Introduction to Spring Boot

 History of Spring Boot

Before Spring Boot enterprise-level development creating an application with the Spring framework was so difficult. As a developer, you have to create and maintain the dependence injection, web configuration, deployment and etc. This also increase the learning curve for the developers. 

Mike Youngstrom opened Spring JIRA # SPR-9888 feature JIRA on 17th Oct 2012. The idea was to reduce the learning curve of any new developer who will be coming in to create application using Spring's Web Application.

What is the Spring Boot?

Spring framework provides a pre-setup of Spring and some third party library using which developer could develop an application without any/much of configurations result in faster development.  Non-functional features are readily available such as an embedded server, health check, security, metrics, and externalised configuration. If we want to differ from Spring-provided default configurations we could simply do so. 

Spring Boot application could be bundled into a jar or a traditional war, as a result, it is easy to deploy. It also provides a command-line interface (CLI) to run the Spring script. 

Why anyone uses Spring Boot?

1. Do prototyping.
2. Creating a minimum viable product for the actual market. 
3. Create Microservice 

How to use/implement Spring Boot?

Spring Boot requirements 

1. Java 8 onwards supported 
2. Maven 3.3+ version build tool supported
3. Gradle 6.3+ version build tool supported (5.6.x is also supported but is deprecated form)
4. Tomcat 9.0 embedded servlet container (Servlet 4.0) supported
5. Jetty 9.4 embedded servlet container (Servlet 3.1) supported
6. Undertow 2.0 embedded servlet container (Servlet 4.0) supported

You can also deploy Spring Boot applications to any Servlet 3.1+ compatible container.

Spring Boot is available in Groovy or Kotlin or Java language for application development. 

To minimise the developer’s effort Spring provide Spring Initializr (https://start.spring.io/) to generate the basic structure of your project with all the dependency in it. The Spring Boot Command Line Interface (CLI) is a command-line tool that you can use to quickly prototype an application. As it uses Groovy script for it, which means there is no boilerplate code that still has flour of Java.

Creating a simple application

Open Spring Initializr (https://start.spring.io/) to generate the basic structure of your project with all the dependency in it.

This will create the basic project structure. 

pom.xml which is generated from Spring Initializr (https://start.spring.io/). 

Note all the official  starters follow the naming pattern spring-boot-starter-*

It has a spring-boot-starter-parent parent. We included only Spring Web and Spring Initializr add the test for unit testing. We will see how to test Spring Boot in another blog. 

	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.5.2</version>
	<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.andy</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>
	<properties>
	<java.version>1.8</java.version>
	</properties>
	<dependencies>
	<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-test</artifactId>
	<scope>test</scope>
	</dependency>
	</dependencies>
	<build>
	<plugins>
	<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	</plugin>
	</plugins>
	</build>
	</project>

view raw pom.xml hosted with ❤ by GitHub

The main class generated by Spring Initializr

	package com.andy.demo;
	import org.springframework.boot.SpringApplication;
	import org.springframework.boot.autoconfigure.SpringBootApplication;
	@SpringBootApplication
	public class DemoApplication {
	public static void main(String[] args) {
	SpringApplication.run(DemoApplication.class, args);
	}
	}

view raw DemoApplication.java hosted with ❤ by GitHub

Created a controller to make REST call

RestContoller annotation let the Spring know this is a controller class
RequestMapping maps HTTP requests to handler methods of MVC and REST controllers

	package com.andy.demo.controller;
	import org.springframework.web.bind.annotation.GetMapping;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.bind.annotation.RestController;
	@RestController("demoBean")
	@RequestMapping("v1/demo")
	public class DemoController {
	@GetMapping("/message")
	public String sayHello() {
	return "Hello World! ";
	}
	}

view raw DemoController.java hosted with ❤ by GitHub

New way to create immutable object in Java ['record'] JEP 384: Records

As a Java developer, we use POJO every day in our coding. We have to write or generate codes of accessor methods and other methods like 'equals', 'toString' and 'hashCode' or use a library like Lombok. 

To make it more simplified Java introducing 'record'. Using which developer need not have to generate or write these code. 

Some of the features of these 'record' class. 

• implicitly they are final so it cannot be extended or abstracted but can implement an interface. 
• java.lang.Record is the superclass of record 
• A record cannot define the native method. 
• A record field(s)  is/are implicitly final

Let's see with an example. 

