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Common Patterns in Distributed Systems

Sample application: https://github.com/microservices-patterns/ftgo-application http://eventuate.io/exampleapps.html Microservices Patterns: https://microservices.io/patterns/index.html Enterprise Integration Patterns: https://www.enterpriseintegrationpatterns.com/patterns/messaging/ Configuration Management Centralizing configuration and secret values: AWS Secrets Manager AWS Key Management Service Apache ZooKeeper Spring Cloud Config (Spring Cloud Vault, Spring Cloud Zookeeper) etcd – distributed reliable key-value store Service Discovery Client make request to Service Registry or Load Balancer (Router): Apache […]

PostgreSQL quick start

How to install PostgreSQL with brew:

$ brew search postgresql
$ brew install postgresql

1 2	$ brew search postgresql $ brew install postgresql

add to startup:

$ ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents

1	$ ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents

start:

brew services start postgresql

1	brew services start postgresql

or manually:

postgres -D /usr/local/var/postgres

1	postgres -D /usr/local/var/postgres

with ctl:

pg_ctl -D /usr/local/var/postgres start

1	pg_ctl -D /usr/local/var/postgres start

check status:

pg_ctl -D /usr/local/var/postgres status

1	pg_ctl -D /usr/local/var/postgres status

port:

egrep 'listen|port' /usr/local/var/postgres/postgresql.conf

1	egrep 'listen\|port' /usr/local/var/postgres/postgresql.conf

logs:

/usr/local/var/log/postgres.log

1	/usr/local/var/log/postgres.log

How to setup PostgreSQL

$ postgres -V

postgres (PostgreSQL) 10.5

$ postgres -V

postgres (PostgreSQL) 10.5

psql -l

psql -l

   Name    |     Owner     | Encoding |   Collate   |    Ctype    |          Access privileges
-----------+---------------+----------+-------------+-------------+-------------------------------------
 postgres  | username      | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 template0 | username      | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/"username"                 +
           |               |          |             |             | "username"=CTc/"username"
 template1 | username      | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/"username"                 +
           |               |          |             |             | "username"=CTc/"username"
(3 rows)

-----------+---------------+----------+-------------+-------------+-------------------------------------

(3 rows)

$ psql postgres
psql (10.5)
Type "help" for help.

postgres=#

$ psql postgres

psql (10.5)

Type "help" for help.

postgres=#

postgres=# \du
                                     List of roles
   Role name   |                         Attributes                         | Member of
---------------+------------------------------------------------------------+-----------
 username      | Superuser, Create role, Create DB, Replication, Bypass RLS | {}

postgres=# \du

List of roles

Role name | Attributes | Member of

---------------+------------------------------------------------------------+-----------

username | Superuser, Create role, Create DB, Replication, Bypass RLS | {}

quit psql:

\q

create application user and database

$ createuser appname
$ createdb -O appname appname

1 2	$ createuser appname $ createdb -O appname appname

setup password for user:

postgres=# \password username

1	postgres=# \password username

Enjoy!

React or Vue

Compiling!!!

Mockito, Spy, PowerMock

Mockito

Mockito.mock(externalService);
Mockito.reset(externalService);

1 2	Mockito.mock(externalService); Mockito.reset(externalService);

when(mock).thenReturn(value);

1	when(mock).thenReturn(value);

when(mock).thenThrow(new IOException());

1	when(mock).thenThrow(new IOException());

doReturn(result).when(mock_object).void_method_call();

1	doReturn(result).when(mock_object).void_method_call();

doThrow(new IOException()).when(mock_object).void_method_call();

1	doThrow(new IOException()).when(mock_object).void_method_call();

Mockito.verify(mock_object).callMethod(Matchers.eq(concrete_object));

1	Mockito.verify(mock_object).callMethod(Matchers.eq(concrete_object));

Mockito Mocks vs. Spies Mock – bare-bones shell instance

List mockedList = Mockito.mock(ArrayList.class);

1	List mockedList = Mockito.mock(ArrayList.class);

Spy – wrap an existing instance

List spyList = Mockito.spy(new ArrayList());

1	List spyList = Mockito.spy(new ArrayList());

PowerMock final classes without interfaces static methods privates

@RunWith(PowerMockRunner.class)
@PrepareForTest({ExternalService.class})

1 2	@RunWith(PowerMockRunner.class) @PrepareForTest({ExternalService.class})

private final ExternalService externalService = PowerMockito.mock(ExternalService.class);

1	private final ExternalService externalService = PowerMockito.mock(ExternalService.class);

PowerMockito.mockStatic(StaticService.class);
PowerMockito.verifyStatic();

1 2	PowerMockito.mockStatic(StaticService.class); PowerMockito.verifyStatic();

Test-driven development: JUnit

gradle:

apply plugin: 'java'

dependencies {
  testCompile 'junit:junit:4.12'
}

apply plugin: 'java'

dependencies {

testCompile 'junit:junit:4.12'

}

maven:

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
</dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

</dependency>

Expected Exceptions Test

    @Test(expected = UnsupportedOperationException.class)
    public void reverseList() {
        list.getReverseList();
    }

@Test(expected = UnsupportedOperationException.class)

public void reverseList() {

list.getReverseList();

}

@RunWith BlockJUnit4ClassRunner – default junit runner SpringJUnit4ClassRunner allows you to use dependency injection in test classes or to create transactional test methods. MockitoJUnitRunner for automatic mock initialization. Suite Parameterized Parameters class

@RunWith(value = Parameterized.class)
public class ParametersTest {
    // ...
      @Parameters
      public static Collection<Object[]> data() {

      @Test //will be run Collection.size times
      public void testData(){
}

@RunWith(value = Parameterized.class)

public class ParametersTest {

// ...

