Spring Boot and Micrometer with InlfuxDB Part 3: Servlets and JDBC

In the previous blog we setup a reactive application with micrometer backed with an InfluxDB.

On this tutorial we shall use our old school blocking Servlet Based Spring Stack with JDBC.
My database of choice would be postgresql. I shall use the same scripts of a previous blog post.

Thus we shall have the script that initializes the database

#!/bin/bash
set -e

psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
    create schema spring_data_jpa_example;

    create table spring_data_jpa_example.employee(
        id  SERIAL PRIMARY KEY,
        firstname   TEXT    NOT NULL,
        lastname    TEXT    NOT NULL,
        email       TEXT    not null,
        age         INT     NOT NULL,
        salary         real,
        unique(email)
    );

    insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 1','john1@doe.com',18,1234.23);
    insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 2','john2@doe.com',19,2234.23);
    insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 3','john3@doe.com',20,3234.23);
    insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 4','john4@doe.com',21,4234.23);
    insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 5','john5@doe.com',22,5234.23);
EOSQL

The we shall have a docker compose file that contains InfluxDB, Postgres and Grafana.

version: '3.5'

services:
  influxdb:
    image: influxdb
    restart: always
    ports:
      - 8086:8086
  grafana:
    image: grafana/grafana
    restart: always
    ports:
      - 3000:3000
  postgres:
    image: postgres
    restart: always
    environment:
      POSTGRES_USER: db-user
      POSTGRES_PASSWORD: your-password
      POSTGRES_DB: postgres
    ports:
      - 5432:5432
    volumes:
      - $PWD/init-db-script.sh:/docker-entrypoint-initdb.d/init-db-script.sh

Now it’s time to build our spring application starting with our maven dependencies.

<?xml version="1.0" encoding="UTF-8"?>
<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>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.4.RELEASE</version>
    </parent>

    <groupId>com.gkatzioura</groupId>
    <artifactId>EmployeeApi</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
        <defaultGoal>spring-boot:run</defaultGoal>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.2.8</version>
        </dependency>
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-core</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-registry-influx</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
            <scope>provided</scope>
        </dependency>
   </dependencies>
</project>

Since this is a JDBC backed dependency we shall create the entities and the repositories.

package com.gkatzioura.employee.model;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.Data;

@Data
@Entity
@Table(name = "employee", schema="spring_data_jpa_example")
public class Employee {

	@Id
	@Column(name = "id")
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Long id;

	@Column(name = "firstname")
	private String firstName;

	@Column(name = "lastname")
	private String lastname;

	@Column(name = "email")
	private String email;

	@Column(name = "age")
	private Integer age;

	@Column(name = "salary")
	private Integer salary;

}

Then let’s add the Repository

package com.gkatzioura.employee.repository;

import com.gkatzioura.employee.model.Employee;
import org.springframework.data.jpa.repository.JpaRepository;

public interface EmployeeRepository extends JpaRepository<Employee,Long> {
}

And the controller

package com.gkatzioura.employee.controller;

import java.util.List;

import com.gkatzioura.employee.model.Employee;
import com.gkatzioura.employee.repository.EmployeeRepository;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class EmployeeController {

	private final EmployeeRepository employeeRepository;

	public EmployeeController(EmployeeRepository employeeRepository) {
		this.employeeRepository = employeeRepository;
	}

	@RequestMapping("/employee")
	public List<Employee> getEmployees() {
		return employeeRepository.findAll();
	}

}

Last but not least the Application class

package com.gkatzioura.employee;


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

@SpringBootApplication
public class Application {

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

As well the configuration

spring:
  datasource:
    platform: postgres
    driverClassName: org.postgresql.Driver
    username: db-user
    password: your-password
    url: jdbc:postgresql://127.0.0.1:5432/postgres
management:
  metrics:
    export:
      influx:
        enabled: true
        db: employeeapi
        uri: http://127.0.0.1:8086
  endpoints:
    web:
      expose: "*"