A simple record with no boilerplate code. It provides field accessor method, 'toString', 'equals' and 'hashCode' readily available. 

	package dto;
	import java.time.LocalDate;
	public record Person(Name name, LocalDate dob, Address address) {
	}

view raw Person.java hosted with ❤ by GitHub

A record with multiple constructors and instance method. 

	package dto;
	public record Address(String line1, String line2,String country,String zipcode) {
	public Address(String line1, String line2, String zipcode) {
	this(line1, line2, "India", zipcode);
	}
	// Instance Method
	public String fullAddress() {
	return line1 + " " + line2 + " " + country + " " + zipcode;
	}
	}

view raw Address.java hosted with ❤ by GitHub

A record with constructor level validation, static method and override 'equals' method. 

	package dto;
	public record Name(Title title, String fname, String lname) {
	public enum Title { Mr, Mrs, Miss, Master, Dr, Prof}
	public Name {
	if(fname == null || lname == null) {
	throw new IllegalArgumentException("First name and / or Last name cannot be null");
	}
	}
	// static method
	public static String fullNameToUpper(Name name) {
	return (name.title() + " " + name.fname() + " " + name.lname()).toUpperCase();
	}
	// Custom equals method. Not considering title here
	// Do remember that hashCode method also need to be changed
	// As this is just an example. Not overriding hashCode method
	@Override
	public boolean equals(Object obj) {
	if(obj == this) {
	return true;
	}
	return obj instanceof Name name && name.fname().equals(fname()) && name.lname().equals(lname());
	}
	}

view raw Name.java hosted with ❤ by GitHub

In this class, we are accessing the field with the internal method and other methods like 'toString', 'equals' and 'hashCode'. 

	import dto.*;
	import java.time.*;
	public class TestRecord {
	public static void main(String[] args) {
	String fname = "Andy";
	String lname = "Banerjee";
	Name name = new Name(Name.Title.Mr, fname, lname);
	LocalDate dob = LocalDate.of(1990,Month.JANUARY,01);
	Address addressInIndia = new Address("Networking Street", "Hacker Avenue", "PINcode");
	Person person = new Person(name, dob, addressInIndia);
	System.out.println("Person Name: " + person.name());
	System.out.println("Date of Birth: " + person.dob());
	System.out.println("Address: " + person.address());
	System.out.println("hashCode() = " + person.hashCode());
	System.out.println("toString() = " + person.toString());
	Person clonePerson = new Person(name, dob, addressInIndia);
	Address addressOutsideIndia = new Address("Networking Street", "Hacker Avenue", "USA", "ZIPcode");
	Person anotherPerson = new Person(name, dob, addressOutsideIndia);
	System.out.println("=====================================");
	System.out.println("\n Person object A : " + person);
	System.out.println("\n Person Object B : " + clonePerson);
	System.out.println("\n Person Object C : " + anotherPerson);
	System.out.println("=====================================");
	System.out.println("Person A & B. Both are equals? => " + person.equals(clonePerson));
	System.out.println("Person A & C. Both are equals ? => " + person.equals(anotherPerson));
	Name nameWithDrTitle = new Name(Name.Title.Dr, fname, lname);
	System.out.println("How custom equals working ? Ignoring the title here => " + name.equals(nameWithDrTitle));
	System.out.println("Invoking the static method => " + Name.fullNameToUpper(nameWithDrTitle));
	System.out.println("Invoking the instance method => " + addressOutsideIndia.fullAddress());
	try {
	Name recordWithValidationCheck = new Name(Name.Title.Mr, null, null);
	} catch (IllegalArgumentException e) {
	System.out.println("Added validation. \t::::::: \t" + e.getMessage());
	}
	}
	}

view raw TestRecord hosted with ❤ by GitHub

Output 

To compile these codes 

javac --enable-preview --release 15 TestRecord.java

To Run these codes 

java --enable-preview TestRecord

Happy coding and keep learning!

Now Java Developer can write their 'Will' [JDK15 JEP 360: Sealed Class (Preview)]

As a developer if you want to control who can extend your class or interface. 

In this enhancement of Java programming language, new keywords are introduced sealed, non-sealed and permit at the class level. 

A sealed class or interface can be extended or implemented only by those classes and interfaces permitted to do so. If you try to implement or extend to other class which is not permitted then the code will not compile. For example,

public sealed class Point permits Line

A permit keyword defines which are the subclasses or interfaces can be extended or implemented from this class. For example, 

public sealed class Point permits Line

Point class only permits Line class to extend directly. 

