Date and Time, I/O Streams

Agenda
Java 7 Date Time API
Java 8 Date Time API
Typical Uses of I/O System
What Is a Stream?
Byte Oriented Streams
Character-Oriented Streams
Buffered Input / Output

Java 7 Date Time API

Backstory
The Date class was the work of James Gosling and Arthur van Hoff.
Added in JDK 1.0, mostly deprecated in JDK 1.1, never removed.
IBM donated Calendar class code to Sun.

The Date class
The Date class available in java.util package, this class encapsulates the current date and time.
The Date class supports two constructors.
Date()
This constructor initializes the object with the current date and time.
Date(long millisec)
This constructor accepts an argument that equals the number of milliseconds that have elapsed since midnight, January 1, 1970.

Getting Current Date and Time
The Date object stores information about current date and time.
Methods getTime() and System.currentTimeMillis() return the current date and time as milliseconds since January 1st 1970.
// Instantiate a Date object
Date date = new Date();
// Display time and date using toString()
System.out.println(date);
Fri Feb 07 09:40:51 EET 2020
Date date = new Date();
long currentTime1 = date.getTime();
System.out.println(currentTime1);
long currentTime2 = System.currentTimeMillis();
System.out.println(currentTime2);
1581061806149
1581061806149

Useful Methods of the Date class
long getTime()
Returns the number of milliseconds that have elapsed since January 1, 1970.
void setTime(long time)
Sets the time and date as specified by time, which represents an elapsed time in milliseconds from midnight, January 1, 1970.
boolean after(Date date)
Returns true if the invoking Date object contains a date that is later than the one specified by date, otherwise, it returns false.
boolean before(Date date)
Returns true if the invoking Date object contains a date that is earlier than the one specified by date, otherwise, it returns false.
int compareTo(Date date)
Compares the value of the invoking object with that of date.

Problems Getting a Date class
Conceptually an instant, not a date
Properties have random offsets:
Some zero-based, like month and hours
Some one-based, like day of the month
Year has an offset of 1900
Mutable, not thread-safe
Not internationalizable
Millisecond granularity
Does not reflect UTC

The GregorianCalendar Class
The GregorianCalendar is a concrete implementation of a Calendar class that implements the normal Gregorian calendar with which you are familiar.
The getInstance() method of Calendar returns a GregorianCalendar initialized with the current date and time in the default locale and time zone.
Calendar calendar = new GregorianCalendar();
//set date to 05.02.2020 15:37
calendar.set(Calendar.YEAR, 2020);
calendar.set(Calendar.MONTH, 1); // 1 = February
calendar.set(Calendar.DAY_OF_MONTH, 5);
calendar.set(Calendar.HOUR_OF_DAY, 15); // 24 hour clock
calendar.set(Calendar.MINUTE, 37);
// get date components
int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH);
int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
int hourOfDay = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);
//add one day
calendar.add(Calendar.DAY_OF_MONTH, 1);
Date date = calendar.getTime();
System.out.println(date);
Thu Feb 06 15:37:27 EET 2020

Useful Methods of the Calendar class
void add(int field, int amount)
Adds the specified (signed) amount of time to the given time field, based on
the calendar's rules.
int get(int field)
Gets the value for a given time field.
Date getTime()
Gets this Calendar's current time.
long getTimeInMillis()
Gets this Calendar's current time as a long.
boolean isLeapYear(int year)
Determines if the given year is a leap year.

Useful Methods of the Calendar class
void set(int field, int value)
Sets the time field with the given value.
void set(int year, int month, int date)
Sets the values for the fields year, month, and date.
void setTime(Date date)
Sets this Calendar's current time with the given Date.
void setTimeInMillis(long millis)
Sets this Calendar's current time from the given long value.
void setGregorianChange(Date date)
Sets the GregorianCalendar change date.

