How to replace an XML Configuration file with a Java Configuration file in a Spring application

How to replace an XML Configuration file with a Java Configuration file in a Spring application

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  How to replacean XML Configuration file with a Java Configuration file in a Spring application This is a guideline/reference document that can be used to understand how to replace an XML Spring Bean Configuration file with a Java Spring Bean Configuration file in a Spring application. This is a reference document for developers. Jayasree Perilakkalam
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  Introduction • This isa reference document that addresses the details regarding how to replace an XML configuration file with a Java configuration file in a Spring application. • This document can also be referenced to understand the steps for configuration using a Java Configuration file for a Spring application. • This document does not indicate that pure Java Configuration for a Spring application per se is better than XML configuration. It will depend on the scope of the application whether to choose one and not the other. • Any questions/suggestions/comments are welcome via the comments section below.
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  Capabilities Addressed • Read“Property” values from “properties” file • Bean configuration
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  Read “properties” froma file • What is a property? - Property is a key/value pair and is available in a file in the “resources” folder in a Java/Spring based project - It is entered in the format -> <key>=<value>
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  Read “properties” froma file • Annotations used - @PropertySource –> This is placed on classes annotated with @Configuration and defines the “properties” file. - @Value –> This is used to specify an expression on fields or methods. This expression can be a placeholder and a property’s key can be specified here. We can also specify default values for the property.
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  Read “properties” froma file • A sample is as follows: @Component(“examp”) public class Example { … … @Value(“${exampInt:111}”) private int exampleInt; @Value(“${nameProperty}”) private String nameProp; … public String getNameProp() { return nameProp; } … }
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  Bean configuration • Annotationsused - @Configuration -> The Java Configuration file will have @Configuration annotation. - @ComponentScan -> This tells Spring to look for other configurations, services, components in the package specified here. Spring will auto detect and register the beans from the package specified. If the package specified does not exist, Spring will scan the package of the class that has this annotation. - @Bean -> This is placed on a method that instantiates the concrete class. It’s usually a better practice to have return type as an interface type for this method. This serves as the bean definition. The name as defined in the @Bean notation is same as “id” as defined in the XML Configuration file. - @Component -> This is used to enable auto-discovery of the particular bean (Java object). When applied on a POJO class, Spring framework will auto-detect this class for dependency injection. - @EnableAspectJAutoProxy -> This is used on @Configuration classes. This enables support for @Aspect annotation, similar to functionality found in Spring’s <aop:aspectj-autoproxy> XML element.
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  Bean configuration • Asample bean configuration is as follows: @Configuration @ComponentScan(basePackages=“com.examplestudy”) @PropertySource(value={“classpath:properties/examp.properties”}) public class ExampleConfig { … … @Bean(“name”) private Name getName() { return new Name(“Hello”, “Hello”); } … }
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  A sample SpringBean Configuration file @Configuration @ComponentScan(basePackages=“com.examplestudy”) @PropertySource(value={“classpath:properties/examp.properties”}) public class ExampleConfig { @Bean public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() { return new PropertySourcesPlaceholderConfigurer(); } … … } This is a standard Spring bean. This is equivalent to <context:property-placeholder/> in a XML Config file. This is used to resolve placeholders against the properties from a local file/environment variable/system properties.
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  A test appusing the concepts learnt • Run the following Java app public class TestApp { public static void main(String[] args) { ApplicationContext context = new AnnotationConfigApplicationContext(ExampleConfig.class); Name name = (Name) context.getBean(“name”); System.out.println(name); Example examp = (Example) context.getBean(“examp”); System.out.println(examp.getNameProp(); ((AnnotationConfigApplicationContext)context).close(); } } // a sample “Name” class is as follows: public class Name { private String firstName; private String lastName; public Name (String firstName. String lastName) { this.firstName = firstName; this.lastName = lastName; } public String toString() { return firstName + “ “ + lastName; } }
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  Conclusion • This documentis meant to be a reference guide for developing re- usable software components and loosely coupled applications. • References I used to create this presentation are wiki pages/internet, my enrolled programming related courses and my past work experience. Thank you