Let’s try it

curl http://localhost:8080/employee

After some requests we can find the entries persisted.

docker exec -it influxdb-local influx
> SHOW DATABASES;
name: databases
name
----
_internal
employeeapi
> use employeeapi
Using database employeeapi
> SHOW MEASUREMENTS
name: measurements
name
----
hikaricp_connections
hikaricp_connections_acquire
hikaricp_connections_active
hikaricp_connections_creation
hikaricp_connections_idle
hikaricp_connections_max
hikaricp_connections_min
hikaricp_connections_pending
hikaricp_connections_timeout
hikaricp_connections_usage
http_server_requests
jdbc_connections_active
jdbc_connections_idle
jdbc_connections_max
jdbc_connections_min
jvm_buffer_count
jvm_buffer_memory_used
jvm_buffer_total_capacity
jvm_classes_loaded
jvm_classes_unloaded
jvm_gc_live_data_size
jvm_gc_max_data_size
jvm_gc_memory_allocated
jvm_gc_memory_promoted
jvm_gc_pause
jvm_memory_committed
jvm_memory_max
jvm_memory_used
jvm_threads_daemon
jvm_threads_live
jvm_threads_peak
jvm_threads_states
logback_events
process_cpu_usage
process_files_max
process_files_open
process_start_time
process_uptime
system_cpu_count
system_cpu_usage
system_load_average_1m
tomcat_sessions_active_current
tomcat_sessions_active_max
tomcat_sessions_alive_max
tomcat_sessions_created
tomcat_sessions_expired
tomcat_sessions_rejected

As you can see the metrics are a bit different from the previous example. We have jdbc connection metrics tomcat metrics and all metrics relevant to our application.
You can find the sourcecode on github.

Debug your container by overriding the command.

The main problem with docker on debugging has to do with images that already have the DockerImageCMD command specified.

If something goes wrong and has to do with the filesystem, or some commands that should have taken effect and they did not you need to do some troubleshooting.

Overriding the command which is executed should be helpful. I do this all the time on custom images since I need some bash in order to be able to troubleshoot.

Supposing I need to troubleshoot something on the default nginx image.

Then nginx image should run like this.

docker run --rm nginx

Now instead of running our server, we shall override the command with a bash session (enter a shell by executing /bin/sh).


docker run --rm -it --entrypoint "/bin/sh" nginx

If you also want to pass arguments to the executable specified there is also another workaround.


docker run --rm -it --entrypoint "ls" nginx -l

 

 

Spring Boot & Hibernate: Print queries and variables

It’s late in the office and you are stuck with this strange Jpa code with JoinColumns and cascades and you cannot find what goes wrong. You wish there is a way to view the icon-spring-frameworkqueries printed and also the values.
With a little tweaking to your Spring Boot application this is possible.

 

With the help of lombock heres is our jpa model.

package com.gkatzioura.hibernatelog.dao;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.Data;

@Data
@Entity
@Table(name = "application_user")
public class ApplicationUser {

    @Id
    private Long id;

    private String username;

    private String password;

}

It’s repository

package com.gkatzioura.hibernatelog.dao;

import org.springframework.data.repository.CrudRepository;

public interface ApplicationUserRepository extends CrudRepository {
}

A not found exception

package com.gkatzioura.hibernatelog.controller;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ResponseStatus;

@ResponseStatus(value = HttpStatus.NOT_FOUND)
class ApplicationUserNotFoundException extends RuntimeException {

    public ApplicationUserNotFoundException() {
    }

    public ApplicationUserNotFoundException(String message) {
        super(message);
    }

    public ApplicationUserNotFoundException(String message, Throwable cause) {
        super(message, cause);
    }

    public ApplicationUserNotFoundException(Throwable cause) {
        super(cause);
    }

    public ApplicationUserNotFoundException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}

