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Showing posts from February, 2017

Spring Boot - Restful webservices with Jersey

In the previous posts, we have created a Spring Boot QuickStart , customized the embedded server and properties and running specific code after spring boot application starts . Now in this post, we will create Restful webservices with Jersey deployed on Undertow as a Spring Boot Application. Adding dependencies in pom.xml We will add spring-boot-starter-parent as parent of our maven based project. The added benefit of this is version management for spring dependencies. <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.0.RELEASE</version> </parent> Adding spring-boot-starter-jersey dependency This will add/ configure the jersey related dependencies. <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jersey</artifactId> </dependency> Adding spring-boot-starter-undertow depend

Spring Boot - ApplicationRunner and CommandLineRunner

Spring Boot provides two interfaces CommandLineRunner and ApplicationRunner to run specific piece of code when application is fully started. These interfaces get called just before run() on SpringApplication completes. CommandLineRunner This interface provides access to application arguments as string array. Let's see the example code for more clarity. @Component public class CommandLineAppStartupRunner implements CommandLineRunner { private static final Logger logger = LoggerFactory.getLogger(CommandLineAppStartupRunner.class); @Override public void run(String... args) throws Exception { logger.info("Application started with command-line arguments: {} . \n To kill this application, press Ctrl + C.", Arrays.toString(args)); } } ApplicationRunner ApplicationRunner wraps the raw application arguments and exposes interface ApplicationArguments which have many convinent methods to get arguments like getOptionNames() return all the arguments names

Spring Boot - changing/ configuring default embedded server

In the previous post , we have created a web-based Spring Boot application which uses Embedded Tomcat as the default server running on default port 8080 . Spring Boot supports Tomcat, Undetow and Jetty as embedded servers. Now, we will change and/ or configure the default embedded server and common properties to all the available servers. Spring Boot provides convenient way of configuring dependencies with its starters. For changing the embedded server, we will user its spring-boot-starter-undertow . Adding dependencies <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-undertow</artifactId> </dependency> spring-boot-starter-web comes with Embedded Tomcat. We need to exclude this dependency. <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <exclusions> <exclusion> <groupId>org.s

Spring Boot - A quick start

In this post, we will create a simple Spring Boot application which will run on embedded Apache Tomcat. What is Spring Boot? Spring Boot helps in creating stand-alone, production-grade application easily with minimum fuss. It is the opinionated view of Spring framework and other third party libraries which believes in convenient configuration based setup. Let's start building Spring Boot Application. Adding dependencies in pom.xml We will first add spring-boot-starter-parent as parent of our maven based project. <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.1.RELEASE</version> </parent> The benefit of adding spring-boot-starter-parent is that version managing of dependency is easy. You can omit the required version on the dependency. It will pick the one configured the parent pom or from starters pom. Also, it conveniently setup the build r

Spring Core - Bean scopes (Prototype vs Singleton)

In this post, we will discuss about various bean scopes and their differences. Bean scopes There are seven bean scopes Spring supports out of which five are only available if your ApplicationContext is web-aware. # Scope Explanation 1 singleton There will be single object of the bean per Spring IoC Container (Default). 2 prototype Scope beans to any number of object instances. Every time you get object of prototype bean from context, it will be brand new. 3 request Scope of the bean definition mapped to the lifecycle of HTTP Request. This is only available web-aware ApplicationContext . 4 session Scope of the bean definition mapped to the lifecycle of HTTP session. This is only available to web-aware ApplicationContext . 5 globalSession Scope of the bean definition mapped to the lifecycle of HTTP session usually used within Portlet context. This is only available to web-aware ApplicationContext . 6 application Scope of the bean definition mapp

Spring Core - Dependency Injection

What is Dependency Injection? Dependency injection is a process in which objects define their dependencies i.e. other objects they require to work, through a constructor, setter methods, factory methods. The container responsibility is to inject those while creating beans. With Dependency inject in place, we have cleaner code and clear way of decoupling. There are two prominent variants of Dependency Injection. Constructor based Dependency Injection Setter based Dependency Injection Constructor based Dependency Injection When you express your dependencies through constructor arguments and your container invoke your constructor with number of arguments, type of arguments expected by the constructor. Let's jump to one quick example. @Component public class ConstructorBasedFileParser { private Parser parser; @Autowired public ConstructorBasedFileParser(Parser parser) { this.parser = parser; } public void setParser(Parser parser) { this.parser = parser;

