Considering the snippet below - is it safe to pass simple not thread-safe HashMap to a SomeHandlerFunction that will use it in other autowired beans in SomeHandlerFunction?
#Bean
RouterFunction<ServerResponse> request(SomeHandlerFunction handlerFunction) {
handlerFunction.setSimpleMapProperties(new HashMap());
return route(GET("/dummy"), handlerFunction);
}
#Service
class SomeHandlerFunction implements HandlerFunction {
#Autowired
List<AnotherBeans> anotherBeans;
Mono<T> handle(ServerRequest var1) {
// code...
}
}
I'm a bit aware about multithreading model in WebFlux, but this case made me confusing.
If that HashMap is mutable, it's not a good idea - not even with Spring MVC.
What should you do instead? It really depends on the use case at hand.
If you're trying to setup a local in-memory cache, you could use a library like Caffeine, or simply a ConcurrentMapCache.
If you'd like to share configuration keys with that bean, you could wrap that map with Collections.unmodifiableMap or even better, make that a proper immutable POJO.
If this is meant to carry temporary data that's linked with the request being processed, you should instead use request attributes or Reactor Context for that.
Related
Somewhat related to this:
We are trying to inject a SecurityService bean so that I can access the authentication object outside of a controller. Unfortunately, like the previous RequestScope implementation, the DefaultSecurityService implementation of getAuthentication relies on the ServerRequestContext.currentRequest() which is using ThreadLocal:
#Override
public Optional<Authentication> getAuthentication() {
return ServerRequestContext.currentRequest()
.flatMap(request -> request.getUserPrincipal(Authentication.class));
}
And since we're also using Kotlin coroutines, we want to find a way of implementing getAuthentication without ThreadLocal. Any suggestions on how we can go about doing that?
I have recently noticed that Spring successfully intercepts intra class function calls in a #Configuration class but not in a regular bean.
A call like this
#Repository
public class CustomerDAO {
#Transactional(value=TxType.REQUIRED)
public void saveCustomer() {
// some DB stuff here...
saveCustomer2();
}
#Transactional(value=TxType.REQUIRES_NEW)
public void saveCustomer2() {
// more DB stuff here
}
}
fails to start a new transaction because while the code of saveCustomer() executes in the CustomerDAO proxy, the code of saveCustomer2() gets executed in the unwrapped CustomerDAO class, as I can see by looking at 'this' in the debugger, and so Spring has no chance to intercept the call to saveCustomer2.
However, in the following example, when transactionManager() calls createDataSource() it is correctly intercepted and calls createDataSource() of the proxy, not of the unwrapped class, as evidenced by looking at 'this' in the debugger.
#Configuration
public class PersistenceJPAConfig {
#Bean
public DriverManagerDataSource createDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
//dataSource.set ... DB stuff here
return dataSource;
}
#Bean
public PlatformTransactionManager transactionManager( ){
DataSourceTransactionManager transactionManager = new DataSourceTransactionManager(createDataSource());
return transactionManager;
}
}
So my question is, why can Spring correctly intercept the intra class function calls in the second example, but not in the first. Is it using different types of dynamic proxies?
Edit:
From the answers here and other sources I now understand the following:
#Transactional is implemented using Spring AOP, where the proxy pattern is carried out by wrapping/composition of the user class. The AOP proxy is generic enough so that many Aspects can be chained together, and may be a CGLib proxy or a Java Dynamic Proxy.
In the #Configuration class, Spring also uses CGLib to create an enhanced class which inherits from the user #Configuration class, and overrides the user's #Bean functions with ones that do some extra work before calling the user's/super function such as check if this is the first invocation of the function or not. Is this class a proxy? It depends on the definition. You may say that it is a proxy which uses inheritance from the real object instead of wrapping it using composition.
To sum up, from the answers given here I understand these are two entirely different mechanisms. Why these design choices were made is another, open question.
Is it using different types of dynamic proxies?
Almost exactly
Let's figure out what's the difference between #Configuration classes and AOP proxies answering the following questions:
Why self-invoked #Transactional method has no transactional semantics even though Spring is capable of intercepting self-invoked methods?
How #Configuration and AOP are related?
Why self-invoked #Transactional method has no transactional semantics?
Short answer:
This is how AOP made.
Long answer:
Declarative transaction management relies on AOP (for the majority of Spring applications on Spring AOP)
The Spring Framework’s declarative transaction management is made possible with Spring aspect-oriented programming (AOP)
It is proxy-based (§5.8.1. Understanding AOP Proxies)
Spring AOP is proxy-based.
