Tag: java8

convert iterator to list in java

Post author By Rajesh Kumar
Post date May 9, 2020
No Comments on convert iterator to list in java

In this tutorial, we will learn convert iterator to list in java

Here we are giving two approach to convert iterator to list in java

Syntax in Java 8

ArrayList<String> list = new ArrayList<String>();
iterator.forEachRemaining(list::add);

Syntax in Java 7

ArrayList<String> list = new ArrayList<String>();
while (iterator.hasNext()) {
  String string = (String) iterator.next();
  list.add(string);
}

Example

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;

public class IteratorToList {

	public static void main(String[] args) {

		Iterator<String> iterator = Arrays.asList("Rajesh", "Kumar", "Beginners", "Bug").iterator();
		convertToListJava7(iterator);
		convertToListJava8(iterator);

	}

	/**
	 * Java 7 Approach
	 * 
	 * @param iterator
	 * @return
	 */
	public static ArrayList<String> convertToListJava7(Iterator<String> iterator) {
		ArrayList<String> list = new ArrayList<String>();
		while (iterator.hasNext()) {
			String string = (String) iterator.next();
			list.add(string);
		}

		return list;
	}

	/**
	 * Java 8 Apporach
	 * 
	 * @param iterator
	 * @return
	 */
	public static ArrayList<String> convertToListJava8(Iterator<String> iterator) {
		ArrayList<String> list = new ArrayList<String>();
		iterator.forEachRemaining(list::add);
		return list;
	}

}

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/list/IteratorToList.java

Iterate list using streams in java

Tags arraylist, collections, iterator, java, java8

microservices spring-boot

how to create spring boot application

Post author By Rajesh Kumar
Post date April 11, 2020
No Comments on how to create spring boot application

database password encryption in spring boot

In this tutorial, we will learn how to create spring boot application

What is Spring boot

Spring Boot makes it easy to create stand-alone, production-grade application. It internally use Spring framework and have embedded tomcat servers, nor need to deploy war in any servers

Also easy to create,configure&run

What You Will learn

End of this tutorial, you will learn to create a spring boot application

Annotation

@SpringBootApplication

Dependency

<parent>                                                              
  <groupId>org.springframework.boot</groupId>                         
  <artifactId>spring-boot-starter-parent</artifactId>                 
  <version>2.2.6.RELEASE</version>                                    
  <relativePath /> <!-- lookup parent from repository -->             
</parent>

Time needed: 30 minutes

Steps

Navigate to Spring initializr website
Click on this url https://start.spring.io/
Choose project as Maven
In this tutorial I am using Maven. You can use gradle or groovy also
Choose language as Java
Here I am using Java. But we have option for Kotlin & Groovy also
Spring Boot Version
Please select the stable version, I am using 2.2.6
Enter Group,artifact,Name & description
Enter the groupid,artifactid&name as you wanted
Packaging as Jar
Choose Jar, But you have option for war also
Java Verison
Here I am using java 8
Add Spring Web as dependency
In case you going you want to expose rest service, Click on the add dependency and select spring web.
Click on the Genreate
Once you filled all these details click on the Generate Button.
It will download .rar format
Extract the downloaded file
Once your download complete, Extract the downloaded .rar file
Import in Eclipse
After Extracting, Import the project in eclipse
Navigate to Main Class
Navigate to Main class which will be under src/main/java
and Make sure the class have @SpringBootApplication annotation
Run
Right click the class and choose the Run As –> Java Application
Verify logs
Once your application starts you can see below logs in console

Tomcat started on port(s): 8080 (http) with context path ''
Updating port to 8080
Started StudentApplication in 22.834 seconds (JVM running for 24.503)

create netflix eureka discovery server using spring boot

register spring boot micro-services to eureka discovery

Tags java, java8, microservices, springboot

java

Base64 Encoding using Java

Post author By Rajesh Kumar
Post date March 11, 2020
No Comments on Base64 Encoding using Java

In Below example we will learn how to use Base64 Encoding using Java

Finally Java8 incorporated Base64 Encoding. Base64 is one of the common Encoding mechanism.

