Java reading text lines without line separators

Question

For processing a searchlog file I'm writing a Java class that should read and handle the file content line by line.

The Text in the Logfile looks like the following

[Integer User ID] [Queury] [Date: YYYY-MM-DD HH:MM:SS] [optional url]

I tried using a scanner and reading the lines with nextLine(), but this reads the whole file as one line. Any idea how I can ensure to only get one line at a time?

Jonathan Payne · Accepted Answer · 2012-04-23 18:31:44Z

3

You can just grab the entire file as you have it, and then split the data:

for ( String line : "the entire file".split( System.getProperty("line.separator") )
{
     System.out.println( line );
}

As a side note: System.getProperty("line.separator") is the universal new line character.

An alternative method:

BufferedReader bufferedReader = new BufferedReader( new FileReader( "absolute file path" ) );

String line;

while ( ( line = bufferedReader.readLine() ) != null)
{
     System.out.println( line );
}

answered Apr 23, 2012 at 18:31

Jonathan Payne

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3 Comments

Fermin Silva Over a year ago

Log files are usually quite big to load into memory at once. Not only that, but the .split will cause to allocate twice as much!

deemel Over a year ago

Pretty much what Fermin Silva said, we're talking about 212mb txt files here

Jonathan Payne Over a year ago

@Rickyfox i added a second method using bufferedReader.

Jon Skeet · Accepted Answer · 2012-04-23 18:31:08Z

3

Try using BufferedReader instead of Scanner. BufferedReader is tolerant of various different types of line terminator - it's possible that Scanner always expects your platform-default line terminator.

Alternatively, use Guava which lets you do this really easily, e.g. with CharStreams.readLines, potentially specifying a LineProcessor.

answered Apr 23, 2012 at 18:31

Jon Skeet

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2 Comments

deemel Over a year ago

If I recall it right I had the same problem when trying bufferedReader, but I'll double-check it

Jon Skeet Over a year ago

@Rickyfox: Well if you did, that would suggest you're either not reading the file properly (encoding issues?) or your file has odd line endings. What encoding is the file in?

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