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Intermediate Spring Matt Wheeler. Notes This is a training NOT a presentation Please ask questions Prerequisites – Introduction to Java Stack – Basic.

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Presentation on theme: "Intermediate Spring Matt Wheeler. Notes This is a training NOT a presentation Please ask questions Prerequisites – Introduction to Java Stack – Basic."— Presentation transcript:

1 Intermediate Spring Matt Wheeler

2 Notes This is a training NOT a presentation Please ask questions Prerequisites – Introduction to Java Stack – Basic Java and XML skills – Introduction to Spring – Introduction to Spring Part 2 – Installed LDSTech IDE (or other equivalent)

3 Review Bean lifecycle XML Schema-based Configuration (namespace handlers) Lifecycle hooks Bean Initialization (JSR 250, @PostConstruct, …) Bean post processors Component scanning Spring Component Annotations DI Annotations (JSR 330, @Inject, @Named)

4 Overview Advanced Injection Providers Spring EL Additional Injection Annotations Application Context web integration Testing framework

5 Providers Providers allow us to defer instantiation of a resource until it is needed Providers facilitate (from the JavaDoc): – Retrieving multiple instances – Lazy or optimal retrieval of an instance – Breaking circular dependencies – Abstracting scope so you can look up an instance in a smaller scope from an instance in a containing scope

6 Previous Training Lab We used the @Named annotation to select the prototypeRabbit to inject into the farm as the prize rabbit The result was something like the following Does anyone see any problem with this? @Component public class Farm { @Inject @Named("prototypeRabbit") private Rabbit prizeRabbit; … }

7 Provider Demo DEMO

8 Spring EL (SpEL) Allows access to Spring beans and properties Supports querying and manipulating object graph at runtime Similar syntax to Unified EL (but more extensive) – Method invocation, string templating Namespace handlers use it to inject references into attributes For more specifics, please see the Spring docs: – g-framework-reference/html/expressions.html

9 Spring EL Examples We recommend only using this when necessary – For example When extracting a property from a map Or injecting a reference into a namespace handler

10 Additional Injection Annotations Many additional injection annotations Please refer to the Spring documentation here: – ng-framework-reference/html/beans.html#beans- annotation-config AnnotationExampleDescription @Value@Value("#{someBean.someProperty}") private String something Spring EL can be used in correlation with @Value to inject a property @Resource private SomeBean someBean; Injects by name instead of type. Can inject Collections unlike @Named. If name not explicitly specified it uses the name of the property being annotated. Does not work with Provider. @Autowired private SomeBean someBean; Spring proprietary annotation almost equivalent to JSR 330 @Inject but with a required attribute.

11 Lab 1: Providers _1_Advanced_Injection

12 Web Context Listener Loading application contexts in a web environment

13 Traditionally Previously we have loaded application contexts with something like: In a web environment however – You will want the context to automatically be loaded on startup – And be shared across the entire application ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); SomeBean someBean = context.getBean(SomeBean.class);

14 Servlet Listeners The Java Servlet spec provides a listener (startup hook) – Listeners are triggered to run on startup Spring utilizes this functionality and has created a listener that will load the application context when the application starts up

15 Context Loader Listener Here is the web.xml configuration: Utilizes the following context parameter: org.springframework.web.context.ContextLoaderListener contextConfigLocation classpath:META- INF/spring/applicationContext.xml,classpath:*beans.xml classpath:anotherContext.xml

16 Application Contexts and Servlets Servlets not instantiated by Spring – Instantiated by the servlet container – Spring unable to inject dependencies However Spring provides a way to access the application context

17 Application Context and Servlet For the given servlet configuration (web.xml) Application Context accessed as follows: servlet servlet /servlet public class TrainingServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //Context loader listener stores context in the servlet context - which is why it is required ApplicationContext applicationContext = WebApplicationContextUtils.getWebApplicationContext(getServletContext()); SomeBean someBean = (SomeBean) applicationContext.getBean(SomeBean.class); someBean.printSomething(); }

18 A Better Way Spring provides a servlet that delegates to a bean that is Spring managed – Called an HttpRequestHandler – Allows annotations and injection – Create a Spring bean that matches the name of the servlet name This provides the mapping between the two

19 Utilizing a Spring Request Handler The configuration: trainingHandler trainingHandler /trainingHandler @Component("trainingHandler") public class TrainingRequestHandler implements HttpRequestHandler { @Inject private SomeBean someBean; public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { someBean.printSomething(); }

20 Spring MVC and Application Contexts Spring MVC provides and even better way to integrate with the web container – Look forward to further discussion of this in a future training

21 Lab 2: Web Context Listener _2_Web_Context_Listener

22 Spring Testing Spring promotes testing in two prominent ways – Making the code more testable – Proving a testing framework

23 Testable Code Dependency injection decouples code from the container – POJOs are normally easier to test Dependencies are clearly defined – Allows you to swap implementations

24 Testing Help Additionally we have an application context that can manage dependencies Reloading the context for each test could be time consuming and unnecessary Spring provides support for loading the context once per JVM (unless you explicitly tell it to reload)

25 Testing Framework Many good testing frameworks available – JUnit – TestNG Spring provides a context loader for tests Currently Spring supports JUnit 3, JUnit 4, and TestNG – We will be using TestNG

26 Spring Test Framework @ContextConfiguration – Allows you to specify application contexts to load – Important: Loaded in the order specified Later bean definitions of the same name will override earlier ones Allows us to utilize everything in the project context – But selectively override bean definitions in the test contexts AbstractTestNGSpringContextTests @ContextConfiguration(locations={"classpath*:*beans.xml","classpath*:*beans- test.xml"}) public class FarmIT extends AbstractTestNGSpringContextTests { //… }


28 For example The application bean definition file The test bean definition file

29 Stack Utils namespace handler (stack- utils:null) Additionally, sometimes you would like the value to be null in a test – This can be accomplished with a Stack provided Xml- schema based configuration – For more information: sites/stack/module.html?module=spring-utils sites/stack/module.html?module=spring-utils/xsddoc/

30 Another example The application bean definition file The test bean definition file

31 Testing with a Database Suppose you wanted to use a database to test – Normally You would add data, run the test, and then clean it up – Spring provides transactional support Data from the test automatically rolls back after the test – Must extend AbstractTransactionalTestNGSpringContextTests Must specify a transaction manager in your bean definition – Additional documentation: framework-reference/html/testing.html#testcontext-tx

32 Spring Provides Useful Testing Stubs Lastly Spring provides many useful stubs (mock objects) – JNDI – Servlet API – These can save a lot of code – Often more usable that dynamic mock objects For further information: – ng-framework-reference/html/testing.html#mock- objects

33 Lab 3: Spring Testing Integration _3_Spring_Testing_Integration

34 Credit where credit is due Spring Recipies 2 nd Edition (Gary Mak, Josh Long and Daniel Rubio)

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