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Using an EJB outside container

I am currently creating a J2EE application and there is a part of it that is running outside the container, using a ServletContextListener to launch it.
However I also need to access the database from this part.
I currently have an Entity and a Stateless Session bean to fetch use the EntityManager.
I tested multiple things ( EntityManagerFactory, Initial Context, EJBContainer ) but I didn't manage to make any of them work.
How do I need to do it ?

You do not need EJB, actually you cannot create Ejbs outside the container. You need JPA, an OR-mapper and JDBC.
These normally are correctly configured in your EJB-Container. Outside the container you have to do that yourself.
You have to define your dependencies right, so that the correct JDBC-Driver is available and the OR-Mapper (probably eclipselink or hibernate?)
After that, you need define a presistence.xml to define the Entities to be used and to define how the DBMS is accessed via JDBC.
If that all is correctly configured EntityManagerFactory is the correct way to create an EntityManger for the persistence-unit defined in persistence.xml.
There are many examples available on the net. e.g.:
https://examples.javacodegeeks.com/enterprise-java/jpa/java-persistence-xml-example/
should work, if you are using eclipselink.
https://docs.jboss.org/hibernate/orm/3.6/quickstart/en-US/html/hibernate-gsg-tutorial-jpa.html
in case of Hibernate.

Why Spring does not recognize #BatchSize annotation

Scenario:
I'm supporting an Enterprise application that runs in Wildfly10. The application (.war) uses J2EE technologies (EJBs, JPA, JAX-RS) and SpringBoot features (like, SpringMVC, SpringRest, SpringData, SpringRestData) ... Both stacks co-exists "happily" because they don't interact between them; however, they do share common classes, like utility or Entity Classes (the stacks map to the same database model). Why the application uses those stacks is out the scope of the question.
Currently, I'm trying to improve the performance of a #RestController that pulls some data from the database using a JPA Spring Repository. I found that we're suffering the N + 1 queries problem when calling the #RestController. In past projects (where there were only J2EE technologies), I have used the #BatchSize hibernate annotation to mitigate this problem with total success.
But, in this project, Spring seems to be skipping such annotation. How do I know that? Because I turned on the hibernate SQL logging (hibernate.show_sql) and I can see the N + 1 queries is still happening ...
Key Points:
Here are some insights about the application that you must know before providing (or trying to guess) any answer:
The application has many sub-modules encapsulated as libraries inside WAR file (/WEB-INF/lib) ... Some of these libraries are the jars that encapsulate the entity classes; others are the jars that encapsulate the REST Services (that could be JAX-RS services or Spring Controllers).
The Spring configuration is done in the classes defined in the WAR artifact: in there, we have a class (that extends from SpringBootServletInitializer) annotated with #SpringBootApplication and another class (that extends from RepositoryRestConfigurerAdapter) annotated with #Configuration. Spring customization is done is such class.
The application works with multiple datasources, which are defined in the Wildly server. Spring DATA JPA must address any query pointing to the right datasource. To accomplish this requirement, the application (Spring) was configured like this:
#Bean(destroyMethod="")
#ConfigurationProperties(prefix="app.datasource")
public DataSource dataSource() {
// the following class extends from AbstractRoutingDataSource
// and resolve datasources using JNDI names (the wildfly mode!)
return new DataSourceRouter();
}
#Bean("entityManagerFactory")
public LocalContainerEntityManagerFactoryBean getEntityManagerFactoryBean() {
LocalContainerEntityManagerFactoryBean lemfb;
lemfb = new LocalContainerEntityManagerFactoryBean();
lemfb.setPersistenceUnitName("abcd-pu");
lemfb.setDataSource(dataSource());
return lemfb;
}
The last #Bean declaration favors the use of a persistence.xml file, which we do have in the route /WEB-INF/classes/META-INF/ (i.e. Spring does find this file!) ... In such file, we define our domain classes, so that Spring JPA can see such entities. Also, we can define special JPA properties like: hibernate.show_sql and hibernate.use_sql_comments without issues (this is how I detected the N + 1 queries problem in the first place) ...
What I have done so far?
I tried to add the #BatchSize annotation to the problematic collection. No luck!
I created a new JAX-RS Service whose purpose was to mimic the behavior of the #RestController. I confirmed that the #BatchSize annotation does work in the application's deployment, at least, in JAX-RS Services! (NOTE: the service uses it own persistence.xml) ...
Test details (Updated 2020/07/30): What I did here was to create a new JAX-RS Service and deployed it inside the WAR application, next to the #RestController that presents the problem (I mean, it is the same WAR and the same physical JVM). Both services pull from database the same entity (same class - same classloader), which has a lazy Collection annotated with #BatchSize! ... If I invoke both services, the JAX-RS honors the #BatchSize and pulls the collection using the expected strategy, the #RestController does not ... So, what it is happening here? The only thing different between the services is that each one has a different persistence.xml: the persistence.xml for the JAX-RS is picked by Wildfly directly, the other one is picked by Spring and delegated to Wildfly (I guess) ...
I tried to add the properties: hibernate.batch_fetch_style (=dynamic) and hibernate.default_batch_fetch_size (=10), to the persistence.xml read by Spring ... No luck. I debug the Spring startup process and I saw that such properties are passed to the Spring Engine, but Spring does not care about them. The weird thing here is that properties like: hibernate.show_sql, Spring does honor them ... For those who are asking: "What does these properties do?" Well, they are global equivalent to apply #BatchSize to any JPA lazy collection or proxy without declaring such annotation in any entity.
I setup a small SpringBoot Project using the same Spring version as enterprise application (which is 1.5.8.RELEASE, by the way) and both the annotation and properties approach worked as supposed to.
I've been stuck with this issue for two days, any help to fix this will be appreciated ... thanks!

