This question is intended to make an answer for a useful issue.
Suppose we have a Spring application with a #Controller, an interface and different implementations of that interface.
We want that the #Controller use the interface with the proper implementation, based on the request that we receive.
Here is the #Controller:
#Controller
public class SampleController {
#RequestMapping(path = "/path/{service}", method = RequestMethod.GET)
public void method(#PathVariable("service") String service){
// here we have to use the right implementation of the interface
}
}
Here is the interface:
public interface SampleInterface {
public void sampleMethod(); // a sample method
}
Here is one of the possibile implementation:
public class SampleInterfaceImpl implements SampleInterface {
public void sampleMethod() {
// ...
}
}
And here is another one:
Here is one of the possibile implementation:
public class SampleInterfaceOtherImpl implements SampleInterface {
public void sampleMethod() {
// ...
}
}
Below I'll show the solution that I've found to use one of the implementations dynamically based on the request.
The solution I've found is this one.
First, we have to autowire the ApplicationContext in the #Controller.
#Autowired
private ApplicationContext appContext;
Second, we have to use the #Service annotation in the implementations of the interface.
In the example, I give them the names "Basic" and "Other".
#Service("Basic")
public class SampleInterfaceImpl implements SampleInterface {
public void sampleMethod() {
// ...
}
}
#Service("Other")
public class SampleInterfaceOtherImpl implements SampleInterface {
public void sampleMethod() {
// ...
}
}
Next, we have to obtain the implementation in the #Controller.
Here's one possible way:
#Controller
public class SampleController {
#Autowired
private ApplicationContext appContext;
#RequestMapping(path = "/path/{service}", method = RequestMethod.GET)
public void method(#PathVariable("service") String service){
SampleInterface sample = appContext.getBean(service, SampleInterface.class);
sample.sampleMethod();
}
}
In this way, Spring injects the right bean in a dynamic context, so the interface is resolved with the properly inmplementation.
I solved that problem like this:
Let the interface implement a method supports(...) and inject a List<SampleInterface> into your controller.
create a method getCurrentImpl(...) in the controller to resolve it with the help of supports
since Spring 4 the autowired list will be ordered if you implement the Ordered interface or use the annotation #Order.
This way you have no need for using the ApplicationContext explicitly.
Honestly I don't think the idea of exposing internal implementation details in the URL just to avoid writing some lines of code is good.
The solution proposed by #kriger at least adds one indirection step using a key / value approach.
I would prefer to create a Factory Bean (to be even more enterprise oriented even an Abstract Factory Pattern) that will choose which concrete implementation to use.
In this way you will be able to choose the interface in a separate place (the factory method) using any custom logic you wish.
And you will be able to decouple the service URL from the concrete implementation (which is not very safe).
If you are creating a very simple service your solution will work, but in an enterprise environment the use of patterns is vital to ensure maintenability and scalability.
I'm not convinced with your solution because there's an implicit link between an HTTP parameter value and a bean qualifier. Innocent change of the bean name would result in a disaster that could be tricky to debug. I would encapsulate all the necessary information in one place to ensure any changes only need to be done in a single bean:
#Controller
public class SampleController {
#Autowired
private SampleInterfaceImpl basic;
#Autowired
private SampleInterfaceOtherImpl other;
Map<String, SampleInterface> services;
#PostConstruct
void init() {
services = new HashMap()<>;
services.put("Basic", basic);
services.put("Other", other);
}
#RequestMapping(path = "/path/{service}", method = RequestMethod.GET)
public void method(#PathVariable("service") String service){
SampleInterface sample = services.get(service);
// remember to handle the case where there's no corresponding service
sample.sampleMethod();
}
}
Also, dependency on the ApplicationContext object will make it more complicated to test.
NB. to make it more robust I'd use enums instead of the "Basic" and "Other" strings.