Syntax

Base64.getEncoder().encodeToString(textForEncoding.getBytes());

Example


import java.util.Base64;

public class Base64Encodng {

	public static void main(String[] args) {
		try {
			String textForEncoding = "QWERTY TEXT";
			String encodedString = Base64.getEncoder().encodeToString(textForEncoding.getBytes());
			System.out.println(encodedString);

		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

Output

UVdFUlRZIFRFWFQ=

The length of output encoded String must be a multiple of 3. else the output will be padded with additional pad characters (`=`).
But we have option to encode without padding also

Syntax

Base64.getEncoder().withoutPadding().encodeToString(textForEncoding.getBytes());

Example without Padding


import java.util.Base64;

public class Base64Encodng {

	public static void main(String[] args) {
		try {
			String textForEncoding = "QWERTY TEXT";
			String encodedString = Base64.getEncoder().withoutPadding().encodeToString(textForEncoding.getBytes());
			System.out.println(encodedString);		

		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

Output

UVdFUlRZIFRFWFQ

Decoding Syntax

Base64.getDecoder().decode(encodedString.getBytes());

Example


import java.util.Base64;

public class Base64Encodng {

	public static void main(String[] args) {
		try {
			String textForEncoding = "QWERTY TEXT";
			String encodedString = Base64.getEncoder().withoutPadding().encodeToString(textForEncoding.getBytes());
			System.out.println(encodedString);
			
			byte[] decodeByte = Base64.getDecoder().decode(encodedString.getBytes());
			String decodedValue=new String(decodeByte);
			System.out.println(decodedValue);

		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

Output

UVdFUlRZIFRFWFQ
QWERTY TEXT

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/Base64Encodng.java

Tags base64, java, java8

collections java

get key and value from hashmap in java

Post author By Rajesh Kumar
Post date February 26, 2020
No Comments on get key and value from hashmap in java

In this tutorial, we will learn about get key and value from hashmap in java

Example Using Java 8


import java.util.HashMap;
import java.util.Map;

public class KeyValueFromHashMap {

	public static void main(String[] args) {
		try {
			Map<String, String> hashMap = new HashMap();
			hashMap.put("1", "Car");
			hashMap.put("2", "Bus");
			hashMap.put("3", "Train");

			// Below code only work above java 8
			hashMap.forEach((key, value) -> {
				System.out.println("Value of " + key + " is " + value);
			});

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output

Value of 1 is Car
Value of 2 is Bus
Value of 3 is Train

Example using java 7


import java.util.HashMap;
import java.util.Map;

public class KeyValueFromHashMap {

	public static void main(String[] args) {
		try {
			Map<String, String> hashMap = new HashMap();
			hashMap.put("1", "Car");
			hashMap.put("2", "Bus");
			hashMap.put("3", "Train");

			for (Map.Entry<String, String> entry : hashMap.entrySet()) {
				System.out.println(entry.getKey() + " Value is " + entry.getValue());
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output

1 Value is Car
2 Value is Bus
3 Value is Train

GitHub Url

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/KeyValueFromHashMap.java

Check key exists in Hashmap Java

Tags hashmap, java8, key, vaue

collections java

iterate stream with index in Java8

Post author By Rajesh Kumar
Post date February 25, 2020
No Comments on iterate stream with index in Java8

In this post, we will learn to iterate stream with index in Java8

We will come across multiple streams tutorials, but in all the tutorials we never iterate with index numbers

In order to find the current index or other numeric operations index number will help us to get the position

In this tutorial, we are going to use IntStream to get index of the arraylist

Because there is no straight way to get index number in streams

Syntax

IntStream.range(start, end)

Example


import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;

public class IterateStreamWithIndex {

	public static void main(String[] args) {
		try {
			List<String> list = new ArrayList<String>();
			list.add("India");
			list.add("USA");
			list.add("Germany");

			IntStream.range(0, list.size())
					.forEach(x -> System.out.println("The index is " + x + " Value is " + list.get(x)));

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}

Output

The index is 0 Value is India
The index is 1 Value is USA
The index is 2 Value is Germany

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateStreamWithIndex.java

foreach in java8 using streams

sorting operations in java using streams

Tags iterate, java8, streams

collections java

foreach in java8 using streams

Post author By Rajesh Kumar
Post date February 22, 2020
No Comments on foreach in java8 using streams

In this tutorial, we will learn about foreach in java8 using streams

In java8, We can easily iterate a list using streams.

Streams API provided a lot of features. In this post, we are going to see about foreach

Syntax

stream().forEach({operations});

Example


import java.util.ArrayList;
import java.util.List;

public class ForEachExample {

	public static void main(String[] args) {
		try {

			List studentList = new ArrayList();
			Student student = null;

			student = new Student();
			student.setId(1);
			student.setName("Rajesh");
			student.setAddress("Mumbai");
			studentList.add(student);

			student = new Student();
			student.setId(1);
			student.setName("Kumar");
			student.setAddress("Chennai");
			studentList.add(student);

			studentList.stream()
					.forEach(x -> System.out.println("Name is " + x.getName() + " Address is " + x.getAddress()));

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}

Student.java


public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

Output

Name is Rajesh Address is Mumbai
Name is Kumar Address is Chennai

sorting operations in java using streams

Iterate list using streams in java

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/ForEachExampleUsingStreams.java

Tags arraylist, foreach, java, java8, streams

collections java

filter operations in streams on java

Post author By Rajesh Kumar
Post date February 11, 2020
No Comments on filter operations in streams on java

In this example we learn filter operations in streams on java

In Java 8 it is easy to filter record from an arraylist

Streams API providing powerful features to filter an record from a list without modifying it

This will returns a stream consisting of the elements of this stream that match the given predicate.

