Spring Boot question and explanations

 Question: What is diff BeanFactory and ApplicationContextFactory?

Solution:

The Spring Framework comes with two IOC containers – BeanFactory and ApplicationContext. The BeanFactory(Lazy Loading is the most basic version of IOC containers, and the ApplicationContext ( Eager Loading) extends the features of BeanFactory.BeanFactory loads beans on-demand, while ApplicationContext loads all beans at startup. 

Ex:  

Resource res = new ClassPathResource("ioc-container-difference-example.xml"); BeanFactory factory = new XmlBeanFactory(res); 

Student student = (Student) factory.getBean("student");

Or 

ApplicationContext context = new ClassPathXmlApplicationContext("ioc-container-difference-example.xml");

Reference: https://www.baeldung.com/spring-beanfactory-vs-applicationcontext

 

Question: What Is Spring Security?

Solution:

Spring Security is a separate module of the Spring framework that focuses on providing authentication and authorization methods in Java applications. It also takes care of most of the common security vulnerabilities such as CSRF attacks.

To use Spring Security in web applications, we can get started with the simple annotation @EnableWebSecurity.

For more information, we have a whole series of articles related to security.

Question: Name Some of the Design Patterns Used in the Spring Framework?

Solution:

• Singleton Pattern – singleton-scoped beans
• Factory Pattern – Bean Factory classes
• Prototype Pattern – prototype-scoped beans
• Adapter Pattern – Spring Web and Spring MVC
• Proxy Pattern – Spring Aspect-Oriented Programming support
• Template Method Pattern – JdbcTemplate, HibernateTemplate, etc.
• Front Controller – Spring MVC DispatcherServlet
• Data Access Object – Spring DAO support
• Model View Controller – Spring MVC

Reference: https://www.baeldung.com/spring-interview-questions

 

Question: Spring WebFlux?

Solution:

The original web framework included in the Spring Framework, Spring Web MVC, was purpose-built for the Servlet API and Servlet containers. The reactive-stack web framework, Spring WebFlux, was added later in version 5.0. It is fully non-blocking, supports Reactive Streams back pressure, and runs on such servers as Netty, Undertow, and Servlet 3.1+ containers.

Reference: https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html#webflux

Question: Spring REST – HTTP OPTIONS Request Handler Example

Solution:

HTTP OPTIONS Method

The HTTP OPTIONS method is used to describe the communication options for the target resource. This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.

• If the Request-URI is an asterisk (“*”), the OPTIONS request is intended to apply to the server in general rather than to a specific resource.
• If the Request-URI is not an asterisk, the OPTIONS request applies only to the options that are available when communicating with that resource.
• Responses to this method are not cacheable.

@RequestMapping(value="/buckets", method = RequestMethod.OPTIONS)

    ResponseEntity<?> collectionOptions() 

    {

         returnResponseEntity

                 .ok()

                 .allow(HttpMethod.GET, HttpMethod.POST, HttpMethod.OPTIONS)

                 .build();

    }

 

Reference: https://howtodoinjava.com/spring-rest/http-options-request-handler/

Question: Spring – Inversion of Control vs Dependency Injection

Solution:

What is Inversion of Control (IoC)

In traditional programming, the flow of the business logic is determined by objects that are statically assigned to one another. With inversion of control, the flow depends on the object graph that is instantiated by the assembler and is made possible by object interactions being defined through abstractions. The binding process is achieved through dependency injection, although some argue that the use of a service locator also provides inversion of control.

Inversion of control as a design guideline serves the following purposes:

1. There is a decoupling of the execution of a certain task from implementation.
2. Every module can focus on what it is designed for.
3. Modules make no assumptions about what other systems do but rely on their contracts.
4. Replacing modules has no side effect on other modules.

What is Dependency Injection (DI)

IoC is a design paradigm with the goal of giving more control to the targeted components of your application, the ones getting the work done. While Dependency injection is a pattern used to create instances of objects that other objects rely on without knowing at compile time which class will be used to provide that functionality. IoC relies on dependency injection because a mechanism is needed in order to activate the components providing the specific functionality.

