Steps to upgrade spring-boot 1.x to 2.x

1. Upgrade gradle/maven wrapper, here gradle
   Ref
   Make sure execute this program on success build.

    ./gradlew wrapper --gradle-version 5.6.4  --distribution-type all  

2. spring-boot-gradle-plugin changes,

   1. bootRepackage to bootJar or bootWar
   
   2. task wrapper(type: Wrapper) { gradleVersion = '5.6.4' }
   to 
   wrapper { gradleVersion = '5.6.4' }

3. Check some of the features deprecate/renamed in gradle, deprecated etc here

4. apache camel dependency on spring boot, kafka, etc, also other libs dependencies
   Note: Kafka 1.1: https://mvnrepository.com/artifact/org.apache.camel/camel-kafka/2.22.4
   kafka 2.0 : https://mvnrepository.com/artifact/org.apache.camel/camel-kafka/2.23.1
   https://github.com/apache/camel/blob/master/components/camel-kafka/src/main/docs/kafka-component.adoc

5. Apache commons upgrade
   Change:
   package import org.apache.commons.lang -> import org.apache.commons.lang3
   groupId: commons-lang -> org.apache.commons
   artifactId: commons-lang -> commons-lang3

6. Spring-boot-2 related properties changes
   https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.0-Migration-Guide

   https://altkomsoftware.pl/en/blog/spring-boot-migration-java/

   • Replace

   org.springframework.boot.test.TestRestTemplate with
   org.springframework.boot.test.web.client.TestRestTemplate

   extends WebMvcConfigurerAdapter  
   with  
   implements WebMvcConfigurer  

   • Change kebab_case properties to snake-case e.g. bank_service.can_be_enable=true to bank-service.can-be-enable=true
     (Note: Changing just property prefix from kebab_case to snake-case e.g. bank_service.can_be_enable=true to bank-service.can_be_enable=true is sufficient to make spring boot work but not encouraged because it may result in inconsist property structure)

   • Properties changes:

   Old property	New property
   server.context-parameters.*	server.servlet.context-parameters.*
   server.context-path	server.servlet.context-path
   server.jsp.class-name	server.servlet.jsp.class-name
   server.jsp.init-parameters.*	server.servlet.jsp.init-parameters.*
   server.jsp.registered	server.servlet.jsp.registered
   server.servlet-path	server.servlet.path

   • Config Keys:

   Old property	New property
   endpoints..*	management.endpoint..*
   endpoints.cors.*	management.endpoints.web.cors.*
   endpoints.jmx.*	management.endpoints.jmx.*
   management.address	management.server.address
   management.context-path	management.server.servlet.context-path
   management.ssl.*	management.server.ssl.*
   management.port	management.server.port

   Exhaustive List of Properties

   • restTemplate change:
     restTemplateBuilder.requestFactory(clientHttpRequestFactory).build();
     To
     new RestTemplate(clientHttpRequestFactory);

   • Testing setup changes [Integration test]

   @ContextConfiguration(loader = SpringApplicationContextLoader.class, classes = MainApplication.class)
   @WebAppConfiguration
   @IntegrationTest("server.port=9090")

   to

   @SpringBootTest(classes = MainApplication.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,properties = [ "server.port:9090", "spring.main.allow-bean-definition-overriding=true"])

   Ref: https://www.jianshu.com/p/6a14001729a7

   https://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#boot-features-external-config-relaxed-binding

7. Mockito from 1.x to 2.x

   • https://asolntsev.github.io/en/2016/10/11/mockito-2.1/
   • https://support.intershop.com/kb/index.php/Display/2M8334
   • https://github.com/mockito/mockito/wiki/What%27s-new-in-Mockito-2
     Replace
     org.mockito.runners.MockitoJUnitRunner; with org.mockito.junit.MockitoJUnitRunner; Ref

   when(mock.method(anyString())).thenReturn(result);
   with
   when(mock.method(nullable(String.class))).thenReturn(result);

   mockitoVersion = '3.1.5'

   If there is any following type of code

   @InjectMock
   @Autowire
   interface interfaceImplementation
   
   // Change it to the following because InjectMock does not work on the interface, it needs concrete implementation
   
   @InjectMock 
   @Autowire
   InterfaceImpl interfaceImplementation

   If older code had used Whitebox functionality then it should be replaced since in Mockito2.x it is not supported
   Ref And If you are using Spring (the spring-test library specifically), you can simply use
   ReflectionTestUtils.setField instead of Whitebox.setInternalState

   incase if you want to use junit-5
   Ref: https://howtodoinjava.com/spring-boot2/junit5-with-spring-boot2/

8. Kafka upgrade:

   • http://kafka.apache.org/documentation.html#upgrade_200_streams_from_11
   • https://spring.io/projects/spring-kafka

9. If you need, just thin jar and not fat jar, then

   bootJar.enable=false
   jar.enable=true

10. Testing spring boot2: @SpringApplicationConfiguration is no longer available, instead you must use @SpringBootTest.

11. Analyze dependencies

12. Dropwizard metrics support is not available for spring boot 2, need to use a micrometer, or need to add it explicitly

    ./gradlew dependencies
    ./gradlew -q dependencyInsight --dependency spring-boot-starter-web
    ./gradlew dependencyInsight --dependency logging

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