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How to autowire a bean inside a Spring #Condition class

I have an interface IInterface.java like below:
public interface IInterface {
void printIt();
}
And there are two implementation classes for this: ImplementationA.java and ImplementationB.java
#Component
public class ImplementationA implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationA");
}
}
#Component
public class ImplementationB implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationB");
}
}
Now I have a listener class, which has this IInterface as a member:
#Component
#AllArgsConstructor
public class Listener {
IInterface iInterface;
public void doStuff(){
iInterface.printIt();
}
}
Now, my requirement is to inject either of ImplementationA.java or ImplementationB.java in the iInterface member of Listener.java based on certain condition.
After some research I started using the #Conditional annotation.
I added two classes ConditionA.java and ConditionB.java:
public class ConditionA implements Condition {
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return false;
}
}
public class ConditionB implements Condition {
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return true;
}
}
And I also changed my implementation classes as below(added the Conditional annotation):
#Component
#Conditional(ConditionA.class)
public class ImplementationA implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationA");
}
}
#Component
#Conditional(ConditionB.class)
public class ImplementationB implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationA");
}
}
This seems to work like a charm for me. Whichever implementation class I need to inject I just return true from its corresponding Condition class and return false from rest of the implementation class's Condition class.
However this next part is where I am facing the challenge:
So from the above solution, I was hardcoding the return true or return false from the matches method of the corresponding Condition class. What if I need to return a dynamic value based on another component.
Lets say I have a spring Component class MyCustomConfig which has a member customFlag and if this member is set to true, we need to inject ImplementationA.class.
I had tried the below(made the class #Component and also autowired MyCustomConfig):
#Component
public class ConditionA implements Condition {
#Autowired
MyCustomConfig myCustomConfig;
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return myCustomConfig.getCustomFlag();
}
}
However this simply does not work. myCustomConfig is not autowired and I get a null pointer exception.
Could someone please help me with this.

I think there is no chance for what you need with the use of implements Condition.
If you inspect the documentation for interface Condition which is what the class that you provide to #Conditional should do, in your case ConditionA and ConditionB it says:
Conditions must follow the same restrictions as
BeanFactoryPostProcessor and take care to never interact with bean
instances. For more fine-grained control of conditions that interact
with #Configuration beans consider implementing the
ConfigurationCondition interface.
Maybe this answer would provide a workaround for you as it mentioned above in documentation that in the case that you want to interfere with other beans you should implement your own custom ConfigurationCondition.
Just check that the phase where this ConfigurationCondition will run will be after the beans that you need are registered

I would register the bean using a configuration class and a #Bean as follows:
#Configuration
public class ImplementationConfig {
#Bean
public IInterface implementation(MyCustomConfig myCustomConfig) {
if (myCustomConfig.getCustomFlag()) {
return new ImplementationA();
} else {
return new ImplementationB();
}
}
}
You simply drop the Spring-related annotations in both ImplementationA and ImplementationB:
public class ImplementationA implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationA");
}
}
public class ImplementationB implements IInterface {
#Override
public void printIt() {
System.out.println("Inside ImplementationA");
}
}
And finally, you can drop the Condition classes.

Check this link https://stackoverflow.com/a/70351394/7237884 here.
The docs say
Conditions must follow the same restrictions as BeanFactoryPostProcessor and take care to never interact with bean instances. For more fine-grained control of conditions that interact with #Configuration beans consider implementing the ConfigurationCondition interface.

Changing the Spring beans implementation at runtime

I have an Interface and multiple implementation. I'm auto wiring the interface in classes for usage. I need to choose different implementation at runtime.
public class Util {
public void getClient();
}
Implementations
public class UtilOne implements Util {
public void getClient() {...}
}
public class UtilTwo implements Util {
public void getClient() {...}
}
#Configuration
public class AppConfig {
#Autowired
#Bean
#Primary
public Util utilOne() {
return new UtilOne();
}
#Autowired
#Bean
public Util utilTwo() {
return new UtilTwo();
}
}
#Component
public class DemoService {
#Autowired
private Util util;
}
For some reason if we are unable to get client in UtilOne, I want to switch to UtilTwo without restarting the app. I want to change the Util object in DemoService to UtilTwo object.
Property active.util will come from DB and can we updated from UI.

