Category: Postgresql

Debezium Server with PostgreSQL and Redis Stream

Debezium is a great tool for capturing the row level changes that happen on a Database and stream those changes to a broker of our choice.

Since this functionality stays in the boundaries of a Database, it helps on keeping our applications simple. For example there in no need for an application to emit events on any database interactions. Debezium will monitor the row changes and will emit the events. Based on the broker solution used with Debezium a consumer can subscribe to the broker thus receive the changes.

PostgreSQL being a popular SQL database, it is supported by Debezium.

Our goal would be to listen to PostgreSQL changes and stream them to a Redis stream through a Debezium Server. It is common to use Debizum with Kafka, in case where Kafka is not present in a team’s Tech stack we can use other brokers.

In our case we would keep things lightweight by using Redis Streams.

Redis will be setup without any extra configurations.

In order to use PostgreSQL with Debezium it is essentials to alter the configuration on postgreSQL.

The configuration we shall use on postgreSQL will be the following

listen_addresses = '*'
port = 5432
max_connections = 20
shared_buffers = 128MB
temp_buffers = 8MB
work_mem = 4MB
wal_level = logical
max_wal_senders = 3

As we can see we use the logical_decoding from PostgreSQL.
From the documentation:

Logical decoding is the process of extracting all persistent changes to a database’s tables into a coherent, easy to understand format which can be interpreted without detailed knowledge of the database’s internal state.

In PostgreSQL, logical decoding is implemented by decoding the contents of the write-ahead log, which describe changes on a storage level, into an application-specific form such as a stream of tuples or SQL statements.

We will also create a namespace and a table for PostgreSQL. The namespace and the table will be the ones to listen for changes.

#!/bin/bash
set -e

psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
  create schema test_schema;
  create table test_schema.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)
      );
EOSQL

This is the table we used in a previous PostgreSQL example.

Debezium will have to be able to interact with the PostgreSQL server as well as the the redis server.
The configuration should be the following.

debezium.sink.type=redis
debezium.sink.redis.address=redis:6379
debezium.source.connector.class=io.debezium.connector.postgresql.PostgresConnector
debezium.source.offset.storage.file.filename=data/offsets.dat
debezium.source.offset.flush.interval.ms=0
debezium.source.database.hostname=postgres
debezium.source.database.port=5432
debezium.source.database.user=postgres
debezium.source.database.password=postgres
debezium.source.database.dbname=postgres
debezium.source.database.server.name=tutorial
debezium.source.schema.whitelist=test_schema
debezium.source.plugin.name=pgoutput

By examining the configuration we can see that we have the necessary information for Debezium to communicate to the PostgreSQL database, also we specify the schema that we created previously. Therefore only changes from that schema will be streamed. We can also make things more restrictive for example whitelisting tables.

Since this demo will involve three different software Components docker compose will come in handy.

version: '3.1'

services:
  redis:
    image: redis
    ports:
      - 6379:6379
    depends_on:
      - postgres
  postgres:
    image: postgres
    restart: always
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
    volumes:
      - ./postgresql.conf:/etc/postgresql/postgresql.conf
      - ./init:/docker-entrypoint-initdb.d
    command:
      - "-c"
      - "config_file=/etc/postgresql/postgresql.conf"
    ports:
      - 5432:5432
  debezium:
    image: debezium/server
    volumes:
      - ./conf:/debezium/conf
      - ./data:/debezium/data
    depends_on:
      - redis

By using Compose we were able to spin up three different software components on the same network. This helps the components to interact with each other by using the dns names of the services as specified on Compose. Also the configuration files we created previously are mounted to the Docker containers. Docker Compose V2 is out there with many good features, you can find more about it on the book I authored
A Developer’s Essential Guide to Docker Compose.

In order to get the stack running we shall execute the following command

$ docker compose up

Since it is up and running, we can now start listening for events.

We shall login to Redis and start listen for any possible database updates.

$ docker exec -it debezium-example-redis-1 redis-cli
> xread block 1000000 streams tutorial.test_schema.employee $

This will make it possible to block until we receive one event from the stream.
If we examine the stream name we should see the pattern of {server-name}.{schema}.{table}. This would allow consumers to subscribe only to the changes of interest.

Onwards we will make an entry.

