So I'm using SpringBootApplication to create a quick server application.
I want to have persistence in this application as well, so I added OrmLite to handle my SQLite database.
Instantiating OrmLite DAOs requires a ConnectionSource to the database. How do I #Autowire this instantiated DAO with the connectionSourceto my controller handling requests, so that I can return whatever they requested from the database? I also have a databaseHelper class that creates the connection to the database, it get instantiated in the application main method.
For example the controller:
#RestController
public class GreetingController {
#AutoWired
GreetingDao greetingDao;
//how does this instance have the connectionSource Dao to the database?
}
DAO:
#Component
public class GreetingDao {
Dao<int, Greeting> greetingDao;
public GreetingDao(ConnectionSource connectionSource) {
greetingDao = Dao.createDao(connectionSource, Greeting.class);
}
}
Okay so after reading a bit further on this, I realized that I can just set default constructors for my DAO classes, and then when my application main is called, I just set the connectionSource for my DAO's in the ApplicationContext.
Then when I have #Autowire for my DAOs inside the controller classes, they will have the same instance that I set my connectionSource to.
//inside #SpringBootApplication class
public void main(String [] args) {
ConfigurableApplicationContext context = SpringApplication.run(Application.class, args)
DatabaseHelper dbHelper = context.getBean(DatabaseHelper.class)
dbHelper.connect();
GreetingAccessor greetingAccessor = context.getBean(GreetingAccessor.class)
greetingAccessor.createDao(dbHelper.getConnectionSource);
}
//inside GreetingAccessor
public void createDao(ConnectionSource connectionSource) {
greetingDao = DaoManager.createDao(connectionSource, Greeting.class);
}
Related
As far as I understood, Spring manages autowiring mechanism with AutowiredAnnotationBeanPostProcessor on postProcessBeforeInitialization stage. But how does it inject proxies that ought to be created on postProcessAfterInitialization stage?
EDIT 1
Suppose I have this Spring configuration
#Service
class RegularBean {
// injected on postProcessBeforeInitialization stage
#Autowired
private TransactionBean tBean;
// invoked in between of postProcessBeforeInitialization and postProcessAfterInitialization
#PostConstruct
void init() {
tBean.transactionMethod();
}
}
#Service
class TransactionBean {
// transactional proxy is created on postProcessAfterInitialization stage
#Transactional
public void transactionMethod() { ... }
}
Transactional proxy is created on postProcessAfterInitialization stage. But #PostConstruct is called right before it. Is injected tBean wrapped with transactional proxy? If it so, then why? Because it should not be. If it is not wrapped, then how transactions are going to be handled in the future?
Suppose that I replace field-injection with constructor-injection. Will it change the behavior somehow?
When you use autowiring on method or field ,Spring Container not always create and inject the required field/attribute instance. Spring internally create smart proxies and inject the proxies to your bean. This smart proxy will resolve the bean at later point and delegate call to actual bean during method invocation. This is a common strategy we use to resolve request and session scoped beans to singleton instance (Say service layer beans) using Scope annotation.
Adding small snippet to show Spring internally create proxies for Object. Consider a classic circular dependency case when we use Constructor injection.
#Component
public class CircularDependencyA {
private CircularDependencyB circB;
public CircularDependencyA(#Lazy CircularDependencyB circB) {
System.out.println("CircularDependencyA Ctr ->"+circB.getClass().getName());
this.circB = circB;
}
}
#Component
public class CircularDependencyB {
private CircularDependencyA circA;
public CircularDependencyB(CircularDependencyA circA) {
System.out.println("CircularDependencyB Ctr ->"+circA.getClass().getName());
this.circA = circA;
}
}
#Configuration
#ComponentScan(basePackages = { "com.example.springdemo.cd" })
public class TestConfig {
}
public class TestCircularDependency {
public static void main(String[] args) {
try(AnnotationConfigApplicationContext context
= new AnnotationConfigApplicationContext(TestConfig.class);){
}
}
}
Based on our hints Spring is creating Proxy(using CGLIB) for CircularDependencyB Object and see the op from the CircularDependencyA Constructor
CircularDependencyA Ctr ->com.example.springdemo.cd.CircularDependencyB$$EnhancerBySpringCGLIB$$e6be3b79
Thanks
have have these two apps which actually do the same (if I am correct)
#SpringBootApplication
public class DemoApplication {
#Autowired
HelloWorld helloWorld;
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
#Bean
public CommandLineRunner run() {
helloWorld.setMessage("wow");
return (load) -> {
helloWorld.getMessage();
};
}
}
and
public class MainApp {
public static void main(String[] args) {
ApplicationContext context = new
ClassPathXmlApplicationContext("Beans.xml");
HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
obj.getMessage();
}
}
both uses
#Component
public class HelloWorld {
private String message;
public void setMessage(String message) {
this.message = message;
}
public void getMessage() {
System.out.println("Your Message : " + message);
}
}
The only difference at the helloWord obj is, that if I use the MainApp-class in my program, then the helloWorld class doesn't need the #Component annotation.
