Skip to main content

Creating Spring Bean dynamically in the Runtime

In my training someone asked me whether it is possible to create an object (a Spring Bean) dynamically so you can choose which implementation you want to have in the runtime. So at the compile time you don't know what object actually should be created yet. The application should decide what object to be created based on a property file.

1. We create an annotation so we can mark the method which should be able to create the object dynamically:

...
package your.package;
...
@Retention(RetentionPolicy.RUNTIME)
public @interface InjectDynamicObject {
}
...

2. Use the new created annotation in your method which should be able to create the object dynamically:

...
@Named("customerBo")
public class CustomerBoImpl implements CustomerBo {
...
    @Override
  @InjectDynamicObject
  public Customer getDynamicCustomer() {
        return this.dynamicCustomer;
}
...

3. Write an aspect with Pointcut and Advise which change the object returned by the method in the step 2:

...
@Named
@Aspect
public class DynamicObjectAspect {

    // This comes from the property file 
@Value("#{objects.object}")
private String object;

@Inject
private ApplicationContext applicationContext;

@Pointcut("execution(@your.package.InjectDynamicObject * *(..))")
public void beanAnnotatedWithInjectDynamicObject() {
}

@Around("beanAnnotatedWithInjectDynamicObject()")
public Object adviceBeanAnnotatedWithInjectDynamicObject(
ProceedingJoinPoint pjp) throws Throwable {
Object returnResult = pjp.proceed();
       // Create the bean or object depends on the property file
Object createdObject = applicationContext.getBean(object);
return createdObject;
}
}
...

4. Write your unit test to test the method:

...
    @Test
public void testCustomerOnlineOrOffline() {
// Dynamic object creation
System.out.println("DYNAMIC CUSTOMER: "
+ customerBo.getDynamicCustomer().getName());
}
...

OK, there is another easier way to do this ;-) Without Aspects and AspectJ, just pure Spring:

Just inject all your component implementations into a Map and get the correct implementation out of it. Just like what we have done in eXTra Client application. Please take a look at our implementation of PluginsLocatorManager as an example: http://goo.gl/itpcb. Spring injects the Map with Bean name as String and the Bean itself automagically. "... Even typed Maps can be autowired as long as the expected key type is String. The Map values will contain all beans of the expected type, and the keys will contain the corresponding bean names" (see Spring documentation for details).

...
@Named("customerBo")
public class CustomerBoImpl implements CustomerBo {
...
    // We inject the customer implementations into a Map
    @Inject
    private Map<String, Customer> customerDynamicMap;


    // This comes from the property file as a key for the Map
@Value("#{objects.object}")
private String object;
    
    @Override
  public Customer getDynamicCustomer() {
        return this.customerDynamicMap.get(object);
}
...

Have fun!
Lofi

Comments

roman said…

SEM SERVICES
I am fully satisfied with the information you have posted. Good job. Keep posting:)
CUSTOMIZED ERP SOLUTIONS
Manju behera said…
Thanks for this awesome post. I was going through the Github link and found ot that dynamicCustomerWithMap is no where set. Can you please let me know where you are setting values in Map(dynamicCustomerWithMap)?
Prayan Learning said…
Great blog. An important
image annotation technique which outlines the object in the image with a box, for object classification and localization models.
Onlineemenu said…
I recently came across your blog and have been reading along. I thought I would leave my first comment. I don't know what to say except that I have enjoyed reading. Nice blog.

Software consultant Company Frisco

Sales Tracking development company

Hire Apple iTv Developers

Hire Certified Hadoop Developers

Popular posts from this blog

Software Development Macro and Micro Process

If you think that in year 2012 all companies which produce software and IT divisions in our world have already their optimized software development process, you are wrong. It seems that we - software architects, software developers or whatever your title is - still need to optimize the software development process in many software companies and IT divisions.

So what do you do if you enter a software company or IT division and you see following things:

1. There is a perfect project management process to handle all those development of software butit is a pure project management without a context to software development. So basically you only take care of cost, time, budget and quality factors. In the software development you still use the old fashioned waterfall process.

2. From the tooling point of view: you have a project management planning and controlling tool but you are still in the beginning of Wiki (almost no collaboration tool) andyou don't use issues tracking system to han…