Category Archives: Java

Create new maven project from scratch

1. Create a new project
$ mvn archetype:generate -DgroupId=com.xyz.myapp -DartifactId=MyApp -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
$ cd MyApp

2. To Build Package:
$ mvn package
//this will create target/MyApp-1.0-SNAPSHOT.jar

3. To Execute
$ java -cp target/MyApp-1.0-SNAPSHOT.jar com.xyz.myapp

# Adding dependency to your project
Let say you wanted to add “json-simple” to your project:
add inside in the pom.xml file:

<dependency>
 <groupId>com.googlecode.json-simple</groupId>
 <artifactId>json-simple</artifactId>
 <version>1.1</version>
</dependency>

– Now to execute a package with dependency you will have to include the path to the jar (I think there is a way to do it with pom.xml, but I don’t know this yet)
– This could complicated if you have multiple dependencies
– And also need to make sure you have the pkgs in the system where you want to deploy your code
– Solution: Create fat jar (a jar that includes all dependent jars, side effect: output file is bigger and takes longer to run ‘mvn package’ command)
– To create fat jar add this to your pom.xml inside :

<build>
 <plugins>
  <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-assembly-plugin</artifactId>
   <version>2.2.1</version>
   <configuration>
    <descriptorRefs>
     <descriptorRef>jar-with-dependencies</descriptorRef>
    </descriptorRefs>
   </configuration>
   <executions>
    <execution>
     <id>assemble-all</id>
     <phase>package</phase>
     <goals>
      <goal>single</goal>
     </goals>
    </execution>
   </executions>
  </plugin>
 </plugins>
</build>

Singleton Design Pattern in Java

Singleton in Java

Singleton is the design pattern that instantiate the class to one object.

Here is the example in java

public class JavaProject {

	public static void main(String args[]){

		System.out.println("IN main class");

		MYClass a = MYClass.mySingleFactory();
		MYClass b = MYClass.mySingleFactory();

		MYClass c = new MYClass(); //Avoid doing this if the class is to be used as Singleton, because this operation returns a new instance of MyClass

		a.setI(1);
		b.setI(2);
		c.setI(3);

		a.printI();
		b.printI();
		c.printI();
		a.printI();
		MYClass.mySingleFactory().printI(); //another way to call the singleton obj
	}
}

public class MYClass {

	private int i;
	static MYClass inst;

	public static MYClass mySingleFactory(){
		if (inst == null){
			inst = new MYClass();
		}
		return inst;
	}

	public void SingletonTest() {

		System.out.println("SingletonTest constructor called");

	}

	public void printI(){
		System.out.println("Value of I is: " + i);
	}

	public void setI(int i_){
		i = i_;
	}
}

Output:
IN main class
Value of I is: 2
Value of I is: 2
Value of I is: 2
Value of I is: 3
Value of I is: 2