There are 2-3 possible issues that I can think off.
For some reason, whatever you modify isnt picked up by wildfly - Wildfly classpath resolution is a separate Topic and some missing configuration can cause you a nightmare. This you can identify if you have access to debug the query, and in if you put a breakpoint in the constructor of your Entity class, you will get a chance to evaluate the entity configuration being used, somewhere in the execution conetxt.
BatchSize doesnt work on OneToOne, It only works on OneToMany relationships.
A typical way to define BatchSize is to do along with Lazy load as mentioned in the example here. If you are not using Lazy fetch, hibernate assumes that you are willing to make an eager load and makes another select query to fetch all the details.Please confirm you are using the same syntax as given in the example above.
New Addition:
Put Conditional Breakpoints in PropertyBinder#setLazy() function, and may be backtrace it and put relavent breakpoints in CollectionBinder and AnnotationBinder. then restart/redeploy the server and see what data you are getting for the relavent properties. That will give you fair idea where it is failing..
Why conditional breakpoint? Its because you will have thousands of properties and if you do not add condition to the breakpoint, you will take 1 hour to reach your actual breakpoint
What should be the condition - If its property binder, the condition shoud be like `this.name == . For other classes also you can use the same approach.
Sorry for too detailed description on conditional breakpoints, you might find it redundent.
Looks like the only way to debug your problem is to debug hibernate framework from server startup, then only we will be able to find out the rootcause

How dynamically define properties for JPA connection with Injected EntityManager

How can I configure persistence.xml for production? My question specifically concerns the definition of parameters such as user, password and bank url, for example.
I would like to not include this data directly in the file, but in an environment variable, for example.
However, it can be any other approach, except overwriting the file settings via the entity manager factory as was said in these questions 1 e 2
This restriction exists because my EntityManager is injected via #PersistenceContext. This even generated a comment
I'm using a JavaEE application with JAX-RS, Hibernate JPA and Spring MVC

Spring Boot REST · #Constraint for delete?

I'm working on a system's back end that uses Spring Boot, REST, HATEOAS, Hibernate and PostgreSQL. For validation, I started using classes that extend org.springframework.validation.Validator. It works well, but only for calls made by the front end. For calls made in the back end, such as by using EntityManager, they don't fire. I've managed to have another validator being called in this situation by using #Constraint for ElementType.TYPE, but it only gets called for create and save methods.
Is it possible to use this validator to validate on delete methods too? There's a project here that's a non operational subset of the project I'm working on, containing the validators I mentioned.
Thanks in advance.
P.S.: I'd rather avoid manually calling the validators whenever I call a repository method in the back end.
P.P.S.: This answer makes me believe it's possible, but I couldn't translate the XML configuration to JavaConfig.

I finally found the answer. In application.properties, add:
spring.jpa.properties.javax.persistence.validation.group.pre-remove=javax.validation.groups.Default
The linked question told me which property I needed, but I didn't know where to place it. I tried to use custom Java configuration and even persistence.xml configuration, but several other things failed.
Here, I learned that "[...] all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created." So I just added that prefix and it worked.

Mybatis useGeneratedKeys Fails in EJB with Proxy

I am using Mybatis 3.3.0 and EJB 3.1 running in a Wildfly 8.2.1 App server.
I modified my EJB's to have a Remote Interface and Injected the interface into all my classes that require the functionality instead of the injecting the LocalBean implementation (as it was before).
This caused all my useGeneratedKeys configurations for my mapper file Insert statements to stop working. Now my ID fields remain Null after the Inserts have run successfullly.
How is it that this caused mybatis to not be able to populate the ID's into my POJOs.

It turns out that mybatis gets confused when your EJB's are proxied and it isn't able to put the generated ID back into the POJO.
To fix it you simply have to inject the EJB Annotated with #javax.ejb.LocalBeanimplementation directly into the class you want to use it in. This is instead of injecting the Interface annotated with #javax.ejb.Remote.
Additionally I tested the same implementation using Remote EJB's and found you still won't be able to get generated Keys back from mybatis if you inject the #javax.ejb.Remote Interface type. I haven't found a solution to getting the generated ID into the POJO when using remoting.