Implement interface in runtime Java EE and Spring - spring

Question

I would like to implement the interface at runtime based on variable.
Example :
Class A implements interface1 {
public getValue() {}
}
Class B implements interface1 {
public getValue() {}
}
So I would like to have variable sitting in configuration..., for example ClasstoImplement=A
So, if ClasstoImplement=A, then I need to call Class A.getValue()
If ClasstoImplement=B, then I need to call Class B.getValue() at runtime. And I should be able to change value of ClasstoImplement at runtime.
My application is Spring based and runs in Tomcat.
Can someone please help me to find out if there is any way??

Answer 1

There are many possible solutions. The one of them is to use org.springframework.aop.target.HotSwappableTargetSource.
take a look at implementation that could be considered:
public class CustomSwappable<T> implements Interface1 {
private HotSwappableTargetSource targetSource;
private String key;
private Map<String, T> swappableBeans;
#PostConstruct
private void init() {
targetSource = new HotSwappableTargetSource(swappableBeans.values().iterator().next()); // first is the default
}
// you need to track changes in config and call this method if any modifications were done
public void configChanged(String key, String value) {
if (!this.key.equals(key)) {
return;
}
if (!swappableBeans.containsKey(value)) {
return;
}
targetSource.swap(swappableBeans.get(value));
}
#Override
public String getValue() {
return ((Interface1)targetSource.getTarget()).execute();
}
#Required
public void setConfigurationKey(String key) {
this.key = key;
}
#Required
public void setSwappableBeans(Map<String, T> swappableBeans) {
this.swappableBeans = swappableBeans;
}
}
and bean declaration should as follows:
<bean id="Interface1Swappable" class="path.to.CustomSwappable">
<property name="configurationKey" value="swappableKey"/>
<property name="swappableBeans">
<util:map value-type="path.toInterface1">
<!-- first is default -->
<entry key="classA">
<bean class="path.to.class.A"/>
</entry>
<entry key="classB">
<bean class="path.to.class.B"/>
</entry>
</util:map>
</property>
</bean>