Problems Getting a Calendar class
Conceptually an instant, not a calendar.
Zero-based offsets
Stores internal state in two different ways
milliseconds from epoch
set of fields
Has bugs and performance issues
Mutable, not thread-safe

Java 8 Date Time API

Backstory
2002 - Stephen Colebourne starts open source Joda-Time project
2005 - Release of Joda-Time 1.0
2007 - JSR 310, for inclusion in Java
2011 - Release of Joda-Time 2.0
2014 - Finally, the date and time API is in Java 8

New Packages
java.time
instants, durations, dates, times, time zones, periods.
java.time.format
formatting and parsing.
java.time.temporal
field, unit, or adjustment access to temporals.
java.time.zone
support for time zones.
java.time.chrono
calendar systems other than ISO-8601.

Design Principles
Distinguish between machine and human views.
Well-defined and clear purpose.
Immutable, thread-safe.
Reject null and bad arguments early.
Extensible, by use of strategy pattern.
Fluent interface with chained methods.

Commonly Used Classes
LocalDate
ISO 8601 date without time zone and time
Corresponds to SQL DATE type
LocalTime
ISO 8601 time without time zone and date
Corresponds to SQL TIME type
LocalDateTime
ISO 8601 date and time without time zone
Corresponds to SQL TIMESTAMP type
DateTimeFormatter
Formatter for displaying and parsing date-time objects

The ISO 8601 Standard
The International standard for representation of dates and times.
Uses the Gregorian calendar system.
Ordered from most to least significant: year, month, day, hour, minute.
Each date and time value has a fixed number of digits with leading zeros.
Uses four-digit year at minimum, YYYY.

The LocalDate Class
Obtain a LocalDate object corresponding to the local date of today.
Create a LocalDate object from year, month and day information.
LocalDate localDateNow = LocalDate.now();
System.out.println(localDateNow);
2020-02-07
LocalDate localDate = LocalDate.of(2020, Month.MARCH, 16);
System.out.println(localDate);
2020-03-16

The LocalDate Class
Access the date information of a LocalDate object.
int year = localDate.getYear();
Month month = localDate.getMonth();
int dayOfMonth = localDate.getDayOfMonth();
int dayOfYear = localDate.getDayOfYear();
DayOfWeek dayOfWeek = localDate.getDayOfWeek();
System.out.println("Year: " + year);
System.out.println("Month: " + month);
System.out.println("Day of Month: " + dayOfMonth);
System.out.println("Day of Year: " + dayOfYear);
System.out.println("Day of Week: " + dayOfWeek);
Year: 2020
Month: MARCH
Day of Month: 16
Day of Year: 76
Day of Week: MONDAY

The LocalDate Class
Simple date calculations with the LocalDate object.
LocalDate localDate = LocalDate.of(2020, Month.MARCH, 16);
System.out.println(localDate);
localDate = localDate.minusYears(2);
localDate = localDate.plusMonths(5);
localDate = localDate.minusDays(132);
localDate = localDate.plusWeeks(4);
System.out.println(localDate);
2020-03-16
2018-05-04

The LocalTime Class
Create a LocalTime object that represents the exact time of now.
Create a LocalTime object from a specific amount of hours, minutes, seconds and nanoseconds.
LocalTime localTimeNow = LocalTine.now();
System.out.println(localTimeNow);
12:10:18.625
LocalTime localTime = LocalTime.of(15, 30, 25, 845);
System.out.println(localTime);
15:30:25.000000855

The LocalTime Class
Access the time information of a LocalTime object.
int hour = localTime.getHour();
int minute = localTime.getMinute();
int second = localTime.getSecond();
int nanoOfSeconds = localTime.getNano();
System.out.println("Hour: " + hour);
System.out.println("Minute: " + minute);
System.out.println("Second: " + second);
System.out.println("Nano of Seconds: " + nanoOfSeconds);
Hour: 15
Minute: 30
Second: 25
Nano of Seconds: 845

The LocalTime Class
Simple time calculations with the LocalTime object.
LocalTime localTime = LocalTime.of(15, 30, 25, 845);
System.out.println(localTime);
localTime = localTime.minusHours(27);
localTime = localTime.plusMinutes(179);
localTime = localTime.minusSeconds(683);
localTime = localTime.plusNanos(8345);
System.out.println(localTime);
15:30:25.000000845
15:18:02.000009190

