4. 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.
9. 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
10. 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
11. 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);
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}
}
OUTPUT: com.commons.examples.Emp@10b30a7[id=7,name=Java,salary=99.99]
12. 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);
}
}
12
13. 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
15. APACHE COMMONS – IO (CONT…)
Task of reading bytes from a URL:
TRADITIONAL
15
IOUtils
16. 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]);
}
19. 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
19
20. WEB SERVER THAT STARTS A NEW THREAD FOR EACH REQUEST
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();
}
}
}
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Drawback: may cause “OutOfMemory” error as there is
no boundary on thread creation.
21. WEB SERVER USING A THREAD POOL
class 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);
} 21
}
}
23. 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
24. 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
25. ATOMIC INTEGER
public class Counter {
private AtomicInteger count = new AtomicInteger(0);
public void incrementCount() {
count.incrementAndGet();
}
public int getCount() {
return count.get();
}
}
25
26. 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
27. 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
28. 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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}