A non-sealed class or interface will allow this class to be extended. 

For example,

public non-sealed class Line

Permitted class Line is open for any unknown class extension. 

	public sealed class Shape permits Circle {
	public void name() {
	System.out.println("This is Shape.");
	}
	public static void main(String args[]) {
	Shape shape = new Shape();
	shape.name();
	Shape newShape = new Circle();
	newShape.name();
	}
	}
	non-sealed class Circle extends Shape {
	@Override
	public void name() {
	System.out.println("This is Circle.");
	}
	}

view raw Shape.java hosted with ❤ by GitHub

To Compile

To Run

A permitted subclass must define whether it could be extended to a specific class (sealed) or open to any unknown class(non-sealed) or not open for any extension (final). 

When a not permitted class extend a sealed class. 

Happy Coding and keep learning!

JDK 15 [Pattern Matching of instanceof operator ]

This is an enhancement of Java language with pattern matching for the instanceof operator. Currently, this feature is in the second preview in JDK 15.

So currently when we need to cast an object, we check it using instanceof operation then only we cast the object to save our self from class cast exception.

In the above code snippet, we have to explicitly cast it to an object. 

In this enhancement, we no more have to do it. 

To run the below code you need to install JDK 14 or above and have to enable the preview feature of javac & java. 

In order to enable that preview feature. 

javac 

      --enable-preview 

        -release <version> 

      <Source file>

java 

    --enable-preview 

       <Compiled class> 

	// Anindya Bandopadhyay (anindyabandopadhyay@gmail.com)
	public class PatternMatchingOfInstance {
	public static void main(final String args[]) {
	PatternMatchingOfInstance instance = new PatternMatchingOfInstance();
	Object obj = instance.getValue((instance.new IntValue(1)));
	if(obj instanceof Integer) {
	final Integer intValue = (Integer) obj;
	System.out.println(String.format("Int value = %d", intValue));
	}
	//JEP 375: Pattern Matching for instanceof (Second Preview)
	if(obj instanceof Integer objInt) {
	System.out.println(String.format("Using Pattern Matching for instanceof: Int value = %d", objInt));
	}
	}
	private Object getValue(final Value value) {
	return value.getValue();
	}
	interface Value {
	Object getValue();
	}
	class IntValue implements Value {
	private final int value;
	public IntValue(final int value) {
	this.value = value;
	}
	@Override
	public Integer getValue() {
	return value;
	}
	}
	class BoolValue implements Value {
	private final boolean value;
	public BoolValue(final boolean value) {
	this.value = value;
	}
	@Override
	public Boolean getValue() {
	return value;
	}
	}
	class StrValue implements Value {
	private final String value;
	public StrValue(final String value) {
	this.value = value;
	}
	@Override
	public String getValue() {
	return value;
	}
	}
	class DoubleValue implements Value {
	private final double value;
	public DoubleValue(final double value) {
	this.value = value;
	}
	@Override
	public Double getValue() {
	return value;
	}
	}
	class FloatValue implements Value {
	private final float value;
	public FloatValue(final float value) {
	this.value = value;
	}
	@Override
	public Float getValue() {
	return value;
	}
	}
	}

view raw PatternMatchingOfInstance.java hosted with ❤ by GitHub

Output

 Happy Coding!

Abstract Data Type

What is the data type?

A data type is an attribute in a programming language which define the domain of values and operations on that domain.

• Define a certain domain of value. 
• Define operations allowed on those values. 

Example 

int type

• Take only integer values
• Operations supported: addition, subtraction, multiplication, bitwise operation etc.  

float type 

• Take only floating values 
• Operations supported: addition, subtraction, multiplication, etc.  (it does not support operations like bitwise and modulus). 

Now, what is the user-defined data type? 

A user data type is NOT an attribute in a programming language but defines by the user which define the domain of values.

In below example, we define the user-defined data type using class. Here Person class is the type which is consist of bunch of String, LocalDate and Address fields. Person class have a user define a data type of Address.

Example

public class Person {
    private String firstName;
    private String lastName;
    private LocalDate dateOfBirth;
    private Address address;
   .....
}

public class Address {
   private String firstLine;
   private String lastLine,
   private State state;
  ....
}

Abstract Data Types (ADT)

Abstract Data Types (ADT) are like user define types which define values and operations on that user define type without specifying how the operation will happen.

