Java BufferedReader

Article

The code refers to the following articles (not yet published):

• English: Java BufferedReader
• German: Java BufferedReader

Contents

Most examples read the small log file files/server.log. Every class with a main() method in eu.happycoders.bufferedreader is one chapter of the article and prints the outputs shown there. Run one from the repository root with java -cp target/classes eu.happycoders.bufferedreader.<ClassName> after mvn compile. Files the examples create go into target/.

• Intro – reads the log file line by line
• Ch1Creating – Files.newBufferedReader(), FileReader, InputStreamReader around a GZIPInputStream, an own buffer size, and a Latin-1 file read as UTF-8
• Ch2ReadLine – line terminators, empty lines, and the end of the input
• Ch3Lines – lines() with filter() and groupingBy(), an UncheckedIOException while streaming, and Files.lines()
• Ch4ReadAll – readAllLines() and readAllAsString() (Java 25), also after a readLine()
• Ch5Characters – read() and read(char[], int, int)
• Ch6MarkReset – an optional header line with mark() and reset(), and skip()
• Ch6Ready – ready() returns false, yet the next readLine() returns a line
• Ch7Console – reading lines from System.in with the charset from stdin.encoding (Java 25)
• Ch7Readln – IO.readln() (Java 25)
• Ch8Scanner – tokens with Scanner and with split(), and how both classes report an IOException
• Ch9Closing – closing the BufferedReader closes the reader inside it
• Ch10Mistakes – calling readLine() twice per loop iteration

Benchmarks

The package eu.happycoders.bufferedreader.benchmark contains the JMH benchmarks of the article's performance section:

• ReadBenchmark – reading a 100,000,000-byte UTF-8 text file with InputStreamReader, FileReader, and BufferedReader (read(), read(char[]), readLine(), lines(), readAllLines()), and with Scanner.nextLine()
• BufferSizeBenchmark – readLine() with buffer sizes from 256 to 1,048,576 characters
• ReadCallCounter – not JMH: counts how often the InputStreamReader reads from the file when a BufferedReader reads it line by line, for buffer sizes from 256 to 1,048,576 characters; the count is the same for every size
• DecoderWarmupCheck – not JMH: decodes the test file with an InputStreamReader in blocks of one size after warming the JVM up with another, one JVM per call; it shows that the speed depends on the warm-up block size, not on the measured one (the command is in the class comment)

The first run creates the test file target/benchmark-input.txt from a fixed seed, so every machine reads the same file. Build and run:

mvn package
java -jar target/benchmarks.jar

The complete run takes about 15 minutes. Close other applications while it runs. The results of the article's run are in results/apple-m5-pro/.

Additional Resources

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