This is an anti pattern, but I am curious what will actually happen.
If you explicitly define a no-args constructor and a constructor with an autowired parameter, how exactly will spring framework initialize it?
#Service
class Clazz {
private MyBean myBean;
public Clazz(){}
#Autowired
public Clazz(MyBean myBean){
this.myBean = myBean;
}
}
On top of above answers, if there is single constructor declared without #autowire, spring uses same constructor for injection.
If there multiple constructors, then Spring uses constructor which is #autowired.
Mentioned in Spring Doc https://docs.spring.io/spring/docs/4.3.x/spring-framework-reference/htmlsingle/#beans-autowired-annotation
As of Spring Framework 4.3, an #Autowired annotation on such a
constructor is no longer necessary if the target bean only defines one
constructor to begin with. However, if several constructors are
available, at least one must be annotated to teach the container which
one to use
The constructor marked by #Autowired will be used by spring. You can validate this by running the following code.
public class Main {
#Component
static class MyBean {}
#Service
static class Clazz {
private MyBean myBean;
public Clazz(){
System.out.println("empty");
}
#Autowired
public Clazz(MyBean myBean){
this.myBean = myBean;
System.out.println("non-empty");
}
}
#Component
#ComponentScan("my.package")
private static class Configuration {
}
public static void main(String[] args) {
var ctx = new AnnotationConfigApplicationContext();
ctx.register(Configuration.class);
ctx.refresh();
ctx.getBean(Clazz.class);
}
}
The code prints non-empty.
Spring choose constructor first by the largest number of parameters
sortConstructors consider preferring public constructors and ones with a maximum number of arguments.
Meaning Clazz(MyBean myBean)
This is the Comparator used:
(e1, e2) -> {
int result = Boolean.compare(Modifier.isPublic(e2.getModifiers()), Modifier.isPublic(e1.getModifiers()));
return result != 0 ? result : Integer.compare(e2.getParameterCount(), e1.getParameterCount());
Related
Colleagues, hello! Is is possible to inject beans inside of class which is created via 'new' operator?
For example:
public class TestClass implements Callback {
#Inject
TestClassRepository repository;
//just only methods...
}
And 'TestClass' is created from another class:
Flyway.configure().collbacks(new TestClass()).load();
I have an issue with this,because 'repository.anyMethods()' inside of TestClass creates 'NullPointer' exception.
'TestClassRepository' is marked with the '#ApplicationScoped' and '#Startup' annotations.
#Singleton
public class TestConfig {
#javax.enterprise.inject.Produces
public TestClass testClass() {
return new TestClass();
}
}
another class annotated with the #ApplicationsScoped or #Singleton:
#Inject
public void method(TestClass testClass) {
Flyway.configure().collbacks(testClass).load();
// your code
}
If you create an object by yourself calling a constructor (new TestClass()) then quarkus doesn't manipulate that object, and doesn't inject a repository.
No you cannot inject beans inside a class that is instanciate with the new keyword.
But you can still find a way around like so :
#Dependent
public class BeanFactory {
#Inject
TestClassRepository repository
#Produces
public TestClass createTestClass() {
return new TestClass(this.repository);
}
You can find more details here : Quarkus Contexts and dependency Injection
Also you can define multiple beans for different profiles as mentionned few lines bellow Here
This means you can create a repository for your tests and one for prod or whatever is best for your case.
Also I do not think the annotation "#Startup" would add anything to your TestClassRepository bean.
I am trying to learn autowire with Qualifier in spring and the autowired class constructor is called twice .
I have the following class:
MainApp:
public class MainApp {
public static void main(String[] args) {
// ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
ApplicationContext ctx =
new AnnotationConfigApplicationContext(HelloWorldConfig.class);
// TextEditor obj = (TextEditor) ctx.getBean("helloWorld");
TextEditor obj = (TextEditor)ctx.getBean(TextEditor.class);
obj.spellCheck();
}
SpellChecker:
public class SpellChecker {
public SpellChecker() {
System.out.println("Inside SpellChecker constructor.");
}
public void checkSpelling() {
System.out.println("Inside checkSpelling.");
}
TextEditor
public class TextEditor {
#Qualifier("a")
#Autowired
private SpellChecker spellChecker;
public SpellChecker getSpellChecker( ) {
return spellChecker;
}
public void spellCheck() {
spellChecker.checkSpelling();
}
}
I have the java based configuration which has multiple bean with same Type and want to select a single bean with Qualifier but the output shows the constructor is called twice.\
HelloWorldConfig
#Component
public class HelloWorldConfig {
#Bean
public HelloWorld helloWorld(){
return new HelloWorld();
}
#Bean
public TextEditor textEditor(){
return new TextEditor();
}
#Bean(name="a")
public SpellChecker spellChecker(){
return new SpellChecker();
}
#Bean(name="b")
public SpellChecker spellChecker1(){
return new SpellChecker();
}
}
OUTPUT:
Inside SpellChecker constructor.
