I am using tomcat-jdbc pool in default spring-boot setup. I would like to run some custom Java code each time new JDBC connection is established in the pool and before it is used for the first time. How to do it, and if there are several possibilities which one is the best?
To extend already accepted answer, you can use Spring AOP without full AspectJ if you use pointcut as this one:
#AfterReturning(pointcut = "execution(* org.apache.tomcat.jdbc.pool.DataSourceProxy.getConnection())")
public void afterConnectionEstablished() {
...
}
Well, I can think of two options:
Create your own wrapper class - either by extending Tomcat's DataSource class or by implementing Java's DataSource interface and delegating to the wrapped DataSource - and then add the logic you want to the desired methods and register a bean in a #Configuration class by manually instantiating your tomcat-jdbc DataSource (for examples on how to do so, refer to DataSourceConfiguration.Tomcat class) and wrapping it with your class.
Create an aspect and use Spring's AOP support to intercept calls to getConnection. Since DataSourceclass is in the javax package, I think you'll have to use AspectJ, and for some examples refer to this link
My suggestion would be to go with the first option, it should give you fewer headaches, here's a small example how you'd define your wrapper bean:
#Bean
public DataSource dataSource(DataSourceProperties properties) {
return new MyDataSourceWrapper(tomcatDataSourceFrom(properties));
}
private org.apache.tomcat.jdbc.pool.DataSource tomcatDataSourceFrom(
DataSourceProperties properties) {
// manual instantiation like in DataSourceConfiguration.Tomcat class
}
Related
I am wondering what is the current best practice as to the use of factory pattern within the context of Spring framework in using dependency injection. My wonder arises about whether the factory pattern is still relevant nowadays in light of the use of Spring dependency injection. I did some searching and see some past discussion (Dependency Injection vs Factory Pattern) but seem there is different view.
I see in some real life project in using a Map to hold all the beans and rely on autowiring to create those beans. When the bean is needed, it get it via the map using the key.
public abstract class Service {
//some methods
}
#Component
public class serviceA extends Service {
//implementation
}
#Component
public class serviceB extends Service {
//implementation
}
Map<String, Service> services;
But I see there is some difference among the two approaches.
Using the above method, all beans are created on application start up and the creation of object is handled by the framework. It also implies there is only one bean for each type.
While for factory pattern, the factory class creates the object on request. And it can create a new object for each request.
I think a deeper question may be, when Spring framework is used in a project, should it be strived to not create any object inside a class, which means the factory pattern ( or any creational design patterns?) should not be used, as Spring is supposed to be the central handler of the objects dependency ?
The answer to this question can be really deep and broad, I'll try to provide some points that hopefully will help.
First off, spring stores its beans (singletons) in the ApplicationContext. Essentially this is the map you're talking about. In a nutshell, it allows getting the bean by name, type, etc.
ApplicationContext, while being a really important concept, is not the whole Spring, in fact Spring framework allows much more flexibility:
You say, using a map implies that all the beans will be created at the beginning of the application and there is one instance of the bean.
Spring has a concept of Lazy beans, basically supporting a concept of beans being actually created only when they're required for the first time, so Spring supports the "delayed" beans initialization
Spring also allows more than one instance of a bean per type. So this map is more "advanced". For example you can create more than one implementation of the interface and use declare both as beans. As long as you provide enough information about what bean should be injected to the class that might use them (for example with a help of qualifiers suppored in spring), you're good to go. In addition, there are features in spring IoC container that allow injecting all registered implementations of an interface into a list:
interface Foo {}
#Component
class FooImpl1 implements Foo {}
#Component
class FooImpl2 implements Foo {}
class Client {
#Autowired
List<Foo> allFoos;
}
Now you say:
While for factory pattern, the factory class creates the object on request. And it can create a new object for each request.
Actually Spring can create objects per request. Not all beans have to be singletons, in general spring has a concept of scopes for this purposes.
