Java type safe

What is type safe compiler?

A type-safe compiler can do following feature:

• Validate type while compiling
• Compiled error if user try to assign wrong type

Define an output package for Spring Boot application with Assembly plugin

 

Add assembly maven plugin

		${project.artifactId}
		
			
				org.springframework.boot
				spring-boot-maven-plugin
				
					
						
							repackage
						
					
				
			
			
				maven-assembly-plugin
				
					true
					
						${project.basedir}/src/assembly/assembly.xml
					
				
				
					
						create-archive
						package
						
							single
						
					
				
			
		
	

Notions in Apache Kafka

Producer

Producers create new messages. In other publish/subscribe systems, these may be called publishers or writers

Producer concern flowing things:

• Generate the message (what to send ?)
• Serialize the message to Kafka format (what is the format of data ?)
• Send to topic and partitions (to where the message are sent ? )

Consumer

Consumers read messages. In other publish/subscribe systems, these clients may be called subscribers or readers.

Kafka doesn’t track the acknowledgment from consumers the way many JMS queues do.

To consume message from Kafka we need to specify following parameters:

• Topic name
• One broker

Consumer Group

Each topic partition is only consumed by one consumer of a group

Number of consumer cannot be larger than number of partition

Partition Rebalance

Poll Loop

Handle following actions:

• Coordination
• Partition rebalance
• Hearth beat
• Data fetching

Commit

The action of updating current position in the partition is commit

 

JSR 343 – JMS Concepts

Messaging: a method to communicate between components

Loosely coupled: receiver doesn’t know anything about sender, and contrary the sender doesn’t know anything about the sender.

Messaging Semantics

Point to Point (PP)

• Participant: sender, queue, receiver ( in message point of view)
• One message has at most one consumer
• Consumer actively fetch message at any point of time ( before expiration time )

Spring Data JPA listen to Postgres notification

Create trigger function

-- FUNCTION: public.table_update_notify()

-- DROP FUNCTION public.table_update_notify();

CREATE FUNCTION public.table_update_notify()
    RETURNS trigger
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE NOT LEAKPROOF
AS $BODY$
DECLARE
  id bigint;
BEGIN
  IF TG_OP = 'INSERT' OR TG_OP = 'UPDATE' THEN
    id = NEW.id;
  ELSE
    id = OLD.id;
  END IF;
  PERFORM pg_notify('employee_channel', json_build_object('table', TG_TABLE_NAME, 'id', id, 'type', TG_OP)::text);
  RETURN NEW;
END;

$BODY$;

ALTER FUNCTION public.table_update_notify()
    OWNER TO postgres;

Create a trigger into table name employee

-- Trigger: employee_notify_update

-- DROP TRIGGER employee_notify_update ON production.employee;

CREATE TRIGGER employee_notify_update
    BEFORE INSERT OR DELETE OR UPDATE
    ON production.employee
    FOR EACH ROW
    EXECUTE PROCEDURE public.table_update_notify();

Now every time, table employee changed, it fire an event with payload is information of the change

Initialize the Spring Data JPA with spring boot starter

Configuration ngoài cho ứng dụng với Spring Boot

1. Sử dụng properties file SpringApplication sẽ load các property từ tất cả các file application.properties trong các vị trí sau, và thêm chúng vào application environment: + Folder /config bên trong folder hiện tại. + Folder hiện tại. + Class path /config + Root class path Mặc định, SpringApplication sẽ load theo thứ tự từ dưới lên trên. Và các property nào load sau sẽ override property load trước. Vì lý do này, bạn cứ đặt property vào class path bình thường, khi muốn config ngoài file jar, thì sẽ đặt file application.properties vào folder /config là được. Như vậy cần phải build dự án với maven sao cho có kết quả trong folder target như sau:

+-target
    +---myapp.jar
    +---config
            +--application.properties

Sử dụng configuration class trong Spring Boot

1. Sử dụng class Configuration
Spring Boot ưu ái việc sử dụng các class Configuration. Mặc dù bạn có thể hoàn toàn sử dụng việc gọi hàm SpringApplication.run() ngay bên trong file XML, nhưng nhìn chung Spring khuyên điểm xuất phát của ứng dụng là một class với annotation @Configuration. Thông thường thì class với hàm main() thì nên là cũng là lớp chứa @Configuration.

import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.Configuration;

@Configuration
public class Application
{
    public static void main(final String[] args)
    {
        SpringApplication.run(Application.class, args);
    }
}