SpringBoot

SpringBoot - Maven - Pom.xml

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.oasissoftech.springboot</groupId>
	<artifactId>SpringBoot-Tutorial-1</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>SpringBoot-Tutorial-1</name>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.2.RELEASE</version>
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

	<properties>
		<java.version>1.8</java.version>
	</properties>

</project>

to get latest Spring Boot Starter Parent pom.xml configurations visit : https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent

to get latest Spring Boot Web Starter pom.xml configurations visit : https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-web

SpringBoot - Application Boot

Spring Boot application startup class :

package com.oasissofttech.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootTutorial1App {
	public static void main(String[] args) {
		SpringApplication.run(SpringBootTutorial1App.class,args);
	}
}

SpringBoot - Controller Class - GET, POST, PUT, DELETE

package com.oasissofttech.springboot.brand;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class BrandController {
	@Autowired
	private BrandService brandService;
	
	@RequestMapping("/brands")
	public List<Brand> getAllBrands() {
		return brandService.getAllBrands();
	}
	
	@RequestMapping("/brand/{brandId}")
	public Brand getBrand(@PathVariable("brandId") int id) {
		return brandService.getBrand(id);
	
	}
	
	@RequestMapping(method=RequestMethod.POST,value="/brands")
	public void addBrand(@RequestBody Brand brand) {
		brandService.addBrand(brand);
	}
	
	@RequestMapping(method=RequestMethod.PUT,value="/brands/{id}")
	public void addBrand(@RequestBody Brand brand,@PathVariable int id) {
		brandService.updateBrand(brand,id);
	}
	
	@RequestMapping(method=RequestMethod.DELETE,value="/brands/{id}")
	public void deleteBrand(@PathVariable int id) {
		brandService.deleteBrand(id);
	}
	
}

SpringBoot - Service Class

package com.oasissofttech.springboot.brand;

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

import org.springframework.stereotype.Service;

@Service
public class BrandService {

	private List<Brand> brands = new ArrayList<>(Arrays.asList(
			new Brand(1,"Aston Martin","(1913–present)"),
			new Brand(2,"Bentley","(1919–present)"),
			new Brand(3,"Jaguar Land Rover","(2013-present)"),
			new Brand(4,"Lotus","(1952–present)"),
			new Brand(5,"Rolls Royce","(1904–present)")
			));
	
	public List<Brand> getAllBrands(){
		return brands;
	}
	
	
	public Brand getBrand(int id) {
		return brands.stream().filter(b->b.getId()==id).findFirst().get();
	}


	public void addBrand(Brand brand) {
		brands.add(brand);
	}


	public void updateBrand(Brand brand, int id) {
		int c = brands.size();
		for(int i=0;i<c;i++) {
			if(brands.get(i).getId()==id) {
				brands.set(i, brand);
				return;
			}
		}
	}


	public void deleteBrand(int id) {
		brands.removeIf(t->t.getId()==id);
	}
	
}

Others

package com.oasissofttech.springboot.brand;

public class Brand {
	private int id;
	private String brandName;
	private String description;

	public Brand() {
	}

	public Brand(int id, String brandName, String description) {
		super();
		this.id = id;
		this.brandName = brandName;
		this.description = description;
	}


	public int getId() {
		return id;
	}

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

	public String getBrandName() {
		return brandName;
	}

	public void setBrandName(String brandName) {
		this.brandName = brandName;
	}

	public String getDescription() {
		return description;
	}

	public void setDescription(String description) {
		this.description = description;
	}

}

Common application properties

application.properties file

#===========================================
#=== application.properties file content ===
server.port=3000 #server HTTP port.
#===================end=====================

springboot properties file manual : https://docs.spring.io/spring-boot/docs/current/reference/html/common-application-properties.html

JPA - Java Persistance API

Making CRUD Operation with Repository

@Repository

import java.util.List;

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

import com.lse.library.model.Books;

@Repository
public interface LseLibraryRepository extends CrudRepository<Books,Long> {
	//ID,ISBN_NO,SUBJECT,AUTHOR,TITLE
    @Query(value="SELECT * FROM LSE_LIBRARY_BOOKS s where s.SHELF_NO = :shelfNo", nativeQuery = true) 
    List<Books> findBooksByShelfNo(@Param("shelfNo") String shelfNo);

    //LOCATION_NO
    @Query(value="SELECT * FROM LSE_LIBRARY_BOOKS s where s.ISBN_NO = :IsbnNo", nativeQuery = true) 
    Books findLocationByIsbnNo(@Param("IsbnNo") String IsbnNo);

