Spring/boot

Question 1

run java application from command line with maven

Answer 1

mvn clean compile exec:java

Question 2

how to view the final created pom file that contains the pom and any parent poms and generated config

Answer 2

mvn help:effective-pom

Question 3

can you have an empty dependencies body in the pom.xml?

Answer 3

yes

Question 4

java.lang.IllegalStateException: Unable to find a @SpringBootConfiguration, you need to use @ContextConfiguration or @SpringBootTest(classes=…) with your test

Answer 4

I didn’t have a class with ‘@SpringBootApplication’ annotated before it

Question 5

the proper way to run from command line a pom.xml file downloaded from spring initializr

Answer 5

./mvnw spring-boot:run or mvn spring-boot:run

Question 6

if you want to run a freshly download spring initialzr project using mvn clean compile exec:java what do you need to do?

Answer 6

mvn -X exec:java -Dstart-class=com.example.demo.DemoApplication

Question 7

@RestController annotation

Answer 7

marks the class as a controller where every method returns a domain object instead of a view. It is shorthand for including both @Controller and @ResponseBody.

Question 8

@SpringBootApplication is a convenience annotation that adds:

Answer 8

@Configuration, @EnableAutoConfiguration, @ComponentScan

Question 9

@Configuration,

Answer 9

Tags the class as a source of bean definitions for the application context.

Question 10

the 2 things to run a project with gradle

Answer 10

1) you have to have set it up with a build.gradle file, e.g. thru the Spring Initializer 2) use ./gradlew bootRun

Question 11

@EnableAutoConfiguration,

Answer 11

Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For example, if spring-webmvc is on the classpath, this annotation flags the application as a web application and activates key behaviors, such as setting up a DispatcherServlet.

Question 12

@ComponentScan

Answer 12

Tells Spring to look for other components, configurations, and services in the com/example package, letting it find the controllers.

Question 13

JavaBeans

Answer 13

classes that encapsulate many objects into a single object (the bean)

Question 14

beans in Spring

Answer 14

The objects that form the backbone of your application and that are managed by the Spring IoC container [ https://www.tutorialspoint.com/spring/spring_bean_definition.htm]

Question 15

How to build jar file using gradle

Answer 15

./gradlew build

Question 16

run spring with gradle on another port - method 1

Answer 16

add following to src/main/java/resources/application.yml: server:\nport: 8081

Question 17

run spring with gradle on another port - method 2

Answer 17

add following to src/main/java/resources/application.properties: server.port=8081

Question 18

POJO

Answer 18

Plain Old Java Object

Question 19

Baeldung’s definition of IoC

Answer 19

is a process in which an object defines its dependencies without creating them

Question 20

In IoC, objects delegate the job of constructing dependencies to

Answer 20

an IoC container

Question 21

JPA

Answer 21

Java Persistence API. Mechanism to interface with databases

Question 22

how to create a new Spring project

Answer 22

spring init –dependencies=web,data-jpa my-project

Question 23

how to create a new Spring project with gradle

Answer 23

spring init –dependencies=web,data-jpa –build=gradle my-project

Question 24

@Data annotation

Answer 24

from “import lombok.Data;” @Data is a convenient shortcut annotation that bundles the features of @ToString, @EqualsAndHashCode, @Getter / @Setter and @RequiredArgsConstructor together: In other words, @Data generates all the boilerplate that is normally associated with simple POJOs (Plain Old Java Objects) and beans: getters for all fields, setters for all non-final fields, and appropriate toString, equals and hashCode implementations that involve the fields of the class, and a constructor that initializes all final fields, as well as all non-final fields with no initializer that have been marked with @NonNull, in order to ensure the field is never null.

Question 25

why wasn't my Junit test running?

Answer 25

I didn't have the @Test annotation beforehand

Question 26

Why weren't my console logs working in my unit test?

Answer 26

I needed to add the following to the bottom of my build.gradle: test { testLogging.showStandardStreams = true }

Question 27

basic Springboot injection layout example

Answer 27

1) have a class called Company annotated with @Component 2) add a property in the class `private Address address`. No need for an annotation 3) Create the Address class. no need for annotations 4) create a config class wrapped with @Configuration, @ComponentScan(basePackageClasses=Company.class),

Question 28

@ComponentScan ensures that the classes decorated with @Component are _____

Answer 28

are found and registered as Spring beans.

Question 29

in my UserPool class why was it that I wasn't able to dependency inject a property using the @Value annotation?

Answer 29

because I had also defined a constructor, and i think particularly because the constructor had properties that had no dependency injection definitions, and the DI system didn't know how to behave in context of this constructor

Question 30

what is hibernate?

Answer 30

an ORM

Question 31

HQL

Answer 31

Hibernate Query Language

Question 32

JPQL

Answer 32

Java Persistence Query Language

Question 33

JPQL vs HQL

Answer 33

JPQL is a subset of HQL

Question 34

what does JPA do?

Answer 34

map your application classes to database tables

Question 35

what handles all the interactions with a database?

Answer 35

EntityManager

Question 36

Hibernate vs JPA

Answer 36

JPA defines the specification. Hibernate is one of the implementations

Question 37

how do i access the entityManager from withinside a Service class?

Answer 37

add a property like @PersistenceContext private EntityManager entityManager;

Question 38

EntityManager is part of the ___ API?

Answer 38

Java Persistence

Question 39

what does JPA do?

Answer 39

implement the programming interfaces and lifecycle rules determined by the JPA specification

Question 40

what are the two types of EntityManager?

Answer 40

Container-Managed and Application Managed

Question 41

what caused the could not initialize proxy [com.sri.api.entities.Organization#15e83f0e-eda5-443b-b1c0-386cadf19fbd] - no Session bug upon Spine login?