Inside SpellChecker constructor.
Inside checkSpelling.
I was expecting a single SpellChecker constructor call since i used Qualifier("a") to specify the bean, however the constructor is called twice even if I used Qualifier to select a sinlge bean. Why is it called twice??
Check Out HelloWorldConfig file. You've declared 2 beans of type SpellChecker:
#Bean(name="a")
public SpellChecker spellChecker(){
return new SpellChecker();
}
#Bean(name="b")
public SpellChecker spellChecker1(){
return new SpellChecker();
}
Both beans are created by spring, although only one bean is injected into the TextEditor.
In spring its perfectly fine to have more than one bean of the same type or beans that implement the same interface (think about listeners - there can be many of them) - so spring container will create them all during the application start.
If you want to inject one of those beans however into another bean (like TextEditor in your case), spring won't have a clue which one to inject, that's why you they've added a "qualifier" feature.
Another note, you've by mistake put a #Component annotation on the configuration class, instead you should use #Configuration annotation to specify that this class contains a series of beans definitions (that you indeed declare with #Bean annotation). Although the "configuration" is also a component (managed by spring) - spring still treats it in a significantly different way than regular beans.
And yet another note: although its not directly related to your question, it seems like you're mixing 2 styles of configurations in the code snippet you've provided: the style with #Qualifier/#Autowired (this way was added in spring 2.5 if I'm not mistaken) and the style of java configurations: #Configuration class with #Bean-s in it.
You can avoid using autowire altogether and inject the dependencies via constructor called from java config like this:
#Configuration
public class HelloWorldConfig {
#Bean
public HelloWorld helloWorld(){
return new HelloWorld();
}
#Bean
public TextEditor textEditor(#Qualifier("a") SpellChecker spellChecker){ // note the dependency here
return new TextEditor(spellChecker);
}
#Bean(name="a")
public SpellChecker spellChecker(){
return new SpellChecker();
}
#Bean(name="b")
public SpellChecker spellChecker1(){
return new SpellChecker();
}
}
// the TextEditor Class should have a constructor with one argument:
public class TextEditor {
private final SpellChecker spellChecker;
public TextEditor(SpellChecker spellChecker) {
this.spellChecker = spellChecker;
}
...
}
// or if you use lombok library:
#AllArgsConstructor
public class TextEditor {
private final SpellChecker spellChecker;
...
}
Now note, that your "business classes" are not even aware of spring all the "resolution" (usage of qualifier and injection rules) is done in spring configuration which is a special class anyway.
I have a requirement where I want to call a parameterised constructor of a class annotated with #Component inside another class which is annotated with #Service
feel free if you didn't get my question.
#Service
Class ServiceClass{
//here I want to create ComponentClass instance by Spring.
Result result=new ComponentClass(sending data to get result);
}
#Component
Class ComponentClass {
Component(received data){
}
}
I think you should try "Autowired" keyword. It says "Hey Spring Framework try to initialize the variable for me".
#Autowired
Result result=new ComponentClass(sending data to get result);
Whenever you define a #Servive or a #Component a bean of that type will be created (keep in mind that all beans are singletons).
A bean can be injected into any other spring managed bean by making use of this annotation:
#Service
Class ServiceClass{
#Autowired
Result result;
}
Using beans (components, services etc.) is not always needed and especially in the case, you need an non-singleton class, things can get tricky because of two reasons:
You won't be able to use annotations on that class
A non-annotated (spring managed bean) class do not support injection.
To inject a bean inside a class that is not annotated you will need to define a spring context:
#Component
public class SpringContext implements ApplicationContextAware {
private static ApplicationContext context
public static <T extends Object> T getBean(Class<T> beanClass) {
return context.getBean(beanClass);
}
#Override
public void setApplicationContext(ApplicationContext context) throws BeansException {
SpringContext.context = context;
}
}
and then into any class:
Class ServiceClass{
Result result = SpringContext.getBean(Result.class);
}
where result is a either component or service.
I have a component defined with prototype scope. I want to use that component in my service class. I want spring to provide me a new instance of that Bean everytime I call for it.
Component Class:
#Getter
#Setter
#Component
#Scope("prototype")
public class ProtoTypeBean {
//.. Field variables
}
Service Class:
#AllArgsConstructor
#Service
public class ServiceClass {
ProtoTypeBean prototypeBean;
ArrayList<ProtoTypeBean> prototypeBeans;
public void demoMethod(ArrayList<String> someArrayList) {
for(var singleString: someArrayList) {
prototypeBean.setFieldValue(singleString);
prototypeBeans.add(prototypeBean);
}
System.out.println(prototypeBeans.toString());
}
}
By using this configuration, I am getting the same instance of ProtoTypeBean in my prototypeBeans ArrayList. The question is, how would I make Spring understand to give me a new instance of prototypeBean every time I am calling it into the foreach loop?
I found I can use ApplicationContext.getBean() to get a new instance of the Bean in foreach loop but I also heard that it's a bad practice. So kindly help me with the best practice.