However, if you know you'll only have two types of the service to choose from, this would be the "keep it simple stupid" way:
#Controller
public class SampleController {
#Autowired
private SampleInterfaceImpl basic;
#Autowired
private SampleInterfaceOtherImpl other;
#RequestMapping(path = "/path/Basic", method = RequestMethod.GET)
public void basic() {
basic.sampleMethod();
}
#RequestMapping(path = "/path/Other", method = RequestMethod.GET)
public void other() {
other.sampleMethod();
}
}
Related
In my Spring Boot app, I am thinking of using an approach as the following interface and service implementations:
PDFService:
public interface PDFService {
String createPdf(UUID uuid);
}
BrandPDFService:
#Service
#RequiredArgsConstructor
public class BrandPDFService implements PDFService {
private final BrandService brandService;
#Override
public String createPdf(UUID uuid) {
Brand brand = brandService.findByUuid(uuid);
// ... code omitted for brevity
return generateHtml(brand);
}
}
ProductPDFService:
#Service
#RequiredArgsConstructor
public class ProductPDFService implements PDFService {
private final ProductService productService;
#Override
public String createPdf(UUID uuid) {
Product product = productService.findByUuid(uuid);
// ... code omitted for brevity
return generateHtml(product);
}
}
For using these services:
// brand way
PDFService pdfService = new BrandService();
pdfService.createPdf(uuid);
// product way
PDFService pdfService = new ProductService();
pdfService.createPdf(uuid);
So, I think I need to use generic and pass it to PDFService and then their implementations, but I am not sure how to make it properly (using generic or passing via constructor). So, in order to use createPdf efficiently without repeating code (I know I can also use Template Pattern method, but I just wanted to know polymorphism side) how should I apply polymorphism to these Spring Boot Services properly?
Since BrandPDFService and ProductPDFService are Spring beans (because you annotated them with the #Service annotation), you should not be instantiating them yourself by using new. Instead, you should let Spring autowire them into the class where you are using them.
Because they are both implementations of interface PDFService, when you autowire them, you need to have something to let Spring distinguish them. Otherwise, if the field you are autowiring them in is of type PDFService, Spring won't know which implementation of the interface to autowire. You can give the beans names and use the #Qualifier annotation:
#Service("brandPDFService")
public class BrandPDFService implements PDFService { ... }
#Service("productPDFService")
public class ProductPDFService implements PDFService { ... }
// Example controller where you autowire them
#RestController
public class MyController {
#Autowired
#Qualifier("brandPDFService")
private PDFService brandPDFService;
#Autowired
#Qualifier("productPDFService")
private PDFService productPDFService;
// ...
}
So, I think I need to use generic and pass it to PDFService and then their implementations
I don't know why you think you need to use generics; this doesn't have anything to do with generics.
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
I have two (more in the future) implementations of ImportantService – VeryImportantService and LessImportantService:
public interface ImportantService<T extends ImportantRequest> {}
#Service
public class VeryImportantService implements ImportantService<VeryImportantRequest> {}
#Service
public class LessImportantService implements ImportantService<LessImportantRequest> {}
And then I have a controller, in which I want to inject all of the implementations of ImportantService:
#RequiredArgsConstructor
#RestController
#RequestMapping("/api/important")
public class ImportantController<T extends ImportantRequest> {
private final ImportantService<T> importantService;
#PostMapping
public ResponseEntity<ImportantResponse> create(#RequestBody #Valid T request) {
// very important code here
}
}
Obviously, such king of injecting fails:
UnsatisfiedDependencyException: Error creating bean with name 'importantController' defined in file ...
...
Consider marking one of the beans as #Primary, updating the consumer to accept multiple beans, or using #Qualifier to identify the bean that should be consumed
What I want is:
Inject all of the implementations of ImportantService, and then, based on the T automatically select required bean. I know I can add method to ImportantService, which returns the type that implementation works with and then inject ImportantService as List<ImportantService> importantServices and then filter like this:
importantServices.stream()
.filter(importantService -> importantService.getType().equals(request.getClass()))
.findFirst()
.ifPresent(importantService -> importantService.doImportantJob(request));
BUT! I have hundreds of services to refactor like this and I really don't want to write additional logic to controllers.
