32-Spring Boot - A Closer Look

Question 1

What is defactor standard?

Answer 1

De facto standards are those which have been accepted as the best standard for their purpose
Spring Boot looks for application.properties by default

Question 2

What locations will Spring Boot look for application.properties?

Answer 2

First, /config: subdirectory of the working directory
Then, working directory
Then, config package in the classpath
Last, classpath root

Question 3

If no profile is active, what properties files will be loaded?

Answer 3

application.properties

application-default.properties

Question 4

How to change the location that Spring boot looks up for properties files?

Answer 4

spring. config.location
e. g.
spring. config.location=classpath:/default.properties,classpath:/override.properties

Question 5

How to change the default application config file that Spring boot looks for?

Answer 5

spring.config.name

default value is “application”

Question 6

Does @PropertySource support YML config files?

Answer 6

No,

YAML is only supported when Spring Boot loads application.yml

Question 7

How to specify multiple profiles config in a single file?

Answer 7

Using --- to separate and spring.profiles for profile name
e.g.
# Sections without spring.profiles are always loaded
# Something
---
spring:
  profiles: local
---
spring:
  profiles: cloud

Question 8

Order that Spring Boot select properties

Answer 8

1. Devtools settings
2. @TestPropertySource and @SpringBootTest properties
3. Command line arguments
4. SPRING_APPLICATION_JSON (inline JSON properties).
5. ServletConfig / ServletContext parameters.
6. JNDI attributes from java:comp/env
7. Java System properties
8. OS environment variables
9. Profile-specific application properties
10. Application properties / YAML
11. @PropertySource files
12. SpringApplication.setDefaultProperties.

Question 9

What is the purpose of using @ConfigurationProperties?

Answer 9

e.g.
@ConfigurationProperties(prefix="rewards.client")
public class ConnectionSettings {
    // .. binding properties start with rewards.client to this class
}

Question 10

Is ConfigurationProperties a part of Spring framework or Spring boot?

Answer 10

It’s a part of Spring boot

Question 11

Ways to enable @ConfigurationProperties?

Answer 11

1. @SpringBootApplication
@EnableConfigurationProperties(ConnectionSettings.class)
public class Application {}
2. @SpringBootApplication
@ConfigurationPropertiesScan
public class Application {}
3. @Component
@ConfigurationProperties(prefix="rewards.client")
public class ConnectionProperties {}

Question 12

What is relaxed binding?

Answer 12

Flexible in properties matching. Only applied for @ConfigurationProperties
e.g.
@ConfigurationProperties("rewards.client-connection")
class Config { String hostUrl; }
Valid matches:
1. rewards.clientConnection.hostUrl
2. rewards.client-connection.host-url
3. rewards.client_connection.host_url
4. REWARDS_CLIENTCONNECTION_HOSTURL

Question 13

List out 6 @Conditional

Answer 13

1, 2. ConditionalOnClass, ConditionalOnMissingClass
3, 4. ConditionalOnBean, ConditionalOnMissingBean
5, 6. ConditionalOnProperty, ConditionalOnMissingProperty

Question 14

What are the targets of @Conditional?

Answer 14

class, bean method

Question 15

What jar file defines auto-configuration logic in Spring boot?

Answer 15

spring-boot-autoconfigure.jar

Question 16

What are inside spring-boot-autoconfigure/META-INF/spring.factories?

Answer 16

1. @EnableAutoConfiguration reads a factories file for list of AutoConfiguration classes used by Spring Boot

Question 17

How to configure schema and default data for DB?

Answer 17

spring. datasource.schema=/testdb/schema.sql

spring. datasource.data=/testdb/data.sql

Question 18

How to configure MySQL db connection?

Answer 18

spring. datasource.url=jdbc:mysql:…
spring. datasource.username=
spring. datasource.password=

Question 19

How to update the default log level of the application?

Answer 19

logging.level.root=INFO

Question 20

How to update the log level of a package?

Answer 20

logging.level.com.myproject=DEBUG

Question 21

Ways to exclude 1 auto-config in Spring Boot app

Answer 21

1. @EnableAutoConfiguration(exclude=DataSourceAutoConfiguration.class)
2. (application.yml) spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

Question 22

What pooled datasources are supported by Spring Boot?

Answer 22

Tomcat
HikariCP
Commons DBCP 1 & 2

Question 23

How to set pooled datasource type in Spring Boot?

Answer 23

spring.datasource.type=
e.g. Tomcat
HikariCP
Commons DBCP 1 & 2

Question 24

What is the order of selecting pooled data source type?

Answer 24

HikariCP (highest precedence) –> Tomcat Commons DBCP2

Question 25

What are logging frameworks supported by Spring? What is the default

Answer 25

Logback(default) Java Util Logging Log4J Log4J2

Question 26

How to set the place of logging files?

Answer 26

Use: logging.file.name=rewards.log OR: logging.file.path=/var/log/rewards