How to choose spring configuration in runtime based on a tenant? - spring

Question

I would like to be able to choose specific Spring (or Grails) context configuration based on the tenant that user belongs to in runtime. Let's say I use Spring Security and I retrieve tenantId during login.
Imagine now I have a two tenants and they pay different commission. How to inject specific service into a controller without too much plumbing? Here are two different contexts. So, I should inject different ExchangeService based on tenant.
#Configuration
public class FooTenant{
#Bean
public ExchangeService bar() {
return new ZeroCommisionExchangeService ();
}
}
#Configuration
public class BarTenant{
#Bean
public ExchangeService bar() {
return new StandardCommisionExchangeService ();
}
}
Edit:
I am aware I can obtain reference to Spring context and ask for service "manually", but I am looking for a more generic solution where this problematic is solved by IoC framework.

Answer 1

A couple of years ago we needed somthing like this but only for DataSources and ViewResolvers. We developed a solution using spring' TargetSource solution. (Initially we used a HotswappableTargetSource but that wasn't adequate for our use-case.
The code we developed is availabe here in the multi-tenant directory.
It is fully configurable and flexible.
Basically what you do is you configura a ContextSwappableTargetSource and tell it what type of interface/class it needs to return.
<bean id="yourTentantBasedServiceId" class="biz.deinum.multitenant.aop.target.ContextSwappableTargetSource">
<constructor-arg value="ExchangeService" />
</bean>
The default is to lookup beans in the ApplicationContext based on the tenantId (see the BeanFactoryTargetRegistry for this). However you can specify one or more of those (we used a JndiLookupTargetRegistry to dynamically lookup datasource, which allowed use to add tenants on the fly without restarting the application).
If you explicitly configure a BeanFactoryTargetRegistry you can add a prefix and suffix.
<bean id="exchangeService" class="biz.deinum.multitenant.aop.target.ContextSwappableTargetSource">
<constructor-arg value="ExchangeService" />
<property name="targetRegistry>
<bean class="biz.deinum.multitenant.aop.target.registry.impl.BeanFactoryTargetRegistry">
<property suffix="ExchangeService"/>
</bean>
</property>
</bean>
Now for foo it would lookup a bean named fooExchangeService and for bar barExchangeService.
The tenantId is stored in a ThreadLocal which is wrapped inside the ContextHolder. You need to find a way to fill and clear this thread local (in general a servlet Filter does that trick.
In your code you can now simply use the interface ExchangeService and at runtime based on the tenantId the correct implemenation will be looked up.
Also see http://mdeinum.wordpress.com/2007/01/05/one-application-per-client-database/

Answer 2

Assuming you have different services already defined, you can get their bean from the context and use it. In my example, all the services have implementation of serviceMethod and based on some criteria pick your proper service. The only thing I am not sure is how Multitenancy might impact this.
import org.springframework.context.ApplicationContext
class ServiceManagerController {
def serviceManager
def index() {
ApplicationContext ctx = grails.util.Holders.grailsApplication.mainContext
serviceManager = ctx.getBean(params.serviceName); //firstService or secondService
render serviceManager.serviceMethod()
}
}
FirstService
class FirstService {
def serviceMethod() {
return "first"
}
}
SecondService:
class SecondService {
def serviceMethod() {
return "second"
}
}

