diff --git a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/config/SecurityConfiguration.java b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/config/SecurityConfiguration.java
index 64111588f6..f07944271e 100644
--- a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/config/SecurityConfiguration.java
+++ b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/config/SecurityConfiguration.java
@@ -101,6 +101,7 @@ public class SecurityConfiguration extends WebSecurityConfigurerAdapter {
             .sessionCreationPolicy(SessionCreationPolicy.STATELESS)
         .and()
             .authorizeRequests()
+            .antMatchers("/api/books/purchase/**").authenticated()
             .antMatchers("/api/register").permitAll()
             .antMatchers("/api/activate").permitAll()
             .antMatchers("/api/authenticate").permitAll()
diff --git a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/BookService.java b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/BookService.java
index bb052dc03c..6422d1a424 100644
--- a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/BookService.java
+++ b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/BookService.java
@@ -40,4 +40,11 @@ public interface BookService {
      * @param id the id of the entity
      */
     void delete(Long id);
+
+    /**
+     * Simulates purchasing a book by reducing the stock of a book by 1.
+     * @param id the id of the book
+     * @return Updated BookDTO, empty if not found, or throws exception if an error occurs.
+     */
+    Optional<BookDTO> purchase(Long id);
 }
diff --git a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/impl/BookServiceImpl.java b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/impl/BookServiceImpl.java
index 00f68b84af..23cd59584c 100644
--- a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/impl/BookServiceImpl.java
+++ b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/service/impl/BookServiceImpl.java
@@ -5,6 +5,7 @@ import com.baeldung.jhipster5.domain.Book;
 import com.baeldung.jhipster5.repository.BookRepository;
 import com.baeldung.jhipster5.service.dto.BookDTO;
 import com.baeldung.jhipster5.service.mapper.BookMapper;
+import com.baeldung.jhipster5.web.rest.errors.BadRequestAlertException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -87,4 +88,22 @@ public class BookServiceImpl implements BookService {
         log.debug("Request to delete Book : {}", id);
         bookRepository.deleteById(id);
     }
+
+    @Override
+    public Optional<BookDTO> purchase(Long id) {
+        Optional<BookDTO> bookDTO = findOne(id);
+        if(bookDTO.isPresent()) {
+            int quantity = bookDTO.get().getQuantity();
+            if(quantity > 0) {
+                bookDTO.get().setQuantity(quantity - 1);
+                Book book = bookMapper.toEntity(bookDTO.get());
+                book = bookRepository.save(book);
+                return bookDTO;
+            }
+            else {
+                throw new BadRequestAlertException("Book is not in stock", "book", "notinstock");
+            }
+        }
+        return Optional.empty();
+    }
 }
diff --git a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/web/rest/BookResource.java b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/web/rest/BookResource.java
index efcc2c3495..0360ea05ed 100644
--- a/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/web/rest/BookResource.java
+++ b/jhipster-5/bookstore-monolith/src/main/java/com/baeldung/jhipster5/web/rest/BookResource.java
@@ -109,4 +109,10 @@ public class BookResource {
         bookService.delete(id);
         return ResponseEntity.ok().headers(HeaderUtil.createEntityDeletionAlert(ENTITY_NAME, id.toString())).build();
     }
+
+    @GetMapping("/books/purchase/{id}")
+    public ResponseEntity<BookDTO> purchase(@PathVariable Long id) {
+        Optional<BookDTO> bookDTO = bookService.purchase(id);
+        return ResponseUtil.wrapOrNotFound(bookDTO);
+    }
 }
diff --git a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.html b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.html
index 0aef73282a..4a3c20e841 100644
--- a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.html
+++ b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.html
@@ -38,6 +38,12 @@
                     class="btn btn-primary">
                 <fa-icon [icon]="'pencil-alt'"></fa-icon>&nbsp;<span> Edit</span>
             </button>
+
+            <button type="button"
+                    class="btn btn-primary"
+                    (click)="purchase(book.id)">
+                <span>Purchase</span>
+            </button>
         </div>
     </div>
 </div>
diff --git a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.ts b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.ts
index 50a6bec9ad..6b84c0ba73 100644
--- a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.ts
+++ b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book-detail.component.ts
@@ -2,6 +2,8 @@ import { Component, OnInit } from '@angular/core';
 import { ActivatedRoute } from '@angular/router';
 
 import { IBook } from 'app/shared/model/book.model';
+import { BookService } from 'app/entities/book/book.service';
+import { HttpErrorResponse, HttpResponse } from '@angular/common/http';
 
 @Component({
     selector: 'jhi-book-detail',
@@ -10,7 +12,7 @@ import { IBook } from 'app/shared/model/book.model';
 export class BookDetailComponent implements OnInit {
     book: IBook;
 
-    constructor(protected activatedRoute: ActivatedRoute) {}
+    constructor(protected activatedRoute: ActivatedRoute, protected bookService: BookService) {}
 
     ngOnInit() {
         this.activatedRoute.data.subscribe(({ book }) => {
@@ -21,4 +23,14 @@ export class BookDetailComponent implements OnInit {
     previousState() {
         window.history.back();
     }
+
+    purchase(id: number) {
+        console.log('Purchasing book ' + id);
+        this.bookService.purchase(id).subscribe(
+            (res: HttpResponse<IBook>) => {
+                this.book = res.body;
+            },
+            (res: HttpErrorResponse) => console.log(res.message)
+        );
+    }
 }
diff --git a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book.service.ts b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book.service.ts
index 3ff649d25d..bff511f7e6 100644
--- a/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book.service.ts
+++ b/jhipster-5/bookstore-monolith/src/main/webapp/app/entities/book/book.service.ts
@@ -38,6 +38,13 @@ export class BookService {
             .pipe(map((res: EntityResponseType) => this.convertDateFromServer(res)));
     }
 
+    purchase(id: number): Observable<EntityResponseType> {
+        console.log('Calling /api/books/purchase/ ' + id);
+        return this.http
+            .get<IBook>(`${this.resourceUrl}/purchase/${id}`, { observe: 'response' })
+            .pipe(map((res: EntityResponseType) => this.convertDateFromServer(res)));
+    }
+
     query(req?: any): Observable<EntityArrayResponseType> {
         const options = createRequestOption(req);
         return this.http