The LocalDateTime Class
The LocalDateTime class represents a local date and time without any time zone information.
You could view the LocalDateTime as a combination of the LocalDate and LocalTime classes.
LocalDateTime localDateTime = LocalDateTime
.of(2020, Month.MARCH, 16, 15, 30, 25, 845);
System.out.println(localDateTime);
2020-03-16T15:30:25.000000845

The DateTimeFormatter Class
The DateTimeFormatter class is used to parse and format dates represented with the classes in the Java 8 date time API.
The DateTimeFormatter class contains
a set of predefined constant which can
parse and format dates from standard
date formats.
Each of these predefined
DateTimeFormatter instances are
preconfigured to format and parse
dates to / from different formats.
// Some of DateTimeFormatter constant
DateTimeFormatter.BASIC_ISO_DATE
DateTimeFormatter.ISO_LOCAL_DATE
DateTimeFormatter.ISO_LOCAL_TIME
DateTimeFormatter.ISO_LOCAL_DATE_TIME
DateTimeFormatter.ISO_DATE
DateTimeFormatter.ISO_TIME
DateTimeFormatter.ISO_DATE_TIME
DateTimeFormatter.ISO_WEEK_DATE
DateTimeFormatter.ISO_ZONED_DATE_TIME
DateTimeFormatter.ISO_INSTANT

The DateTimeFormatter Class
The format() method is declared on both the formatter objects and the date/time objects.
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime);
String basicIsoDate = localDateTime.format(
DateTimeFormatter.BASIC_ISO_DATE);
String isoDateTime = localDateTime.format(
DateTimeFormatter.ISO_DATE_TIME);
String isoLocalDateTime = localDateTime.format(
DateTimeFormatter.ISO_LOCAL_DATE_TIME);
String isoWeekDate = localDateTime.format(
DateTimeFormatter.ISO_WEEK_DATE);
2020-02-07T13:16:46.454
20200207
2020-02-07T13:16:46.454
2020-02-07T13:16:46.454
2020-W06-5

Others useful Classes and Interfaces
Temporal
Basic interface for DateTime classes
LocalDate / LocalTime / LocalDateTime …
Instant
Start of nanoseconds in timeline. Useful for timestamp
Clock
Allowing Temporal creation with alternate clock
TemporalAmount
Basic interface for classes that represent amount of time
Duration / Period

The Instant Class
Point on a discretized time-line
Stored to nanosecond resolution
long for seconds since epoch, and
int for nanosecond of second
Convert to any date time field using a Chronology
Use for event time-stamps

The Clock Class
Gets the current instant using a time-zone
Use instead of System.currentTimeMillis()
Use an alternate clock for testing Clock
2020-02-07T13:48:25.821+02:00[Europe/Kiev]
ZoneId zoneId = ZoneId.of("Europe/Kiev");
ZonedDateTime localDateTime = ZonedDateTime.now(Clock.system(zoneId));
System.out.println(localDateTime);

The Period Class
A length of elapsed time. Defined using calendar fields
years, months, and days (not minutes and seconds).
Takes time zones into account for calculation.
LocalDateTime localDateTime = LocalDateTime.now();
String dateTime = localDateTime.format(
DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM));
System.out.println(dateTime);
Period period = Period.of(2, 7, 15);
localDateTime = localDateTime.plus(period);
dateTime = localDateTime.format(
DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM));
System.out.println(dateTime);
7 лют. 2020 14:00:56
22 вер. 2022 14:00:56

The Duration and Chronology
The Duration class
Precise length of elapsed time, in nanoseconds
Does not use date-based constructs like years, months, and days
Can be negative, if end is before start
The Chronology interface
Pluggable calendar system
Provides access to date and time fields
Built-in
ISO8601 (default): IsoChronology
Chinese: MinguoChronology
Japanese: JapaneseChronology
Thai Buddhist: ThaiBuddhistChronology
Islamic: HijrahChronology

Staying Constant
Day of week, for example
DayOfWeek.FRIDAY
Month , for example
Month.MAY
Time units, for example
ChronoUnit.DAYS
Other useful constants:
LocalTime.MIDNIGHT // 00:00
LocalTime.NOON // 12:00

Input/Output Streams API

What Is a Stream?
A stream is an ordered sequence of bytes of undetermined length.
Input streams move bytes of data from some generally external source to Java program.
Output streams move bytes of data from Java program to some generally external source.