And a controller

package com.gkatzioura.hibernatelog.controller;

import java.util.Optional;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.gkatzioura.hibernatelog.dao.ApplicationUser;
import com.gkatzioura.hibernatelog.dao.ApplicationUserRepository;

@RestController
public class ApplicationUserController {

    private final ApplicationUserRepository applicationUserRepository;

    public ApplicationUserController(ApplicationUserRepository applicationUserRepository) {
        this.applicationUserRepository = applicationUserRepository;
    }

    @GetMapping("/user/{id}")
    @ResponseBody
    public ApplicationUser getApplicationUser(@PathVariable Long id) {
        Optional applicationUser = applicationUserRepository.findById(id);
        if(applicationUser.isPresent()) {
            return applicationUser.get();
        } else {
            throw new ApplicationUserNotFoundException();
        }
    }

}

By adding the following to application.yaml we ensure the creation of the table through hibernate, the logging of the queries, the formatting of the sql queries logged and also the actual parameters values displayed.

spring:
  jpa:
    hibernate:
      ddl-auto: create
    properties:
      hibernate:
        show_sql: true
        use_sql_comments: true
        format_sql: true
logging:
  level:
    org:
      hibernate:
        type: trace

Just

curl http://localhost:8080/user/1

And you got your logs.

Docker compose: run stack dynamically

I use docker compose every day for my local development needs.

DockerImage

During the day I might turn on/off various databases or servers thus I need to do it fast and in a managed way.

Usually your docker-compose files contains the configuration for many containers, network, volumes etc.

stack.yaml

version: '3.5'

services:
  mongo:
    image: mongo
    restart: always
    ports:
      - 27017:27017
    environment:
      MONGO_INITDB_ROOT_USERNAME: username
      MONGO_INITDB_ROOT_PASSWORD: password
  mongo-express:
    image: mongo-express
    restart: always
    ports:
      - 8081:8081
    environment:
      ME_CONFIG_MONGODB_ADMINUSERNAME: username
      ME_CONFIG_MONGODB_ADMINPASSWORD: password

This works if you always want the same services up and running.

However it does have a cost on resources, and most of the times you don’t need the full stack.

What you can do in this cases, would be to split them into files and choose what to use.

mongo.yaml

version: '3.5'

services:
  mongo:
    image: mongo
    restart: always
    ports:
      - 27017:27017
    environment:
      MONGO_INITDB_ROOT_USERNAME: username
      MONGO_INITDB_ROOT_PASSWORD: password

express.yaml

version: '3.5'

services:
  mongo-express:
    image: mongo-express
    restart: always
    ports:
      - 8081:8081
    environment:
      ME_CONFIG_MONGODB_ADMINUSERNAME: username
      ME_CONFIG_MONGODB_ADMINPASSWORD: password

Then choosing what to use becomes very easy, just omit the file

docker-compose -f mongo.yaml -f express.yaml up

Create a wildcard certificate using let’s encrypt manually

Let’s encrypt has become the number one choice on certificates since it is free and although it is short lived, there is an abundance of tools out there making sure that your certificate will be updated on time.
This post will go through creating a wildcard let’s encrypt certificate using the dns challenge.
All you need is a domain name registered and you being able to add a txt dns record.

I assume you have the latest version of certbot installed. If not you can always run certbot through docker.

docker run -it --entrypoint=/bin/sh certbot/certbot

First step is to issue

certbot certonly --server https://acme-v02.api.letsencrypt.org/directory --work-dir ./work-dir/ --config-dir ./config-dir --logs-dir ./logs-dir/ --manual --preferred-challenges dns -d *.{your domain name}

You will have some questions on the command prompt which you should answer.
Once done you will end up with a screen asking you to take action and add a DNS txt record.