Use an ObjectProvider to lazily get the result you want. However the first prototype scoped bean will not be represented in the list of beans as, well they are prototype scoped.
#AllArgsConstructor
#Service
public class ServiceClass {
private final ObjectProvider<ProtoTypeBean> provider;
public void demoMethod(ArrayList<String> someArrayList) {
PrototypeBean pb = provider.getIfUnique();
for(var singleString: someArrayList) {
pb.setFieldValue(singleString);
pb.add(prototypeBean);
}
System.out.println(prototypeBean.toString());
}
}
Also if you don't need all the dependency injection, proxy creation etc. for your object then why bother. There is nothing wrong with just the new keyword in a Spring application. Not everything has to be managed by Spring.
Set up your prototype bean similar to this:
#Getter
#Setter
#Component
#Scope("prototype")
public class ProtoTypeBean {
final private String param;
public ProtoTypeBean(final String p) {
this.param = p;
}
}
Now, in your service class use a BeanFactory to create the beans for you:
#Service
#AllArgsConstructor
public class ServiceClass {
private final BeanFactory factory;
private List<ProtoTypeBean> prototypeBeans;
#Autowired
public ServiceClass(final BeanFactory f) {
this.factory = f;
}
public void demoMethod(List<String> someArrayList) {
this.prototypeBeans = someArrayList
.stream()
.map(param -> factory.getBean(ProtoTypeBean.class, param))
.collect(Collectors.toList());
}
}
I came across this issue recently. I am sure there must be a better way than mine, but this is how I did it:
public class ServiceClass {
ArrayList<ProtoTypeBean> prototypeBeans = new ArrayList<>();
#Autowired
ApplicationContext ctx;
public void demoMethod(ArrayList<String> someArrayList) {
for(var singleString: someArrayList) {
//magic is in below line.. getting a bean from ApplicatioContext.
ProtoTypeBean prototypeBean= ctx.getBean("protoTypeBean"); //Or ctx.getBean(ProtoTypeBean.class);
prototypeBean.setFieldValue(qBean.getFieldValue());
prototypeBeans.add(prototypeBean);
}
System.out.println(prototypeBeans.toString());
}
This way, Spring container always give you a new instance. And it is totally managed by Spring container.
The way you tried it, I tried that as well, but it would always inject one instance at the time of autowiring, hence defeating the purpose of prototyping.
You could have gone the route of using new Keyword. But then that is just regular Java instantiation and I think that new instance is not managed by Spring because it is annotated with #Component instead of #Configuration. I could be wrong here though.
I have a class that is annotated #Component that was then #Autowired into another class. However, I need to remove this #Component annotation and instead, create it with an #Bean annotated method in the class where its was previously autowired.
Where previously the classes looked like:
#Component
public class MyClass implements IMyClass
{
// Stuff
}
#Configuration
public class MyUsingClass
{
#Autowired
private IMyClass myClass;
private void methodUsingMyClass()
{
myClass.doStuff();
}
}
So now I have removed the #Component annotation and written a #Bean annotated method like this:
public class MyClass implements IMyClass
{
// Stuff
}
#Configuration
public class MyUsingClass
{
#Bean
public IMyClass getMyClass()
{
return new MyClass();
}
....
}
My question is around replacing the previous call of myClass.doStuff() to use the new bean. Do I now pass in a parameter of type MyClass to the private method:
private void methodUsingMyClass(final MyClass myClass)
{
myClass.doStuff();
}
... or do I call this method directly (doesn't seem the correct way to me):
private void methodUsingMyClass()
{
getMyClass().doStuff();
}
... or are neither of these correct?
I think you misunderstand the #Bean annotation. It can be used to create a Bean. So basically spring will scan all classes, will find your #Bean and create a Bean, not more. You can now use this bean, like if you would use one created with <bean></bean>. To actually use the bean you need to either get it from ApplicationContext or #Autowire it. Of course you can still use that function like any other function in your code, to create a new instance of that object, but that would contradict to what you want to achieve with beans
Using Annotations that solutions
public class MyClass implements IMyClass{
private OtherClassInjection otherClassInjection;
private OtherClassInjection2 otherClassInjection2;
MyClass(OtherClassInjection otherClassInjection, OtherClassInjection2 otherClassInjection2){
this.otherClassInjection=otherClassInjection;
this.otherClassInjection2=otherClassInjection2;
}
public void useObject(){
otherClassInjection.user();
}
}
#Bean(name = "myClass")
#Autowired
#Scope("prototype") //Define scope as needed
public MyClass getMyClass(#Qualifier("otherClassInjection") OtherClassInjection otherClassInjection,
OtherClassInjection2 otherClassInjection2) throws Exception
{
return new MyClass(otherClassInjection, otherClassInjection2);
}
that logical, it's work injection #Autowired when create a Bean if context are know that bean, that you will to want inject.
I'm use that way.