Use of Apache Commons and Utilities

UTILITIES @ WORK
- don’t reinvent when it is ready to use

AGENDA
 Discussion on apache commons utilities
 Java Concurrency Framework

 Mutable vs. Immutable

2

APACHE COMMONS UTILITIES
 Configuration
 Lang

 IO

 BeanUtils

3

APACHE COMMONS - CONFIGURATION
 org.apache.commons.configuration
 To load a properties file:

PropertiesConfiguration config = new
PropertiesConfiguration(“usergui.properties”);
 If we do not specify an absolute path, the file will be
searched automatically in the following locations:
 in the current directory
 in the user home directory
 in the classpath

 If a property is named “include” and the value of that
property is the name of a file on the disk, that file will 4
be included into the configuration.

APACHE COMMONS – CONFIGURATION (CONT..)
Example Properties files

usergui.properties color.properties

window.width = 500 colors.background = #FFFFFF
window.height = 300 colors.foreground = #000080
include = color.properties
# chart colors
colors.background = #FFFFFF colors.pie = #FF0000, #00FF00
colors.foreground = #000080

# chart colors
colors.pie = #FF0000, #00FF00

5

APACHE COMMONS – CONFIGURATION (CONT..)
Sample Code

6

APACHE COMMONS – LANG
 StringUtils
 ToStringBuilder

 ArrayUtils

8

APACHE COMMONS – LANG - STRINGUTILS
 org.apache.commons.lang.StringUtils
 Methods:
1. isEmpty :- Checks if a String is empty (“”) or null.
2. isBlank :- Checks if a String is whitespace, empty or null.
3. isAlpha :- Checks if a String contains only alphabets
4. isNumeric :- Checks if a String contains only nuerics
5. defaultIfEmpty(String str, String defString) :- If str is
empty or null, “defString” is returned else “str” is
returned
6. reverseDelimited :-Reverses a String that is delimited by
a specific character
7. leftPad / rightPad 9

APACHE COMMONS – LANG – STRINGUTILS (CONT…)
String str1 = null;
boolean result = false;

result = StringUtils.isEmpty(str1); // true

str1 = "str123";
result = StringUtils.isAlphanumeric(str1); //true
result = StringUtils.isNumeric(str1); //false

str1 = "7";
str1 = StringUtils.leftPad(str1, 3, '0'); //007

str1 = "172.168.1.44";
str1 = StringUtils.reverseDelimited(str1, '.'); //44.1.168.172
10

APACHE COMMONS – LANG - TOSTRINGBUILDER
public class ToStringBuilderDemo {
public static void main(String args[]){
System.out.println(new Emp(7,"Java",99.99));
}
}
class Emp{
int id;
String name;
double salary;
public Emp(int id, String name, double salary){
this.id = id; this.name = name; this.salary = salary;
}
/* here comes accessors and mutators */

public String toString(){
return ToStringBuilder.reflectionToString(this);
11
}
}
OUTPUT: com.commons.examples.Emp@10b30a7[id=7,name=Java,salary=99.99]

APACHE COMMONS – LANG - ARRAYUTILS
import java.util.Arrays;
import org.apache.commons.lang.ArrayUtils;
public class ArrayUtilsDemo {
String weekends[] = {"friday","saturday","sunday"};
String weekdays[] = {"monday", "tuesday", "wednesday", "thursday"};

String days[] = (String[])ArrayUtils.addAll(weekends, weekdays);
System.out.println(ArrayUtils.isEmpty(days));
System.out.println(ArrayUtils.isSameLength(weekends, weekdays));

Integer values[] = new Integer[10];
Arrays.fill(values, 1);
int intValues[] = ArrayUtils.toPrimitive(values,0);
}
}
12

I I I I O O O
I II
I I I O O O
I O O O
I II I I O O O O

Input Output 13

APACHE COMMONS – IO
 IOUtils
 FileUtils

 FileSystemUtils

 FileFilter

 LineIterator

14

APACHE COMMONS – IO (CONT…)
Task of reading bytes from a URL:

TRADITIONAL

15

IOUtils

APACHE COMMONS – IO (CONT…)

File dir = new File(".");
String[] files = dir.list( new
PrefixFileFilter("Test") );

for ( int i = 0; i < files.length; i++ ) { 16
System.out.println(files[i]);
}

Executor
Framework
18

SEQUENTIAL WEB SERVER
class SingleThreadWebServer{
ServerSocket socket = new ServerSocket(80);
while(true){
Socket connection = socket.accept();
handleRequest(connection);
}
}
}

Drawback: thread “main” is responsible for handling all
requests one after the other
19

WEB SERVER THAT STARTS A NEW THREAD FOR EACH REQUEST
class ThreadPerTaskWebServer{
while(true){
final Socket connection = socket.accept();
Runnable r = new Runnable(){
public void run(){
}
};
new Thread(r).start();
}
}
}
20
Drawback: may cause “OutOfMemory” error as there is
no boundary on thread creation.

WEB SERVER USING A THREAD POOL
class TaskExecutionWebServer{
private static final int NTHREADS = 100;
private static final Executor exec =
Executors.newFixedThreadPool(NTHREADS);
while(true){
final Socket connection = socket.accept();
Runnable task = new Runnable(){
public void run(){
}
};
exec.execute(task);
} 21
}
}

synchronization
volatile
atomic
22

SYNCHRONIZATION
 Synchronization is built around an internal entity known as the
intrinsic lock or monitor lock. Intrinsic lock play a role in both
aspects of synchronization: enforcing exclusive access to an object’s
state and establishing happens-before relationships that are
essential to visibility.

 Drawbacks:
 Locking
 Blocking
 Context Switching
 Possibility of Deadlock

23

VOLATILE
 A volatile variable is not allowed to have a local copy
of a variable that is different from the value currently
held in “main” memory.
 Volatile variables cannot be used to construct
atomic compound actions(i++). This means that
volatile variables cannot be used:
 when one variable depends on another
 when the new value of a variable depends on its old value.

24

ATOMIC INTEGER
public class Counter {
private AtomicInteger count = new AtomicInteger(0);

public void incrementCount() {
count.incrementAndGet();
}
public int getCount() {
return count.get();
}
}

25

MUTABLE VS. IMMUTABLE
 Mutable: When we have a reference to an instance of
an object, the contents of that instance can be altered.
For Ex: class
Person, Employee, java.math.BigInteger, etc.
 Immutable: When you have a reference to an instance
of an object, the contents of that instance cannot be
altered.
For Ex: all wrapper classes (Integer,String,etc)

26

BUILDING AN IMMUTABLE CLASS
 Make all fields private.
 Don’t provide mutators (setter methods)

 Ensure that methods can't be overridden by either
making the class final (Strong Immutability) or
making your methods final (Weak Immutability).
 If a field isn't primitive or immutable, make a deep
clone on the way in and the way out.

27

public final class BetterPerson{
private String firstName;
private String lastName;
private Date dob;

public BetterPerson( String firstName, String lastName, Date dob){
this.firstName = firstName;
this.lastName = lastName;
this.dob = new Date( dob.getTime() ); //way in
}
public String getFirstName(){
return this.firstName;
}
public String getLastName(){
return this.lastName;
}
public Date getDOB(){
return new Date( this.dob.getTime() ); //way out
}

//No mutators at all i.e., setter methods
28
}

Use of Apache Commons and Utilities

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