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Category: Spring Framework

Spring Config Server – (search paths)

in the previous post sprig config server we have seen how to start a spring config server with a sample application config.

Let us see some more variations that spring allows us with spring config server.

The spring config server allows for using placeholders {application} and {profile} .

With this flexibility we can configure one repository per application against one repository for all the applications as we did in the previous post, let us see how. We will change what we did in earlier post so I will make changes to the same project to demonstrate the feature.

Let us first create two repositories for two applications “my-app-1” and “my-app-2”

Below I have created and initialized the first repo

add two files into this directory as application.yml and application-dev.yml

application.yml

app:
 name: my-app-1

application-dev.yml

app:
 name: my-app-1-dev

commit this file into the git repo with “git add .” and “git commit”

Now, similarity create another repo in the same root directory with name “my-app-2”, in my case it was “C:\Users\<user>\git”

So we have two repositories for the two apps now, one with name “my-app-1” and another with “my-app-2”. Now lets add this config to the server application config.

Navigate to the configuration of the config-server and update the git url to use application placeholder like below.

spring:
  application:
    name: my-config-server
  cloud:
    config:
      server:
        git:
          uri: file://c://Users/<user>/git/{application}

Now lets start the config server and see the application in action
browse the url – http://localhost:8001/my-app-1/dev to view dev profile and http://localhost:8001/my-app-1/master to view the master or the default profile. Similarly you can use http://localhost:8001/my-app-2/dev or http://localhost:8001/my-app-2/master for the “my-app-2” config.

With the placeholder “{profile}” we can also create various other combinations. For e.g. we can create directories within the application repo for each of different profile instead of the suffix used in our example or in case of single repository for all the applications, we can use profile for dev and test or any folder of your choice within the repository.

You can also use the placeholder {application} or {profile} in searchpath config which basically is instruction to the spring config server on the whereabouts of your app config.

I have created two directories under the single repository configuration from my previous post and instead of having the config with the app name into the root directory, now I have created 2 directories for each app within the same root directory like below

I will have to also update the config-server application configuration to instruct on this new application locations.

spring:
  application:
    name: my-config-server
  cloud:
    config:
      server:
        git:
          uri: file://c://Users/<user>/git/app-config
          searchPaths: '{application}'


server:
  port: 8001

Now restart the server and browse urls – “http://localhost:8001/my-app-1/master&#8221; or “http://localhost:8001/my-app-2/master&#8221; or their dev profiles. You should be able to see the change consistent with the expectations. Spring config server will now pull the configuration from the application directories.

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Spring Config Server

Spring config server is one of the very important module of spring cloud to basically externalize application configuration. In a microservice architecture, spring config server provides a central place where all the microservices can look for the application configuration. It has support for multiple applications and environments.

We will look into a sample spring server application supported by git as storage for the application config. Although we can use a different form of storage but then it will require some additional changes.

Navigate to spring https://start.spring.io/ and add config server to dependencies, provide the artifact details as per the screenshot below or choose one of your own and click on generate


This will download a zip to you local filesystem. Unzip the directory and import/open the project into your favorite IDE. I am using Intellij.

The imported project will look like below.

Take a look at the pom.xml, it will have dependency for spring cloud config server apart from the spring boot starter dependency. Also it will import spring cloud dependencies using the maven import pom.

<dependency>
 <groupId>org.springframework.cloud</groupId>
 <artifactId>spring-cloud-config-server</artifactId>
</dependency>

delete the application.properties file and create application.yml instead. Set the application name and set the server port to 8001 as below 

spring:
  application:
    name: my-config-server

server:
  port: 8001


let us create a git repository on our local and then migrate it on to the github.

create a directory app-config and navigate into the directory on command line and fire command “git init”

create a file inside the app-config directory. lets say myapp.yml and add a property like below 

app:
 name: my-first-app

Now add this file to the git repo using git add and then git commit as below

let us add reference to this repo in our spring boot application. To do this, just open the application.yml file use the spring.cloud.config.git.url to the repository we created like below 

spring:
  application:
    name: my-config-server
  cloud:
    config:
      server:
        git:
          uri: file://c://Users/Amey/git/app-config

Now to initialize our spring boot application as config server, we have to add the annotation @EnableConfigServer to our main class like below 

@SpringBootApplication
@EnableConfigServer
public class MyConfigServerApplication {
	public static void main(String[] args) {
		SpringApplication.run(MyConfigServerApplication.class, args);
	}

}

Now we are ready to run the spring config server application. Right click on the class and run the application.