$ docker exec -it debezium-example-postgres-1 psql postgres postgres
> insert into test_schema.employee (firstname,lastname,email,age,salary) values ('John','Doe 1','john1@doe.com',18,1234.23);
> \q

If we check the redis session we should see that we received an event from the Redis stream

127.0.0.1:6379> xread block 1000000 streams tutorial.test_schema.employee $
1) 1) "tutorial.test_schema.employee"
   2) 1) 1) "1663796657336-0"
         2) 1) "{\"schema\":{\"type\":\"struct\",\"fields\":[{\"type\":\"int32\",\"optional\":false,\"default\":0,\"field\":\"id\"}],\"optional\":false,\"name\":\"tutorial.test_schema.employee.Key\"},\"payload\":{\"id\":1}}"
            2) "{\"schema\":{\"type\":\"struct\",\"fields\":[{\"type\":\"struct\",\"fields\":[{\"type\":\"int32\",\"optional\":false,\"default\":0,\"field\":\"id\"},{\"type\":\"string\",\"optional\":false,\"field\":\"firstname\"},{\"type\":\"string\",\"optional\":false,\"field\":\"lastname\"},{\"type\":\"string\",\"optional\":false,\"field\":\"email\"},{\"type\":\"int32\",\"optional\":false,\"field\":\"age\"},{\"type\":\"float\",\"optional\":true,\"field\":\"salary\"}],\"optional\":true,\"name\":\"tutorial.test_schema.employee.Value\",\"field\":\"before\"},{\"type\":\"struct\",\"fields\":[{\"type\":\"int32\",\"optional\":false,\"default\":0,\"field\":\"id\"},{\"type\":\"string\",\"optional\":false,\"field\":\"firstname\"},{\"type\":\"string\",\"optional\":false,\"field\":\"lastname\"},{\"type\":\"string\",\"optional\":false,\"field\":\"email\"},{\"type\":\"int32\",\"optional\":false,\"field\":\"age\"},{\"type\":\"float\",\"optional\":true,\"field\":\"salary\"}],\"optional\":true,\"name\":\"tutorial.test_schema.employee.Value\",\"field\":\"after\"},{\"type\":\"struct\",\"fields\":[{\"type\":\"string\",\"optional\":false,\"field\":\"version\"},{\"type\":\"string\",\"optional\":false,\"field\":\"connector\"},{\"type\":\"string\",\"optional\":false,\"field\":\"name\"},{\"type\":\"int64\",\"optional\":false,\"field\":\"ts_ms\"},{\"type\":\"string\",\"optional\":true,\"name\":\"io.debezium.data.Enum\",\"version\":1,\"parameters\":{\"allowed\":\"true,last,false,incremental\"},\"default\":\"false\",\"field\":\"snapshot\"},{\"type\":\"string\",\"optional\":false,\"field\":\"db\"},{\"type\":\"string\",\"optional\":true,\"field\":\"sequence\"},{\"type\":\"string\",\"optional\":false,\"field\":\"schema\"},{\"type\":\"string\",\"optional\":false,\"field\":\"table\"},{\"type\":\"int64\",\"optional\":true,\"field\":\"txId\"},{\"type\":\"int64\",\"optional\":true,\"field\":\"lsn\"},{\"type\":\"int64\",\"optional\":true,\"field\":\"xmin\"}],\"optional\":false,\"name\":\"io.debezium.connector.postgresql.Source\",\"field\":\"source\"},{\"type\":\"string\",\"optional\":false,\"field\":\"op\"},{\"type\":\"int64\",\"optional\":true,\"field\":\"ts_ms\"},{\"type\":\"struct\",\"fields\":[{\"type\":\"string\",\"optional\":false,\"field\":\"id\"},{\"type\":\"int64\",\"optional\":false,\"field\":\"total_order\"},{\"type\":\"int64\",\"optional\":false,\"field\":\"data_collection_order\"}],\"optional\":true,\"field\":\"transaction\"}],\"optional\":false,\"name\":\"tutorial.test_schema.employee.Envelope\"},\"payload\":{\"before\":null,\"after\":{\"id\":1,\"firstname\":\"John\",\"lastname\":\"Doe 1\",\"email\":\"john1@doe.com\",\"age\":18,\"salary\":1234.23},\"source\":{\"version\":\"1.9.5.Final\",\"connector\":\"postgresql\",\"name\":\"tutorial\",\"ts_ms\":1663796656393,\"snapshot\":\"false\",\"db\":\"postgres\",\"sequence\":\"[null,\\\"24289128\\\"]\",\"schema\":\"test_schema\",\"table\":\"employee\",\"txId\":738,\"lsn\":24289128,\"xmin\":null},\"op\":\"c\",\"ts_ms\":1663796657106,\"transaction\":null}}"
(10.17s)
127.0.0.1:6379>

How cool is that? We can now start streaming our databases changes to the broker of our choice.