How to implement IoC

In object-oriented programming, there are several basic techniques to implement inversion of control. These are:

1. using a factory pattern
2. using a service locator pattern
3. using a dependency injection of any given below type:
• a constructor injection
• a setter injection
• an interface injection

Inversion of control in Spring

The org.springframework.beans and org.springframework.context packages provide the basis for the Spring Framework’s IoC container. The BeanFactory interface provides an advanced configuration mechanism capable of managing objects of any nature. The ApplicationContext interface builds on top of the BeanFactory (it is a sub-interface) and adds other functionality such as easier integration with Spring’s AOP features, message resource handling (for use in internationalization), event propagation, and application-layer specific contexts such as the WebApplicationContext for use in we

Reference: https://stackoverflow.com/questions/3715967/when-should-we-call-system-exit-in-java

Question: What  is System.exit()?

Solution:

The java.lang.System.exit() method exits current program by terminating running Java virtual machine. This method takes a status code. A non-zero value of status code is generally used to indicate abnormal termination. This is similar exit in C/C++.

Following is the declaration for java.lang.System.exit() method:

public static void exit(int status)

exit(0) : Generally used to indicate successful termination.
exit(1) or exit(-1) or any other non-zero value – Generally indicates unsuccessful termination.

Additional info:

System.exit(0);

System.out.println("This line will never be reached");

System.exit(0) terminates the JVM. The parameter is passed back to the OS and is normally used to indicate abnormal termination (eg some kind of fatal error), so if you called java from a batch file or shell script you'd be able to get this value and get an idea if the application was successful.

System.exit(42)  == A script that called the application. Works in Windows, Unix and all other scriptable environments.

Reference: https://www.geeksforgeeks.org/system-exit-in-java/

Question: What is spring bean lifecycle?

Solution:

Bean life cycle is managed by the spring container. When we run the program then, first of all, the spring container gets started. After that, the container creates the instance of a bean as per the request, and then dependencies are injected. And finally, the bean is destroyed when the spring container is closed

  

Reference: https://www.geeksforgeeks.org/bean-life-cycle-in-java-spring/

https://reflectoring.io/spring-bean-lifecycle/

Question: Error Handling for REST with Spring  or Spring Boot @ControllerAdvice

Solution:

There are couple of ways to handle exception in springbok

Solution 1: the Controller-Level @ExceptionHandler

Solution 2: the HandlerExceptionResolver

Solution 3: @ControllerAdvice

Solution 4: ResponseStatusException (Spring 5 and Above)

Handle the Access Denied in Spring Security

Default Spring Boot Support exception messages:

In a nutshell, it serves a fallback error page for browsers (a.k.a. the Whitelabel Error Page) and a JSON response for RESTful, non-HTML requests:

{

    "timestamp": "2019-01-17T16:12:45.977+0000",

    "status": 500,

    "error": "Internal Server Error",

    "message": "Error processing the request!",

    "path": "/my-endpoint-with-exceptions"

}

Using @ControllerAdvice:

• SpringBoot @ControllerAdvice tutorial shows how to use @ControllerAdvice annotation to manage exceptions in a Spring Boot application.
• @ControllerAdvice is a specialization of the @Component annotation which allows to handle exceptions across the whole application in one global handling component. It can be viewed as an interceptor of exceptions thrown by methods annotated with @RequestMapping and similar.
• ResponseEntityExceptionHandler is a convenient base class for @ControllerAdvice classes that wish to provide centralized exception handling across all @RequestMapping methods through @ExceptionHandler methods. It provides an methods for handling internal Spring MVC exceptions. It returns a ResponseEntity in contrast to DefaultHandlerExceptionResolver which returns a ModelAndView.

Using the Controller-Level @ExceptionHandler:

The first solution works at the @Controller level. We will define a method to handle exceptions and annotate that with @ExceptionHandler:

public class FooController{

    //...

    @ExceptionHandler({ CustomException1.class, CustomException2.class })

    public void handleException() {

        //

    }

}

Reference: https://zetcode.com/springboot/controlleradvice/

https://www.baeldung.com/exception-handling-for-rest-with-spring

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AWS S3 CURD Operations using spring boot

AWS S3 CURD Operations including spring boot actuator features

README file mentioned to run procedure

GITURL: https://github.com/ramanujadasu/aws-curd-apis

GIT SSH link:

git@github.com:ramanujadasu/aws-curd-apis.git

Spring Boot AWS Cloud Support

https://spring.io/projects/spring-cloud-aws#overview

 

Samples:

https://github.com/spring-cloud-samples

https://github.com/ramanujadasu/aws-refapp

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Spring boot concepts and unit testing with mockito

Its very useful material spring boot concepts and unit testing with mockito:

https://drive.google.com/drive/folders/1V0L6ECAdvVXamlutHVnEc4MCIqdQPA3F?usp=sharing

 

Docker images:

https://hub.docker.com/search?q=in28min&type=image

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How to encrypt values in application properties in spring boot application (using Jasypt)

Jasypt (Java Simplified Encryption) Spring Boot provides utilities for encrypting property sources in Boot applications. In this article, we’ll discuss how we can add jasypt-spring-boot‘s support and use it. For more information on using Jasypt as a framework for encryption, take a look at our Introduction to Jasypt here.

