Spring / Spring Boot

Spring Boot is a framework for building and running Spring applications by providing defaults for code and annotation configuration to quick start new Spring projects within no time. It follows "Opinionated Defaults Configuration" Approach to avoid lot of boilerplate code and configuration to imp...

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To ease the Java-based applications Development, Unit Test and Integration Test Process. To reduce development, unit Test and integration Test time by providing some defaults. To increase productivity. It avoids writing lots of boilerplate code, annotations and XML configuration. It is very easy ...

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We can convert all kinds of spring projects into Spring Boot Applications however it is time consuming process to convert existing or legacy Spring Framework projects into Spring Boot Applications.

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No. Spring Boot is limited to work with Spring based applications (Java/groovy).

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2.2.1 is the latest version.

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CommandLineRunner Interface is used to indicate that a bean should run when it is contained within a Spring application. Multiple CommandLineRunner beans can be defined within the same application context and can be ordered using the Ordered interface or @Order annotation.

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Both are similar in terms of functionality and the difference is that If you need access to ApplicationArguments instead of the raw String array consider using ApplicationRunner than CommandLineRunner.

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Micro service is an architectural style that structures an application as a collection of loosely coupled services, which implement business capabilities. The microservice architecture enables the continuous delivery/deployment of large, complex applications. It also enables an organization to ev...

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The components are, Spring Boot Starter, Spring Boot AutoConfigurator, Spring Boot Actuator, Spring Boot CLI, Spring Boot IDE, and Spring Boot Initilizr.

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Configuration file used in Spring boot projects is application.properties. It is used to override all default configurations.

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Spring boot actuator is one of the important features of Spring boot. It is used to access the current state of running applications in a production environment. There are various metrics that you can use to check the current state of the application. Spring boot actuator provides restful web ser...

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Spring boot supports embedded containers such as Tomcat (default), Jetty and undertow servers.

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Spring Boot Initializr is a Spring Boot tool to bootstrap Spring Boot or Spring Applications easily. Spring Boot Initializr is available in the below forms: Spring Boot Initializr With Web Interface, Spring Boot Initializr With IDEs/IDE Plugins, Spring Boot Initializr With Spring Boot CLI, Spring...

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Spring Boot provides the @SpringBootTest annotation for writing Unit Test Cases.

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You may change the port in spring boot by adding a property server.port = in application.properties file.

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Spring Boot Starters are a set of convenient dependency descriptors that you can include in your application. You get all the Spring and related technology at one-stop-shop that you need without having to deal with sample code and copy paste loads of dependency descriptors. It minimizes the effor...

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spring-boot-starter-data-jpa for Spring Data JPA. spring-boot-starter-web for Spring Web applcation and creating Restful services. spring-boot-starter-security for Spring security. spring-boot-starter-test for unit testing your application. spring-boot-starter-batch for creating spring batch jobs...

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Spring boot may include dependencies that are not used thereby causing huge deployment file size. Turning legacy spring applications into Spring boot requires a lot of effort and a time-consuming process. Limited control of your application.

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Use Spring boot starter spring-boot-starter-activemq dependency in your applcation POM xml file and it takes care of all dependencies and configuration required for activeMQ projects. Under application.properties add a property spring.activemq.broker-url along with the URL to configure external A...

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Using Spring Boot Dev Tools module we can achieve auto reload. It is a powerful tool that helps developers to lessen the development cycle and enable easy deployment and testing during development. To enable this feature, add the below dependency to Maven POM file.

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The banner that is printed on start up can be changed by adding a banner.txt file to your classpath or by setting the spring.banner.location property to the location. In addition to a text file, you can also add a banner.gif, banner.jpg, or banner.png image file to your classpath or set the sprin...

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When upgrading Spring boot, some properties may have been renamed or removed. Spring Boot provides a way to analyze your application's environment and print diagnostics at startup, but also temporarily migrate properties at runtime. To enable that feature, add the following dependency to your pro...

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To create an executable jar, add the spring-boot-maven-plugin to our pom.xml. Insert the following lines just below the dependencies section in your project's POM.xml: org.springframework.boot spring-boot-maven-plugin

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It is possible to get Spring Boot to work with other build systems such as Ant, but they are not well supported. It is recommended to use with Gradle or Maven.

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Tomcat is the default embedded container when we specify web since spring-boot-starter-web dependency declares spring-boot-starter-tomcat as its dependency. To change from tomcat to Jetty, we need to remove tomcat dependency by specifying the exclusion in pom.xml if you are using maven.

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The default tomcat port is 8080. To change it, specify the server.port property with desired port in the application properties or yaml. application.properties: server.port=8091 application.yml: server: port: 8091 Alternatively, you may pass the property as JVM option as -Dserver.port=8091 .