Syntax

Stream filter(Predicate<? super T> predicate)<br><br>

list.stream().filter({operations});

Example

import java.util.ArrayList;
import java.util.List;

public class FilterExample {

	public static void main(String[] args) {

		List studentList = new ArrayList();
		Student student = null;

		student = new Student();
		student.setId(1);
		student.setName("Rajesh");
		student.setAddress("Mumbai");
		studentList.add(student);

		student = new Student();
		student.setId(1);
		student.setName("Kumar");
		student.setAddress("Chennai");
		studentList.add(student);

		studentList.stream().filter(x -> x.getName().equals("Rajesh"))
		.forEach(x -> System.out.print(x.getAddress()));

	}

}

Person.java

public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

Output

Mumbai

Reference

oracle docs

Iterate list using streams in java

iterate stream with index in Java8

Tags filter, java8, streams

collections java

Iterate list using streams in java

Post author By Rajesh Kumar
Post date February 5, 2020
No Comments on Iterate list using streams in java

In this example, we will learn about iterate list using streams in java with example
It was introduced on Java 8

Features of Streams

No Storage
we can do arithmetic operations
we can filter the data without removing.

Syntax

list.stream().forEach((x) -> {operations});

Example

import java.util.ArrayList;
import java.util.List;

public class IterateListUsingStreams {

    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("Apple");
        list.add("Pineapple");
        list.add("Papaya");
        list.stream().forEach((x) -> System.out.println(x));
    }

}

Output

Apple
Pineapple
Papaya

Example with Pojo

Student.java

public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

IterateListUsingStreams2 .java

import java.util.ArrayList;
import java.util.List;

public class IterateListUsingStreams2 {

	public static void main(String[] args) {

		List studentList = new ArrayList();
		Student student = null;

		student = new Student();
		student.setId(1);
		student.setName("Rajesh");
		student.setAddress("Chennai");
		studentList.add(student);

		student = new Student();
		student.setId(1);
		student.setName("Kumar");
		student.setAddress("Chennai");
		studentList.add(student);

		studentList.stream().forEach((x) -> System.out.println("Student Id is "+x.getId()+" Name is "+x.getName()));

	}

}

Output

Student Id is 1 Name is Rajesh
Student Id is 1 Name is Kumar

References

https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html

GitHub

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateListUsingStreams.java

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateListUsingStreams2.java

iterate stream with index in Java8

ArrayList in java with example

Tags java8, streams

collections java

HashMap in java with example

Post author By Rajesh Kumar
Post date January 7, 2020
No Comments on HashMap in java with example

HashMap in java with example

In this tutorial we will learn about HashMap in java with example

Hashmap is used store key and value pair in java which implemented map interface internally

Features

It will not allow duplicate keys
We can store null value as a key
It is not thread safe

Example


import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class HashmapExample {
	public static void main(String[] args) {
		try {
			Map<String, String> hashMap = new HashMap();
			hashMap.put("1", "Car");
			hashMap.put("2", "Bus");
			hashMap.put("3", "Train");

			for (Map.Entry<String, String> entry : hashMap.entrySet()) {
				System.out.println(entry.getKey() + " Value is " + entry.getValue());
			}
			System.out.println("---------------");
			// Below code only work above java 8
			hashMap.forEach((key, value) -> {
				System.out.println("Value of " + key + " is " + value);
			});

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output

1 Value is Car
2 Value is Bus
3 Value is Train
---------------
Value of 1 is Car
Value of 2 is Bus
Value of 3 is Train

Reference

https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
https://beginnersbug.com/check-key-exists-in-hashmap-java/

Download

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/HashmapExample.java

Tags foreach, hashmap, java, java8, map

Syntax in Java 8

Syntax in Java 7

Example

Github

Related Articles

What is Spring boot

What You Will learn

Annotation

Dependency

Related Articles

Syntax

Example

Output

Syntax

Example without Padding

Output

Decoding Syntax

Example

Output

Github

Example Using Java 8

Output

Example using java 7

Output

GitHub Url

Related Articles

Syntax

Example

Output

Github

Related Articles

Syntax

Example

Student.java

Output

Related Article

Github

Syntax

Example

Person.java

Output

Reference

Related Articles

Features of Streams

Syntax

Example

Output

Example with Pojo

Student.java

IterateListUsingStreams2 .java

Output

References

GitHub

Related Articles

Features

Example

Output

Reference

Download