Why Jasypt?
Whenever we need to store sensitive information in the configuration file – that means we’re essentially making that information vulnerable; this includes any kind of sensitive information, such as credentials, but certainly a lot more than that.
By using Jasypt, we can provide encryption for the property file attributes and our application will do the job of decrypting it and retrieving the original value.
Unfortunately we can't use user personal values plain text in application.properties file.
Jasypt (Java Simplified Encryption) is a java library which allows the developer to add basic encryption capabilities to his/her projects with minimum effort, and without the need of having deep knowledge on how cryptography works.

First, add the related dependency to the project. I am using maven so I will add the maven dependency to my pom.xml
https://mvnrepository.com/artifact/com.github.ulisesbocchio/jasypt-spring-boot-starter

    com.github.ulisesbocchio
    jasypt-spring-boot-starter
    2.0.0

In the application.properties (or yaml), we will write our encrypted properties between parenthesis and put ENC keyword before it. Like;
MyProperty=ENC(23ClLWiedLx8v6XT6Wk+Bg==)

How to generate those encrpyted values? We will use Jasypt for that! Go to http://www.jasypt.org/ and download the latest version. When you are done, go into jasypt\bin and use the encrypt.sh or encrypt.bat to encrypt your variables. There are several algorithms to pick but I will leave it as default and only give my property value and secret to encrpyt it.

We only need to add @EnableConfigurationProperties annotation to our application and jasypt will automaticly detect encrypted values and decrypt them before they are being used. The CommandLineRunner I have added below is just to test the decryption mechanism.

@EnableEncryptableProperties
@SpringBootApplication
public class JasyptExampleApplication {

  public static void main(String[] args) {
    SpringApplication.run(JasyptExampleApplication.class, args);
  }
 
  @Component
  public class MyRunner implements CommandLineRunner {
   
    @Value("${myProperty}")
    private String myProperty;

    @Override
    public void run(String... args) throws Exception {
      System.out.println("My property is = " + myProperty);
    }
   
  }
}

But if you run your code like this, you will get the below error:
Error creating bean with name 'demo.JasyptExampleApplication$MyRunner': Injection of autowired dependencies failed; nested exception is java.lang.IllegalStateException: Required Encryption configuration property missing: jasypt.encryptor.password
This is because Jasypt needs to know the secret(password) to decrypt the property. We can tell this to our program several ways:
1- We can give it as a command line argument when running the application;
–jasypt.encryptor.password=MY_SECRET
2- We can set it as an environment variable, this is also useful when you are running your application on Tomcat. You can give it to Tomcat’s setenv.sh file;
export CATALINA_OPTS=”-Djasypt.encryptor.password=MY_SECRET”
You can also unset the environment variable after running the application, so there will be no doorway left behind, at least in a human-readable sense.
3- You can give it in application.properties but this might be the dumbest way as it has no difference with giving the property as plain text.
If you know a better way, write a comment below!


2018-04-25 14:03:26.948 INFO 10028 --- [ main] demo.JasyptExampleApplication : Started JasyptExampleApplication in 1.264 seconds (JVM running for 2.06)
My property is MBcoder


As you can see it picked up the PBEWithMD5AndDES algorithm as default value and with the given password, MY_SECRET, it successfully decrypted myProperty
I hope this article was useful, see you another time!

Reference:
https://www.baeldung.com/spring-boot-jasypt
http://mbcoder.com/spring-boot-how-to-encrypt-properties-in-application-properties/

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Fail to initialize due to unknown Zone Id while running springboot application

Fail to initialize due to unknown Zone Id while running springboot application:

> Errors while running application:

- Application startup failed java.time.zone.ZoneRulesException: Unknown time-zone ID: America/Fort_Nelson

- Caused by: java.time.zone.ZoneRulesException: Unknown time-zone ID: America/Fort_Nelson
at java.time.zone.ZoneRulesProvider.getProvider(ZoneRulesProvider.java:272)
at java.time.zone.ZoneRulesProvider.getRules(ZoneRulesProvider.java:227)
at java.time.ZoneRegion.ofId(ZoneRegion.java:120)


> For using the latest version of Timeshape, the 2018d.3 or 2018d.4: We are facing this issue,



net.iakovlev
timeshape
2018d.5


> After so much analysis, released 2018d.5 where this change is merged and working fine with out any issues.