Streams
Usual Purpose:
Storing data to «nonvolatile» devices, e.g. harddisk.
Classes provided by package java.io.
Data is transferred to devices by streams
Program
Device
output - stream
Program
Device
input - stream

Streams
JAVA distinguishes between 2 types of streams:
Text Streams, containing “characters”
Binary Streams, containing 8 bit information
I
‘
M
A
S
T
R
I
N
G
\n
Program
Device
01101001
Program
Device
11101101
00000000

Streams
Streams in JAVA are Objects, of course!
2 types of streams (text / binary) and
2 directions (input / output)
Results in 4 base-classes dealing with I/O:
Reader : text-input
Writer : text-output
InputStream : byte-input
OutputStream : byte-output

The File Class
A File object can refer to either a file:
or a directory:
File file = new File("data.txt");
File file = new File("D:\\development");

The File Class
String dirName = "D:\\Development";
String fileName = "data.txt";
File newDirectory = new File(dirName);
boolean isDirCreated = newDirectory.mkdir();
if (isDirCreated) {
File newFile = new File(dirName + File.separator + fileName);
boolean isFileCreated = newFile.createNewFile();
if (isFileCreated) {
System.out.println(newFile.getCanonicalPath());
}
}

Useful Methods of the File class
isFile() / isDirectory()
Returns true if and only if the file denoted by this abstract pathname is a file (directory).
canRead()
Returns true, if the specified file exists its path name and the file is allowed
to be read by the application.
canWrite()
Returns true if the application to write to the file, else the method returns false.
length()
Length of the file in bytes (long) or 0 if nonexistent.
list()
If the File object is a directory, returns a String array of all the files and directories contained in the directory; otherwise, null.
mkdir()
Creates a new subdirectory.
delete()
Deletes the directory or file and returns true if successful.

Binary Files
Stores binary images of information identical to the binary images stored in main memory.
Example: writing of the integer '42'
Text-File: "42" (internally translated to 2 16-bit representations of the characters '4' and '2')
Binary-File: 00101010, one byte (= 42 decimal)

Byte-Oriented Output Stream Classes
The following is the byte-oriented output stream class hierarchy:
OutputStream
ByteArrayOutputStream
FileOutputStream
FilterOutputStream
ObjectOutputStream
PipedOutputStream
BufferedOutputStream
DataOutputStream
PrintStream
ZipOutputStream
The ZipOutputStream is defined in java.util.zip package

Methods of OutputStream Class
Writing data:
write(...) methods write data to the stream. Written data is buffered.
Use flush() method to flush any buffered data from the stream.
throws IOException if an I/O error occurs.
There are 3 main write methods:
void write(int data)
Writes a single character (even though data is an integer, data must be set such that: 0 <= data <= 255)
void write(byte[] buffer)
Writes all the bytes contained in buffer to the stream
void write(byte[] buffer, int offset, int length)
Writes length bytes to stream starting from buffer[offset]

Methods of OutputStream Class
flush()
To improve performance, almost all output protocols buffer output.
Data written to a stream is not actually sent until buffering thresholds are met.
Invoking flush() causes the OutputStream to clear its internal buffers.
close()
Closes stream and releases any system resources.

Creating a FileOutputStream Instance
String fileName = "data.txt";
String str = "Hello I/O!";
byte[] wData = str.getBytes();
try (FileOutputStream fileOutputStream =
new FileOutputStream(fileName /*, true */)) {
fileOutputStream.write(wData);
System.out.println("Was wrote " + wData.length + " bytes");
} catch (IOException e) {
e.printStackTrace();
}
Was wrote 10 bytes

Byte-Oriented Input Stream Classes
The following is the byte-oriented input stream class hierarchy:
InputStream
ByteArrayInputStream
FileInputStream
FilterInputStream
ObjectInputStream
PipedInputStream
SequenceInputStream
BufferedInputStream
DataInputStream
PushbackInputStream
ZipInputStream
The ZipInputStream is defined in java.util.zip package