My Question:
If I am correct the SpringBoot annotation makes it unnecessary to define a ClassPathXMLApplicationContext. #Autowire does that for me.
I am now interested if I AutoWire lets say 100 objects at the beginning, all these objects are now in the IoC container correct?
If so: Is not possible to just hand out that container in a CTOR of another class and have access to all saved objects there like:
(HelloWorld) context.getBean("helloWorld"); or
(someRandomClass) context.getBean("someRandomClass")
public CTOR(IOCContainer container) {
this.container = container;
}
Instead of that implementation
public CTOR(HelloWorld helloWorld, SomeRandomClass someRandomClass) {
this.helloWorld = helloWorld;
this.someRandomClass = someRandomClass;
}
And if that is possible, how can I do that?
(There is no use case/task behind my question, i am just interested if that is possible)
The XML'ish way of configuration where you define your bean and wiring via
<bean ... etc. pp.
can be completely replaced by either using
#Component
public class MyClass ....
or by
#Bean
public MyClass myClass() {return new MyClass();}
definition in a configuration class. Both ways place the entity in the IoC container of Spring.
The #Autowire just informs the IoC container of Spring that you would like to have a bean fulfilling the contract of the entity marked with #Autowire injected into this place.
In order to get access to the container you just need to inject the ApplicationContext where you would like to have it.
There are two ways of creating beans in Spring. One is through XML config and the other is through annotation config. Annotation config is the preferred approach as it has lot of advantages over xml config.
Spring boot doesnt have any thing to do with annotation or xml config. Its just a easy way to boot spring application. #Component creates the object of the annotated bean in the application context. #Import or #ImportResource are the annotations used to load the configs from Annotations or through XML configs in Spring boot. With Spring boot u need not create ClassPathXMlCOntext or AnnotationContext objects, but its created internally by spring boot.
#Autowired is a way of getting the beans into any object by injecting rather than tight coupling to the code. Spring container(Application context) do this job of injecting. Just autowiring any class wont create the objects in Spring context. Its just an indication for the Spring context to set the object in the Application context here. You need to create them explicitly inside a xml config/ or annotations like #Component #Service others.
There is no need of hand out of container anywhere. U can just #Autowire ApplicationContext context; in any other spring bean object. With which you can call getBean(YourBean.class) to get that bean.
I am trying to save data on gemfire using crud repository. I have created one operation class to call save method of repository but at autowired instance I am getting null pointer exception. Below is my code:
public interface GeodeRepository extends CrudRepository<KeyValueBean, String> {
#Override
public KeyValueBean findOne(String name);
#Override
public <S extends KeyValueBean> Iterable<S> save(Iterable<S> entities);
}
#EnableGemfireRepositories(basePackageClasses = GeodeRepository.class)
#EnableAutoConfiguration
#Configuration
public class Operations {
#Autowired
private GeodeRepository repository;
public void saveKeyValueData(KeyValueBean keyValueBean) {
System.out.println("Repository is : " + repository);
repository.save(Arrays.asList(keyValueBean)); // <--- i am getting
// repository as null so
// getting null pointer
// exception
}
}
When we #Autowired any class make sure, you have declared that class as a #Component.
for example:
#Component
public class Operations {
#Autowired
private GeodeRepository repository;
public void saveKeyValueData(KeyValueBean keyValueBean) {
System.out.println("Repository is : " + repository);
repository.save(Arrays.asList(keyValueBean));
}
}
and try using #Autowired to Operation class to your class
in which class your are calling your saveKeyValueData() method.
So, what is not apparent from your example is how you "bootstrap" your application and it's features (e.g. Repositories) into action.