Please deploy a DNS TXT record under the name
_acme-challenge.{your domain} with the following value:

Once you put the entry to your dns record you need to wait until your txt record gets propagated

One of the ways to check if it is ready, is to use the nslookup method on another terminal.

nslookup -type=TXT _acme-challenge.{your domain}

This might take a while so feel free to use the watch command

watch -n 1 nslookup -type=TXT _acme-challenge.{your domain}

Once done you can press enter and your let’s encrypt certificates shall be generated and this would be the result on your screen.

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   {path}/fullchain.pem
   Your key file has been saved at:
   {path}privkey.pem
   Your cert will expire on 2018-08-28. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le

Now that you have your chain certificate and your private key and your are ready to use them to your applications.

Spring boot and Spring data JPA integration

Nowadays spring and JPA integration has become a piece of cake thanks to Spring Boot and spring Data.

I am gonna setup a postgresql server

docker pull postgres
#run the container
docker run --name postgreslocal -e POSTGRES_PASSWORD=postgres -d postgres
#get the ip
docker inspect --format '{{ .NetworkSettings.IPAddress }}' postgreslocal
#get the port
docker inspect --format '{{ .NetworkSettings.Ports }}' postgreslocal

Create the employees Table

create schema spring_data_jpa_example;

create table spring_data_jpa_example.employee(
	id  SERIAL PRIMARY KEY,
	firstname	TEXT	NOT NULL,
	lastname	TEXT	NOT NULL,	
   	email		TEXT 	not null,
   	age         INT     NOT NULL,
   	salary         real,
	unique(email)
);

insert into spring_data_jpa_example.employee (firstname,lastname,email,age,salary) 
values ('Emmanouil','Gkatziouras','gkatzioura@gmail.com',18,3000.23);

Let’s begin with our gradle file

group 'com.gkatzioura'
version '1.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.8

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.3.3.RELEASE")
    }
}

apply plugin: 'idea'
apply plugin: 'spring-boot'

repositories {
    mavenCentral()
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web") {
        exclude module: "spring-boot-starter-tomcat"
    }
    compile("org.postgresql:postgresql:9.4-1206-jdbc42")
    compile("org.springframework.boot:spring-boot-starter-jetty")
    compile("org.springframework.boot:spring-boot-starter-data-jpa:1.3.3.RELEASE")
    compile("com.mchange:c3p0:0.9.5.2")
    testCompile("junit:junit:4.11");
}

As you see we added the c3p0 connection pool, the spring-boot-starter-data-jpa for hibernate and the postgres driver. That’s all we need.

The Application class

package com.gkatzioura.springdata.jpa;

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

/**
 * Created by gkatzioura on 6/2/16.
 */
@SpringBootApplication
public class Application {


    public static void main(String[] args) {

        SpringApplication springApplication = new SpringApplication();
        ApplicationContext ctx = springApplication.run(Application.class, args);
    }
}

The DataSource configuration

package com.gkatzioura.springdata.jpa.config;

import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

/**
 * Created by gkatzioura on 6/2/16.
 */
@Configuration
public class DataSourceConfig {

    @Bean
    public DataSource createDataSource() throws Exception {

        ComboPooledDataSource ds = new ComboPooledDataSource();
        ds.setJdbcUrl("jdbc:postgresql://172.17.0.3:5432/postgres?user=postgres&password=postgres");
        ds.setDriverClass("org.postgresql.Driver");

        return ds;
    }

}

Our entity for the table employee

package com.gkatzioura.springdata.jpa.persistence.entity;

import javax.persistence.*;

/**
 * Created by gkatzioura on 6/2/16.
 */
@Entity
@Table(name = "employee", schema="spring_data_jpa_example")
public class Employee {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Long id;

    @Column(name = "firstname")
    private String firstName;

    @Column(name = "lastname")
    private String lastname;

    @Column(name = "email")
    private String email;

    @Column(name = "age")
    private Integer age;

    @Column(name = "salary")
    private Integer salary;

    public Long getId() {
        return id;
    }

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

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getSalary() {
        return salary;
    }

    public void setSalary(Integer salary) {
        this.salary = salary;
    }
}

The repository that will help us access all users

package com.gkatzioura.springdata.jpa.persistence.repository;

import com.gkatzioura.springdata.jpa.persistence.entity.Employee;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