It doesn't work this way - if you have a certain implementation of Util wired to, say, class SampleClass (which is a singleton) you can't really change the implementation of the Util to something different without restarting the application context.
So instead of going this way, I suggest an alternative. You say that under certain conditions that evaluate in runtime you want to switch implementations. What kind of condition it is? Is it possible to extract this condition decision logic?
If so, you can autowire a special DynamicUtil that will hold the reference to all the utils and will call the required util depending on the condition:
// represents all possible business 'runtime' outcomes
enum ConditionOutcome {
A, B, C
}
interface ConditionEvaluator {
ConditionOutcome evaluate(); // when called in runtime will evaluate a condition that currently exists in the system
}
interface Util {
void foo();
ConditionOutcome relevantOfOutcome();
}
class Utill1Impl implements Util {
public void foo() {...}
public ConditionOutcome relevantOfOutcome() {return ConditionOutcome.A;}
}
class Utill2Impl implements Util {
public void foo() {...}
public ConditionOutcome relevantOfOutcome() {return ConditionOutcome.B;}
}
class Utill3Impl implements Util {
public void foo() {...}
public ConditionOutcome relevantOfOutcome() {return ConditionOutcome.C;}
}
class DynamicUtil {
private final Map<ConditionOutcome, Util> possibleImpls;
private final ConditionEvaluator evaluator;
public class DynamicUtil(List<Util> allImplementations, ConditionEvaluator evaluator) {
// create a map by calling the 'relevantOfOutcome' per util impl in a loop
this.evaluator = evaluator;
}
public void foo() {
ConditionOutcome key = evaluator.evaluate();
// pick the relevant implementation based on evaluated key
possibleImpls.get(key).foo();
}
}
Now with such a design you can dynamically add new possible outcomes (along with utils that should implement them. You classes in the system will have to autowire DynamicUtil though, so effectively you'll introduce one additional level of indirection but will gain flexibility
class SampleClass { // a business class that will need to work with util capable of being changed during the runtime
#Autowired
private DynamicUtil util;
...
}

You can try approach with delegating proxy. Have a primary Util bean that is just wrapper around actual implementation and allow to change its internal delegate at runtime. In addition you can create something like manager/helper class that holds references to all actual implementation beans to simplify switching between them.
#Component
#Primary
public class DelegatingUtil implements Util {
private Util delegate;
public void setDelegate(Util delegate){ this.delegate = delegate; }
public Util getDelegate(){ return delegate; }
public void getClient() {
return delegate.getClient();
}
}
And where switching logic applies:
// Use #Named or #Qualifier or any other way to obtain references to actual implementations
private Util defaultImpl;
private Util fallbackImpl;
#Autowired
private DelegatingUtil switcher;
public void switchToFallback(){
this.switcher.setDelegate(this.fallbackImpl);
}
Note, this is only schematic example, you should take care about details like bean creation order, injection with qualifiers (maybe conditional), initialization and so on.

Here is a simple approach based on your situation. The main idea is that read active.util property from DB by PropertyService and wrap your Utils into RouteUtil:
#Component
public class RouteUtil {
#Autowired
private PropertyService propertyService;
#Qualifier("one")
#Autowired
private Util utilOne;
#Qualifier("two")
#Autowired
private Util utilTwo;
public void getClient() {
if ("one".equals(propertyService.read("active.util"))) {
utilOne.getClient();
} else {
utilTwo.getClient();
}
}
}
and in DemoService:
#Service
public class DemoService {
#Autowired
private RouteUtil util;
// RouteUtil.getClient() ...
}
You can change active.util to select which Util will be used at runtime without restarting the app.

