CODEWITHSUNDEEP
javaspringspring-boot
Ojama Tang
Ojama Tang

Reputation: 33

How to use abstract classes in Spring Boot?

@Component
public abstract class AbstractProcessTask implements Task {

  @Resource
  protected WorkOrderEventService workOrderEventService;
  @Resource
  protected NodeService nodeService;
  @Resource
  protected ConfigReader configReader;

  protected void updateStatus(WorkOrderEvent workOrderEvent, String status, String description) {
    workOrderEvent.setStatus(status);
    workOrderEvent.setComments(description);
    workOrderEventService.saveWorkOrderEvent(workOrderEvent);
  }
}

I write a abstract class for use,But I don't know how to use. At Old spring version,We can write abstract="true" in xml. for example:

<bean id="BaseEventAction" class="com.sinosig.evaluation.fcff.web.event.BasicEventAction"
        abstract="true" parent="BaseAction">
        <property name="rowFactory" ref="FcffCacheAdapter" />
        <property name="caculate" ref="CaculateService" />
        <property name="diffusion" ref="DeffusionService" />
</bean>

What should I do?

Upvotes: 3

Views: 19153

Answers (3)

Tsvetoslav Tsvetkov
Tsvetoslav Tsvetkov

Reputation: 1176

The abstract class should not be annotated by either @Service or @Component annotation as:

  1. Abstract class isn’t component-scanned since it can’t be instantiated without a concrete subclass
  2. Spring doesn’t support constructor injection in an abstract class, we should generally let the concrete subclasses provide the constructor arguments

So, for example:

abstract class Vehicle() {

  private final Helper helper;

  protected(Helper helper) {
    this.helper = helper;
  }
}


@Component
public class Car extends Vehicle() {

  public Car(Helper helper) {
    super(helper);
  }
}

Upvotes: 1

Shafin Mahmud
Shafin Mahmud

Reputation: 4071

Using @Component over an abstract class would not help Spring to create a bean from that (As of course, you know, you can not instantiate an object from an abstract class). Use @Component annotation over the concrete classes.

@Component
public class MyProcessTask extends AbstractProcessTask {
...
}

And the rest are okay. If spring finds the concrete classes in the scan path, the associated beans will be created automatically.

Don't confuse with attribute 'abstract=true'

When you mention the attribute abstract=true in a bean declaration, you are just abstracting the bean. Abstract beans in Spring are somewhat different from abstract classes. In fact, the abstract bean in Spring doesn't even have to be mapped to any class.

See this nice answer for more about What is meant by abstract=“true” in spring?

Upvotes: 4

Shariq
Shariq

Reputation: 506

You can simply extend the abstract class with another class, and use @Component in the subclass. You may also need to implement any methods in the superclass. 

@Component
public class AbstractChild extends AbstractProcessTask {
}

Upvotes: 3

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