Programming notes

 mvn --encrypt-master-password does not create a file security-settings.xml. Use the command mvn --encrypt-master-password to generate a master password. Remember this password.Create a new file security-settings.xml in ${user.home}/.m2/. For example, on Mac OS X or Ubuntu as ~/.m2/settings-security.xml.Write into this file:<settingsSecurity> <master>OUTPUT OF THE COMMAND: mvn --encrypt-master-password</master> </settingsSecurity>e.g.:<settingsSecurity> <master>{jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+9EF1iFQyJQ=}</master> </settingsSecurity>After that the maven encrypt command works on the command line:mvn --encrypt-passwordAs mentioned by khmarbaise, more detailed information can be found here: https://maven.apache.org/guides/mini/guide-encryption.htmlsource 

I've heard previously about test-containers but didn't have chance to read about it. Testcontainers is a Java library that supports JUnit tests, providing lightweight, throwaway instances of common databases, Selenium web browsers, or anything else that can run in a Docker container. So basically it simplify you process of creating and maintaining end-to-end tests. You no need external containers you simple can run in on jenkins during your usual testing life cycle. Two articles illustrate this approach with  Selenium and one more with WireMock

I've faced recently with some not trivial mongo aggregation queries and found there are not so many examples available, so main source is official docs https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#introduction also was useful tests of the Spring Framework: https://github.com/spring-projects/spring-data-mongodb/blob/master/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java https://github.com/spring-projects/spring-data-mongodb/blob/master/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java use to profile query db.events.explain("executionStats").aggregate("query") 

Cool tool to test interaction between you apps without running all of them. Need just describe contract of you service and inject in via wiremock were it is needed.  Here is a tutorial

I was migrating recently to the new Spring Boot version 2. And most annoying thing was that PageImpl (component used for pagination)  changed format. Also I had some issues with Mockito 2, but all of them could be solved read here. Well I found this article and it all looked easy despite the fact that Spring did not want to use my JsonSerializer. Here how it looks: import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; import org.springframework.boot.jackson.JsonComponent; import org.springframework.data.domain.PageImpl; import org.springframework.data.domain.Sort; import java.io.IOException; @JsonComponent public class PageImplJacksonSerializer extends JsonSerializer {     @Override     public void serialize(PageImpl page, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {         jsonGenerator.writeStartObject();         jsonGenerator.writeObjectField("content", page.getContent());         jsonGenerator.writeBooleanField("first", page.isFirst());         jsonGenerator.writeBooleanField("last", page.isLast());         jsonGenerator.writeNumberField("totalPages", page.getTotalPages());         jsonGenerator.writeNumberField("totalElements", page.getTotalElements());         jsonGenerator.writeNumberField("numberOfElements", page.getNumberOfElements());         jsonGenerator.writeNumberField("size", page.getSize());         jsonGenerator.writeNumberField("number", page.getNumber());         Sort sort = page.getSort();         jsonGenerator.writeArrayFieldStart("sort");         for (Sort.Order order : sort) {             jsonGenerator.writeStartObject();             jsonGenerator.writeStringField("property", order.getProperty());             jsonGenerator.writeStringField("direction", order.getDirection().name());             jsonGenerator.writeBooleanField("ignoreCase", order.isIgnoreCase());             jsonGenerator.writeStringField("nullHandling", order.getNullHandling().name());             jsonGenerator.writeEndObject();         }         jsonGenerator.writeEndArray();         jsonGenerator.writeEndObject();     } } Next I read Spring docs of how can I customize Serializer here and here They suggested to create jacksonBuilder with your specific module or register JsonComponentModule that will find your serializer that will be used by spring during mapper creation. Unfortunately none of this worked for me:     @Bean     public Module jsonComponentModule() {         return new JsonComponentModule();     } And this also didn't work:     @Bean     @Primary     public Jackson2ObjectMapperBuilder jacksonBuilder() {         JsonComponentModule module  = new JsonComponentModule();         module.addSerializer(PageImpl.class, new PageImplJacksonSerializer());         Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();         builder.modulesToInstall(module);         return builder;     } I continued with my last idea, suggested by docs is configuring HttpMessageConverter. And here I figured out that my config extends WebMvcConfigurationSupport to enable MVC and after debugging spring context creation. I found that Spring registers default converters with method addDefaultHttpMessageConverters and following line of code and for some reason it does not register serializer here: messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build())); So here is working solution for me, with configuring default converter created by Spring: @Override     protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {         MappingJackson2HttpMessageConverter converter = (MappingJackson2HttpMessageConverter)                 converters.stream()                         .filter(c -> c instanceof MappingJackson2HttpMessageConverter)                         .findFirst().get();         Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();         JsonComponentModule module  = new JsonComponentModule();         module.addSerializer(PageImpl.class, new PageImplJacksonSerializer());         ObjectMapper objectMapper = builder.modules(module).build();         converter.setObjectMapper(objectMapper);     }

A JVM benchmark example from real project (QuickFIX/J is library that implements finacial FIX protocol) https://github.com/quickfix-j/quickfixj/wiki/JMH-benchmark-for-%2339-and-%2342

Recently I have played a bit with Spring 5 and embedded database HSQLDB. It is very not usual for me to create Spring app even without single xml. Also I used cool library called Lombok it provides auto getter/setter generation. What was interesting for me that spring-boot auto configure for you following features: mvc, transactions, json serialization, jpa, tests. It has even embedded tomcat) Here is my github repository