Spring provides you a solution which I personally didn't like. What you can do is declare a
#MyInterface
List<MyIntercase> myimpls
Where MyInterface is your interface and list will contain all the implementations. However, I (since I didn't like this solution) wrote my own solution, where you can have a static factory that is self-populated by all implementations. So you don't have to inject all your implementations but choose them at run-time from a factory either by class name or by custom-defined name. An additional advantage is that the custom-defined name must be unique per factory. So lets say you have some staged process and for each stage you have your own interface and your own factory. So you can have the same custom defined names for your implementations of different interfaces. Say you working with text formats XML, JSON and CSV and have an interface (and related factory) for say stage-1 stage-2 stage-3. So for each stage-X inteface you can have implemetations named JSON, XML and CSV so all you have to do is have a variable called currentType that will hold one of the values - JSON, XML and CSV and for each stage you can use the factory to get the appropriate implementation:
Stage1Handler handler = stage-1-factory.getInstance(currentValue);
Stage2Handler handler = stage-2-factory.getInstance(currentValue);
Stage3Handler handler = stage-3-factory.getInstance(currentValue);
where Stage[X]Handler is your interface. But this is just an additional benifit. My solution is available in Open-source MgntUtils library. The article about this particular fiture could be found here: Non-intrusive access to "Orphaned" Beans in Spring framework Also, I describe this feature in my library javadoc here. The library could be found as Maven artifact and on Github including source code and Javadoc

Calling method depending on environment in spring boot

I have two methods, implementations differ depending on environment (dev / prod).
Is it a good idea to use a variable from application.properties? For example:
production-mode:true
and use it:
#Value("${production-mode}")
private boolean isProd;
...
if (isProd) {
methodForProduction();
} else {
methodForDevelopment();
}
Do you have any suggestions or could you point me in the direction of some useful resources?

Spring boot comes with a profile management system that allow you to active or swap functionnality and behaviour depending on those.
Here is a link to the official documentation.
What you could do is create an interface and 2 implementations as such :
public interface MyClass {
void myMethod();
}
public class MyClassForDevelopment implements MyClass {
#Override
public void myMethod() { // your code for developement }
}
public class MyClassForProduction implements MyClass {
#Override
public void myMethod() { // your code for production }
}
And use the configuration of Spring boot as such :
#Configuration
public class MyConfiguration {
#Bean
#Profile("dev")
public MyClass myClassDev() { return new MyClassForDevelopment(); }
#Bean
#Profile("prod")
public MyClass myClassProd() { return new MyClassForProduction(); }
}

TestNG Listener equivalent for #BeforeClass, with access to context

I've spent several days looking for a way to move one of my #BeforeClass methods to listener class I can reference in xml where I define content os test suite.
Problem I'm facing is that I'm using Spring for DI, and in #BeforeClass method I add some attributes to testng context, so I can use them in other places (other listeners).
I tried using onStart(final ITestContext context) from ITestListener. But that method seems to be invoked before spring manages to create beans, and I cannot perform my operations, because all my beans are nulls.
I tried using onBeforeClass(ITestClass testClass) from IClassListener. But that method only provides ITestClass, which does not give me access to context, so I can't set my attributes.
Now I'm experimenting with onConfigurationSuccess(final ITestResult itr) from IConfigurationListener, but that requires using if statement to run my code only if configuration method name is equal to springTestContextPrepareTestInstance.
Does anyone know a better way of doing this?
[EDIT] code sample
#Component
public class CleanupHelper {
private static SomeBean someBean;
#Autowired
public CleanupHelper(SomeBean someBean){
CleanupHelper.someBean = someBean;
}
public static Object getSomething(){
return someBean.getSomething();
}
}
public class ExcludedGroupsListener implements IConfigurationListener {
#Override
public void onConfigurationSuccess(final ITestResult itr) {
if (itr.getName().contains("springTestContextPrepareTestInstance")) {
var something = CleanupHelper.getSomething();
if (something != null && someOtherCondition) {
itr.setAttribute("someObject", something);
}
}
}
}
#ContextConfiguration(classes = TestConfig.class)
public class SomeTests extends AbstractTestNGSpringContextTests {
#Test
public void someTest(){
// doSomething
}
}
#Configuration
#ComponentScan(basePackages = "com.some",
excludeFilters = #Filter(type = FilterType.REGEX, pattern = "com.some.else..*"))
public class TestConfig {
}
Above code works... unfortunately onConfigurationSuccess method is invoked after each configuration method.

