Intermediate Spring Matt Wheeler

Notes This is a training NOT a presentation Please ask questions Prerequisites – Introduction to Java Stack – Basic Java and XML skills – Installed LdsTech IDE (or other equivalent – good luck there ;)

Review Bean lifecycle XML Schema-based Configuration (namespace handlers) Lifecycle hooks Bean Initialization (JSR …) Bean post processors Component scanning Spring Component Annotations DI Annotations

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

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

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 <data-source driver-class="org.h2.Driver" url="jdbc:h2:mem:stack-starter;MODE=Oracle" user="#{databaseUsername}" password="#{databasePassword}" override="true" db-env="EMBEDDED"/>

Additional Injection Annotations Many additional injection annotations Please refer to the Spring documentation here: – ng-framework-reference/html/beans.html#beans- annotation-config AnnotationExampleDescription private String something Spring EL can be used in correlation to inject a property private SomeBean someBean; Injects by name instead of type. Slight differences Used for injecting Collections. If name not explicitly specified it uses the name of the property being private SomeBean someBean; Spring proprietary annotation almost equivalent to JSR but with a required attribute.

Providers Providers allow us to defer instantiation or accessing a resource until it is accessed 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

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 public class private Provider prizeRabbit; … }

Provider Demo DEMO

Lab 1: Providers _1_Advanced_Injection

Web Context Listener Loading application context in a web environment

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);

Servlet Listeners The Java Servlet spec provides a listener (startup hook) – Triggers these listeners to run on startup Spring utilized this functionality and created a listener – Will load the application context on start up

Context Loader Listener Specifically the following configures this listener in web.xml: And utilizes the following context parameter org.springframework.web.context.ContextLoaderListener contextConfigLocation classpath:META- INF/spring/applicationContext.xml,classpath:*beans.xml classpath:anotherContext.xml

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

Application Context and Servlet For the given servlet configuration (web.xml) Application Context accessed as follows: servlet org.lds.training.TrainingServlet servlet /servlet public class TrainingServlet extends HttpServlet 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(); }

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

Utilizing a Spring Request Handler The configuration: trainingHandler org.springframework.web.context.support.HttpRequestHandlerServlet trainingHandler /trainingHandler //Java Implementations public class TrainingRequestHandler implements HttpRequestHandler private SomeBean someBean; public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { someBean.printSomething(); }

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

Lab 2: Web Context Listener _2_Web_Context_Listener

Template for code

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