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@SpringBootApplication annotation can be used to enable those three features below. @EnableAutoConfiguration enable Spring Boot's auto-configuration mechanism. @ComponentScan enable @Component scan on the package where the application is located. @Configuration allow to register extra beans in th...

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Yes, the Spring Boot Maven plugin includes a run goal that is used to quickly compile and run your application. mvn spring-boot:run Similarly, Spring Boot Gradle plugin also includes a bootRun task that can be used to run your application gradle bootRun

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Property Defaults : spring-boot-devtools module automatically applies sensible development-time configuration by disabling properties such as caching to false during development; Sets DEBUG mode for web logging group which helps get more information about incoming request. Automatic Restart : App...

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Spring boot automatically configures a lot of dependencies just by its availability in the classpath. For example, it can auto configure tomcat if the server container is not available. This is why spring boot is opinionated because it auto-configure many dependencies if it is not needed and we c...

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Starter dependencies combine many libraries into one based on its functionality/dependency and acts as a single starter package. It eliminates the need to manually add dependencies in build script and also manages compatibility and version mismatch issues.

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An ApplicationStartingEvent is sent at the start of a run but before any processing, except for the registration of listeners and initializers. An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in the context is known but before the context is created. An ApplicationP...

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Thymeleaf is a server-side Java template engine for web applications to bring elegant natural templates for your web apps. It is easy to integrate with spring Framework and works well with HTML5 Java-based web applications. In order to use thymeleaf in your project, add the dependency in your pro...

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The Spring Boot restart technology works by using 2 classloaders. Class that don't change ( 3rd party jars, as an example) are loaded into base classloader. Classes that actively change during development are loaded into restart classloader. When the application restarts, the restart classloader ...

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WebApplicationType is an enumeration that represent possible types of web application. NONE : The application is NOT an web application and should not start an embedded web server. REACTIVE : The application should run as a reactive web application and should start an embedded reactive web server...

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Both interfaces, CommandLineRunner and ApplicationRunner works in the same way and offers a single run method. The difference is, the CommandLineRunner interface provides access to the application arguments as a simple String array , while ApplcationRunner uses the ApplicationArguments interface,...

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The EnvironmentPostProcessor interface allows us to manipulate the Environment before even the application starts. This interface allows us to create support for encrypting/decrypting property values/ add new properties etc.

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Spring Boot uses commons-logging and LogBack implementation by default.

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This question is already answered here.

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You may enable auto-reload of spring boot application by adding the spring-boot-devtools dependency in the pom.xml file. org.springframework.boot spring-boot-devtools true

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As per wikipedia, Hypermedia as the Engine of Application State (HATEOAS) is a component of the REST application architecture that distinguishes it from other network application architectures. With HATEOAS, a client interacts with a network application which provide information dynamically throu...

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Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments. For example, swagger may be enabled only for lower environments and can be disabled for the production environment. @Configuration @EnableSwagger2 @Profile ( "...

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Include starter dependencies spring-boot-starter-jdbc or spring-boot-starterdata-jpa and include a JDBC driver on classpath. Spring boot will configure the database with the properties defined in application.properties. spring.datasource.url=jdbc:mysql://localhost:2001/mydb spring.datasource.user...

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Configure Spring Security in the application. If Spring Security is on the classpath, then Spring Boot automatically secures all HTTP endpoints with "basic" authentication. dependencies { ... compile("org.springframework. boot:spring-boot-starter-security " ) ... } Add the security configuration ...

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Swagger UI enables users to visualize and interact with the API's resources without having any of the implementation logic in place. It is automatically generated from your OpenAPI (formerly known as Swagger) Specification, with the visual documentation making it easy for back end implementation ...

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Use exclude property to disable specific auto-configuration. @EnableAutoConfiguration (exclude = {DataSourceAutoConfiguration . class})

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Reloading the changes without restarting the server is called hot swapping, Modern IDEs such as Eclipse, Intellij IDEA support hot-swapping of byte-code, so if you make a change that doesn't affect the class or method signatures it should reload cleanly with no side effects.

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Any Spring @RestController in a Spring Boot application should render JSON response by default as long as Jackson2 is on the classpath.

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HTTP response compression is supported by Jetty, Tomcat, and Undertow embedded containers. It can be enabled by adding server.compression.enabled=true in application.properties.

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Spring Boot provides error mapping by default that handles all errors in a sensible way, and it is registered as a 'global' error page in the servlet container.

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Spring Boot configures Spring MVC with a maximum file of 1MB per file and a maximum of 10MB of file data in a single request.