Answer 41

removing the @Transactional flag from login(..) and adding it for each of the child methods completeAnyPendingTrainingIdentityVerification and markUserRolesPendingApprovalForRolesWithAllTrainingsComplete. Why? I'm not sure

Question 42

what caused this bug upon login? "Not allowed to create transaction on shared EntityManager - use Spring transactions or EJB CMT instead"

Answer 42

trying to use persist on entityManager (which was injected with @PersistenceContext) inside of a method that was a callee of userService.login method (which was wrapped with @Transactional). using an em created from an entityManageFactory does not work either

Question 43

purpose of transaction

Answer 43

if writing code that interfaces with the database, the later parts interacting with the database won't be written if the first parts failed

Question 44

SPI

Answer 44

service provider interface

Question 45

JNDI

Answer 45

Java Naming and Directory Interface

Question 46

can you call an @transactional method from inside of a non @transactional method?

Answer 46

only if the called method is in a different bean

Question 47

another consequence of adding @transactioal to a method

Answer 47

spring will handle Hibernate sessions

Question 48

what does it mean for spring to handle hibernate sessions

Answer 48

it will let you do something like the following after having obtained a user from the userRepository: user.getOrganization().getStage(). without it managing the sessions, the db session would be closed and .getOrganization() would be null, as that is lazily loaded.

Question 49

what happened when i tried manually injecting in an entityManager in a bean being called by another bean's method that was marked by @transactional?

Answer 49

"Not allowed to create transaction on shared EntityManager - use Spring transactions or EJB CMT instead"

Question 50

cause of "could not initialize proxy [com.sri.api.entities.Organization#15e83f0e-eda5-443b-b1c0-386cadf19fbd] - no Session"

Answer 50

a user.getOrg().something call was inside of a method that was not wrapped with @transactional

Question 51

if I try to access a lazily loaded value inside c2.a(), which is in turn called by c1.a(), and c1.a() is marked @Transactional(), does c2.a() need to be marked @Transactional()?

Answer 51

no

Question 52

if I try to access a lazily loaded value inside c2.b(), which is in turn called by c2.a(), which is in turn called by c1.a(), and c1.a() is marked @Transactional(), what methods of c2 need to be labeled @Transactional()

Answer 52

neither

Question 53

why was our agent.getOrganization() call returning null properties in our debugger?

Answer 53

it was returning an object of instance Organization$HibernateProxy, which by default will set each property equal to null upon inspection, but upon actual evaluation of a property of that proxy object, it will return the actual value from the database - e.g. agent.getOrganization().getGuid() will return a value of the form "15e83f0e-eda5-443b-b1c0-386cadf19fbd"

Question 54

What was the original scenario in which we had to learn about transactions?

Answer 54

in userController.login() we had subroutine a() and b(). a set data in the db that b then had to access. b wasn't able to access any of that new data because the transaction a (and b) was a part of hadn't finished yet. To solve this we put a and b in separate classes from the userController, as in A.a() and B.b() and marked a and b both transactional, and userController.login() not transactional. this let a and b both operate in different transactions, letting a save the data to the db before b started accessing the db.

Question 55

What happens if @transactional A.a() calls B.b() and B.b() is marked Transactional as well()

Answer 55

not sure yet. [ do both a and b share the same transaction?? ] [ do both a and b share the same hibernate session?? are these separate questions ? ]]

Question 56

What happens if you call @Transactional A.b() from @Transactional A.a() and a() was the first method in the call chain marked @Transactional

Answer 56

If you call a method with a @Transactional annotation from a method with @Transactional within the same instance, then the called methods transactional behavior will not have any impact on the transaction. But the transaction+session will still continue, as if the child method didn't even have @Transactional on it. https://stackoverflow.com/a/6222624/2453293

Question 57

What happens if you call @Transactional A.b() from @Transactional A.a() and actually the caller of a() was marked @Transactional too

Answer 57

pretty sure A.b() is treated as if there was no @Transactional tag, because of how AOP proxies behave in Spring [ https://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/transaction.html#tx-decl-explained, https://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/aop.html#aop-understanding-aop-proxies]

Question 58

What happens if you call [not marked @Transitional] A.b() from @Transactional A.a() and a() was the first method in the call chain marked @Transactional

Answer 58

When you call a method without @Transactional within a transaction block, the parent transaction will continue to the new method. It will use the same connection from the parent method(with @Transactional) and any exception caused in the called method(without @Transactional will cause the transaction to rollback as configured in the transaction definition. [ https://stackoverflow.com/questions/6222600/transactional-method-calling-another-method-without-transactional-anotation/6222624#6222624]. I'm guessing this applies for methods called on other instances, too, but not sure.

Question 59

can you you have an inner method in the same bean use a different transaction as that of an outer method in the same bean?

Answer 59

yes.by doing @Transactional(propagation=Propagation.REQUIRES_NEW) on the inner method https://stackoverflow.com/a/55540186/2453293

Question 60

can you you have an inner method in the same bean use a different transaction as that of an outer method in the same bean?

Answer 60

yes.by doing @Transactional(propagation=Propagation.REQUIRES_NEW) on the inner method https://stackoverflow.com/a/55540186/2453293

Question 61

@Transaction default Propagation behavior

Answer 61

Required

Question 62

JDO

Answer 62

Java Data Object

Question 63

CGLIB

Answer 63

Code Generation Library aka "Byte Code Generation Library"

Question 64

Byte Code Generation Library

Answer 64

a high level API to generate and transform Java byte code. It is used by AOP, testing, data access frameworks to generate to generate dynamic proxy objects and intercept field access

Question 65

What does calling a method on a transactional proxy look like?

Answer 65

Caller -> AOP proxy -> Transactional Advisor -> Custom Advisors -> Target Method