Example

In this example, we will define an ADT where will create a data type named MyString class and define operations like addition, subtraction, multiplication and division. 

User Define Data Type 

• MyString is a wrapper object of string. 

Let's define the operations of MyString data type.

User Define Operations 

• The addition will concatenation two MyString. Example: "Hello" + " world" will result in "Hello world".
• The subtraction will substring the difference of length. If the difference of length is zero or negative then it will have an empty string. Example: 
• "Hello" - "world" will result in an empty string
• "Hello" - "hi" will result in "Hel" 
• "hi" - "Hello" will also result in an empty string. 
• The division will remove common character(s) from MyString. Example: "Hello" / "world" will result in "He".
• The multiplication will concatenate characters alternatively. Example: "Hello" * "world" will result in "Hweolrllod".

Actual Implementation 

	package com.andy.adt;
	import java.util.Objects;
	public class MyString {
	private final String myString;
	public MyString(String myString) {
	this.myString = myString;
	}
	public MyString add(MyString str2) {
	return new MyString(myString + str2.toString());
	}
	public MyString subtract(MyString str2) {
	int differenceInLength = myString.length() - str2.toString().length();
	if (differenceInLength > 0) {
	return new MyString(myString.substring(0, differenceInLength));
	}
	return new MyString("");
	}
	public MyString multiple(MyString str2) {
	StringBuilder stringBuilder = new StringBuilder("");
	int maxLength = Math.max(myString.length(), str2.toString().length());
	for (int index = 0; index < maxLength; index++) {
	if(index < myString.length()) {
	stringBuilder.append(myString.charAt(index));
	}
	if(index < str2.toString().length()) {
	stringBuilder.append(str2.toString().charAt(index));
	}
	}
	return new MyString(stringBuilder.toString());
	}
	public MyString divide(MyString str2) {
	char[] denominator = str2.toString().toCharArray();
	String str = myString.toString();
	for (char ch:
	denominator) {
	str = str.replaceAll(String.valueOf(ch), "");
	}
	return new MyString(str);
	}
	@Override
	public String toString() {
	return myString;
	}
	@Override
	public boolean equals(Object o) {
	if (this == o) return true;
	if (!(o instanceof MyString)) return false;
	MyString myString1 = (MyString) o;
	return Objects.equals(myString, myString1.myString);
	}
	@Override
	public int hashCode() {
	return myString != null ? myString.hashCode() : 0;
	}
	}

view raw MyString.java hosted with ❤ by GitHub

Sample Unit Test of the Implementation 

	package com.andy.adt;
	import org.junit.jupiter.api.Test;
	import static org.junit.jupiter.api.Assertions.*;
	class MyStringTest {
	private MyString myString;
	@Test
	public void testAdd(){
	myString = new MyString("Hello");
	MyString result = myString.add(new MyString(" World!"));
	assertEquals("Hello World!", result.toString());
	}
	@Test
	public void testSubtract_WhenSecondParameterIsLong() {
	myString = new MyString("Hello");
	MyString result = myString.subtract(new MyString(" World!"));
	assertEquals("", result.toString());
	}
	@Test
	public void testSubtract_WhenFirstParameterIsLong() {
	myString = new MyString("Robot");
	MyString result = myString.subtract(new MyString("Ok"));
	assertEquals("Rob", result.toString());
	}
	@Test
	public void testDivide() {
	myString = new MyString("Hello");
	MyString result = myString.divide(new MyString("world"));
	assertEquals("He", result.toString());
	}
	@Test
	public void testMultiple() {
	myString = new MyString("Hello");
	MyString result = myString.multiple(new MyString("world"));
	assertEquals("Hweolrllod", result.toString());
	}
	}

view raw MyStringTest.java hosted with ❤ by GitHub

One Time Password Generator

Simple code to generate One Time Password.
We are using java.util.SplittableRandom which was introduced in Java 8.

	import java.util.SplittableRandom;
	public class OTPgenerator {
	public static void main(String[] p) {
	int len = 6;
	if(p.length > 0) {
	len = Integer.valueOf(p[0]);
	}
	StringBuilder sb = new StringBuilder();
	SplittableRandom ran = new SplittableRandom();
	for(int i =0; i < len; i++) {
	int n = ran.nextInt(1,10);
	sb.append(n);
	}
	System.out.println(" Gnerated OTP " + sb.toString());
	}
	}

view raw OTPgenerator.java hosted with ❤ by GitHub

Output

Exception flow control could be expensive.