You can find the source code on GitHub.

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Run a docker PostgreSQL instance locally for Testing

Running a PostgreSQL instance ad-hoc for testing is not always as bootstraping as it should be. This blog will run a PostgreSQL instance that connects to your workstation’s network and instead of using one of the popular tools like dbeaver we shall use the client that comes with the instance. Also we shall run a bootstrap script to have some data pre-inserted.

Let’s get started by running the instance. On purpose I will use another port. On scenarios of multiple instances running in your workstation, port collisions are likely. The workaround would be to choose port 5433.

docker run --rm --name test-instance -e POSTGRES_PASSWORD=password -p 5433:5432 postgres

This will run PostgreSQL and you shall be able to connect to port 5433. On a CTRL-C the instance will be stopped and destroyed.

Now instead of using an external tool to connect let’s use the instance itself, it comes with psql pre-installed.

docker exec -it test-instance /bin/bash
> psql postgres postgres
postgres=# \h
Available help:
  ABORT                            ALTER TRIGGER                    CREATE RULE                      DROP GROUP                       LISTEN
  ALTER AGGREGATE                  ALTER TYPE                       CREATE SCHEMA                    DROP INDEX                       LOAD
  ALTER COLLATION                  ALTER USER                       CREATE SEQUENCE                  DROP LANGUAGE                    LOCK
.....
postgres=# \q

The instance works and connections from the outside are possible.

Next step would be to bootstrap a db initialization script.

#!/bin/bash
set -e
 
psql -v ON_ERROR_STOP=1 --username postgres --dbname postgres <<-EOSQL
    create schema test_schema;
 
    create table test_schema.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 test_schema.employee (firstname,lastname,email,age,salary)
    values ('John','Doe 1','john1@doe.com',18,1234.23);

EOSQL

Supposing the file with the script is called init_db.sh

Let’s run the command with the initialization schema mounted.

docker run --rm --name test-instance -v /path/to/init_db.sh:/docker-entrypoint-initdb.d/init-db-script.sh -e POSTGRES_PASSWORD=password -p 5433:5432 postgres

And let’s check the results.

docker exec -it test-instance /bin/bash
>psql postgres postgres
postgres=# SELECT*FROM test_schema.employee;
 id | firstname | lastname |     email     | age | salary
----+-----------+----------+---------------+-----+---------
  1 | John      | Doe 1    | john1@doe.com |  18 | 1234.23
(1 row)

That’s it! You created a Postgresql database through docker, you did connect to it also you added a bootstrap script with data.

Read replicas and Spring Data Part 4: Configuring the read repository

Previously we set up two EntityManagers in the same application. One for the reads and one for the writes. Now it’s time to create our read repository.

The read only repository will use the secondary read only EntityManager.

In order to make it a read only repository, it is essential not to have any save and persist actions.

package com.gkatzioura.springdatareadreplica.repository;

import java.util.List;

import org.springframework.data.repository.Repository;

import com.gkatzioura.springdatareadreplica.config.ReadOnlyRepository;
import com.gkatzioura.springdatareadreplica.entity.Employee;

/**
 * This is a read only repository
 */
public interface ReadEmployeeRepository extends Repository {

    List findAll();

}

Our next task would be to create this repository with the read database entity manager.
This means that all repositories shall be created using the default entity manager except from the read only repositories.

I would create an Annotation first. This annotation will declare my repository as Read only. Also I will use this annotation for the scanning operation so that the appropriate EntityManager will be used.

package com.gkatzioura.springdatareadreplica.config;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
public @interface ReadOnlyRepository {
}

Now I know that spring boot removes the need for annotations and does repository creation in an automated way however our case is a peculiar one.