For example, scope prototype means that Spring will create a bean upon each usage. In particular one interesting usage that spring supports in variety of ways is Injecting prototype bean into singleton. Some solutions use exactly like a factory (read about annotation #Lookup others rely on auto-generated proxy in runtime (like javax.inject.Provider). Prototype scope beans are not held in the application context, so here again spring goes beyond a simple map abstraction.
Last feature that you haven't mentioned is that sometimes even for singletons the initialization can be a little bit more complicated then calling a constructor with Parameters. Spring can address that by using Java Configurations:
#Configuration
public class MyConfig {
public SomeComplicatedObject foo(#Value("...") config, Bar bar) {
SomeComplicatedObject obj = new SomeComplicatedObject() // lets pretend this object is from some thirdparty, it only has no-op constructor, and you can't place spring annotations on it (basically you can't change it):
obj.setConfig(config);
obj.setBar(bar);
return obj;
}
}
The method foo here initializes the object SomeComplicatedObject and returns it. This can be used instead of factories to integrate "legacy" code (well, java configurations go way beyond this, but its out of scope for this question).
So bottom line, you Spring as an IoC container can provide many different ways to deal with object creation, in particular it can do everything that factory design pattern offers.
Now, I would like to also refer to your last sentense:
I think a deeper question may be, when Spring framework is used in a project, should it be strived to not create any object inside a class, which means the factory pattern ( or any creational design patterns?) should not be used, as Spring is supposed to be the central handler of the objects dependency ?
Indeed you don't have to use Factory Pattern when using Spring, since (as I hopefully have convinced you) provides everything that factory can do and more.
Also I agree that spring is supposed to be the central handler of the objects dependency (unless there are also parts of the application which are written in a different manner so you have to support both :) )
I don't think we should avoid using "new" altogether, not everything should/can be a bean, but I do see (from my subjective experience, so this is arguable) that you use it much less leaving the creation of most of the objects to Spring.
Should we avoid a usage of any creation design pattern? I don't think so, sometimes you can opt for implementing "builder" design pattern for example, its also a creational pattern but spring doesn't provide a similar abstraction.
I think if your project uses Spring framework you should use it. Although it depends on your project design e.g. You may use creational patterns along side with Spring IoC. e.g when you have abstraction layers not framework dependant (agnostic code)
interface ServiceFactory {
Service create(String type);
}
#Component
class SpringServiceFactory implements ServiceFactory {
#Autowired private ApplicationContext context;
Service create(String type) {
return context.getBean(type)
}
}
I use Factory pattern as well when I refactor legacy not unit testable code which also uses Spring Framework in order to implement unit tests.
// legacy service impossible to mock
class LegacyApiClient implements Closeable {...}
#Component
class LegacyApiClientFactory {
LegacyApiClient create(String endpoint) {
return new LegacyApiClient(endpoint);
}
}
#Component
class OtherService {
private final String endpoint
private final LegacyApiClientFactory factory;
OtherService(#Value("${post.endpoint}") String endpoint,
LegacyApiClientFactory factory) {...}
void doCall {
try (LegacyApiClient client = factory.create(endpoint)) {
client.postSomething();
}
}
}
....
// a random unit test
LegacyApiClient client = mock(LegacyApiClient.class)
LegacyApiClientFactory factory = mock(LegacyApiClientFactory.class)
OtherService service = new OtherService("http://scxsc", factory);
when(factory.create(any())).thenReturn(client)
service.doCall()
....
I am porting an existing JBOSS JEE application to Quarkus. I am using a number of HV custom validators that require injection.
For that purpose I've defined all custom validators that require injection as bean in my libraries like this:
#ApplicationScoped
public class SomeValidator implements ConstraintValidator<SomeValidation, AnObject> {
#Inject
public BeanUsingEntityManager bean;
Note: It is common code, so it should remain working on JBOSS as well
Next I defined a REST service. The REST service makes use of an application scoped bean like this.
#ApplicationScoped
public class ApplicationContext {
#PersistenceContext( unitName = "A" )
EntityManager em;
#Produces
#EnityManagerA // required qualifier to make datasource unique in JEE context (there are more)
public EntityManager produce() {
return em;
}
// NOTE: quarkus does not allow the #Produces on a field, which is allowed in JBOSS hence the method
#Produces
public BeanUsingEntityManager createBeanUsingEntityManager () {
// some logic that requires the entity manager.