/**
 * Created by gkatzioura on 6/2/16.
 */
public interface EmployeeRepository extends JpaRepository<Employee,Long>{
}

And a controller that will fetch all the data

package com.gkatzioura.springdata.jpa.controller;

import com.gkatzioura.springdata.jpa.persistence.entity.Employee;
import com.gkatzioura.springdata.jpa.persistence.repository.EmployeeRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * Created by gkatzioura on 6/2/16.
 */
@RestController
public class TestController {

    @Autowired
    private EmployeeRepository employeeRepository;

    @RequestMapping("/employee")
    public List<Employee> getTest() {

        return employeeRepository.findAll();
    }
}

Pretty convenient considering the dependencies and the xml configuration overhead of the past.

You can find the source code on github .

Systemd and Upstart Services

Most linux servers that I use are either Debian based or RedHat based.

A common task is adding daemon services.

Suppose that we want to start a tomcat application on startup

First we shall install tomcat

mkdir /opt/tomcat
groupadd tomcat
useradd -s /bin/false -g tomcat -d /opt/tomcat tomcat
wget http://apache.cc.uoc.gr/tomcat/tomcat-8/v8.0.33/bin/apache-tomcat-8.0.33.tar.gz
tar xvf apache-tomcat-8.0.33.tar.gz
mv apache-tomcat-8.0.33/* /opt/tomcat
rm -r apache-tomcat-8.0.33 apache-tomcat-8.0.33.tar.gz 
cd /opt/tomcat
chgrp -R tomcat conf
chmod g+rwx conf
chmod g+r conf/*
chown -R tomcat work/ temp/ logs/

In case of Systemd we should add a tomcat.service file on /etc/systemd/system.
The file /etc/systemd/system/tomcat.service shall contain

[Unit]
Description=Apache Tomcat Web Application Container
After=syslog.target network.target

[Service]
Type=forking

Environment=JAVA_HOME=/usr/java/default
Environment=CATALINA_PID=/opt/tomcat/temp/tomcat.pid
Environment=CATALINA_HOME=/opt/tomcat
Environment=CATALINA_BASE=/opt/tomcat
Environment='CATALINA_OPTS=-Xms512M -Xmx1024M -server -XX:+UseParallelGC'
Environment='JAVA_OPTS=-Duser.timezone=UTC -Djava.awt.headless=true -Djava.security.egd=file:/dev/./urandom'

ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/bin/kill -15 $MAINPID

User=tomcat
Group=tomcat

[Install]
WantedBy=multi-user.target

I specified the script to start after syslog and network are enabled
As we can see systemd handles the tomcat as a daemon and kills the pid.
With User and Group we specify the user and the group that the process should be run as.
Systemd will handle the upstart process and kill it using the PID.

to enable and run you have to issue

systemctl enable tomcat
systemctl start tomcat

In case of upstart we should create a tomcat.conf file in /etc/init/
The content of /etc/init/tomcat.conf

description     "Tomcat instance"
author          "Emmanouil Gkatziouras"

respawn
respawn limit 2 5

start on runlevel [2345]
stop on runlevel [!2345]

setuid tomcat
setgid tomcat

env CATALINA_HOME=/opt/tomcat

script
        $CATALINA_HOME/bin/catalina.sh run
end script

post-stop script
        rm -rf $CATALINA_HOME/temp/*
end script

It will start on run levels 2,3,4 or 5
The group and the user id to be executed would be tomcat
After tomcat is stopped the post script block will remove the temp files.
Instead of starting the process inn the background as a daemon,, upstart will handle the process on the foreground.

To start just issue

sudo initctl start tomcat

Async for Node.js

Async module for node.js saves the day when it comes to synchronizing asynchronous tasks, or executing them in a serial manner.