Try with Annotation Transformers.
You can add it in your testng.xml like any other listener.
And in there you can do things like:
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import org.testng.IAnnotationTransformer;
import org.testng.annotations.ITestAnnotation;
public class TestAnnotationTransformer implements IAnnotationTransformer {
#SuppressWarnings("rawtypes")
#Override
public void transform(ITestAnnotation annotation, Class testClass, Constructor testConstructor, Method testMethod) {
if (testMethod.getName().equals("MyTest1"))
annotation.setGroups( new String[] {"GroupA" });
if(ignoreTestDependencies)
annotation.setIgnoreMissingDependencies(true);
}
}
Just an example, but you have many things there to play with.
Just bear in mind that, as I stated in the comments, this runs before runtime, so you won't be able to change things on the go like you would do with a normal listener.

Inject spring bean dynamically

In a java-spring web-app I would like to be able to dynamically inject beans.
For example I have an interface with 2 different implementations:
In my app I'm using some properties file to configure injections:
#Determines the interface type the app uses. Possible values: implA, implB
myinterface.type=implA
My injections actually loaded conditionally relaying on the properties values in the properties file. For example in this case myinterface.type=implA wherever I inject MyInterface the implementation that will be injected will be ImplA (I accomplished that by extending the Conditional annotation).
I would like that during runtime - once the properties are changed the following will happen (without server restart):
The right implementation will be injected. For example when setting myinterface.type=implB ImplB will be injected where-ever MyInterface is used
Spring Environment should be refreshed with the new values and re-injected as well to beans.
I thought of refreshing my context but that creates problems.
I thought maybe to use setters for injection and re-use those setters once properties are re-configured. Is there a working practice for such a requirement?
Any ideas?
UPDATE
As some suggested I can use a factory/registry that holds both implementations (ImplA and ImplB) and returns the right one by querying the relevant property.
If I do that I still have the second challenge - the environment. for example if my registry looks like this:
#Service
public class MyRegistry {
private String configurationValue;
private final MyInterface implA;
private final MyInterface implB;
#Inject
public MyRegistry(Environmant env, MyInterface implA, MyInterface ImplB) {
this.implA = implA;
this.implB = implB;
this.configurationValue = env.getProperty("myinterface.type");
}
public MyInterface getMyInterface() {
switch(configurationValue) {
case "implA":
return implA;
case "implB":
return implB;
}
}
}
Once property has changed I should re-inject my environment. any suggestions for that?
I know I can query that env inside the method instead of constructor but this is a performance reduction and also I would like to think of an ider for re-injecting environment (again, maybe using a setter injection?).

I would keep this task as simple as possible. Instead of conditionally load one implementation of the MyInterface interface at startup and then fire an event that triggers dynamic loading of another implementation of the same interface, I would tackle this problem in a different way, that is much simpler to implement and maintain.
First of all, I'd just load all possible implementations:
#Component
public class MyInterfaceImplementationsHolder {
#Autowired
private Map<String, MyInterface> implementations;
public MyInterface get(String impl) {
return this.implementations.get(impl);
}
}
This bean is just a holder for all implementations of the MyInterface interface. Nothing magic here, just common Spring autowiring behavior.
Now, wherever you need to inject a specific implementation of MyInterface, you could do it with the help of an interface:
public interface MyInterfaceReloader {
void changeImplementation(MyInterface impl);
}
Then, for every class that needs to be notified of a change of the implementation, just make it implement the MyInterfaceReloader interface. For instance:
#Component
public class SomeBean implements MyInterfaceReloader {
// Do not autowire
private MyInterface myInterface;
#Override
public void changeImplementation(MyInterface impl) {
this.myInterface = impl;
}
}
Finally, you need a bean that actually changes the implementation in every bean that has MyInterface as an attribute:
#Component
public class MyInterfaceImplementationUpdater {
#Autowired
private Map<String, MyInterfaceReloader> reloaders;
#Autowired
private MyInterfaceImplementationsHolder holder;
public void updateImplementations(String implBeanName) {
this.reloaders.forEach((k, v) ->
v.changeImplementation(this.holder.get(implBeanName)));
}
}
This simply autowires all beans that implement the MyInterfaceReloader interface and updates each one of them with the new implementation, which is retrieved from the holder and passed as an argument. Again, common Spring autowiring rules.
Whenever you want the implementation to be changed, you should just invoke the updateImplementations method with the name of the bean of the new implementation, which is the lower camel case simple name of the class, i.e. myImplA or myImplB for classes MyImplA and MyImplB.
You should also invoke this method at startup, so that an initial implementation is set on every bean that implements the MyInterfaceReloader interface.