It is not simply enough to add the Spring #Configuration, Spring Boot's #EnableAutoConfiguration and SD GemFire's #EnableGemfireRepositories annotations and expect everything to be auto-configured and wired up successfully. I.e. you need a bootstrapping mechanism, like Spring Boot, especially if you are using the #EnableAutoConfiguration annotation.
For example...
import org.springframework.boot.SpringApplication;
...
class MyApplication {
public static void main(String[] args) {
SpringApplication.run(Operations.class, args);
}
}
Now, you could remove the #EnableAutoConfiguration from your Operations class and add the #SpringBootApplication to the MyApplication class, like so...
#SpringBootApplication
class MyApplication {
...
}
#SpringBootAppliation combines together Spring's #Configuration with Spring Boot's #EnableAutoConfiguration, along with many other useful meta-annotations, like Spring's #ComponentScan, enabling all sorts of magic to happen.
But, if you are not using Spring Boot, you can always bootstrap you application with the AnnotationConfigApplicationContext, like so..
class MyApplication
public static void main(String[] args) {
AnnotationConfigApplicationContext applicationContext =
new AnnotationConfigApplicationContext(Operations.class);
applicationContext.registerShutdownHook();
}
}
This is essentially what the Spring Boot, SpringApplication class does for you anyway.
If you are developing a Web application, then of course you can specify the type of ApplicationContext created since you are using Java config, for instance. See here for more details.
Hope this helps!
Cheers,
John
I'm testing a web application using JUnit. The buisness layer of this application is writed in EJB stateless classes.
So I do "in container" tests with JUnit and Glassfish-embedded.
All works fine so far, EJBs are injected using lookup functions.
Here are a simple test case :
public class SupportTest {
private static EJBContainer container;
private static MyEJB myEjb;
#BeforeClass
public static void setUpServices() throws NamingException {
Map<String, Object> properties = new HashMap<String, Object>();
properties.put(EJBContainer.MODULES, new File("target/classes"));
container = EJBContainer.createEJBContainer(properties);
myEjb = (MyEJB) container.getContext().lookup("java:global/classes/MyEJB");
}
#Test
public void test() {
myEjb.doSomething("user_login");
}
}
Now I have a SessionScoped POJO (CDI) which keep information such as user login and so on.
This Pojo is injected inside a static class. Like this :
public class MyStaticClass {
public static boolean verifyLogin(String login) {
MySessionPojo mySessionPojo = CDI.current().select(MySessionPojo.class).get();
return mySessionPojo.getLogin().equals(login);
}
}
This static class is used in EJB to secure the buisness code, like this :
#Stateless
public class MyEJB {
public void doSomething(String login) {
if(MyStaticClass.verifyLogin(login)){
//do something
}
}
}
Inside a normal Glassfish 4.1 server, the injection of the POJO inside the static class works fine.
Inside the Glassfish-embedded, the POJO injection fails with this message :
WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped
I assume this is because there is no Http Session bound to it.
Is there a way to simulate/create à SessionContext programmatically?
Thanks.
Ok, I finally find a workaround. I use the framework JMockit to replace the static class by a mock class, with fake methods which always return TRUE. (I had already tested Mockito and PowerMock, but both didn't work).
What exactly is the advantages of autowiring is Spring?
An example of autowiring in spring would be like
public class TestClass {
testMethod() {
// .....
};
}
public class MainClass {
public static void main(String[] args) {
ApplicationContext ctx = new ClasspathXmlApplicationContext("test.xml");
TestMethod obj = (TestClass) ctx.getBean("test");
obj.testMethod();
}
}
test.xml
<bean id="test" class="TestClass">
same in a normal operation could be done using:
public class MainClass {
public static void main(String[] args) {
TestClass obj = new TestClass();
obj.testMethod();
}
}
What is the advantage of Spring, I mean I have heard about terms Inversion of control and Dependency Injection.
In both the examples a reference of TestClass is used once through Spring XML again through new oerator. So can someone in simple terms explain what is the advantage.
Spring is taking care of creating of the objects. Let's say in spring boot you are creating a service:
#Service
public class CreditService { ....
with this you are saying to spring boot that he needs to create an object from type CreditService and whenever you want to use it you don't need to create it you can just say:
#Autowired
private CreditService creditService;
With that you are getting an reference: creditService , that will point to the object that spring boot created for you and call the methods (services). So basically spring is taking care of creation of the object and you are just calling it, not to worry about creating new object anywhere.