Now on the browser, navigate to the url “http://localhost:8001/my-first-app/master&#8221; to see spring config server responding as below


Here the spring has assumed the default profile as master or assumed that the branch is the default profile.

Now lets add another file to the git repo with name “my-first-app-dev.yml” and add the following property to the config 

app:
 name: my-first-app-dev

lets go back to the browser and now instead of master lets use dev as the profile in the url and check what the server responds with ( “ http://localhost:8001/my-first-app/dev“) .

Now our spring config server has done the magic trick. It has returned us the dev profile for our application. if you see the app.name is now my-first-app-dev and also we did not restart the server. Spring has picked up the change and responded with new profile we just added.

In the next blog, we will see various other configurations that we can use with spring config server.

Configure H2 DB with Spring Boot and Generate table from Entity classes

Prerequisite

Below tools should be installed on your machine

  1. Java
  2. Maven
  3. STS/Eclipse

GO to https://start.spring.io/

Add dependency as

  1. H2 Database 
  2. Spring Web
  3. Spring Data JPA

NOTE: Kindly select java version according to your project need ..I am using java 1.8 else you will get below exception when you run mvn clean install

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project Maven: Compilation failure: Compilation failure

Dependencies will look like below

Kindly add required dependencies as shown in above screenshot and down load project by clicking on “GENERATE” button. ZIP will get downloaded.

NOTE: if you are downloading on office laptop then you might need to unblock zip before unzipping. for doing this right click on zip file and go to properties and unblock it. so you will able to unzip it completely.

After unzip you will see folder generate like below screenshot

POM.XML 

<?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>2.3.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>
	<properties>
	
		
	</properties>
	<dependencies>
	<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
			<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

Go to your editor and import project.

For eclipse or STS Users..

1 GO to file

2 click on import

3 type maven and select Existing maven project

4 It will show pop up to select folder of your project. Kindly select folder which you unzipped.

5 Select pom.xml and click on Finish button

6. Now your project will get created in workspace and all dependencies will get downloaded by maven.Make sure maven is installed on your machine.

In below screenshot and in highlighted part you can see its showing “boot” project in bracket because spring tool suit will automatically detect it as spring project. For this in eclipse you need to download plugins.

Your project will be visible in workspace now

7. Right click on project and go to run and do maven install as shown in below screen shot

On console you will see below logs

8. Once build is successful then add below code in DemoApplication.java and add below configurations to application.properties file as well

DemoApplication.java

package com.example.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);
		
	System.out.println("Welcome to spring boot");
	}
}

application.properties

spring.datasource.url=jdbc:h2:file:C:/data/demo
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
server.port=9000
spring.h2.console.path=/h2-console
spring.h2.console.settings.trace=false
spring.h2.console.settings.web-allow-others=false
spring.jpa.hibernate.ddl-auto=none

Above code will have datasource related to H2 DB and it will tell spring boot on which path database whould be accessible in browser. Your application will run on 8888 port

Add below files in resources folder

Add data.sql file as shown below

data.sql

DROP TABLE IF EXISTS employee;
 
CREATE TABLE employee (
  id INT AUTO_INCREMENT  PRIMARY KEY,
  first_name VARCHAR(250) NOT NULL,
  last_name VARCHAR(250) NOT NULL
  
);
 
INSERT INTO employee (first_name, last_name) VALUES
  ('James', 'mill')

schema.sql

DROP TABLE IF EXISTS NATION;
CREATE TABLE NATION (
    id   INTEGER      NOT NULL AUTO_INCREMENT,
    name VARCHAR(128) NOT NULL,
    PRIMARY KEY (id)
);

9. Now Run application as spring boot app shown in below screenshot

10. Congrats now your application is running successfully and your H2 Db is running

11. Now go to http://localhost:9000/h2-console

you will see below screen and please enter jdbc url and pasword used in applicaiton.properties file

Enter password and click on connect and you will able to see DB console

Now you can able to use this DB for configuration with JPA library or any other purpose

Now you have ran your application with spring and h2 DB and generated tables using data.sql and schema.sql.

Now we are going to see instead of using data.sql and shema.sql how we can generate table using Entity classes.

Create Entity class

We are going to create country class customer and some more entity classes

customer.java

package com.example.demo;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Customer {

  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  private Long id;
  private String firstName;
  private String lastName;

  protected Customer() {}

  public Customer(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }

  @Override
  public String toString() {
    return String.format(
        "Customer[id=%d, firstName='%s', lastName='%s']",
        id, firstName, lastName);
  }

  public Long getId() {
    return id;
  }

  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }
}

Country.java

package com.example.demo;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Table(name="country")
@Entity
public class Country {
 
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;
    
    @Column(nullable = false)
    private String name;
 
    //...
}

Here in both classes as you see we have used annotation like @Table(name=”country”) ,@Entity,@Id and @Column ,They will help spring JPA to understand that its entity class and with which table its associated

@Id marks a field in a model class as the primary key:

@Table: Specifies the primary table for the annotated entity

@Column :Specifies the mapped column for a persistent property or field. If no Column annotation is specified, the default values apply.