I solved a similar issue by using org.apache.commons.configuration.PropertiesConfiguration and org.springframework.beans.factory.config.ServiceLocatorFactoryBean:
Let VehicleRepairService be an interface:
public interface VehicleRepairService {
void repair();
}
and CarRepairService and TruckRepairService two classes that implements it:
public class CarRepairService implements VehicleRepairService {
#Override
public void repair() {
System.out.println("repair a car");
}
}
public class TruckRepairService implements VehicleRepairService {
#Override
public void repair() {
System.out.println("repair a truck");
}
}
I create an interface for a service factory:
public interface VehicleRepairServiceFactory {
VehicleRepairService getRepairService(String serviceType);
}
Let use Config as configuration class:
#Configuration()
#ComponentScan(basePackages = "config.test")
public class Config {
#Bean
public PropertiesConfiguration configuration(){
try {
PropertiesConfiguration configuration = new PropertiesConfiguration("example.properties");
configuration
.setReloadingStrategy(new FileChangedReloadingStrategy());
return configuration;
} catch (ConfigurationException e) {
throw new IllegalStateException(e);
}
}
#Bean
public ServiceLocatorFactoryBean serviceLocatorFactoryBean() {
ServiceLocatorFactoryBean serviceLocatorFactoryBean = new ServiceLocatorFactoryBean();
serviceLocatorFactoryBean
.setServiceLocatorInterface(VehicleRepairServiceFactory.class);
return serviceLocatorFactoryBean;
}
#Bean
public CarRepairService carRepairService() {
return new CarRepairService();
}
#Bean
public TruckRepairService truckRepairService() {
return new TruckRepairService();
}
#Bean
public SomeService someService(){
return new SomeService();
}
}
By using FileChangedReloadingStrategy your configuration be reload when you change the property file.
service=truckRepairService
#service=carRepairService
Having the configuration and the factory in your service, let you can get the appropriate service from the factory using the current value of the property.
#Service
public class SomeService {
#Autowired
private VehicleRepairServiceFactory factory;
#Autowired
private PropertiesConfiguration configuration;
public void doSomething() {
String service = configuration.getString("service");
VehicleRepairService vehicleRepairService = factory.getRepairService(service);
vehicleRepairService.repair();
}
}
Hope it helps.

If I understand you correctly then the goal is not to replace injected object instances but to use different implementations during interface method call depends on some condition at run time.
If it is so then you can try to look at the Sring TargetSource mechanism in combination with ProxyFactoryBean. The point is that proxy objects will be injected to beans that uses your interface, and all the interface method calls will be sent to TargetSource target.
Let's call this "Polymorphic Proxy".
Have a look at example below:
ConditionalTargetSource.java
#Component
public class ConditionalTargetSource implements TargetSource {
#Autowired
private MyRegistry registry;
#Override
public Class<?> getTargetClass() {
return MyInterface.class;
}
#Override
public boolean isStatic() {
return false;
}
#Override
public Object getTarget() throws Exception {
return registry.getMyInterface();
}
#Override
public void releaseTarget(Object target) throws Exception {
//Do some staff here if you want to release something related to interface instances that was created with MyRegistry.
}
}
applicationContext.xml
<bean id="myInterfaceFactoryBean" class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="proxyInterfaces" value="MyInterface"/>
<property name="targetSource" ref="conditionalTargetSource"/>
</bean>
<bean name="conditionalTargetSource" class="ConditionalTargetSource"/>
SomeService.java
#Service
public class SomeService {
#Autowired
private MyInterface myInterfaceBean;
public void foo(){
//Here we have `myInterfaceBean` proxy that will do `conditionalTargetSource.getTarget().bar()`
myInterfaceBean.bar();
}
}
Also if you want to have both MyInterface implementations to be Spring beans, and the Spring context could not contains both instances at the same time then you can try to use ServiceLocatorFactoryBean with prototype target beans scope and Conditional annotation on target implementation classes. This approach can be used instead of MyRegistry.
P.S.
Probably Application Context refresh operation also can do what you want but it can cause other problems such as performance overheads.