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Spring Boot provides spring-boot-starter-data-jpa, which is one of the Spring Boot Starters, to easily connect relational database with Spring MVC applications. org.springframework.boot spring-boot-starter-data-jpa

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You may use the exclude attribute with the annotation @SpringBootApplication. @SpringBootApplication (exclude = {Employee . class}) public class AppConfiguration {}

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IP whitelisting restricts access from unauthorized resource. Run service endpoints in HTTPS in PROD environment. Enable CSRF tokens. Prevent XSS attacks by using content security policies. Always upgrade to the latest versions of dependencies. Use vulnerability monitoring tools such as snyk. Don'...

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Mono and Flux are both reactive streams. A Mono is a stream of 0 to 1 element, whereas a Flux is a stream of 0 to N elements.

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Spring Boot Admin is a community project from codecentric. Spring boot admin helps manage and monitor your Spring Boot applications. The spring boot apps register with Spring Boot Admin Client (through HTTP) or discovered using Spring Cloud (for example, Eureka, Consul). The UI is just a Vue.js a...

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HttpMessageConverter is a strategy interface that specifies a converter that can convert from and to HTTP requests and responses. By default, the following HttpMessageConverters are loaded by Spring. ByteArrayHttpMessageConverter that can read and write byte arrays. ResourceHttpMessageConverter c...

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Apache Tomcat is a Web Server and Servlet system which is open source (freely available on the internet). It is created by Apache Software Foundation. Apache Tomcat is required to run Java Web Applications on the host and server based system. It runs JSP and Servlets within its web container.

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Catalina is the inbuilt web container of Apache tomcat. It can be located in bin directory. Catalina loads all the HTTP requests and instantiate the objects of GET and POST methods.

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Embedded container let Spring Boot application run as a JAR directly from the command prompt without setting up a web server. Embedded container auto configure web server and run the application. But to run a WAR file, you need to first set up a web server like Tomcat which has Servlet container ...

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Spring boot can control logging by specifying log levels on application.properties file. Spring Boot uses Commons Logging for all internal logging and you can change log levels by adding following lines in the application.properties file. logging.level.org.springframework.web=ERROR logging.level....

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The Spring Boot Maven Plugin provides Spring Boot support in Maven, packages executable jar or war archives and run an application "in-place". The Spring Boot Plugin has the following goals. spring-boot:run runs/executes your Spring Boot application. spring-boot:repackage repackages your jar/war ...

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Default is 200 threads. The property is maxThreads .

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"beans" endpoint displays a complete list of all the Spring beans in your application.

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Spring. Spring Boot. Spring framework provides comprehensive infrastructure support for developing Java applications.. Spring Boot is an extension of the Spring framework which eliminated the boilerplate configurations required for setting up a Spring application.. Spring takes an unopinionated v...

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Hibernate.

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Relaxed binding maps the Environment property to the bean property name even it is not an exact match. For example, dash-separated environment properties (app-name bound to appName) or capitalized properties as in PORT (bound to port). Spring boot supports relaxed binding. @Component @Configurati...

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Spring profiles provide a way to segregate parts of your application configuration, allows logical grouping of configurations based on environment and make it be available only in certain environments. Spring Boot by default, creates the property file, application.properties . To create spring pr...

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@SpringBootApplication. @EnableAutoConfiguration. @SpringBootApplication allows you to run the Main class as a JAR with an embedded container. It enables Java configuration, and it also enables Component Scanning. @EnableAutoConfiguration enables automatic configuration features of the Spring Boo...

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Spring Boot Maven Plugin plugin provides several goals to work with a Spring Boot application: Creates a jar or war file that is auto-executable, runs your Spring Boot application, integrate your Spring Boot application to the integration-test phase so that the application starts before it. gener...

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@Value annotation can be used to access the property defined in the application.properties. @Value also can set a default value to use if the property is missing in the application.properties. @Value ( "${host.name}" ) private String hostName; Using default value, @Value ( "${host.name:default-ho...

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SpringApplication allows an application to be initialized lazily. When lazy initialization is enabled, beans are created as they are needed rather than during application startup. This reduces the startup time and especially in web apps, the bean is not loaded until an HTTP request is received. s...

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Yes. Spring Boot supports XML based configuration although it supports Java-based configuration. To load XML configurations, create a @Configuration class and use @ImportResource annotation to load XML configuration files.

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Spring boot has a starter for ActiveMQ known as "spring-boot-starter-activemq" can be added in your project build configuration as a dependency that provides default settings. To configure your external ActiveMQ Broker, configure the ActiveMQ broker URL details in the spring.activemq.broker-url c...

