Tutorial 2 : Extend Your App

Extend With In-place Code Templates

Extend/Customize with In-place Code Templates For Backend Spring-Java.

Extend Java Backend

Practice building and coding for Spring Java backend development with examples in generated code.

info

Reference is made to generated code for sample tables

• erp_customer: Java Classes named ErpCustomer*
• erp_product: Java Classes named ErpProduct*

You can locate your own table's respective & relevant files if not using above tables.

Q: Most Needed Topics

Here are some most needed topics:

• Singleton
• Exception Handling
• Collections

They are covered in sections below.

Q: Singleton

Singleton class in Java: Implement a singleton class

A: A class that can possess only one object at a time is called a singleton class.

In Spring Boot, @Configuration class and @Bean annotation will always provide you same bean instance.

Locate file in generated code to see example:

emapi\lib\base-app\src\main\java\com\example\emapi\app\EmApiRequestLoggingFilterConfig.java

@Configuration
public class EmApiRequestLoggingFilterConfig {

    @Bean
    public CommonsRequestLoggingFilter logFilter() {

Q: Exception Handling

Implement Exception Handling in Java | in Spring Boot | in Spring Boot for GraphQL

A:

Declare a Custom Exception and use it.

Locate file in generated code to see example:

emapi\lib\base-app\src\main\java\com\example\emapi\app\EmResourceNotFoundException.java

Used in Service Class:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerService.java

Used in GraphQL Custom Exception Resolver:

emapi\app\dbgraphql\src\main\java\com\example\emapi\app\EmGqlCustomExceptionResolver.java

In-place code Templates File

Locate file in generated code to see examples:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceExtend.java

Q: Using Java Collections

Practice coding for various Java Collections usages.

Locate file in generated code to see examples:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceExtend.java

• Sort Collection List

  • Using stream().sorted()

• Sort Collection List Via Custom Sorting

  • Using Comparator and Collections.sort(...)

• See more examples included under "Java 8 Features".

Q: Implementing Validation

Implementing Java Object Validation.

Locate file in generated code to see examples:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceExtend.java

• EXAMPLE FOR implementing Validation
  • See ErpCustomerValidate()

Q: Java 8+ Features

Locate file in generated code to see examples for all below:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceExtend.java

• EXAMPLE FOR using: Java Lambda Expression

  • See ErpCustomerListLambda() , ErpCustomerLambda()

• EXAMPLE FOR using: Stream Reduce

  • Use for: calculate aggregates, sum, averages, count
  • See ErpCustomerListReduce()

• EXAMPLE FOR using: Stream Filter

  • Use for filter/exclude records from list
  • See ErpCustomerListFilter()

• EXAMPLE FOR using: Stream Filter & Count

  • Use for filter/exclude records from list
    • Count matching value records and return
  • See ErpCustomerListFilterCount()

• Implement Functional Interfaces

• EXAMPLE FOR implementing: Function<T,R>

  • Use for Implementing Calculations, Transformations
  • See ErpCustomerFunction
    • Need to @Override method apply()

• EXAMPLE FOR implementing: Consumer<T>

  • Use for: Use it for 1-way action flow e.g. create shipping record after order create, returns no result
  • See ErpCustomerConsumer
    • Need to @Override method accept()

• Implement and Use: Misc Usage Collections, Iterators, Thread-safe Collections

  • See examples inside ErpCustomerListMiscUsageCollections() for all below:
    • Set Interface - no duplicate elements, no random access, iterator to traverse elements
      • Set implementations - HashSet , TreeSet , and LinkedHashSet
    • Map Interface - map keys to values, no duplicate keys. Operations: put, get, containsKey, containsValue, size, isEmpty
      • Map implementations - HashMap, TreeMap, and LinkedHashMap.
    • ListIterator Interface
    • Fail-Safe Iterators
      • ConcurrentHashMap, CopyOnWriteArrayList
    • binarySearch: how it works? locates middle then takes half half and checks-continue, input needs to be sorted list (beforehand)
    • Collections static Methods
      • Collections.sort() static method using one of below:
        • Comparator and using Comparator.comparing
        • reverseOrder()
        • custom lambda Comparator with compareTo
      • Collections - Shuffle, addAll
    • Arrays.sort()
    • Get Synchronized Collections via static methods
    • Synchronized vs Concurrent Collections examples

• Implement and Use: EXAMPLE FOR implementing: Misc Usage Threads

  • Thread examples
    • Create Thread with Runnable instance lambda
    • Create Thread with inner anonymous subclass
  • Use threads for runnableTaskExample
    • Thread run with start()
    • Thread run with Executor execute()
  • Use ExecutorService : For Running tasks in asynchronous mode
    • runnableTask example
      • Runnable, executorService.execute()
    • callableTask example - with returnig Future result
      • Callable, executorService.submit(), Future, futureResult.get()
        • alternatively call with executorService.invokeAny(), executorService.invokeAll()
    • ExecutorService shut down shutdown() and shut down immediately shutdownNow()

Cloud Functions code Templates File

Locate file in generated code to see examples for all below:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceCloudFunctions.java

Q: Implementing Serverless Functions

• Enabling Serverless Functions with Spring Cloud Function

Locate file in generated code to see examples for all below:

emapi\lib\base-app\src\main\java\com\example\emapi\app\ErpCustomer\ErpCustomerServiceCloudFunctions.java

• Implement : Spring Cloud Functions

  • These can be Integrated Further with any target Cloud: AWS, GCP, or Azure

  • Cloud Function implementing Function<I, O>

    • See ErpCustomerCfFunction()

  • Cloud Function implementing Supplier<O> reactive

    • See ErpCustomerCfSupplierFlux()

  • Cloud Function implementing Supplier<O> imperative

    • See ErpCustomerCfSupplier()

  • Cloud Function implementing Consumer<I>

    • See ErpCustomerCfConsumer()