By making some adjustments our read only repository will look like this

package com.gkatzioura.springdatareadreplica.repository;

import java.util.List;

import org.springframework.data.repository.Repository;

import com.gkatzioura.springdatareadreplica.config.ReadOnlyRepository;
import com.gkatzioura.springdatareadreplica.entity.Employee;

/**
 * This is a read only repository
 */
@ReadOnlyRepository
public interface ReadEmployeeRepository extends Repository {

    List findAll();

}

And now it’s time to work with our repository scanning. All the repositories will be injected with the main EntityManager except from the ones annotated with the @ReadOnlyRepository annotation.

package com.gkatzioura.springdatareadreplica.config;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

@Configuration
@EnableJpaRepositories(
        basePackages = "com.gkatzioura",
        excludeFilters = @ComponentScan.Filter(ReadOnlyRepository.class),
        entityManagerFactoryRef = "entityManagerFactory"
)
public class PrimaryEntityManagerConfiguration {

    @Value("${spring.datasource.username}")
    private String username;

    @Value("${spring.datasource.password}")
    private String password;

    @Value("${spring.datasource.url}")
    private String url;

    @Bean
    @Primary
    public DataSource dataSource() throws Exception {
        return DataSourceBuilder.create()
                                .url(url)
                                .username(username)
                                .password(password)
                                .driverClassName("org.postgresql.Driver")
                                .build();
    }

    @Bean
    @Primary
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(
            EntityManagerFactoryBuilder builder,
            @Qualifier("dataSource") DataSource dataSource) {
        return builder.dataSource(dataSource)
                      .packages("com.gkatzioura.springdatareadreplica")
                      .persistenceUnit("main")
                      .build();
    }

}

Also we will add the configuration for the read only repositories.

package com.gkatzioura.springdatareadreplica.config;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

@Configuration
@EnableJpaRepositories(
        basePackages = "com.gkatzioura",
        includeFilters= @ComponentScan.Filter(ReadOnlyRepository.class),
        entityManagerFactoryRef = "readEntityManagerFactory"
)
public class ReadOnlyEntityManagerConfiguration {

    @Value("${spring.datasource.username}")
    private String username;

    @Value("${spring.datasource.password}")
    private String password;

    @Value("${spring.datasource.readUrl}")
    private String readUrl;

    @Bean
    public DataSource readDataSource() throws Exception {
        return DataSourceBuilder.create()
                                .url(readUrl)
                                .username(username)
                                .password(password)
                                .driverClassName("org.postgresql.Driver")
                                .build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean readEntityManagerFactory(
            EntityManagerFactoryBuilder builder,
            @Qualifier("readDataSource") DataSource dataSource) {
        return builder.dataSource(dataSource)
                      .packages("com.gkatzioura.springdatareadreplica")
                      .persistenceUnit("read")
                      .build();
    }

}

The secondary entity manager will be injected only to the repositories that only have the @ReadOnlyRepository annotation.

And to show this let’s make some changes to our controller.

package com.gkatzioura.springdatareadreplica.controller;

import java.util.List;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;

import com.gkatzioura.springdatareadreplica.entity.Employee;
import com.gkatzioura.springdatareadreplica.repository.EmployeeRepository;
import com.gkatzioura.springdatareadreplica.repository.ReadEmployeeRepository;

@RestController
public class EmployeeContoller {

    private final EmployeeRepository employeeRepository;
    private final ReadEmployeeRepository readEmployeeRepository;

    public EmployeeContoller(EmployeeRepository employeeRepository,
                             ReadEmployeeRepository readEmployeeRepository) {
        this.employeeRepository = employeeRepository;
        this.readEmployeeRepository = readEmployeeRepository;
    }

    @GetMapping("/employee")
    public List getEmployees() {
        return employeeRepository.findAll();
    }

    @GetMapping("/employee/read")
    public List getEmployeesRead() {
        return readEmployeeRepository.findAll();
    }

    @PostMapping("/employee")
    @ResponseStatus(HttpStatus.CREATED)
    public void addEmployee(@RequestBody Employee employee) {
        employeeRepository.save(employee);
    }

}

As you add employees to the system the read only repository will keep fetching the old employees while the main repository will fetch all of them including the recently persisted.

Read replicas and Spring Data Part 3: Configuring two entity managers

Our previous setup works as expected. What we shall do now is to get one step further and configure two separate entity managers without affecting the functionality we achieved previously.