To execute tasks in order, you can use the series method.


var async = require('async');

var somethingAsynchronous = function(callback) { 
    console.log('Called something asynchronous'); 
    callback(); 
};

var somethingElseAsynchronous = function(callback) { 
    console.log('called something else asynchronous'); 
    callback() 
};

async.series([
function(callback) {
  somethingAsynchronous(function(err,result) {
    if(err) {
      callback(err);
    } else {
      callback(result);
    }
  });
},
function(callback) {
  somethingElseAsynchronous(function(err,result) {
    if(err) {
      callback(err);
    } else {
      callback(result);
    }
  });
],function(err,result) {

});

To execute tasks in order and use the results of previous tasks, you have to use the waterfall method.
The last function specified will handle the result of the tasks executed. When an error occurs prior to executing all the specified tasks, then the other tasks will not execute and the last function will handle the error.


var somethingAsynchronous = function(callback) { 
    callback(null,'This is a result'); 
};

var somethingElseAsynchronous = function(firstResult,callback) { 
   callback(null,firstResult+" and this is appended");
};

async.waterfall([
  function (callback){
    somethingAsynchronous(callback);
  },
  function(result,callback) {
    somethingElseAsynchronous(result,callback);
  }
],
function(err,result) {
  console.log('The end result is: '+result);
});

The method parallel is used to execute tasks in parallel and synchronize them after their execution.


var somethingAsynchronous = function(callback) { 
    
    /*
        Asynchronous code
    */
    
    callback(null,'23'); 
};

var somethingElseAsynchronous = function(callback) { 

    /*
        Asynchronous code
    */
    
    callback(null,'sad');
};

async.parallel([
somethingAsynchronous,
somethingElseAsynchronous
],function(err,result){
  console.log('The result is '+result);
});

In case of an array of objects that need to be processed in an asynchronous manner then we can use map.


var items = ['a','b','c','d'];

async.map(items,function(item,callback) {

   callback(null,'Did something asynchronous with '+item);
},
function(err,results){

  results.forEach(function(result) {
      console.log(result);
  });
});

Integrate MongoDB to your Spring project

This article shows how to integrate MongoDB to your spring project through annotation configuration.

We will begin with our Gradle configuration.

group 'com.gkatzioura.spring'
version '1.0-SNAPSHOT'


buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.7.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'spring-boot'

jar {
    baseName = 'mdb-spring-boot'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {


    compile("org.springframework.boot:spring-boot-starter-web")


    compile('com.googlecode.json-simple:json-simple:1.1.1')
    compile("org.springframework.boot:spring-boot-starter-actuator")
    compile("org.springframework.data:spring-data-mongodb:1.8.0.RELEASE")
    compile("ch.qos.logback:logback-classic:1.1.3")
    compile("ch.qos.logback:logback-core:1.1.3")
    compile("org.json:json:20150729")
    compile("com.google.code.gson:gson:2.4")

    compile("org.slf4j:slf4j-api:1.7.12")

    testCompile("junit:junit")
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

task wrapper(type: Wrapper) {
    gradleVersion = '2.3'
}

We will proceed with the MongoDB configuration using spring annotations.

package com.gkatzioura.spring.config;

import com.mongodb.MongoClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.MongoDbFactory;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.SimpleMongoDbFactory;

import java.net.UnknownHostException;

/**
 * Created by oSeven3 on 21/10/2015.
 */
@Configuration
public class MongoDbConfiguration {

    public @Bean MongoDbFactory getMongoDbFactory() throws UnknownHostException {
        return new SimpleMongoDbFactory(new MongoClient("localhost",27017),"mongotest");
    }

    public @Bean(name = "mongoTemplate") MongoTemplate getMongoTemplate() throws UnknownHostException {

        MongoTemplate mongoTemplate = new MongoTemplate(getMongoDbFactory());
        return mongoTemplate;
    }

}

Next we will define our model.
We shall create the Location model which will contain the latitude longitude.

