Injecting a Spring Bean into a Servlet

I've done some searching on the web for how to cleanly inject a spring-managed bean into a servlet. There are a number of ways, but I believe this is the cleanest.

Assuming you have a bean, limaBean, that you want to inject into a servlet, here is the applicationContext.xml:

  <bean id="limaBean" class="com.example.LimaBeanImpl">

  <bean class="org.springframework.web.context.support.ServletContextAttributeExporter">
      <property name="attributes">
          <map>
              <entry key="limaBeanInServletContext">
                  <ref bean="limaBean">
              </ref>
          </entry></map>
      </property>
  </bean>

The ServletContextAttributeExporter takes an existing managed bean, 'limaBean', and injects it into the ServletContext under the name 'limaBeanInServletContext'.

The servlet accesses this bean like:

public class DocumentViewerServlet extends HttpServlet
{

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException
  {
      LimaBean limaBean = getLimaBean();
      limaBean.doSomething();

     ...
  }

  private DocumentService getLimaBean()
  {
      ServletContext servletContext = this.getServletContext();

      return (LimaBean) servletContext
          .getAttribute("limaBeanInServletContext");
  }
}

At runtime, Spring will inject the bean and everything works.

The reason you wanted to inject the bean in the first place, though, was so that you could easily write a test that injects the bean.

Set the attribute on org.springframework.mock.web.MockServletConfig and pass that into the servlets init(ServletConfig) method.

public class VegetableServletTest extends TestCase
{
  private VegetableServlet servlet = null;
  private LimaBean fakeLimaBean = null;

  protected void setUp() throws Exception
  {
      super.setUp();

      servlet = new VegetableServlet();
      fakeLimaBean = new FakeLimaBean();

      MockServletConfig config = new MockServletConfig();
           config.getServletContext().setAttribute("limaBeanInServletContext", 
           fakeLimaBean);
   
      servlet.init(config);
   }

}