The first step would be to set the default entity manager configuration to a primary one.
This is the first step

package com.gkatzioura.springdatareadreplica.config;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

@Configuration
public class PrimaryEntityManagerConfiguration {

    @Value("${spring.datasource.username}")
    private String username;

    @Value("${spring.datasource.password}")
    private String password;

    @Value("${spring.datasource.url}")
    private String url;

    @Bean
    @Primary
    public DataSource dataSource() throws Exception {
        return DataSourceBuilder.create()
                                .url(url)
                                .username(username)
                                .password(password)
                                .driverClassName("org.postgresql.Driver")
                                .build();
    }

    @Bean
    @Primary
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(
            EntityManagerFactoryBuilder builder,
            @Qualifier("dataSource") DataSource dataSource) {
        return builder.dataSource(dataSource)
                      .packages("com.gkatzioura.springdatareadreplica")
                      .persistenceUnit("main")
                      .build();
    }

}

If you run your application with this configuration it will run just like our application previously.
Now it is time to configure the read only entity manager.

package com.gkatzioura.springdatareadreplica.config;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Primary;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

@Configuration
public class ReadOnlyEntityManagerConfiguration {

    @Value("${spring.datasource.username}")
    private String username;

    @Value("${spring.datasource.password}")
    private String password;

    @Value("${spring.datasource.readUrl}")
    private String readUrl;

    @Bean
    public DataSource readDataSource() throws Exception {
        return DataSourceBuilder.create()
                                .url(readUrl)
                                .username(username)
                                .password(password)
                                .driverClassName("org.postgresql.Driver")
                                .build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean readEntityManagerFactory(
            EntityManagerFactoryBuilder builder,
            @Qualifier("readDataSource") DataSource dataSource) {
        return builder.dataSource(dataSource)
                      .packages("com.gkatzioura.springdatareadreplica")
                      .persistenceUnit("read")
                      .build();
    }

}

Also I will add a method to a controller in order to save the models.

package com.gkatzioura.springdatareadreplica.controller;

import java.util.List;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;

import com.gkatzioura.springdatareadreplica.entity.Employee;
import com.gkatzioura.springdatareadreplica.repository.EmployeeRepository;

@RestController
public class EmployeeContoller {

    private final EmployeeRepository employeeRepository;

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

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

    @PostMapping("/employee")
    @ResponseStatus(HttpStatus.CREATED)
    public void addEmployee(@RequestBody Employee employee) {
        employeeRepository.save(employee);
    }

}

If you do try to add the an employee using the controller and then query the read database you shall see that no entry is being added at all.

So we have our primary entity manager up and running and we also have a secondary one. The secondary one is not used yet. The next blog focuses on putting the secondary read only entity manager in use.

Read replicas and Spring Data Part 2: Configuring the base project

In our previous post we set up multiple PostgreSQL instances with the same data.
Our next step would be to configure our spring project by using the both servers.

As stated previously we shall use some of the code taken from the Spring Boot JPA post, since we use exactly the same database.

This shall be our gradle build file

plugins {
	id 'org.springframework.boot' version '2.1.9.RELEASE'
	id 'io.spring.dependency-management' version '1.0.8.RELEASE'
	id 'java'
}

group = 'com.gkatzioura'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
}

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
	implementation 'org.springframework.boot:spring-boot-starter-web'
	implementation "org.postgresql:postgresql:42.2.8"
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

Now let’s proceed on creating the model based on the table created on the previous blog.

package com.gkatzioura.springdatareadreplica.entity;

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

@Entity
@Table(name = "employee", catalog="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;

    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;
    }

}

And the next step is to create a spring data repository.

package com.gkatzioura.springdatareadreplica.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import com.gkatzioura.springdatareadreplica.entity.Employee;

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

Also we are going to add a controller.

package com.gkatzioura.springdatareadreplica.controller;

import java.util.List;

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

import com.gkatzioura.springdatareadreplica.entity.Employee;
import com.gkatzioura.springdatareadreplica.repository.EmployeeRepository;

@RestController
public class EmployeeContoller {

    private final EmployeeRepository employeeRepository;

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

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

}

All that it takes is to just add the right properties in you application.yaml

spring:
  datasource:
    platform: postgres
    driverClassName: org.postgresql.Driver
    username: db-user
    password: your-password
    url: jdbc:postgresql://127.0.0.2:5432/postgres

Spring boot has made it possible nowadays not to bother with any JPA configurations.

This is all you need in order to run the application. Once your application is running just try to fetch the employees.

curl http://localhost:8080/employee

As you have seen we did not do any JPA configuration. Since Spring Boot 2 specifying the database url is sufficient for the auto configuration to kick in and do all this configuration for you.