Choosing the right estimator http://scikit-learn.org/stable/tutorial/machine_learning_map/index.html https://www.dropbox.com/s/nz2d6uquwn59fz6/ml_map.png later i will add here more machine learning stuff Первые шаги в машинном обучении Machine Learning is Fun! The world’s easiest introduction to Machine Learning https://oracle.github.io/graphpipe/#/ https://github.com/neomatrix369/awesome-ai-ml-dl

I think most enterprise java world is suffering  from Anemic Domain Model. One of the ways that can help you is DDD. I've started researching DDD area, and I've found couple of good books and sources for them: Implementing Domain-Driven Design by Vaughn Vernon (I think it is good to start book) and source code is here : https://github.com/VaughnVernon/IDDD_Samples And one more book called Domain-Driven Design: Tackling Complexity in the Heart of Software by Eric Evans  and source code is here: https://github.com/citerus/dddsample-core more code samples https://github.com/ddd-by-examples/library https://github.com/mploed/ddd-with-spring

Top 5: #1 Working Effectively with Legacy Code Michael C. Feathers #2 Design Patterns Ralph Johnson, Erich Gamma, John Vlissides, Richard Helm #3 Clean Code Robert C. Martin #4 Java concurrency in practice Brian Goetz, Tim Peierls #5 Domain-driven Design Eric Evans See more here http://www.dev-books.com/

Note about scrum. It is mostly based on Scum Guide but in much shorter way and with some examples from my experience. Scrum is a framework for developing and sustaining complex products Roles The Product Owner -  is the person responsible for managing the Product Backlog (describing items, ordering and prioritization ). Also Product owner may delegate his responsibilities to the Dev Team.  However, the Product Owner remains accountable, and you should consult with him. The Development Team  - decide how to turn Product Backlog into Increments of potentially releasable functionality.  Are cross-functional, with all of the skills to create a product Increment; Usually having 3-9 members. The Scrum Master -is responsible for ensuring Scrum is understood and enacted.  Service to the Product Owner (help in Product Backlog management, helping the Scrum Team understand product backlog items, Facilitating Scrum events) Service to the Development Team (Coaching, Helping the Development Team to create product, Facilitating Scrum events, Removing impediments) Scrum Events The heart of Scrum is a Sprint, a time-box of one month or less during which a “Done”, usable, and potentially releasable product Increment is created. Sprints best have consistent duration throughout a development effort. A new Sprint starts immediately after the conclusion of the previous Sprint. Sprints contain and consist of the Sprint Planning, Daily Scrums, the development work, the Sprint Review, and the Sprint Retrospective. Sprint Planning  Sprint Planning answers the following: What can be delivered in the Increment resulting from the upcoming Sprint?  How will the work needed to deliver the Increment be achieved?  The input to this meeting is the Product Backlog, the latest product Increment, projected capacity of the Development Team during the Sprint, and past performance of the Development Team. The number of items selected from the Product Backlog for the Sprint is solely up to the Development Team. Only the Development Team can assess what it can accomplish over the upcoming Sprint. The Development Team usually starts by designing the system and the work needed to convert the Product Backlog into a working product Increment. The Product Owner can help to clarify the selected Product Backlog items and make trade-offs. If the Development Team determines it has too much or too little work, it may renegotiate the selected Product Backlog items with the Product Owner. For example each member says his capacity. Scrum master displays all jiras with some release version. All team estimates jiras. You could also use excell to group planned tasks. Frequent approach is sending email with sprint backlogs items after planning to Product Owner (if he can't participate) Sprint Goal  The Sprint Goal is an objective set for the Sprint that can be met through the implementation of Product Backlog. It provides guidance to the Development Team on why it is building the Increment. Try to make it clear, you could use SMART approach  Daily Scrum The Daily Scrum is a 15-minute time-boxed event for the Development Team to synchronize activities and create a plan for the next 24 hours. This is done by inspecting the work since the last Daily Scrum and forecasting the work that could be done before the next one.  the Development Team members explain: What did I do yesterday that helped the Development Team meet the Sprint Goal?  What will I do today to help the Development Team meet the Sprint Goal?  Do I see any impediment that prevents me or the Development Team from meeting the Sprint Goal?  Very useful is tracking progress of each individual task (maybe visually), tracking time (ex member A done 2h from 15h ), use color markers for each task (red/green/blue approach depending on item, status).  It could be on scrum board with three main parts todo/ in progress/ done. Sprint Review A Sprint Review is held at the end of the Sprint to inspect the Increment and adapt the Product Backlog if needed.During the Sprint Review, the Scrum Team and stakeholders, product owner collaborate about what was done in the Sprint.The entire group collaborates on what to do next. The result of the Sprint Review is a revised Product Backlog For example demo of new features is good thing here.  Sprint Retrospective The Sprint Retrospective is an opportunity for the Scrum Team to inspect itself and create a plan for improvements to be enacted during the next Sprint. Inspect how the last Sprint went with regards to people, relationships, process,and tools. Good approach here to write on board pluses and minuses and possible todo plan to implement in new sprint. Scrum Artifacts  Product Backlog - is an ordered list of everything that might be needed in the product. Good technique sometimes is to refine some big or complex product backlog items for the next sprint, to be able to estimate them well on the planning Sprint Backlog - is the set of Product Backlog items selected for the Sprint, plus a plan for delivering the product Increment and realizing the Sprint Goal. It is only forecast. Good technique is to add label in jira with sprint number Definition of “Done” - when a Product Backlog item or an Increment is described as “Done”, everyone must understand what “Done” means. For example developer committed change and closed an jira, QA passed jira, Reporter closed it.  Good technique is to have it printed somewhere to be visible for all team. References Download the official Scrum Guide Stuff Every Agile Development Team Needs to Know: A Primer

https://dzone.com/articles/jdk-9-is-feature-complete