As a developer sometimes we use exceptions as flow control. It could be expensive. I am going to show you how a simple change could help you to save a lot of time by simply not accepting exception as your code flow controller.
In this example, I will throw an exception if required data is not available during execution I will throw an IllegalArgumentException and in another case, I simply return a value using which call is going to take the decision based on the value then we will see how different it will be.

	package com.andy.control;
	public class FlowControlExample {
	public static void main(String[] args) {
	FlowControlExample example = new FlowControlExample();
	long startTime = System.currentTimeMillis();
	for (int i = 0; i < 100_000_000; i++) {
	try {
	String fullName = example.getFullNameThrowException(null, "middle", "");
	} catch (IllegalArgumentException e) {
	}
	}
	long timeTaken = System.currentTimeMillis() - startTime;
	System.out.println(" Time taken to complete in case of exception is thrown. " + (timeTaken / 1000) + " in secs.");
	startTime = System.currentTimeMillis();
	for (int i = 0; i < 100_000_000; i++) {
	String fullName = example.getFullNameReturnValue(null, "middle", "");
	}
	timeTaken = System.currentTimeMillis() - startTime;
	System.out.println(" Time taken to complete in case of a value returned. " + (timeTaken / 1000) + " in secs.");
	}
	private String getFullNameThrowException(String firstName, String middleName, String lastName) {
	if ((firstName == null || firstName.isEmpty()) && (lastName == null || lastName.isEmpty())) {
	throw new IllegalArgumentException(" First and / or Last name cannot be null or empty.");
	}
	return firstName + " " + middleName + " " + lastName;
	}
	private String getFullNameReturnValue(String firstName, String middleName, String lastName) {
	if ((firstName == null || firstName.isEmpty()) && (lastName == null || lastName.isEmpty())) {
	return "";
	}
	return firstName + " " + middleName + " " + lastName;
	}
	}

view raw FlowControlExample.java hosted with ❤ by GitHub

Code Output

In case of exception, it will take around a minute for execution and in another case it is insignificant. Both methods are invoked one million times to determine the impact.

Code Output

I request you to think again if you are using exception as your flow controller in a code which will be invoked many times.

Then what if I have to address an exception scenario 

If I need to address an exception scenario then for optimization I could pre-allocate the exception object so that I can use them multiple times.

	package com.andy.control;
	public class FlowControlExample {
	private static final IllegalArgumentException ILLEGAL_ARGUMENT_EXCEPTION = new IllegalArgumentException(" First and / or Last name cannot be null or empty.");
	public static void main(String[] args) {
	FlowControlExample example = new FlowControlExample();
	long startTime = System.currentTimeMillis();
	for (int i = 0; i < 100_000_000; i++) {
	try {
	String fullName = example.getFullNameThrowException(null, "middle", "");
	} catch (IllegalArgumentException e) {
	}
	}
	long timeTaken = System.currentTimeMillis() - startTime;
	System.out.println(" Time taken to complete in case of exception is thrown. " + timeTaken + " in milliSecs.");
	startTime = System.currentTimeMillis();
	for (int i = 0; i < 100_000_000; i++) {
	String fullName = example.getFullNameReturnValue(null, "middle", "");
	}
	timeTaken = System.currentTimeMillis() - startTime;
	System.out.println(" Time taken to complete in case of a value returned. " + timeTaken + " in milliSecs.");
	}
	private String getFullNameThrowException(String firstName, String middleName, String lastName) {
	if ((firstName == null || firstName.isEmpty()) && (lastName == null || lastName.isEmpty())) {
	throw ILLEGAL_ARGUMENT_EXCEPTION;
	}
	return firstName + " " + middleName + " " + lastName;
	}
	private String getFullNameReturnValue(String firstName, String middleName, String lastName) {
	if ((firstName == null || firstName.isEmpty()) && (lastName == null || lastName.isEmpty())) {
	return "";
	}
	return firstName + " " + middleName + " " + lastName;
	}
	}

view raw FlowControlExample.java hosted with ❤ by GitHub

Code Output

In this case, you can see the result is much better but still high than return statement.

Let me know your thoughts about it.