However in our case we want to have multiple datasource and entity manager configurations. In the next post we shall configure the entity managers for our application.

Spring Data with JPA and @NamedQueries

If you use Spring Data and @NamedQuery annotations at your JPA entity you can easily use them in a more convenient way using the spring data repository.

On a previous blog we created a spring data project using spring boot and docker. We will use the pretty same project and enhance our repository’s functionality.

We will implement a named query that will fetch employees only if their Last Name has as many characters as the ones specified.

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")
@NamedQuery(name = "Employee.fetchByLastNameLength",
        query = "SELECT e FROM Employee e WHERE CHAR_LENGTH(e.lastname) =:length "
)
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;
    }
}

Pay extra attention to the query name and the convention we follow @{EntityName}.{queryName}.
Then we will add the method to our spring data repository.

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.data.repository.query.Param;
import org.springframework.stereotype.Repository;

import java.util.List;

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

    List<Employee> fetchByLastNameLength(@Param("length") Long length);
}

And last but not least add some functionality to our controller.

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.RequestParam;
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();
    }

    @RequestMapping("/employee/filter")
    public List<Employee> getFiltered(String firstName,@RequestParam(defaultValue = "0") Double bonusAmount) {

        return employeeRepository.getFirstNamesLikeAndBonusBigger(firstName,bonusAmount);
    }

    @RequestMapping("/employee/lastnameLength")
    public List<Employee> fetchByLength(Long length) {
        return employeeRepository.fetchByLastNameLength(length);
    }

}

You can find the source code on github.

Hibernate Caching with HazelCast: Basic configuration

Previously we went through an introduction on JPA caching, the mechanisms and what hibernate offers.

What comes next is a hibernate project using Hazelcast as a second level cache.

We will use a basic spring boot project for this purpose with JPA. Spring boot uses hibernate as the default JPA provider.
Our setup will be pretty close to the one of a previous post.
We will use postgresql with docker for our sql database.

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

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.5.1.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'

repositories {
    mavenCentral()
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    compile group: 'org.springframework.boot', name: 'spring-boot-starter-data-jpa'
    compile group: 'org.postgresql', name:'postgresql', version:'9.4-1206-jdbc42'
    compile group: 'org.springframework', name: 'spring-jdbc'
    compile group: 'com.zaxxer', name: 'HikariCP', version: '2.6.0'
    compile group: 'com.hazelcast', name: 'hazelcast-hibernate5', version: '1.2'
    compile group: 'com.hazelcast', name: 'hazelcast', version: '3.7.5'
    testCompile group: 'junit', name: 'junit', version: '4.11'
}

By examining the dependencies carefully we see the hikari pool, the postgresql driver, spring data jpa and of course hazelcast.

Instead of creating the database manually we will automate it by utilizing the database initialization feature of Spring boot.

We shall create a file called schema.sql under the resources folder.

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 ('Test','Me','test@me.com',18,3000.23);

To keep it simple and avoid any further configurations we shall put the configurations for datasource, jpa and caching inside the application.yml file.

spring:
  datasource:
    continue-on-error: true
    type: com.zaxxer.hikari.HikariDataSource
    url: jdbc:postgresql://172.17.0.2:5432/postgres
    driver-class-name: org.postgresql.Driver
    username: postgres
    password: postgres
    hikari:
      idle-timeout: 10000
  jpa:
    properties:
      hibernate:
        cache:
          use_second_level_cache: true
          use_query_cache: true
          region:
            factory_class: com.hazelcast.hibernate.HazelcastCacheRegionFactory
    show-sql: true

The configuration spring.datasource.continue-on-error is crucial since once the application relaunches, there should be a second attempt to create the database and thus a crash is inevitable.

Any hibernate specific properties reside at the spring.jpa.properties path. We enabled the second level cache and the query cache.

Also we set show-sql to true. This means that once a query hits the database it shall be logged through the console.