package com.gkatzioura.spring.persistence.entities;

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

import java.math.BigDecimal;
import java.util.Date;
import java.util.UUID;

@Document(collection = "location")
public class Location {

    @Id
    private String id;
    private BigDecimal latitude;
    private BigDecimal longitude;
    private Date timestamp;

    public String getId() {
        return id;
    }

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

    public BigDecimal getLatitude() {
        return latitude;
    }

    public void setLatitude(BigDecimal latitude) {
        this.latitude = latitude;
    }

    public BigDecimal getLongitude() {
        return longitude;
    }

    public void setLongitude(BigDecimal longitude) {
        this.longitude = longitude;
    }

    public Date getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(Date timestamp) {
        this.timestamp = timestamp;
    }
}

Then we shall create our repository

package com.gkatzioura.spring.persistence.repositories;

import com.gkatzioura.spring.persistence.entities.Location;
import org.springframework.data.repository.CrudRepository;

import java.util.UUID;

public interface LocationRepository extends CrudRepository<Location,String> {
}

Then we shall define our controller

package com.gkatzioura.spring.controller;

import com.gkatzioura.spring.persistence.entities.Location;
import com.gkatzioura.spring.persistence.repositories.LocationRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

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

import java.io.IOException;

/**
 * Created by oSeven3 on 21/10/2015.
 */

@RestController
@RequestMapping("/location")
public class LocationController {

    @Autowired
    private LocationRepository locationRepository;

    private static final Logger LOGGER = LoggerFactory.getLogger(LocationRepository.class);

    @RequestMapping(value = "/",method = RequestMethod.POST)
    @ResponseBody
    public String post(@RequestBody Location location) {

        locationRepository.save(location);

        return "OK";
    }

    @RequestMapping(value = "/",method = RequestMethod.GET)
    @ResponseBody
    public List<Location> get() {

        List<Location> locations = new ArrayList<>();
        locationRepository.findAll().forEach(l->locations.add(l));
        return locations;
    }

}

Last but not least our Application class

package com.gkatzioura.spring;

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

/**
 * Created by gkatziourasemmanouil on 8/15/15.
 */
@SpringBootApplication
public class Application {

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

}

In order to run just run

gradle bootRun

Why I use Node.js

It has been a while since I took up Node.js development.
My early impressions were pretty positive and after some months of Node.js development I have to say that I am amazed.

There are many reasons to continue using Node.js for my projects.

Great for applications with heavy I/O

The asynchronous nature of Node.js enables you to stay focused on your implementation. You don’t need to proceed to any extra configurations as you do with multithreaded environments. Also long I/O operations don’t have to be dispatched to any custom mechanisms, enabling you to avoid any extra costs on development.
Provided your application is mostly based on I/O and less on computation, chances are that Node.js will work for you.

Bootstrapping

Node.js is one of the most bootstrapping experiences that I had with a programming environment. All you need is to have node and npm installed. There are libraries for almost everything you need and the configurations needed are minimal.
Also getting started with the implementation of your Node.js extension takes you no time at all.

Set up Simplicity

All it takes to setup your project is your source code and a package.json file with your dependencies.

Make use of your Javascript skills

Although a backend developer I had to write some javascript in the past. The same applies to other developers I know, even to the most backend focused. Learning a language is an investment.You can make more out of your javascript knowledge, by using Node.js on your projects provided it suits to their needs.

Not another web framework

Node.js is not another web application framework. Due to It’s asynchronous nature and efficiency it can be applied to many problems. For example it can be used as a glue among components of your infrastructure. Also due to heavy development you don’t just have a runtime environment, you have a whole ecosystem with tools that apply to a wide variety of problems.

Conclusion

Node.js is already a part of the tools that I use on a daily basis. However it should be used wise and make sure that it fits your project’s nature.
It is really challenging to deal with the callback hell, but in exchange you get a pretty promising and fast growing ecosystem.