Sleep

//Pause for 4 seconds
Thread.sleep(4000);

Write file

public void writeFile() {
    try(FileOutputStream fos = newFileOutputStream("movies.txt");
        DataOutputStream dos = newDataOutputStream(fos)) {

        dos.writeUTF("Java 7 Block Buster");

    } catch(IOException e) {

        // log the exception

    }
}

Read file

Java 7

Read all contents at once

String content = new String(Files.readAllBytes(Paths.get(fileName)));

Line by line

package com.mkyong;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

public class ReadTextFile {

    public static void main(String[] args) throws IOException {

        try {

            File f = new File("src/com/mkyong/data.txt");

            BufferedReader b = new BufferedReader(new FileReader(f));

            String readLine = "";

            System.out.println("Reading file using Buffered Reader");

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

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

Java 8

Stream<String> lines = Files.lines(path);
lines.forEach(line -> data.append(line).append("\n"));
lines.close();

@Test
public void givenFilePath_whenUsingFilesLines_thenFileData() {
   String expectedData = "Hello World from fileTest.txt!!!";

   Path path = Paths.get(getClass().getClassLoader()
           .getResource("fileTest.txt").toURI());

   StringBuilder data = new StringBuilder();
   Stream<String> lines = Files.lines(path);
   lines.forEach(line -> data.append(line).append("\n"));
   lines.close();

   Assert.assertEquals(expectedData, data.toString().trim());
}

Read file extension

http://commons.apache.org/proper/commons-io/javadocs/api-2.5/org/apache/commons/io/FilenameUtils.html#getExtension

String ext1 = FilenameUtils.getExtension("/path/to/file/foo.txt"); // returns "txt"
String ext2 = FilenameUtils.getExtension("bar.exe"); // returns "exe"

// https://mvnrepository.com/artifact/commons-io/commons-io
compile group: 'commons-io', name: 'commons-io', version: '2.4'

Get file last updated date

import java.io.File;
import java.text.SimpleDateFormat;

public class GetFileLastModifiedExample
{
    public static void main(String[] args)
    {
    File file = new File("c:\\logfile.log");

    System.out.println("Before Format : " + file.lastModified());

    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");

    System.out.println("After Format : " + sdf.format(file.lastModified()));
    }
}

Empty stack trace

From here. Useful for custom exceptions, or when a quicker error handling is required.

/**
* efficient exception that has no stacktrace; we use this for flow-control.
*/
@Immutable
static final class ResourceNotFound extends Exception
{
ResourceNotFound()
{}
@Override
public Throwable fillInStackTrace()
{
return this;
}
}

Create temp file/folder

import java.nio.file.Files;

tempCheckpointFolder = Files.createTempDirectory("checkpoints");
//the directory must be empty in order to be deleted.
tempCheckpointFolder.toFile().deleteOnExit();

Compute time difference

LocalDateTime now = LocalDateTime.now();
boolean olderThanAday = ChronoUnit.DAYS.between(startSessionDate, now ) >= 1;
if (olderThanAday){
    System.out.println("The stored timestamp is older than a day")
    startSessionDate = now;
}

Random alphanumeric string

``` org.apache.commons commons-lang3 3.8

RandomStringUtils.randomAlphanumeric(10);

### Difference between two dates

LocalDateTime now = LocalDateTime.now(); boolean olderThanAday = ChronoUnit.DAYS.between(startSessionDate, now ) >= 1; if (startSessionDate == null || olderThanAday){ AuthLoginResponseType response = this.serviceV12.startSession(this.username, this.password, this.locale); this.sessionId = response.getResult().getValue().getSessionId(); startSessionDate = now; }```