Then create our employee entity.

package com.gkatzioura.hibernate.enitites;

import javax.persistence.*;

import java.io.Serializable;

import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;

/**
 * Created by gkatzioura on 2/6/17.
 */
@Entity
@Table(name = "employee", schema="spring_data_jpa_example")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Employee implements Serializable {

    @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;
    }
}

Everything is setup. Spring boot will detect the entity and create an EntityManagerFactory on its own.
What comes next is the repository class for employee.

package com.gkatzioura.hibernate.repository;

import com.gkatzioura.hibernate.enitites.Employee;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.CrudRepository;

/**
 * Created by gkatzioura on 2/11/17.
 */
public interface EmployeeRepository extends JpaRepository {
}

And the last one is the controller

package com.gkatzioura.hibernate.controller;

import com.gkatzioura.hibernate.enitites.Employee;
import com.gkatzioura.hibernate.repository.EmployeeRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * Created by gkatzioura on 2/6/17.
 */
@RestController
public class EmployeeController {

    @Autowired
    private EmployeeRepository employeeRepository;

    @RequestMapping("/employee")
    public List testIt() {

        return employeeRepository.findAll();
    }

    @RequestMapping("/employee/{employeeId}")
    public Employee getEmployee(@PathVariable Long employeeId) {

        return employeeRepository.findOne(employeeId);
    }

}

Once we issue a request at
http://localhost:8080/employee/1

Console will display the query issued at the database

Hibernate: select employee0_.id as id1_0_0_, employee0_.age as age2_0_0_, employee0_.email as email3_0_0_, employee0_.firstname as firstnam4_0_0_, employee0_.lastname as lastname5_0_0_, employee0_.salary as salary6_0_0_ from spring_data_jpa_example.employee employee0_ where employee0_.id=?

The second time we issue the request, since we have the second cache enabled there won’t be a query issued upon the database. Instead the entity shall be fetched from the second level cache.

You can download the project from github.

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 .

Add ssl to Mysql and Postgresql

Adding ssl support to a relational database like mysql or postgresql is a standard task.

First we need to have our certificates ready.
We can either use mysql workbench which has a nice wizard.
Or we can create them using openssl.

In the end we will end up with three files

ssl-ca=ca.pem
ssl-cert=server-cert.pem
ssl-key=server-key.pem

We can also check that everything is ok by making a basic test.
Start an open ssl server

/usr/bin/openssl s_server -cert server-cert.pem -key server-key.pem

and a client to connect

openssl s_client -CAfile ca.pem -connect 127.0.0.1:4433

In case of no errors you are good to go.

In case of mysql we shall create a directory and put our certificates in it

mkdir /etc/mysql-ssl
mv ca.pem /etc/mysql-ssl
mv server-cert.pem /etc/mysql-ssl
mv server-key.pem /etc/mysql-ssl
chown -R mysql mysql-ssl

Now we shall edit /etc/my.cnf and on the [mysqld] section add

[mysqld]
ssl-ca=/etc/mysql-ssl/ca.pem
ssl-cert=/etc/mysql-ssl/server-cert.pem
ssl-key=/etc/mysql-ssl/server-key.pem

Now when we login to mysql by issuing show global variables like ‘%ssl%’ we get

mysql> show global variables like '%ssl%';
+---------------+--------------------------------+
| Variable_name | Value                          |
+---------------+--------------------------------+
| have_openssl  | YES                            |
| have_ssl      | YES                            |
| ssl_ca        | /etc/mysql-ssl/ca.pem          |
| ssl_capath    |                                |
| ssl_cert      | /etc/mysql-ssl/server-cert.pem |
| ssl_cipher    |                                |
| ssl_crl       |                                |
| ssl_crlpath   |                                |
| ssl_key       | /etc/mysql-ssl/server-key.pem  |
+---------------+--------------------------------+

Suppose we have a database called tutorial_database, we will create a user that will have access to it only through ssl

create user 'tutorial_user'@'%' identified by 'yourpass';
grant all privileges on tutorial_database.* to 'tutorial_user'@'%' REQUIRE SSL;;

It order to connect with this user for example by using mysql client you need 

mysql --ssl-ca=ca.pem -u tutorial_user -h yourhost -p

Using the ca.pem created previously

Now on postgresql things are easy too

Place your server certificate and your server key to your postgres data directory

cp server-cert.pem $PGDATA/server.crt
cp server-key.pem $PGDATA/server.key

Also change your server key properties or else postgresql will not start

chmod og-rwx server.key

Next step is to edit postgresql.conf and add

ssl=on

After restarting we will be able to connect through ssl to postgres. Just add the ssl setting.

psql "sslmode=require host=yourhost dbname=tutorial_database" tutorial_user

However if we want a specific user to connect to a database with ssl then we should edit pg_hba.conf

# TYPE  DATABASE          USER            ADDRESS  METHOD
hostssl tutorial_database tutorial_user   all      md5