@Entity:Specifies that the class is an entity. This annotation is applied to the entity class.

@GeneratedValue :Provides for the specification of generation strategies for the values of primary keys

Edit Application.properties

Add below entries in application.properties file


spring.datasource.url=jdbc:h2:file:C:/data/dbtest
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
server.port=8080


spring.jpa.generate-ddl=true
spring.jpa.show-sql = true

spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.properties.hibernate.format_sql=true


spring.jpa.properties.hibernate.generate_statistics=true

spring.h2.console.path=/h2-console
spring.h2.console.settings.trace=false
spring.h2.console.settings.web-allow-others=false

Spring provide spring.jpa.hibernate.ddl-auto property for automatic schema genration so base on its value spring jpa will generate

tables for entity classes ,possible values for this are create ,update,create-drop,validate ,none

spring.jpa.generate-ddl (boolean) switches the feature on and off and is vendor independent.

Start spring boot application

After starting app you will see below log on console


  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.3.RELEASE)

2020-09-12 17:26:44.540  INFO 12852 --- [           main] com.example.demo.DemoApplication         : Starting DemoApplication on DESKTOP-V5245JB with PID 12852 (D:\SpringFramework\SpringBootwithHAndJPAAutoGenerateTables\target\classes started by admin in D:\SpringFramework\SpringBootwithHAndJPAAutoGenerateTables)
2020-09-12 17:26:44.543  INFO 12852 --- [           main] com.example.demo.DemoApplication         : No active profile set, falling back to default profiles: default
2020-09-12 17:26:45.294  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Multiple Spring Data modules found, entering strict repository configuration mode!
2020-09-12 17:26:45.295  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JDBC repositories in DEFAULT mode.
2020-09-12 17:26:45.357  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 47ms. Found 0 JDBC repository interfaces.
2020-09-12 17:26:45.385  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Multiple Spring Data modules found, entering strict repository configuration mode!
2020-09-12 17:26:45.385  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFERRED mode.
2020-09-12 17:26:45.393  INFO 12852 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 2ms. Found 0 JPA repository interfaces.
2020-09-12 17:26:45.861  INFO 12852 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-09-12 17:26:45.868  INFO 12852 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-09-12 17:26:45.869  INFO 12852 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.37]
2020-09-12 17:26:45.979  INFO 12852 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-09-12 17:26:45.979  INFO 12852 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1387 ms
2020-09-12 17:26:46.033  INFO 12852 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2020-09-12 17:26:46.316  INFO 12852 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
2020-09-12 17:26:46.322  INFO 12852 --- [           main] o.s.b.a.h2.H2ConsoleAutoConfiguration    : H2 console available at '/h2-console'. Database available at 'jdbc:h2:file:C:/data/dbtest'
2020-09-12 17:26:46.532  INFO 12852 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-09-12 17:26:46.670  INFO 12852 --- [         task-1] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
2020-09-12 17:26:46.697  WARN 12852 --- [           main] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
2020-09-12 17:26:46.787  INFO 12852 --- [         task-1] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.4.20.Final
2020-09-12 17:26:47.266  INFO 12852 --- [         task-1] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
2020-09-12 17:26:47.659  INFO 12852 --- [         task-1] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
2020-09-12 17:26:47.752  INFO 12852 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-09-12 17:26:47.754  INFO 12852 --- [           main] DeferredRepositoryInitializationListener : Triggering deferred initialization of Spring Data repositories…
2020-09-12 17:26:47.754  INFO 12852 --- [           main] DeferredRepositoryInitializationListener : Spring Data repositories initialized!
2020-09-12 17:26:47.778  INFO 12852 --- [           main] com.example.demo.DemoApplication         : Started DemoApplication in 3.538 seconds (JVM running for 5.291)
2020-09-12 17:26:48.377  INFO 12852 --- [         task-1] org.hibernate.tuple.PojoInstantiator     : HHH000182: No default (no-argument) constructor for class: com.example.demo.EmployeeInformation (class must be instantiated by Interceptor)
Hibernate: 
    
    drop table if exists country CASCADE 
Hibernate: 
    