From the same paragraph SimplePojo.java:
public class SimplePojo implements Pojo {
public void foo() {
// this next method invocation is a direct call on the 'this' reference
this.bar();
}
public void bar() {
// some logic...
}
}
And a snippet proxying it:
public class Main {
public static void main(String[] args) {
ProxyFactory factory = new ProxyFactory(new SimplePojo());
factory.addInterface(Pojo.class);
factory.addAdvice(new RetryAdvice());
Pojo pojo = (Pojo) factory.getProxy();
// this is a method call on the proxy!
pojo.foo();
}
}
The key thing to understand here is that the client code inside the main(..) method of the Main class has a reference to the proxy.
This means that method calls on that object reference are calls on the proxy.
As a result, the proxy can delegate to all of the interceptors (advice) that are relevant to that particular method call.
However, once the call has finally reached the target object (the SimplePojo, reference in this case), any method calls that it may make on itself, such as this.bar() or this.foo(), are going to be invoked against the this reference, and not the proxy.
This has important implications. It means that self-invocation is not going to result in the advice associated with a method invocation getting a chance to execute.
(Key parts are emphasized.)
You may think that aop works as follows:
Imagine we have a Foo class which we want to proxy:
Foo.java:
public class Foo {
public int getInt() {
return 42;
}
}
There is nothing special. Just getInt method returning 42
An interceptor:
Interceptor.java:
public interface Interceptor {
Object invoke(InterceptingFoo interceptingFoo);
}
LogInterceptor.java (for demonstration):
public class LogInterceptor implements Interceptor {
#Override
public Object invoke(InterceptingFoo interceptingFoo) {
System.out.println("log. before");
try {
return interceptingFoo.getInt();
} finally {
System.out.println("log. after");
}
}
}
InvokeTargetInterceptor.java:
public class InvokeTargetInterceptor implements Interceptor {
#Override
public Object invoke(InterceptingFoo interceptingFoo) {
try {
System.out.println("Invoking target");
Object targetRetVal = interceptingFoo.method.invoke(interceptingFoo.target);
System.out.println("Target returned " + targetRetVal);
return targetRetVal;
} catch (Throwable t) {
throw new RuntimeException(t);
} finally {
System.out.println("Invoked target");
}
}
}
Finally InterceptingFoo.java:
public class InterceptingFoo extends Foo {
public Foo target;
public List<Interceptor> interceptors = new ArrayList<>();
public int index = 0;
public Method method;
#Override
public int getInt() {
try {
Interceptor interceptor = interceptors.get(index++);
return (Integer) interceptor.invoke(this);
} finally {
index--;
}
}
}
Wiring everything together:
public static void main(String[] args) throws Throwable {
Foo target = new Foo();
InterceptingFoo interceptingFoo = new InterceptingFoo();
interceptingFoo.method = Foo.class.getDeclaredMethod("getInt");
interceptingFoo.target = target;
interceptingFoo.interceptors.add(new LogInterceptor());
interceptingFoo.interceptors.add(new InvokeTargetInterceptor());
interceptingFoo.getInt();
interceptingFoo.getInt();
}
Will print:
log. before
Invoking target
Target returned 42
Invoked target
log. after
log. before
Invoking target
Target returned 42
Invoked target
log. after
Now let's take a look at ReflectiveMethodInvocation.
Here is a part of its proceed method:
Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
++this.currentInterceptorIndex should look familiar now
Here is the target
And there are interceptors
the method
the index
You may try introducing several aspects into your application and see the stack growing at the proceed method when advised method is invoked
Finally everything ends up at MethodProxy.
From its invoke method javadoc:
Invoke the original method, on a different object of the same type.
And as I mentioned previously documentation:
once the call has finally reached the target object any method calls that it may make on itself are going to be invoked against the this reference, and not the proxy
I hope now, more or less, it's clear why.
How #Configuration and AOP are related?
The answer is they are not related.
So Spring here is free to do whatever it wants. Here it is not tied to the proxy AOP semantics.
It enhances such classes using ConfigurationClassEnhancer.
Take a look at:
CALLBACKS
BeanMethodInterceptor
BeanFactoryAwareMethodInterceptor
Returning to the question
If Spring can successfully intercept intra class function calls in a #Configuration class, why does it not support it in a regular bean?
I hope from technical point of view it is clear why.
Now my thoughts from non-technical side:
I think it is not done because Spring AOP is here long enough...
Since Spring Framework 5 the Spring WebFlux framework has been introduced.
