CODEWITHSUNDEEP
javajava.util.scanner
Blue Label
Blue Label

Reputation: 437

Java file scanner move the cursor back

I am using the java scanner class for scanning log file and search for exception then once I find the exception I want to print 20 lines before it and 20 lines after it. Is there an option to return 20 lines once I found my exception The code like this.

Scanner in = null;
        try {
            in = new Scanner(new FileReader(f));
            while(in.hasNextLine() && !result) {
                result = in.nextLine().indexOf(searchString) >= 0;
                if (result)
                {
                    //return 20 lines
                }
            }
        }

Thanks in advance.

Upvotes: 0

Views: 2566

Answers (2)

Rodrigo Eggea
Rodrigo Eggea

Reputation: 124

You can read the file to a List and use ListIterator.

List<String> logList = Files.readAllLines(Paths.get(filename));
ListIterator iter = logList.listIterator();
String result = "match string";
while(iter.hasNext() && !result);
int indexMatch = iter.previousIndex();
    // Print previous 20 lines and next 20 lines
    for(int i=-20;i<40;i++){
        System.out.println(logList.get(indexMatch+i));
    } 
}

Upvotes: 0

Kevin D
Kevin D

Reputation: 3594

Buffer the lines as you read them. When you find the error, read the next 20 and buffer those also. Then return the buffer.

Upvotes: 4

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