    drop table if exists customer CASCADE 
Hibernate: 
    
    drop table if exists employee_information CASCADE 
Hibernate: 
    
    drop table if exists task CASCADE 
Hibernate: 
    
    drop sequence if exists hibernate_sequence
Hibernate: create sequence hibernate_sequence start with 1 increment by 1
Hibernate: 
    
    create table country (
       id integer not null,
        name varchar(255) not null,
        primary key (id)
    )
Hibernate: 
    
    create table customer (
       id bigint not null,
        first_name varchar(255),
        last_name varchar(255),
        primary key (id)
    )
Hibernate: 
    
    create table employee_information (
       id bigint not null,
        first_name varchar(255),
        last_name varchar(255),
        primary key (id)
    )
Hibernate: 
    
    create table task (
       id integer not null,
        description varchar(255),
        is_done boolean,
        target_date date,
        primary key (id)
    )
2020-09-12 17:26:48.708  INFO 12852 --- [         task-1] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
2020-09-12 17:26:48.714  INFO 12852 --- [         task-1] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2020-09-12 17:39:04.343  INFO 12852 --- [nio-8080-exec-6] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-09-12 17:39:04.343  INFO 12852 --- [nio-8080-exec-6] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-09-12 17:39:04.350  INFO 12852 --- [nio-8080-exec-6] o.s.web.servlet.DispatcherServlet        : Completed initialization in 7 ms
2020-09-12 17:39:04.451  INFO 12852 --- [nio-8080-exec-6] i.StatisticalLoggingSessionEventListener : Session Metrics {
    0 nanoseconds spent acquiring 0 JDBC connections;
    0 nanoseconds spent releasing 0 JDBC connections;
    0 nanoseconds spent preparing 0 JDBC statements;
    0 nanoseconds spent executing 0 JDBC statements;
    0 nanoseconds spent executing 0 JDBC batches;
    0 nanoseconds spent performing 0 L2C puts;
    0 nanoseconds spent performing 0 L2C hits;
    0 nanoseconds spent performing 0 L2C misses;
    0 nanoseconds spent executing 0 flushes (flushing a total of 0 entities and 0 collections);
    0 nanoseconds spent executing 0 partial-flushes (flushing a total of 0 entities and 0 collections)
}
2020-09-12 17:39:04.582  INFO 12852 --- [nio-8080-exec-6] i.StatisticalLoggingSessionEventListener : Session Metrics {
    0 nanoseconds spent acquiring 0 JDBC connections;
    0 nanoseconds spent releasing 0 JDBC connections;
    0 nanoseconds spent preparing 0 JDBC statements;
    0 nanoseconds spent executing 0 JDBC statements;
    0 nanoseconds spent executing 0 JDBC batches;
    0 nanoseconds spent performing 0 L2C puts;
    0 nanoseconds spent performing 0 L2C hits;
    0 nanoseconds spent performing 0 L2C misses;
    0 nanoseconds spent executing 0 flushes (flushing a total of 0 entities and 0 collections);
    0 nanoseconds spent executing 0 partial-flushes (flushing a total of 0 entities and 0 collections)
}

As you can see in log its has created tables when we have started app ad also shown sql on console as we have added property to show sql.

Now we will check on h2 db

Click on connect

Here you can see 5 tables are created for 5 entity classes

You can check source code on below link

https://github.com/letsbeadeveloper/SpringTutorial/tree/master/SpringBootwithHAndJPAAutoGenerateTables

Create REST API with Spring Boot Application in 5 min

Prerequisite

Below tools should be installed on your machine

  1. Java
  2. Maven
  3. STS/Eclipse

GO to https://start.spring.io/

Below is Screen shot to make you familiar with spring initializer

Add dependency and generate project

Spring Web

Kindly add required dependencies as shown in above screenshot and down load project by clicking on “GENERATE” button. ZIP will get downloaded.

NOTE: Kindly select java version according to your project need ..I am using java 1.8 else you will get below exception when you run mvn clean install

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project Maven: Compilation failure: Compilation failure

NOTE: if you are downloading on office laptop then you might need to unblock zip before unzipping. for doing this right click on zip file and go to properties and unblock it. so you will able to unzip it completely.

After unzip you will see folder generate like below screenshot

Go to your editor and import project.

For eclipse or STS Users..

1 GO to file

2 click on import

3 type maven and select Existing maven project

4 It will show pop up to select folder of your project. Kindly select folder which you unzipped.

5 Select pom.xml and click on Finish button

6. Now your project will get created in workspace and all dependencies will get downloaded by maven.Make sure maven is installed on your machine.