    //STACK_NO,SHELF_NO
    @Query(value="SELECT * FROM LSE_LIBRARY_BOOKS s where s.SUBJECT like CONCAT('%',:subject,'%')", nativeQuery = true)   
    List<Books> findStacksAndShelvesBySubject(@Param("subject") String subject);

    @Query(value="SELECT count(*) ID FROM LSE_LIBRARY_BOOKS s where s.SHELF_NO = :shelfNo", nativeQuery = true) 
    int findCountOfBooksByShelfNo(@Param("shelfNo") String shelfNo);

    //SHELF_NO
    @Query(value="SELECT * FROM LSE_LIBRARY_BOOKS s where s.SUBJECT = :subject1 or s.SUBJECT = :subject2 ", nativeQuery = true)   
    List<Books> findShelvesBySubjects(@Param("subject1") String subject1,@Param("subject2") String subject2);

    //SHELF_NO
    @Query(value="SELECT * FROM LSE_LIBRARY_BOOKS s where s.SUBJECT = :subject", nativeQuery = true)   
    List<Books> findShelvesByOneSubject(@Param("subject") String subject);

}

BrandRepository interface

package com.oasissofttech.springboot.brand;

import org.springframework.data.repository.CrudRepository;

@Repository
public interface BrandRepository extends CrudRepository<Brand, Integer> {

}

BrandService Class

package com.oasissofttech.springboot.brand;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class BrandService {
	@Autowired
	private BrandRepository brandRepository;
	
	public List<Brand> getAllBrands(){
		List<Brand> brands = new ArrayList<>();
		brandRepository.findAll()
		.forEach(brands::add);
		
		return brands;
	}
	
	
	public Optional<Brand> getBrand(int id) {
		return brandRepository.findById(id);
	}


	public void addBrand(Brand brand) {
		brandRepository.save(brand);
	}


	public void updateBrand(Brand brand, int id) {
		brandRepository.save(brand);
	}


	public void deleteBrand(int id) {
		brandRepository.deleteById(id);
	}
	
}

Error Handling for REST with Spring & SpringBoot

Overview

Before Spring 3.2, the two main approaches to handling exceptions in a Spring MVC application were: HandlerExceptionResolver or the @ExceptionHandler annotation. Both of these have some clear downsides.

After 3.2 we now have the new @ControllerAdvice annotation to address the limitations of the previous two solutions.

All of these do have one thing in common – they deal with the separation of concerns very well. The app can throw exception normally to indicate a failure of some kind – exceptions which will then be handled separately.

The Controller level @ExceptionHandler

The New @ControllerAdvice (Spring 3.2 And Above)

Spring 3.2 brings support for a global @ExceptionHandler with the new @ControllerAdvice annotation. This enables a mechanism that breaks away from the older MVC model and makes use of ResponseEntity along with the type safety and flexibility of @ExceptionHandler:

@ControllerAdvice
public class RestResponseEntityExceptionHandler 
  extends ResponseEntityExceptionHandler {
 
    @ExceptionHandler(value 
      = { IllegalArgumentException.class, IllegalStateException.class })
    protected ResponseEntity<Object> handleConflict(
      RuntimeException ex, WebRequest request) {
        String bodyOfResponse = "This should be application specific";
        return handleExceptionInternal(ex, bodyOfResponse, 
          new HttpHeaders(), HttpStatus.CONFLICT, request);
    }
}

The new annotation allows the multiple scattered @ExceptionHandler from before to be consolidated into a single, global error handling component.

The actual mechanism is extremely simple but also very flexible:

• it allows full control over the body of the response as well as the status code
• it allows mapping of several exceptions to the same method, to be handled together
• it makes good use of the newer RESTful ResposeEntity response

One thing to keep in mind here is to match the exceptions declared with @ExceptionHandler with the exception used as the argument of the method. If these don’t match, the compiler will not complain – no reason it should, and Spring will not complain either.

However, when the exception is actually thrown at runtime, the exception resolving mechanism will fail with:

java.lang.IllegalStateException: No suitable resolver for argument [0] [type=...]
HandlerMethod details: ...

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

Spring Boot Interview Questions and Answers

• Spring Boot Interview Questions and Answers-1 - http://www.javainuse.com/spring/SpringBootInterviewQuestions

• Spring Boot Interview Questions and Answers-2 - http://www.springboottutorial.com/spring-boot-interview-questions