Answer 3

While it is possible to swap beans instantiated in a spring context at runtime (HotswappableTargetSource), it is not meant for use cases such as yours.
Remember there is one Spring Context for your application, all threads use the same instances (in most cases), this implies when you swap out a bean implementation, you are affectively doing this for all your application's users. To prevent this, you run into issues of ensuring Thread Safety, employing Thread Locals, as listed in another answer.
While it is possible to continue this approach and arrive at an implementation that gets the job done, it would definitely be a very contrived way of solving this problem.
You should take a step back and look at your problem in a more wholesome, system wide design point of view. Bust out your patterns books and look at how this can be resolved, regardless of whether you use Spring or an other framework. Service Locator, Factory bean etc described in some of the answers above is a step in the correct direction.
Your Use Case is pretty common for multi-tenant applications. You need to narrow down things that are likely to change based on a tenantId versus things that are constant across.
For instance as mentioned in the question, each Tenant might have a different commission amount or even different algorithm for commission calculation. A simple solution to this would be to implement a CommissionCalculationService which accepts a tenantId, and any other domain object based on which commission is to be calculated, I would imagine this would be something like Order or Sale, whatever makes sense in your application.
You now need a CommissionServiceFactory or a ServiceLocator which will contain tenant specific implementations of the CommissionCalculationService. The Service Locator is instantiated when the Spring context loads, and is injected with implementation classes also at application startup.
When you want to calculate commission for a tenant, you basically obtain the tenantId from the user's login, pass the tenant id to your service locator, based on the tenantId passed, the service locator returns the appropriate instance of a Service Implementation. In your calling class, use this instance to calculate the commission for the tenant.
Another pattern to consider is the Strategy Pattern, or even Template Pattern.
Bottom line, even if you want tenant specific logic implemented cleanly, don't thing about changing the beans loaded in the context. Have classes in your context that can handle all your tenant specific logic. Rely on design patterns to use the correct bean from the context based on the tenant id.
I apologize if the answer was a little verbose, I felt it was needed to explain why I think updating beans in a loaded Spring Context is not the appropriate solution.

Answer 4

I use the following code:
public class ConfigurableProxyFactoryBean implements FactoryBean<Object>, BeanNameAware {
#Autowired
private ApplicationContextProvider applicationContextProvider;
private Class<?> proxyType;
private String beanName;
private Object object;
private Object fallbackObject;
private Object monitor = new Object();
private ConfigurableProxy proxy;
public ConfigurableProxyFactoryBean(Class<?> proxyType) {
this.proxyType = proxyType;
}
public Object getFallbackObject() {
return fallbackObject;
}
public void setFallbackObject(Object fallbackObject) {
synchronized (monitor) {
this.fallbackObject = fallbackObject;
if (proxy != null) {
proxy.setFallbackObject(fallbackObject);
}
}
}
#Override
public void setBeanName(String name) {
beanName = name;
}
#Override
public Object getObject() throws Exception {
synchronized (monitor) {
if (object == null) {
#SuppressWarnings("unchecked")
Class<Object> type = (Class<Object>)proxyType;
proxy = new ConfigurableProxy(applicationContextProvider, beanName);
proxy.setFallbackObject(fallbackObject);
object = Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
new Class<?>[] { type }, proxy);
}
return object;
}
}
#Override
public Class<?> getObjectType() {
return proxyType;
}
#Override
public boolean isSingleton() {
return true;
}
}
class ConfigurableProxy implements InvocationHandler {
public ConfigurableProxy(ApplicationContextProvider appContextProvider, String beanName) {
this.appContextProvider = appContextProvider;
this.beanName = beanName;
}
private ApplicationContextProvider appContextProvider;
private String beanName;
private Object fallbackObject;
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
ApplicationContext appContext = appContextProvider.getApplicationContext();
String name = "$&&#" + beanName;
Object bean = appContext.containsBean(name) ? appContext.getBean(name) : fallbackObject;
return method.invoke(bean, args);
}
public void setFallbackObject(Object fallbackObject) {
this.fallbackObject = fallbackObject;
}
}
ApplicationContextProvider has implementation, that chooses ApplicationContext according to current tennant.
In XML configuration it is used like this:
<bean class="my.package.infrastructure.ConfigurableProxyFactoryBean" name="beanName">
<constructor-arg>
<value type="java.lang.Class">my.package.model.ServiceInterface</value>
</constructor-arg>
<property name="fallbackObject">
<bean class="my.package.service.DefaultServiceImplementation"/>
</property>
</bean>
And in tennant configuration that way:
<bean class="my.package.service.ServiceImplementationA" name="$&&#beanName"/>
To inject this service somewhere you just write:
public class MyController {
#Autowired
private ServiceInterface service;
}
Also you are to implement ApplicationContextProvider, I won't share mine. It is not very hard to implement. For example, your implementation can just store context in ThreadLocal. And you create your own ServletContextListener, which for every query gets the current tennant and stores it into your ApplicationContextProvider implementation.