For applicaiton instalization:

@Component
public class AppStartUpConfig implements ApplicationListener {
@Autowired
TimeZone timeZone;
@Override
public void onApplicationEvent(ApplicationReadyEvent arg0) {
timeZone.setTimeZoneEngine(TimeZoneEngine.initialize());
}
}

In dto:
@GeoSpatialIndexed
private Point geoCoordinates;

For actual usage class:
@Autowired
TimeZone timeZoneEngine;

To get the geoCoordinates:
Optional zoneId = timeZoneEngine.getTimeZoneEngine().query(
geoCoordinates.getY(),
geoCoordinates.getX());
String timezoneId = zoneId.get().getId();


Reference:
https://github.com/RomanIakovlev/timeshape/issues/12

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Upload a file in cloud space(multipart upload operation) using HttpClient

To use below program, to upload a file easily in could space.
we will illustrate how to do a multipart upload operation using HttpClient.

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.LinkedHashMap;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.HttpMultipartMode;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.tomcat.util.http.fileupload.FileItem;
import org.apache.tomcat.util.http.fileupload.disk.DiskFileItem;
import org.springframework.web.multipart.MultipartFile;
import org.w3c.dom.Document;
import org.xml.sax.InputSource;

/**
* This class is used for uploading image in cloud
*/
public class UploadImage {

public static void main(String[] args) throws IOException {
httpImageTest();
//convertFileFromMultipartFile - convert multipart file to file object

     }

    private static void httpImageTest() throws ClientProtocolException, IOException {
        File file = new File(""); //c:/image/test.jpeg
        CloseableHttpClient client = HttpClients.createDefault();
        HttpPost post = new HttpPost("");
        post.addHeader("", "");
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
        builder.addTextBody("Content-Type", "image/jpeg");
        builder.addBinaryBody("file", file, ContentType.DEFAULT_BINARY, "fileName.jpeg");

        HttpEntity entity = builder.build();
        post.setEntity(entity);
        HttpResponse response = client.execute(post);
        System.out.println(response.getStatusLine());
        BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
        StringBuffer result = new StringBuffer();
        String line = "";
        while ((line = rd.readLine()) != null)
            result.append(line);
        System.out.println(formatXML(result.toString()));
        client.close();
    }

private static File convertFileFromMultipartFile(MultipartFile file) throws IOException {
        File convFile = new File(file.getOriginalFilename());
        convFile.createNewFile();
        FileOutputStream fos = new FileOutputStream(convFile);
        fos.write(file.getBytes());
        fos.close();
        return convFile;
    }

    private static String formatXML(String input) {
        try {
            Transformer transformer = TransformerFactory.newInstance().newTransformer();
            transformer.setOutputProperty(OutputKeys.INDENT, "yes");
            transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "3");

            StreamResult result = new StreamResult(new StringWriter());
            DOMSource source = new DOMSource(parseXml(input));
            transformer.transform(source, result);
            return result.getWriter().toString();
        } catch (Exception e) {
            e.printStackTrace();
            return input;
        }
    }

    private static Document parseXml(String in) {
        try {
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();
            InputSource is = new InputSource(new StringReader(in));
            return db.parse(is);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

Reference: http://www.baeldung.com/httpclient-multipart-upload

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Spring Boot Interview Questions

In this post, we will look at Spring Boot Interview questions. Examples are provided with an explanation. 

Q: What is Spring Boot?
A: Over the years spring has become more and more complex as new functionalities have been added. Just visit the page-https://spring.io/projects and we will see all the spring projects we can use in our application for different functionalities. If one has to start a new spring project we have to add build path or add maven dependencies, configure application server, add spring configuration. So a lot of effort is required to start a new spring project as we have to currently do everything from scratch. Spring Boot is the solution to this problem. Spring boot has been built on top of existing spring framework. Using spring boot we avoid all the boilerplate code and configurations that we had to do previously. Spring boot thus helps us use the existing Spring functionalities more robustly and with minimum efforts.

