Use of Apache Commons and Utilities

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

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AGENDA

Discussion on apache commons utilities Java Concurrency Framework Mutable vs. Immutable

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APACHE COMMONS UTILITIES

Configuration Lang IO BeanUtils

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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 be included into the configuration.

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APACHE COMMONS – CONFIGURATION (CONT..)

usergui.properties color.properties

window.width = 500 window.height = 300include = color.properties

colors.background = #FFFFFF colors.foreground = #000080

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

Example Properties files

colors.background = #FFFFFF colors.foreground = #000080

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

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APACHE COMMONS – CONFIGURATION (CONT..)

Sample Code

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null

blank (“”)

whitespace(“ “)

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APACHE COMMONS – LANG

StringUtils ToStringBuilder ArrayUtils

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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 alphabets4. isNumeric :- Checks if a String contains only nuerics5. 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

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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

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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); }}OUTPUT: com.commons.examples.Emp@10b30a7[id=7,name=Java,salary=99.99]

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APACHE COMMONS – LANG - ARRAYUTILS

import java.util.Arrays;import org.apache.commons.lang.ArrayUtils;public class ArrayUtilsDemo { public static void main(String args[]){ 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); }}

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Input Output

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APACHE COMMONS – IO IOUtils FileUtils FileSystemUtils FileFilter LineIterator

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APACHE COMMONS – IO (CONT…)

Task of reading bytes from a URL:

TRADITIONAL

IOUtils

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APACHE COMMONS – IO (CONT…)

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

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

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Executor Framework

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SEQUENTIAL WEB SERVER

class SingleThreadWebServer{ public static void main(String args[]){ 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

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WEB SERVER THAT STARTS A NEW THREAD FOR EACH REQUEST

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class ThreadPerTaskWebServer{ public static void main(String args[]){ ServerSocket socket = new ServerSocket(80); while(true){

final Socket connection = socket.accept();Runnable r = new Runnable(){

public void run(){handleRequest(connection);

}};

new Thread(r).start(); }}}

Drawback: may cause “OutOfMemory” error as there is no boundary on thread creation.

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WEB SERVER USING A THREAD POOLclass TaskExecutionWebServer{ private static final int NTHREADS = 100; private static final Executor exec =

Executors.newFixedThreadPool(NTHREADS); public static void main(String args[]){ ServerSocket socket = new ServerSocket(80); while(true){

final Socket connection = socket.accept();Runnable task = new Runnable(){

public void run(){handleRequest(connection);

}};

exec.execute(task); } }}

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synchronization

volatile

atomic

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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

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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.

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ATOMIC INTEGER

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

public void incrementCount() {

count.incrementAndGet(); } public int getCount() {

return count.get(); }

}

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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)

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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.

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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}

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- PRAMOD