I know about #Conditional annotation and Condition interface, but AFAIK there's no way to make them do what I want.
Why not implement the proxy pattern?
example:
#Service
#Primary
#RequiredArgsConstructor
public class ImportantServiceProxy implements ImportantService<T extends ImportantRequest> {
private final List<ImportantService> importantServices;
private ImportantService getImportantService(ImportantRequest request){
return this.importantServices.stream()
.filter(importantService -> importantService.getType().equals(request.getClass()))
.findFirst()
.get();
}
public void doImportantJob(ImportantRequest request){
this.getImportantService(request).doImportantJob(request);
}
}
Then in your controller you can call the function without check the type.
#RequiredArgsConstructor
#RestController
#RequestMapping("/api/important")
public class ImportantController<T extends ImportantRequest> {
private final ImportantService<T> importantService;
#PostMapping
public ResponseEntity<ImportantResponse> create(#RequestBody #Valid T request) {
importantService.doImportantJob(request);
}
}
what you want is a list of beans which are of type ImportantService
so you have to declare a variable like this.
final List<ImportantService> importantServices;
demoController(List<ImportantService> importantServices) {
this.importantServices = importantServices;
}
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;
}
}
Let's assume I have this code:
#Controller
#RequestMapping("/something")
public class SomeController {
#Autowired
private SomeService aService;
#RequestMapping("/doStuff")
public void doStuff(#RequestParam("type") String type) {
aService.doStuff();
}
}
In my application I need to call a specific service depending on the specified type. All services implements the same interface. If I understand correctly SomeService cannot be an interface. I could use a service factory and instantiate the service depending on the type every time a new request is done, but this doesn't look very efficient.
Alternatively I could use a different controller for each different type of service (and encode the type in the REST URI), but this would imply a lot of code duplication since all the services basically implements the same interface.
My question is, assuming the called service depends on the passed parameter, what is the best pattern to adopt for this scenario?
Similar to RC.'s answer, instead of using a Map and adding the values by you, just let the Spring BeanFactory handle this for you:
#Controller
#RequestMapping("/something")
public class SomeController {
#Autowired
private BeanFactory beanFactory;
#RequestMapping("/doStuff")
public void login(#RequestParam("type") String type) {
SomeService aService = (SomeService)beanFactory.getBean(type);
aService.doStuff();
}
}
You could use a map here, something along this:
#Controller
#RequestMapping("/something")
public class SomeController {
#Autowired
private SomeService someService;
#Autowired
private SomeOtherService someOtherService;
// ...
private final Map<String, ServiceCommonInterface> serviceMap = new HashMap<>();
#PostConstruct
private void postConstruct() {
serviceMap.put(typeForSomeService, someService);
serviceMap.put(typeForSomeOtherService, someOtherService);
}
#RequestMapping("/doStuff")
public void login(#RequestParam("type") String type) {
// TODO: ensure type is correct (an enum might be handy here)
serviceMap.get(type).doStuff();
}
}
Or better, as stated in comments you can leverage qualifiers:
#Controller
#RequestMapping("/something")
public class SomeController {
#Autowired
private ApplicationContext applicationContext;
#RequestMapping("/doStuff")
public void login(#RequestParam("type") String type) {
// TODO: ensure type is a correct bean name
applicationContext.getBean(type, ServiceCommonInterface.class).doStuff();
}
}
Depending on the number of types you wish to support there are two options I see.
1) Autowire in a factory as you mentioned and lazily create each service as needed. If the services are stateless you could keep a reference to the object after created so would only need to create once per type.
2) Autowire in a Spring Map with the key being your types and the value being the correct service to use. Then when your receive the type, can retrieve the correct service impl for your map.
For example for map: http://www.mkyong.com/spring/spring-collections-list-set-map-and-properties-example/ or see How to inject a Map<String, List> in java springs?
Both of these require you to create an interface for your service which is something you said is possible.