Spring Core - @Import annotation

In this post, we will learn about @Import annotation and its usage. You can see my previous post on how to create a simple spring core project. What is @Import annotation and usage? @Import annotation is equivalent to <import/> element in Spring XML configuration. It helps in splitting the single Java based configuration file into small, modular, maintainable and component based configuration. Let's see it with example. @Configuration @Import(value = { DBConfig.class, WelcomeGbConfig.class }) public class HelloGbAppConfig { } In above code snippet, we are importing two different configuration files viz. DBConfig , WelcomeGbConfig in application level configuration file HelloGbAppConfig . The above code is equivalent to Spring XML based configuration below. <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/bean

Spring Core - Java configuration example

In this post, we will create a spring context and will register bean via Java configuration file. You can see my previous post on how to create a simple spring core project. What is @Configuration annotation? @Configuration annotation indicates that there is one or more bean methods and spring containers can process to generate bean definitions at runtime. Also, @Bean annotation is used at method level to signifies that this will be registered as bean in spring context. Let's create a quick configuration class. @Configuration public class WelcomeGbConfig { @Bean GreetingService greetingService() { return new GreetingService(); } } Now, we will create spring context as follows. // using try with resources so that this context closes automatically try (ConfigurableApplicationContext context = new AnnotationConfigApplicationContext( WelcomeGbConfig.class);) { GreetingService greetingService = context.getBean(GreetingService.class); greetingService.gre

Spring Core - A quick start

In this post, we will create a Spring context and will get a bean object from it. What is Spring context? Spring context is also termed as Spring IoC container which is responsible for instantiate, configure and assemble the beans by reading configuration meta data from XML, Java annotations and/ or Java code in configuration files. Technologies used Spring 4.3.6.RELEASE, Maven Compiler 3.6.0 and Java 1.8 We will first create a simple maven project. You can select the maven-archtype-quickstart as archtype. Adding dependencies in pom.xml We will add spring-framework-bom in the dependency management. <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-framework-bom</artifactId> <version>4.3.6.RELEASE</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </depe

Java 8 - Method references

This article is in continuation to my other posts on Functional Interfaces , static and default methods and Lambda expressions . Method references are the special form of Lambda expression . When your lambda expression are doing nothing other than invoking existing behaviour (method), you can achieve same by referring it by name. :: is used to refer to a method. Method type arguments are infered by JRE at runtime from context it is defined. Types of method references Static method reference Instance method reference of particular object Instance method reference of an arbitrary object of particular type Constructor reference Static method reference When you refer static method of Containing class. e.g. ClassName::someStaticMethodName class MethodReferenceExample { public static int compareByAge(Employee first, Employee second) { return Integer.compare(first.age, second.age); } } Comparator compareByAge = MethodReferenceExample::compareByAge; Instanc

Java 8 - Streams in Action

In this post, we will cover following topics. What are Streams? What is a pipeline? Key points to remember for Streams. How to create Streams? What are Streams? Java 8 introduced new package java.util.stream which contains classes to perform SQL-like operations on elements. Stream is a sequence of elements on which you can perform aggregate operations (reduction, filtering, mapping, average, min, max etc.). It is not a data structure that stores elements like collection but carries values often lazily computed from source through pipeline . What is a pipeline? A pipeline is sequence of aggregate (reduction and terminal) operations on the source. It has following components. A source: Collections, Generator Function, array, I/O channel etc. zero or more intermediate operations: filter, map, sequential, sorted, distinct, limit, flatMap, parallel etc. Intermediate operations returns/produces stream. a termination operation: forEach, reduction, noneMatch, allMatch, c

Java 8 - Aggregate operations on Streams

This post is in continuation with my earlier posts on Streams . In this post we will discuss about aggregate operations on Streams. Aggregate operations on Streams You can perform intermediate and terminal operations on Streams. Intermediate operations result in a new stream and are lazily evaluated and will start when terminal operation is called. persons.stream().filter(p -> p.getGender() == Gender.MALE).forEach(System.out::println); In the snippet above, filter() doesn't start filtering immediately but create a new stream. It will only start when terminal operation is called and in above case when forEach() . Intermediate operations There are many intermediate operations that you can perform on Streams. Some of them are filter() , distinct() , sorted() , limit() , parallel() , sequential , map() , flatMap . filter() operation This takes Predicate functional interface as argument and the output stream of this operation will have only those elements which pass th