}
}
Now the problem is simplified, but I keep on running into an error message.
Caused by: javax.enterprise.inject.CreationException: Synthetic bean instance for javax.persistence.EntityManager not initialized yet: javax_persistence_EntityManager_b60c51739990fc921960fc78caeb075a811a91a6
- a synthetic bean initialized during RUNTIME_INIT must not be accessed during STATIC_INIT
- RUNTIME_INIT build steps that require access to synthetic beans initialized during RUNTIME_INIT should consume the SyntheticBeansRuntimeInitBuildItem
at javax.persistence.EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.create(EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.zig:167)
at javax.persistence.EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.create(EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.zig:190)
at io.quarkus.arc.impl.AbstractSharedContext.createInstanceHandle(AbstractSharedContext.java:96)
at io.quarkus.arc.impl.AbstractSharedContext.access$000(AbstractSharedContext.java:14)
at io.quarkus.arc.impl.AbstractSharedContext$1.get(AbstractSharedContext.java:29)
at io.quarkus.arc.impl.AbstractSharedContext$1.get(AbstractSharedContext.java:26)
at io.quarkus.arc.impl.LazyValue.get(LazyValue.java:26)
at io.quarkus.arc.impl.ComputingCache.computeIfAbsent(ComputingCache.java:69)
at io.quarkus.arc.impl.AbstractSharedContext.get(AbstractSharedContext.java:26)
at javax.persistence.EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.get(EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.zig:222)
at javax.persistence.EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.get(EntityManager_e1903961aa3b05f292293ca76e991dd812f3e90e_Synthetic_Bean.zig:238)
at nl.bro.gm.gmw.dispatch.resources.ApplicationContext_Bean.create(ApplicationContext_Bean.zig:131)
... 59 more
I'm new to Quarkus. So, not sure to how to handle this issue or even if I make the correct assumptions. I can imagine that Quarkus wants to give me a fresh entitymanager each request (which I understand), but that poses a problem for my application scoped beans.
What am I doing wrong here?
So, the full answer is that the EntityManager is created at the runtime init phase whereas the ValidatorFactory (and the ConstraintValidators) are created at static init time.
The Quarkus bootstrap goes static init -> runtime init.
So in your case, you can't access a #Singleton bean which uses the EntityManager during static init as it's not yet available.
Making your bean #ApplicationScoped will create a proxy and avoid this chicken and egg problem.
You will have only one BeanUsingEntityManager for your whole application.
The EntityManager is a bit different because we wrap it and you will get one new EntityManager/Session per transaction, which is what is expected as EntityManagers/Sessions are not thread safe.
Java configuration allows us to manage bean creation within a configuration file. Annotated #Component, #Service classes used with component scanning does the same. However, I'm concerned about using these two mechanisms at the same time.
Should Java configuration and annotated component scans be avoided in the same project? I ask because the result is unclear in the following scenario:
#Configuration
public class MyConfig {
#Bean
public Foo foo() {
return new Foo(500);
}
}
...
#Component
public class Foo {
private int value;
public Foo() {
}
public Foo(int value) {
this.value = value;
}
}
...
public class Consumer {
#Autowired
Foo foo;
...
}
So, in the above situation, will the Consumer get a Foo instance with a 500 value or 0 value? I've tested locally and it appears that the Java configured Foo (with value 500) is created consistently. However, I'm concerned that my testing isn't thorough enough to be conclusive.
What is the real answer? Using both Java config and component scanning on #Component beans of the same type seems like a bad thing.
I think your concern is more like raised by the following use case:
You have a custom spring-starter-library that have its own #Configuration classes and #Bean definitions, BUT if you have #Component/#Service in this library, you will need to explicitly #ComponentScan these packages from your service, since the default #ComponentScan (see #SpringBootApplication) will perform component scanning from the main class, to all sub-packages of your app, BUT not the packages inside the external library. For that purpose, you only need to have #Bean definitions in your external library, and to inject these external configurations via #EnableSomething annotation used on your app's main class (using #Import(YourConfigurationAnnotatedClass.class) OR via using spring.factories in case you always need the external configuration to be used/injected.