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Most of the embedded servers and external servers support HTTP compression. It can be enabled by adding server.compression.enabled=true in application.properties.

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Endpoints. Details. env This endpoint exposes properties from Spring Configurable environment. health Displays the health information of application. shutdown Allows the application to shutdown gracefully. auditevents exposes all audit event for the application. metrics displays "metrics" informa...

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Use exclude attribute of @EnableAutoConfiguration to specific auto-configuration classes that you do not want being auto-configured. @EnableAutoConfiguration (exclude = {DataSourceAutoConfiguration . class,SecurityAutoConfiguration . class}) if the class is not on the classpath, use the excludeNa...

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Spring boot automatically maps / src/main/resources/static as static resource folder. To add css or js, create subdirectories like /src/main/resources/static/css/ and /src/main/resources/static/js.

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Batch processing involves the processing of large volumes of data. Spring boot batch provides reusable components, provides services and features for optimization and partition techniques, resulting in high volume and high-performance batch jobs. Use spring-boot-starter-batch to implement batch p...

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io.spring.dependency-management gradle plugin provides Maven-like dependency management functionality. buildscript { repositories { maven { url ' https: // repo . spring . io / plugins-snapshot ' } } dependencies { classpath ' io . spring . gradle : dependency-management-plugin : 1.0.7 . BUILD-SN...

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To enable SSL or HTTPS for your Spring Boot web application, place the certificate ( .p12 or .jks extension) under the resources folder, and define the server.ssl.* configuration in the application.properties. server.port=8443 server.ssl.enabled=true server.ssl.key-alias=tomcatApp-localhost serve...

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@ConditionalOnBean annotation can be used to declare a condition. Only if the specified condition is satisfied then only bean will be added to the application context.

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No.

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@ConfigurationProperties support Relaxed binding & Metadata features while @Value doesn't. @Value support SpEL evaluation while @ConfigurationProperties doesn't.

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The "spring-boot-starter-parent" is a special starter that provides useful Maven defaults. It provides default configurations to your application and also the complete dependency tree to quickly build your Spring Boot project. Default java version is 1.6. you may override this by specifying a pro...

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ApplicationContext is the core interface, represents the Spring IoC container and is responsible for instantiating, configuring, and assembling the beans. ApplicationContext is responsible for bean factory methods for accessing application components, loading file resources, internalization, etc....

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The application starts using the "main method" which calls the "run" method. From the run method, the main application context kicks off which searches for the classes annotated with @Configuration and initializes all the declared beans in those configuration classes. Based on the scope of those ...

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Both the Maven plugin and the Gradle plugin allow generating build information containing the coordinates, name, and version of the project. build-info goal, as shown in the following example: org.springframework.boot spring-boot-maven-...

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info and health are enabled by default. All others need to be enabled using configuration.

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JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way of securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. The client will need to authenticate with the serve...

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Spring Boot provides the following auto-configuration features for Spring MVC that works well with most applications. Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans. Support for serving static resources , including support for WebJars. Automatic registration of Convert...

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With Inbuilt Http Message conversion, we may implement minimal changes. @PostMapping (path = "/mapJsontoXML" , consumes = MediaType . APPLICATION_JSON_VALUE, produces = MediaType . APPLICATION_XML_VALUE) public @ResponseBody RequestModel mapJsonToXML( @RequestBody final RequestModel request) { re...

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"beans" endpoint is not enabled by default as it exposes certain sensitive information. However, for troubleshooting purposes, we can enable by configuration management.endpoints.web.exposure.include property in application.properties file or application.yaml. management.endpoints.web.exposure.in...

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We may use "metrics" actuator endpoint. Spring Boot provides "metrics" endpoint that can be used diagnostically to examine the metrics collected by an application. The endpoint is not available by default and must be exposed. management.endpoints.web.exposure.include=info,health,metrics When the ...

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Rename tne application.properties as required, for example, ConverterProj.properties and specify the JVM parameter -Dspring.config.name=ConverterProj so that the properties loads from the properties file.

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Spring Boot Application properties may contain sensitive information such as database passwords, MQ config details, CERT passwords. The password stored in the application properties is not recommended to be PLAIN-TEXT and needs to be encrypted. #Plain password not recommended app.mysql.password=M...

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The @ConditionalOnMissingBean annotation is a spring conditional annotation for registering beans only when they are not already in the application context. @Bean @ConditionalOnMissingBean (SomeBean . class) public SomeBean otherBean(){ return new SomeBean(); } The above bean will get loaded by S...

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Spring provides an easy way to handle exceptions using ControllerAdvice annotation. We handle all exceptions thrown by the controller class by implementing a ControlerAdvice class. Spring 3.2 brings support for a global @ExceptionHandler with the @ControllerAdvice annotation that enables a mechan...