More details and miscellaneous examples 

Q: What are advantages of Spring Boot?
A: The advantages of Spring Boot are

• Reduce Development, Testing time and efforts.
• Use of JavaConfig helps avoid usage of XML.
• Avoid lots of maven imports and the various version conflicts.
• Provide Opinionated Development approach.
• Quick start to development by providing defaults.
• No Separate Web Server Needed.Which means that you no longer have to boot up Tomcat, Glassfish, or anything else.
• Requires less configuration-Since there is no web.xml file. Simply add classes annotated with@Configuration and then you can add methods annotated with@Bean, and Spring will automatically load up the object and manage it like it always has. You can even add @Autowired to the bean method to have Spring autowire in dependencies needed for the bean.
• Environment Based Configuration-Using these properties, you can pass into the application which environment you are using with:-Dspring.profiles.active={enviornment}. Spring will then load up the subsequent application properties file at (application-{environment}.properties) after loading up the main application properties file.

Q: Which build tool have you used to develop Spring Boot Application?
A: Spring Boot application can be developed using Maven as well as Gradle. 
Spring Boot application using Maven 
Spring Boot application using Gradle 

Q: What is JavaConfig?
A: Spring JavaConfig is a product of the Spring community that provides a pure-Java approach to configuring the Spring IoC Container. It thus helps avoid using XML configurations. The advantages of using JavaConfig are
The advantages of JavaConfig are

• Object-oriented configuration. Because configurations are defined as classes in JavaConfig, users can take full advantage of object-oriented features in Java. One configuration class may subclass another, overriding it's @Bean methods, etc.
• Reduced or eliminated XML configuration. The benefits of externalized configuration based on the principles of dependency injection have been proven. However, many developers would prefer not to switch back and forth between XML and Java. JavaConfig provides developers with a pure-Java approach to configuring the Spring container that is conceptually similar to XML configuration. It is technically possible to configure the container using only JavaConfig configuration classes, however in practice, many have found it ideal to mix-and-match JavaConfig with XML.
• Type-safe and refactoring-friendly. JavaConfig provides a type-safe approach to configuring the Spring container. Thanks to Java 5.0's support for generics, it is now possible to retrieve beans by type rather than by name, free of any casting or string-based lookups.

Added security configuration without XML using java config.

Q: How to reload my changes on Spring Boot without having to restart the server?
A: This can be achieved using DEV Tools. With this dependency any changes you save, the embedded tomcat will restart. Spring Boot has a Developer tool (DevTools) module which helps to improve the productivity of developers. One of the key challenges for the Java developers is to auto-deploy the file changes to server and auto restart the server. Developers can reload changes on Spring Boot without having to restart my server. This will eliminate the need for manually deploying the changes every time. Spring Boot doesn’t have this feature when it has released it’s first version. This was a most requested feature for the developers. The module DevTools does exactly what is needed for the developers. This module will be disabled in the production environment. It also provides an H2-database console for better testing the application. The following dependency is used

   
   org.springframework.boot
   spring-boot-devtools
   true
    
   

DevTool dependency usage for autostart and H2 DB console is illustrated in this example

QWhat is Actuator in Spring Boot?
A: Spring boot actuator is one of the important features in spring boot framework. Spring boot actuator helps you to access the current state of the running application in production environment. There are several metrics that have to be checked and monitored in the production environment. Even some external applications may be using those services to trigger the alert message to the concerned person. Actuator module exposes set of REST endpoints that can be directly accessed as an HTTP URL to check the status.

Q: How to run Spring boot application to custom port?
A: In order to run a spring boot application on a custom port you can specify the port in application.properties.
server.port=8090 

Q: Have you written Test cases using Spring Boot?
A: Spring Boot provides the @SpringBootTest for writing Unit Test Cases
Spring Boot Unit Test Simple Example

Q: What is YAML?
A: YAML is a human-readable data serialization language. It is commonly used for configuration files.
Compared to the properties file, YAML file is much more structured and less confusing in case we want to add complex properties in the configuration file. As can be seen, YAML has hierarchical configuration data. 
Use YAML properties in Spring Boot

Q: How to implement security for Spring boot application?
A: For Implementing security for Spring Boot we use the spring-boot-starter-security dependency and have to add the Security config. It requires very little code. Config class will have to extend WebSecurityConfigurerAdapter and override its methods.
Spring Boot Security example and explanation 

Q: Have you integrated Spring Boot and ActiveMQ?
A: For integrating Spring Boot and ActiveMQ we use the spring-boot-starter-activemq dependency
It requires very little configuration and no boilerplate code.
Spring Boot ActiveMQ explanation 

Q: Have you integrated Spring Boot and Apache Kafka?
A: For integrating Spring Boot and Apache Kafka we use the spring-kafka dependency.
Spring Boot + Apache Kafka Example 