Of course, you CAN have #Components in this library, but the explicit usage of #ComponentScan annotation may lead to unintended behaviour in some cases, so I would recommend to avoid that.
So, to answer your question -> You can have both approaches of defining beans, only if they're inside your app, but bean definitions outside your app (e.g. library) should be explicitly defined with #Bean inside a #Configuration class.
It is perfectly valid to have Java configuration and annotated component scans in the same project because they server different purposes.
#Component (#Service,#Repository etc) are used to auto-detect and auto-configure beans.
#Bean annotation is used to explicitly declare a single bean, instead of letting Spring do it automatically.
You can do the following with #Bean. But, this is not possible with #Component
#Bean
public MyService myService(boolean someCondition) {
if(someCondition) {
return new MyServiceImpl1();
}else{
return new MyServiceImpl2();
}
}
Haven't really faced a situation where both Java config and component scanning on the bean of the same type were required.
As per the spring documentation,
To declare a bean, simply annotate a method with the #Bean annotation.
When JavaConfig encounters such a method, it will execute that method
and register the return value as a bean within a BeanFactory. By
default, the bean name will be the same as the method name
So, As per this, it is returning the correct Foo (with value 500).
In general, there is nothing wrong with component scanning and explicit bean definitions in the same application context. I tend to use component scanning where possible, and create the few beans that need more setup with #Bean methods.
There is no upside to include classes in the component scan when you create beans of their type explicitly. Component scanning can easily be targeted at certain classes and packages. If you design your packages accordingly, you can component scan only the packages without "special" bean classes (or else use more advanced filters on scanning).
In a quick look I didn't find any clear information about bean definition precedence in such a case. Typically there is a deterministic and fairly stable order in which these are processed, but if it is not documented it maybe could change in some future Spring version.
I am using a custom filter in my Spring Boot application and it seems there are 2 ways of getting the filter registered.
--> Register the filter using the #Bean
#Bean
public Filter AuthenticationFilter() {
return new AuthenticationFilter();
}
--> Anotate the Filter using #Component
#Component
public class AuthenticationFilter implements Filter {}
I am puzzled on what the difference is and why i should use one over the other?
It's largely down to personal preference.
Using #Component requires component scanning to be enabled. Some people prefer not to use component scanning as they find that it makes it hard to determine where your beans are coming from. Declaring everything using #Bean methods avoids this but at the cost of writing (slightly) more Java configuration.
Another reason to use #Bean is that you may not have any control over the Filter's source, i.e. you can't annotate it with #Component so declaring it using an #Bean method is your only option.
I use Spring and have an aspect that wraps around some class:
#Aspect
public class LoggingAspect{
#Around("execution(public * com.service.MyService.doStuff(..))")
public Object log(){
...
}
}
and in context xml:
<aop:aspectj-autoproxy/>
<bean id="loggingAspect" class="com.bla.bla.bla.LoggingAspect"/>
The problem is that instances of MyService are created at runtime so Spring knows nothing about this class during context initialization phase. Is it possible to use aspects in this case to wrap method calls of a class instantiated using new (not Spring)?
If my reading of the Spring docs is correct, you do it like this (for Spring proxy-based weaving):
ProxyFactory factory = new ProxyFactory(new SimplePojo());
factory.addInterface(Pojo.class);
factory.addAdvice(new RetryAdvice());
Pojo pojo = (Pojo) factory.getProxy();
or like this (for AspectJ-style weaving):
AspectJProxyFactory factory = new AspectJProxyFactory(new SimplePojo());
factory.addAspect(new RetryAspect());
Pojo proxy = factory.getProxy();
(I drive all my AOP weaving through my bean configuration so I've not needed to use this sort of thing in practice.)
No, you can only use Spring AOP to advise Spring beans (because Spring creates a proxy object behind the scenes). You'll have to use full AspectJ, or create your MyService in the Spring container. See http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/aop.html#aop-choosing.