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Add Jackson XML extension (Jackson-dataformat-XML) on the classpath, it will be used to render XML responses.

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The @ImportResource annotation is used to import one or more XML configuration files containing bean definitions.

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We can run Spring Boot inside docker by defining "Docker image" using Dockerfiles. Dockerfiles are a manifest of commands used to build and configure our docker container. To configure our Docker image to run our Spring Boot application, we will want to: Install latest CentOS (OS) image from Dock...

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Cloud Foundry is a PaaS (Platform as a Service) service where we can easily deploy and manage our spring/spring boot applications and the Cloud Foundry will take care of the rest of the cloud-based features like scalability, high availability, etc.

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Spring Boot provides a number of utilities and annotations to help to test your application. Use the spring-boot-starter-test "Starter", which imports both Spring Boot test modules (spring-boot-test and spring-boot-test-autoconfigure) as well as other below libraries. spring-boot-test, a spring b...

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CORS (Cross-Origin Resource Sharing) is a mechanism implemented by browsers and helps users to authorize cross-domain requests. This mechanism serves as an alternative to less secure and less powerful hacks of the kinds of IFrame or JSONP.

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To create SOAP web service, we need spring-boot-starter-web-services as following. org.springframework.boot spring-boot-starter-web-services wsdl4j wsdl4j

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Response Entity is an HTTP response object that includes headers,status code and payload/body of your response.

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There are 4 primary components of a Blockchain ecosystem: Node application, Shared ledger, Consensus algorithm, and Virtual Machine.

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Spring Boot Framework supports CORS and offers different ways to configure. Global CORS configuration: When a global CORS configuration needs to be defined with annotation-based, fine-grained configurations, then the same has to be declared in Spring MVC and combined with @CrossOrigin configurati...

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Docker is a software platform for building applications based on containers, small and lightweight execution environments that make shared use of the operating system kernel but otherwise run in isolation from one another. Docker is an open source project launched in 2013.

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Docker enables you to deploy a server environment in containers. A container is a unit of software that assembles code, provide runtime, inject dependencies, configure settings, and initialize the entire app in a single package that you can run reliably from one computing environment to another. ...

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Spring boot provides, single, independent executable JAR packaging with required dependencies. production-ready services for building microservices. actuator, that facilitates health check of the application and monitoring. embedded, pre-configured servers like tomcat. less development effort. mi...

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To register an auto-configuration class, you must have its fully-qualified name listed under the EnableAutoConfiguration key in the META-INF/spring.factories file: org.springframework.boot.autoconfigure.EnableAutoConfiguration=net.javapedia.autoconfigure.CustomAutoConfigurationExample

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When running integration tests for a Spring application, we must have an ApplicationContext. Spring Boot provides a special annotation for testing @SpringBootTest . This annotation creates an ApplicationContext from configuration classes indicated by its classes attribute. Spring Boot searches fo...

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Shutdown is an endpoint that allows the application to be gracefully shutdown. This feature is not enabled by default. You may enable this by using management.endpoint.shutdown.enabled=true in your application.properties file.

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We can use the application.properties to configure the web application type to disable web server. spring.main.web-application-type=none

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Spring @Profile allow developers to register beans by condition. For example, register beans based on what operating system (Windows, Linux/Unix) your application is running, or load database properties file based on the application running in development, test, staging or production environment....

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In Spring Boot, data validation can be performed using various mechanisms. One common approach is to use the validation annotations provided by the Bean Validation API, such as @NotNull, @Size, and @Pattern , on the fields of model objects. By including the necessary validation annotations, Sprin...

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The @TransactionalEventListener annotation in Spring Boot lets you listen to transactional events and perform actions based on those events . You can use this annotation on methods that should be invoked when a specific transactional event occurs such as before or after a transaction is committed...

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The @ModelAttribute annotation is used in Spring Boot to bind request parameters or form data to method parameters or model attributes. It can be applied to method parameters or method return values. When applied to method parameters, the @ModelAttribute annotation binds the incoming request para...

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You can change log levels in a running Spring Boot application without a restart using the Spring Boot Actuator's /actuator/loggers endpoint. This allows you to dynamically view and modify logging configurations via a simple HTTP request. Steps to Implement and Use Dynamic Logging 1. Add the Actu...

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HttpServletRequest is part of the standard Java Servlet API, designed for use in traditional, thread-per-request servlet containers. ServerHttpRequest is an abstraction introduced by the Spring Framework, primarily for use in reactive programming environments (like Spring WebFlux), which is not t...

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