Q: How to implement Pagination and Sorting with Spring Boot?
A: Using Spring Boot achieving pagination is very simple. Using the Spring Data-JPA this is achieved passing pageable org.springframework.data.domain.Pageable to the repository methods.
Spring Boot pagination explanation

Q: What is Swagger? Have you implemented it using Spring Boot?
A: Swagger is widely used for visualizing APIs, and with Swagger UI it provides online sandbox for frontend developers. For the tutorial, we will use the Springfox implementation of the Swagger 2 specification. A swagger is a tool, a specification and a complete framework implementation for producing the visual representation of RESTful Web Services. It enables documentation to be updated at the same pace as the server. When properly defined via Swagger, a consumer can understand and interact with the remote service with a minimal amount of implementation logic. Thus Swagger removes the guesswork in calling the service.
Spring Boot + Swagger2 

Q: What is Spring Profiles? How do you implement it using Spring Boot?
A: Spring Profiles allows users to register beans depending on the profile(dev, test, prod etc). So when the application is running in DEVELOPMENT only certain beans can be loaded and when in PRODUCTION certain other beans can be loaded. Suppose our requirement is that the Swagger documentation be enabled only for the QA environment and disabled for all others. This can be done using Profiles. Spring Boot makes using Profiles very easy. 
Spring Boot + profiles 

Q: What is Spring Batch? How do you implement it using Spring Boot?
A: Spring Boot Batch provides reusable functions that are essential in processing large volumes of records, including logging/tracing, transaction management, job processing statistics, job restart, skip, and resource management. It also provides more advanced technical services and features that will enable extremely high-volume and high-performance batch jobs through optimization and partitioning techniques.Simple as well as complex, high-volume batch jobs can leverage the framework in a highly scalable manner to process significant volumes of information. 
Spring Boot + Batch 

Q: What is FreeMarker Template? How do you implement it using Spring Boot?
A: FreeMarker is a Java-based Template Engine, originally focusing on dynamic web page generation with MVC software architecture. The major advantage of using Freemarker is the complete separation of the Presentation layer and the Business Layer. The Programmers can work on the application code while the designers can work on the HTML page design. Finally using freemarker these can then be combined to give the final output page. 
Spring Boot + FreeMarker Example 

Q: How did you perform database operations using Spring Boot?
A: Spring Boot Tutorial-Spring Data JPA
Spring Boot JDBC Example 

Q: How to upload a file using Spring?
A: Spring Boot + File Upload Example

Q: How to implement interceptors with Spring Boot?
A: Using Spring MVC HandlerInterceptor with Spring Boot 

Q: How to use schedulers with Spring Boot?
A: Spring Boot Task Scheduler Example 

Q: Which all starter maven dependencies have you used?
A: Have used different starter dependencies like spring-boot-starter-ActiveMQ dependency, spring-boot-starter-security dependency, spring-boot-starter-web dependency 
. This helps in adding less number of dependencies and also in reducing version conflicts. 
Spring Boot Security example and explanation 

Q: Have you used any integration framework with Spring Boot?
A: Have integrated Apache Camel with Spring Boot. Made use of Apache Camel Spring Boot starter dependency. Spring Boot +Apache Camel 

Q: What is Apache Freemarker? When to use it instead of JSP? How to integrate it with Spring Boot?
A: JSP is tailor-made for Web pages, Freemarker template is a more generic templating language - it can be used to generate HTML, plain text, emails, etc.
Spring Boot + FreeMarker Example

Q: What is AOP? How to use it with Spring Boot?
A: During software development, functions that span multiple points of an application are called cross-cutting concerns. These cross-cutting concerns differ from the application’s main business logic. Hence, separating these cross-cutting concerns from the business logic is where aspect-oriented programming (AOP) comes into the picture.
Spring Boot + AOP Example 
Q: What is Apache Kafka? How to integrate it with Spring Boot?
A: Apache Kafka is a distributed publish-subscribe messaging system. It is a scalable, fault-tolerant, publish-subscribe messaging system which enables us to build distributed applications. It is an Apache Top-Level project. Kafka is suitable for both offline and online message consumption.
Spring Boot + Apache Kafka Example 

Q: Have you used any Spring Cloud Components with Spring Boot?
A: Have used Spring Cloud components like Netflix Eureka for Service Registration, Ribbon for Load Balancing.
Spring Boot + Cloud Components

Reference: http://www.javainuse.com/spring/SpringBootInterviewQuestions

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