from the last line which it has already read previous execution. – ARUP BAROI Sep 24 '16 at 12:21
@ARUPBAROI why will normal file reading not work, but other than that, what you are saying is correct. – Rohan Jhunjhunwala Sep 24 '16 at 12:23
Is there ant API which can do the purpose with very less time? I want to avoid fileInputStream reading. – ARUP BAROI Sep 24 '16 at 12:28
@ARUPBAROI you can easily home grow this. – Rohan Jhunjhunwala Sep 24 '16 at 12:30
For a log file of size in GB's it will be a performance issue.The code you have written is ok for small size file which even I know. But here I am talking about file size over 10 GB. – ARUP BAROI Sep 24 '16 at 13:03
@ARUPBAROI see my link – Rohan Jhunjhunwala Sep 24 '16 at 13:15
Chat is not opened for me I have to increase my reputation – ARUP BAROI Sep 24 '16 at 13:25
@ARUPBAROI it does not let you join a room? – Rohan Jhunjhunwala Sep 24 '16 at 13:46

Log file auto monitoring in java which is incrimenting every time and always want to monitor new line

1 Answers1