Methods of InpupStream Class
Reading data:
read() methods will block until data is available to be read and return the number of bytes read.
-1 is returned if the Stream has ended.
throws IOException if an I/O error occurs.
There are 3 main read methods:
int read()
Reads a single byte. Returns it as integer.
int read(byte[] buffer)
Reads bytes and places them into buffer. Returns the number of bytes read.
int read(byte[] buffer, int offset, int length)
Reads up to length bytes and places them into buffer. First byte read is stored in buffer[offset]. Returns the number of bytes read.

Methods of InpupStream Class
available()
Returns the number of bytes which can be read without blocking.
skip(long n)
Skips over a number of bytes in the input stream.
close()
Closes stream and release any system resources.

Creating a FileInputStream Instance
byte[] rData = new byte[15];
try (FileInputStream fileInputStream = new FileInputStream(fileName)) {
int byteAvailable = fileInputStream.available();
int byteCount = fileInputStream.read(rData, 0, byteAvailable);
System.out.println("Was read " + byteCount + " bytes");
System.out.println(Arrays.toString(rData));
System.out.println(new String(rData));
} catch (IOException e) {
e.printStackTrace();
}
Was read 10 bytes
[72, 101, 108, 108, 111, 32, 73, 47, 79, 33, 0, 0, 0, 0, 0]
Hello I/O!

Creating a FileInputStream Instance
String fileName = "data.txt";
try (FileInputStream fileInputStream = new FileInputStream(fileName)) {
int b = 0;
while ((b = fileInputStream.read()) != -1) {
System.out.print( (char)b );
}
} catch (IOException e) {
e.printStackTrace();
}
Hello I/O!

Character-Oriented Writer Classes
The following is the character-oriented output stream class hierarchy:
Writer
BufferedWriter
CharArrayWriter
OutputStreamWriter
PipedWriter
FilterWriter
PrintWriter
FileWriter
StringWriter

Character-Oriented Reader Classes
The following is the character-oriented input stream class hierarchy:
Reader
BufferedReader
CharArrayReader
FilterReader
PipedReader
StringReader
InputStreamReader
LineNumberReader
PushbackReader
FileReader

FileReader and FileWriter Classes
String fileName = "data.txt";
String data = "Hello Java I/O! Streams";
try (FileWriter fileWriter = new FileWriter(fileName /*, true*/ )) {
fileWriter.write(data);
} catch (IOException e) {
e.printStackTrace();
}
try (FileReader fileReader = new FileReader(fileName)) {
int c = 0;
while((c = fileReader.read()) != -1) {
System.out.print( (char)c );
}
} catch (IOException e) {
e.printStackTrace();
}

BufferedWriter and BufferedReader Classes
The BufferedReader and BufferedWriter classes use an internal buffer to store data while reading and writing, respectively.
The BufferedReader class provides a new method readLine(), which reads a line and returns a String (without the line delimiter).
The BufferedWriter class provides a new method newLine(), which write a separator to the buffered writer stream.

BufferedWriter and BufferedReader Classes
String fileName = "data.txt";
String data = "Hello Java I/O Streams!";
try (BufferedWriter bufferedWriter = new BufferedWriter(
new FileWriter(fileName , true))) {
bufferedWriter.write(data);
bufferedWriter.newLine();
bufferedWriter.flush();
} catch (IOException e) {
e.printStackTrace();
}

BufferedWriter and BufferedReader Classes
try (BufferedReader bufferedReader = new BufferedReader(
new FileReader(fileName))) { String line = null;
while((line = bufferedReader.readLine()) != null) {
System.out.print(line);
}
} catch (IOException e) {
e.printStackTrace();
}
Hello Java I/O Streams!
Hello Java I/O Streams!
Hello Java I/O Streams!
Hello Java I/O Streams!

Useful Links
Java Basic I/O Tutorial
http://docs.oracle.com/javase/tutorial/essential/io
Tutorialspoint Java.io package tutorial
http://www.tutorialspoint.com/java/io