In below screenshot and in highlighted part you can see its showing “boot” project in bracket because spring tool suit will automatically detect it as spring project. For this in eclipse you need to download plugins.

Your project will be visible in workspace now

7. Right click on project and go to run and do maven install as shown in below screen shot

On console you will see below logs

8. Once build is successful then add below code in DemoApplication.java

DemoApplication.java

package com.example.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);
		
	System.out.println("Welcome to spring boot");
	}

}

POM.xml

<?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>2.3.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</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>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

9. Now Run application as spring boot app shown in below screenshot

10. Congrats now your application is running succesfully

Create Rest End Point

  1. Create Class name HelloController
  2. Create Method name getMessage
  3. Add annotation @RestController to create this class as restcontorller
  4. Add @GetMapping(“/hello”) on your method to expose this method as rest API
  5. Add @RequestParam(value = “name”) String name so you can accept variable value in rest endpoint
  6. Below is code of HelloController

HelloController.java

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HelloController {
	
	@GetMapping("/hello")
	public String getMessage(@RequestParam(value = "name") String name)
	{
		return "Hello  " +name;
	}

}

Your rest endpoint is: http://localhost:8080/hello?name=john

Now build your project and run as spring boot application

Once you tun it you will see below logs

Go to browser and hit your end point and you will see output in browser window

http://localhost:8080/hello?name=john

Congrats your rest end point is created

Configure H2 DB with Spring Boot

Prerequisite

Below tools should be installed on your machine

  1. Java
  2. Maven
  3. STS/Eclipse

GO to https://start.spring.io/

Add dependency as

  1. H2 Database 
  2. Spring Web
  3. Spring Data JPA

NOTE: Kindly select java version according to your project need ..I am using java 1.8 else you will get below exception when you run mvn clean install

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project Maven: Compilation failure: Compilation failure

Dependencies will look like below

Kindly add required dependencies as shown in above screenshot and down load project by clicking on “GENERATE” button. ZIP will get downloaded.

NOTE: if you are downloading on office laptop then you might need to unblock zip before unzipping. for doing this right click on zip file and go to properties and unblock it. so you will able to unzip it completely.

After unzip you will see folder generate like below screenshot

POM.XML 

<?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>2.3.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>
	<properties>
	
		
	</properties>
	<dependencies>
	<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
			<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

Go to your editor and import project.

For eclipse or STS Users..

1 GO to file

2 click on import

3 type maven and select Existing maven project

4 It will show pop up to select folder of your project. Kindly select folder which you unzipped.

5 Select pom.xml and click on Finish button

6. Now your project will get created in workspace and all dependencies will get downloaded by maven.Make sure maven is installed on your machine.

In below screenshot and in highlighted part you can see its showing “boot” project in bracket because spring tool suit will automatically detect it as spring project. For this in eclipse you need to download plugins.

Your project will be visible in workspace now

7. Right click on project and go to run and do maven install as shown in below screen shot

On console you will see below logs

8. Once build is successful then add below code in DemoApplication.java and add below configurations to application.properties file as well

DemoApplication.java

package com.example.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);
		
	System.out.println("Welcome to spring boot");
	}
}

application.properties

spring.datasource.url=jdbc:h2:file:C:/data/demo
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
server.port=9000
spring.h2.console.path=/h2-console
spring.h2.console.settings.trace=false
spring.h2.console.settings.web-allow-others=false
spring.jpa.hibernate.ddl-auto=none

Above code will have datasource related to H2 DB and it will tell spring boot on which path database whould be accessible in browser. Your application will run on 8888 port

Add below files in resources folder

Add data.sql file as shown below

data.sql

DROP TABLE IF EXISTS employee;
 
CREATE TABLE employee (
  id INT AUTO_INCREMENT  PRIMARY KEY,
  first_name VARCHAR(250) NOT NULL,
  last_name VARCHAR(250) NOT NULL
  
);
 
INSERT INTO employee (first_name, last_name) VALUES
  ('James', 'mill')

schema.sql

DROP TABLE IF EXISTS NATION;
CREATE TABLE NATION (
    id   INTEGER      NOT NULL AUTO_INCREMENT,
    name VARCHAR(128) NOT NULL,
    PRIMARY KEY (id)
);

9. Now Run application as spring boot app shown in below screenshot

10. Congrats now your application is running successfully and your H2 Db is running

11. Now go to http://localhost:9000/h2-console

you will see below screen and please enter jdbc url and pasword used in applicaiton.properties file

Enter password and click on connect and you will able to see DB console

Now you can able to use this DB for configuration with JPA library or any other purpose