@Parameters

public static Collection<Object[]> data() {

@Test //will be run Collection.size times

public void testData(){

}

JUnit 5 – @ExtendWith

@RunWith(SpringJUnit4ClassRunner.class)

1	@RunWith(SpringJUnit4ClassRunner.class)

replace with

@ExtendWith(SpringExtension.class)

1	@ExtendWith(SpringExtension.class)

@Rule

@Rule public ExpectedException exception = ExpectedException.none();

1	@Rule public ExpectedException exception = ExpectedException.none();

@Rule public TemporaryFolder folder = new TemporaryFolder();

1	@Rule public TemporaryFolder folder = new TemporaryFolder();

or your custom rule: […]

Hibernate – OneToOne, OneToMany, ManyToOne, ManyToMany mappings

By specifying the @JoinColumn on both models you don’t have a two way relationship. mappedby One to One

@Entity(name = "PostDetails")
@Table(name = "post_details")
public class PostDetails {
    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "post_id")
    private Post post;
}

@Entity(name = "Post")
@Table(name = "post")
public class Post {
    @OneToOne(mappedBy = "post", cascade = CascadeType.ALL, 
              fetch = FetchType.LAZY, optional = false)
    private PostDetails details;
}

@Entity(name = "PostDetails")

@Table(name = "post_details")

public class PostDetails {

@OneToOne(fetch = FetchType.LAZY)

@JoinColumn(name = "post_id")

private Post post;

}

@Entity(name = "Post")

@Table(name = "post")

public class Post {

@OneToOne(mappedBy = "post", cascade = CascadeType.ALL,

fetch = FetchType.LAZY, optional = false)

private PostDetails details;

}

bidirectional One to One is EAGER @MapsId (before jpa2 – @PrimaryKeyJoinColumn)

@Entity(name = "PostDetails")
@Table(name = "post_details")
public class PostDetails { 
    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private Post post;
}

@Entity(name = "PostDetails")

@Table(name = "post_details")

public class PostDetails {

@OneToOne(fetch = FetchType.LAZY)

@MapsId

private Post post;

}

One To Many, Many To One Unidirectional without @JoinColumn requires additional table for joining

@Entity(name = "Post")
@Table(name = "post")
public class Post {
    @OneToMany(
        cascade = CascadeType.ALL, 
        orphanRemoval = true
    )
    private List<PostComment> comments = new ArrayList<>();
}

@Entity(name = "Post")

@Table(name = "post")

public class Post {

@OneToMany(

cascade = CascadeType.ALL,

orphanRemoval = true

)

private List<PostComment> comments = new ArrayList<>();

}

@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
@JoinColumn(name = "post_id")
private List<PostComment> comments = new ArrayList<>();

@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)

@JoinColumn(name = "post_id")

private List<PostComment> comments = new ArrayList<>();

Bidirectional

@Entity(name = "Post")
@Table(name = "post")
public class Post {
    @OneToMany(
        mappedBy = "post", 
        cascade = CascadeType.ALL, 
        orphanRemoval = true
    )
    private List<PostComment> comments = new ArrayList<>();
}

@Entity(name = "PostComment")
@Table(name = "post_comment")
public class PostComment {
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "post_id")
    private Post post;

@Entity(name = "Post")

@Table(name = "post")

public class Post {

@OneToMany(

mappedBy = "post",

cascade = CascadeType.ALL,

orphanRemoval = true

)

private List<PostComment> comments = new ArrayList<>();

}

@Entity(name = "PostComment")

@Table(name = "post_comment")

public class PostComment {

@ManyToOne(fetch = FetchType.LAZY)

@JoinColumn(name = "post_id")

private Post post;

Is it possible to limit the […]

Hibernate – JPA

<dependency>
   <groupId>org.hibernate</groupId>
   <artifactId>hibernate-core</artifactId>
   <version>5.2.17.Final</version>
</dependency>

<groupId>org.hibernate</groupId>

<artifactId>hibernate-core</artifactId>

<version>5.2.17.Final</version>

</dependency>

SessionFactory (jpa: EntityManagerFactory) – thread-safe (and immutable) representation of the mapping of the application domain model to a database Session (jpa: EntityManager) – A single-threaded, short-lived object conceptually modeling a “Unit of Work” StatelessSession – like JDBC Transaction (jpa: EntityTransaction) – A single-threaded, short-lived object used by the application to demarcate individual physical transaction […]

Spring Bean Life Cycle

By implementing InitializingBean and DisposableBean interfaces Providing init-method and destroy-method in xml configuration or @PostConstruct and @PreDestroy annotations for methods

@Bean(initMethodName="init")

1	@Bean(initMethodName="init")

<bean id="service" class="Service" init-method="init" destroy-method="destroy">

1	<bean id="service" class="Service" init-method="init" destroy-method="destroy">

For activating post processor annotation annotations use

<bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />

1	<bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />

or by

<context:annotation-config>

1	<context:annotation-config>

used to activate applied annotations in already registered beans in application context (context:component-scan does what context:annotation-config does, but additionally it scan the […]