Answer 5

The new tenant scope and a servicelocator can helps
Tenant scope will guarantee than service is created one time for a tenant
Sample code:
<bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
<property name="scopes">
<map>
<entry key="tenant" value="foo.TenantScope"/>
</map>
</property>
</bean>
<bean id="service" class="foo.Service" factory-bean="tenantServiceLocator" factory-method="createInstance" scope="tenant"/>
<bean id="fooService" class="FooService">
<bean id="barService" class="BarService">
<bean id="tenantServiceLocator" class="foo.TenantServiceLocator">
<property name="services">
<map>
<entry key="foo" value-ref="fooService"/>
<entry key="bar" value-ref="barService"/>
</map>
</property>
</bean>
TenantServiceLocator should know the user tenantId
public class TenantServiceLocator {
private Map<String, Service> services;
public String getTenantId() {
return "foo"; // get it from user in session
}
public Map<String, Service> getServices() {
return services;
}
public void setServices(Map<String, Service> services) {
this.services = services;
}
public Service createInstance(){
return services.get(tenantId);
}
}
public class FooController{
#Autowired
private Service service;
}
A sample TenantScope implementation
public class TenantScope implements Scope {
private static Map<String, Map<String, Object>> scopeMap = new HashMap<String, Map<String, Object>>();
#Override
public Object get(String name, ObjectFactory<?> objectFactory) {
Map<String, Object> scope = getTenantScope(getTenantId());
Object object = scope.get(name);
if(object == null){
object = objectFactory.getObject();
scope.put(name, object);
}
return object;
}
private Map<String, Object> getTenantScope(String tenantId) {
if (!scopeMap.containsKey(tenantId)) {
scopeMap.put(tenantId, new HashMap<String, Object>());
}
return scopeMap.get(tenantId);
}
private String getTenantId() {
return "foo"; // load you tenantId
}
#Override
public Object remove(String name) {
Map<String, Object> scope = getTenantScope(getTenantId());
return scope.remove(name);
}
#Override
public void registerDestructionCallback(String name, Runnable callback) {
}
#Override
public Object resolveContextualObject(String key) {
return null;
}
#Override
public String getConversationId() {
return null;
}
}

Answer 6

Transforming my comment in an answer, one possible solution is to create a spring factory bean, that receive all he needs to decide which service needs to be returned when creating the instance.
Translating to Grails:
public interface ChoosableServiceIntf {
String getName();
}
class NormalService implements ChoosableServiceIntf {
public String getName() {
return getClass().name;
}
}
class ExtendedService implements ChoosableServiceIntf {
public String getName() {
return getClass().name
}
}
class ChoosableServiceFactory {
static ChoosableServiceIntf getInstance(String decisionParam) {
if(decisionParam == 'X') {
return applicationContext.getBean('extendedService')
}
return applicationContext.getBean('normalService')
}
static ApplicationContext getApplicationContext() {
return Holders.grailsApplication.mainContext
}
}
Here we have two services and ChoosableServiceFactory is responsible to know witch is the correct one.
Then you will need to use the method ApplicationContext#getBean(String, Object[]) to return the correct instance and will also make the factory prototyped scope because of the runtime params.
A controller to test it:
class MyController {
def grailsApplication
def index() {
ChoosableServiceIntf service = grailsApplication.mainContext.getBean('choosableServiceFactory', ["X"] as Object[])
ChoosableServiceIntf serviceNormal = grailsApplication.mainContext.getBean('choosableServiceFactory', ["N"] as Object[])
render text: "#1 - ${service.class.name} , #2 - ${serviceNormal.class.name}"
}
}
This will print #1 - dummy.ExtendedService , #2 - dummy.NormalService
The declaration of the beans will be:
choosableServiceFactory(ChoosableServiceFactory) { bean ->
bean.scope = 'prototype'
bean.factoryMethod = 'getInstance'
}
normalService(NormalService)
extendedService(ExtendedService)