This may be a duplicate question or at least very similar, anyway I answered this sort of question here: Spring bean partial autowire prototype constructor
Pretty much when you want a different beans for a dependency at run-time you need to use a prototype scope. Then you can use a configuration to return different implementations of the prototype bean. You will need to handle the logic on which implementation to return yourself, (they could even be returning 2 different singleton beans it doesn't matter) But say you want new beans, and the logic for returning the implementation is in a bean called SomeBeanWithLogic.isSomeBooleanExpression(), then you can make a configuration:
#Configuration
public class SpringConfiguration
{
#Bean
#Autowired
#Scope("prototype")
public MyInterface createBean(SomeBeanWithLogic someBeanWithLogic )
{
if (someBeanWithLogic .isSomeBooleanExpression())
{
return new ImplA(); // I could be a singleton bean
}
else
{
return new ImplB(); // I could also be a singleton bean
}
}
}
There should never be a need to reload the context. If for instance, you want the implementation of a bean to change at run-time, use the above. If you really need to reload your application, because this bean was used in constructors of a singleton bean or something weird, then you need to re-think your design, and if these beans are really singleton beans. You shouldn't be reloading the context to re-create singleton beans to achieve different run-time behavior, that is not needed.
Edit The first part of this answer answered the question about dynamically injecting beans. As asked, but I think the question is more of one: 'how can I change the implementation of a singleton bean at run-time'. This could be done with a proxy design pattern.
interface MyInterface
{
public String doStuff();
}
#Component
public class Bean implements MyInterface
{
boolean todo = false; // change me as needed
// autowire implementations or create instances within this class as needed
#Qualifier("implA")
#Autowired
MyInterface implA;
#Qualifier("implB")
#Autowired
MyInterface implB;
public String doStuff()
{
if (todo)
{
return implA.doStuff();
}
else
{
return implB.doStuff();
}
}
}

You can use #Resource annotation for injection as originally answered here
e.g.
#Component("implA")
public class ImplA implements MyInterface {
...
}
#Component("implB")
public class ImplB implements MyInterface {
...
}
#Component
public class DependentClass {
#Resource(name = "\${myinterface.type}")
private MyInterface impl;
}
and then set the implementation type in properties file as -
myinterface.type=implA

Be aware that - if interesting to know about - FileChangedReloadingStrategy makes your project highly dependent on the deployment conditions: the WAR/EAR should be exploded by container and your should have direct access to the file system, conditions that are not always met in all situations and environments.

You can use Spring #Conditional on a property value. Give both Beans the same name and it should work as only one Instance will be created.
Have a look here on how to use #Conditional on Services and Components:
http://blog.codeleak.pl/2015/11/how-to-register-components-using.html

public abstract class SystemService {
}
public class FooSystemService extends FileSystemService {
}
public class GoSystemService extends FileSystemService {
}
#Configuration
public class SystemServiceConf {
#Bean
#Conditional(SystemServiceCondition.class)
public SystemService systemService(#Value("${value.key}") value) {
switch (value) {
case A:
return new FooSystemService();
case B:
return new GoSystemService();
default:
throw new RuntimeException("unknown value ");
}
}
}
public class SystemServiceCondition implements Condition {
#Override
public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
return true;
}
}