Currently Spring Team is working hard towards enhancing reactive programming model
See some notable recent blog posts:
Reactive Transactions with Spring
Spring Data R2DBC 1.0 M2 and Spring Boot starter released
Going Reactive with Spring, Coroutines and Kotlin Flow
More and more features towards less-proxying approach of building Spring applications are introduced. (see this commit for example)
So I think that even though it might be possible to do what you've described it is far from Spring Team's #1 priority for now
Because AOP proxies and #Configuration class serve a different purpose, and are implemented in a significantly different ways (even though both involve using proxies).
Basically, AOP uses composition while #Configuration uses inheritance.
AOP proxies
The way these work is basically that they create proxies that do the relevant advice logic before/after delegating the call to the original (proxied) object. The container registers this proxy instead of the proxied object itself, so all dependencies are set to this proxy and all calls from one bean to another go through this proxy. However, the proxied object itself has no pointer to the proxy (it doesn't know it's proxied, only the proxy has a pointer to the target object). So any calls within that object to other methods don't go through the proxy.
(I'm only adding this here for contrast with #Configuration, since you seem to have correct understanding of this part.)
#Configuration
Now while the objects that you usually apply the AOP proxy to are a standard part of your application, the #Configuration class is different - for one, you probably never intend to create any instances of that class directly yourself. This class truly is just a way to write configuration of the bean container, has no meaning outside Spring and you know that it will be used by Spring in a special way and that it has some special semantics outside of just plain Java code - e.g. that #Bean-annotated methods actually define Spring beans.
Because of this, Spring can do much more radical things to this class without worrying that it will break something in your code (remember, you know that you only provide this class for Spring, and you aren't going to ever create or use its instance directly).
What it actually does is it creates a proxy that's subclass of the #Configuration class. This way, it can intercept invocation of every (non-final non-private) method of the #Configuration class, even within the same object (because the methods are effectively all overriden by the proxy, and Java has all the methods virtual). The proxy does exactly this to redirect any method calls that it recognizes to be (semantically) references to Spring beans to the actual bean instances instead of invoking the superclass method.
read a bit spring source code. I try to answer it.
the point is how spring deal with the #Configurationand #bean.
in the ConfigurationClassPostProcessor which is a BeanFactoryPostProcessor, it will enhance all ConfigurationClasses and creat a Enhancer as a subClass.
this Enhancer register two CALLBACKS(BeanMethodInterceptor,BeanFactoryAwareMethodInterceptor).
you call PersistenceJPAConfig method will go through the CALLBACKS. in BeanMethodInterceptor,it will get bean from spring container.
it may be not clearly. you can see the source code in ConfigurationClassEnhancer.java BeanMethodInterceptor.ConfigurationClassPostProcessor.java enhanceConfigurationClasses
You can't call #Transactional method in same class
It's a limitation of Spring AOP (dynamic objects and cglib).
If you configure Spring to use AspectJ to handle the transactions, your code will work.
The simple and probably best alternative is to refactor your code. For example one class that handles users and one that process each user. Then default transaction handling with Spring AOP will work.
Also #Transactional should be on Service layer and not on #Repository
transactions belong on the Service layer. It's the one that knows about units of work and use cases. It's the right answer if you have several DAOs injected into a Service that need to work together in a single transaction.
So you need to rethink your transaction approach, so your methods can be reuse in a flow including several other DAO operations that are roll-able
Spring uses proxying for method invocation and when you use this... it bypasses that proxy. For #Bean annotations Spring uses reflection to find them.
I am trying to find out what's the best way to use Spring (or not) for loading beans on demand. Here's an example. Let's say that there are two types of mechanic beans
#Bean("japanese-mechanic")
public Mechanic japaneseMechanic(){
return new JapaneseMechanicImpl
}
#Bean("german-mechanic")
public Mechanic germanMechanic(){
return new GermanMechanicImpl
}
My question is how do I load the right bean per request. Currently, the way we do it is using "Context.getBean", so it would look something like
String beanName = request.getParameter("typeOfCar") + "-mechanic";
Mechanic mechanic = Context.getBean(beanName,Mechanic.class);
I understand that calling "Context.getBean" this way violates IOC, so looking for a better way to do this, if available. Can someone suggest some alternatives to doing this? Thanks!
You could avoid accessing the context directly by wiring all the mechanics to your own map like the following:
#Autowired
Map<String, Mechanic> mechanics;
Mechanic mechanic = mechanics.get(beanName);
So instead of fetching the bean from the context map, you autowire them to your own map and fetch them from there. Could be considered better style, or if you have requirements that you can't access the context directly.
I've been struggling for a few days to get this working, but it seems that I cannot find a solution to it. That's why I'd like to ask it here.
