Tag: spring

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Application context XML configuration in a Spring Boot web service

A colleague told me recently he didn’t use Spring for his latest REST project because he couldn’t get the beans defined in a XML configuration file loaded. He was familiar with Spring but had never boot strapped a brand new project. I didn’t realise this could be a problem because I have used Spring MVC for a very long time. He was right. It was not obvious. For example, in the Spring Boot tutorial Building a RESTful Web Service, everything is @Autowired. In a real application, you might need to define some beans in a XML configuration file. For example, database connection information for the persistence layer.

Using the example from my previous post on Spring Boot. You can use the annotation @ImportResource to load XML configuration files.

@SpringBootApplication
@ComponentScan
@ImportResource("classpath:spring-config.xml")
public class Application extends SpringBootServletInitializer {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
}

Spring will auto scan classes annotated with @Service, @Repository, @Controller and @Component. Because Spring AOP is proxy-based, your DAO classes should implement interfaces. For example, 

public interface OrderDao {
  Order getOrder(int id) throw OrderNotFoundException;
}

@Repository
public class OrderDaoImpl implements OrderDao {
  private JdbcTemplate jdbcTemplate;
  @Autowired 
  public void setMyDataSource(DataSource myDataSource) {
    this.jdbcTemplate = new JdbcTemplate(myDataSource);
  }
}

For some reason, Spring’s own JdbcDaoSupport class is not autowired enabled. If you choose to extend JdbcDaoSupport, you will need to use XML configuration to set the datasource manually. I prefer to have JdbcTemplate as a member and @Autowired the setter instead.

The datasource is defined in the XML file spring-config.xml. The file is located in src/main/resources in a maven project. (Please use a connection pool in a real application. I’m using BasicDataSource here for simplicity sake).

<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
  <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
  <property name="url" value="${db.url}"/>
  <property name="username" value="${db.username}"/>
  <property name="password" value="${db.password}"/>
</bean>

The properties are defined in application.properties, also in src/main/resources.

db.url=jdbc:sqlserver://localhost:1433;DatabaseName=Orders
db.username=Luser
db.password=Pwd

Note: I’m using Spring Boot 1.3.5

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Spring dependency injection for Struts Actions

Being used to Spring MVC, I was surprised when I discovered Struts did not use the Action bean I created in the Spring config file when handling web requests. Basically I needed a DAO wired into an existing Struts Action. I created a bean with the appropriate setter for the Struts Action in the Spring config file. However, I got a nasty null pointer exception because the setter was never called.

This should have been obvious if I have given it a thought. The Struts Actions in the web app are managed by Struts, not Spring. To get Spring to perform dependency injection on Struts Actions, you need to use the DelegatingActionProxy.

In the Struts config file

<action path="/store/order" type="org.springframework.web.struts.DelegatingActionProxy" name="orderForm" validate="false">
	<forward name="success" path="/jsp/view.jsp" />
</action>

In the Spring config file

<bean name="/store/order" class="com.whileloop.web.action.OrderAction">
    <property name="basketDao" ref="basketDao"/>
</bean>