Short version
I have a multi tenant implementation which works with Spring boot, Spring Data JPA and Hibernate. This works like a charm. But now I'd like to implement a functionality where I switch the database (data source) during a single transaction. For example I use similar code in my service class
#Autowired
private CustomRepository customRepository;
#Autorwired
private CustomTenantIdentifierResolver customResolver;
#Transactional
public Custom getCustom(String name) {
// Set the datasource to "one";
this.customResolver.setIdentifier("one");
Custom result = this.customRepository.findOneByName(name);
//If the result is null, switch datasource to default and try again
this.customResolver.setIdentifier("default");
result = this.customRepository.findOneByName(name);
return result;
}
The problem is, my data source does not switch. It uses the same source for the second request. I guess I'm doing something terribly wrong here.
What is the correct way to switch the data source during a single transaction?
EDIT (07-06-2016)
Since I noticed that switching the data source for a single transaction is not going to work, I'll add a followup.
Would it be possible to switch the data source in between two transactions for a single user request? If so, what would be the correct way to do this?
Long Version
Before moving on, I'd like to mention that my multi tenant implementation is based on the tutorial provided on this blog.
Now, my goal is to use the default data source as a fallback when the dynamic one (chosen by a custom identifier) fails to find a result. All this needs to be done in a single user request. It doesn't make a difference in the solution uses a single or multiple transactional annotated methods.
Until now I tried a couple things, one of them is described above, another includes the use of multiple transaction managers. That implementation uses a configuration file to create two transaction manager beans which each a different data source.
#Configuration
#EnableTransactionManagement
public class TransactionConfig {
#Autowired
private EntityManagerFactory entityManagerFactory;
#Autowired
private DataSourceProvider dataSourceProvider;
#Bean(name = "defaultTransactionManager")
public PlatformTransactionManager defaultTransactionManager() {
JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();
jpaTransactionManager.setEntityManagerFactory(entityManagerFactory);
jpaTransactionManager.setDataSource(dataSourceProvider.getDefaultDataSource());
jpaTransactionManager.afterPropertiesSet();
return jpaTransactionManager;
}
#Bean(name = "dynamicTransactionManager")
public PlatformTransactionManager dynamicTransactionManager() {
JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();
jpaTransactionManager.setEntityManagerFactory(entityManagerFactory);
jpaTransactionManager.afterPropertiesSet();
return jpaTransactionManager;
}
}
Next I split the service method into two separate ones and added the #Transactional annotation including the right bean name
#Transactional("dynamicTransactionManager")
public Custom getDynamicCustom(String name) {
...stuff...
}
#Transactional("defaultTransactionManager")
public Custom getDefaultCustom(String name) {
...stuff...
}
But it didn't make any difference, the first data source was still used for the second method call (which should use the default transaction manager).
I hope someone can help me find a solution to this.
Thanks in advance.
Spring provides a variation of DataSource, called AbstractRoutingDatasource. It can be used in place of standard DataSource implementations and enables a mechanism to determine which concrete DataSource to use for each operation at runtime. All you need to do is to extend it and to provide an implementation of an abstract determineCurrentLookupKey method.
Keep in mind that determineCurrentLookupKey method will be called whenever TransactionsManager requests a connection. So, if you want to switch DataSource, you just need to open new transaction.
You can find example here
http://fedulov.website/2015/10/14/dynamic-datasource-routing-with-spring/
You can't just move a transaction over to another datasource. While there is a concept of distributed (or XA) transactions, it consists of separate transactions (in separate data sources) that are treated as if they were part of a single (distributed) transaction.
I do not know if it is possible, but i think you should try to avoid switching source during a transaction, for the following reason:
If an error occurs during the second request you will want to roll back the entire transaction, which means switching back to the old source. In order to be able to do that you will need to hold an open connection to that old source: When the transaction is complete you will need to confirm the transaction to that old source.
I would recommend to rethink if you really want this, beside the point if it is possible at all.
In spring it is possible to do this. Does anybody have code samples?
If you want to notify a bean about something, simply call a method:
#Service
public class Notifier {
#Autowired
private Notified notified;
public void something() {
notified.notify(..);
}
}
But event handling is usually asynchronous. In that case you will have to create a new Thread (or use the executors framework since Java 5), pass a reference to / inject the target bean, and let it notify it.
And if instead you want to notify multiple beans, without knowing which exactly, then use the event mechanism that spring provides as an implementation of the observer pattern.
You can use Spring Integration for messaging between beans in your context. Look at MessageChannel and ServiceActivator. You can route, filter, split messages to your beans how ever you need.