the below bean of Class I want to inject in other non-managed bean, but it is not working as expected
#Component
#Setter
#Getter
public class AbstractLayoutProperties {
#Value("${spring.application.name}")
private String appName;
#Autowired
S3Service s3Service;
#Autowired
S3Client s3Client;
}
Below is the class which is not managed by the spring, but I am using #Configurable
#Configurable(preConstruction = true, autowire = Autowire.BY_NAME)
#EnableSpringConfigured
public class OverlayServiceImpl
implements GenericVehicleOverlayService<T, R> {
public findOnlyActive(){
appName = layoutProperties.getAppName(); // throwint NullPointerException beacuse the object not injected properly
}
#Autowired
AbstractLayoutProperties layoutProperties;
}
One more point, findOnlyActive method I am not calling directly, I am calling this from another service, lets say
#Service
public class OtherService{
public void findActive(){
OverlayServiceImpl impl=new OverlayServiceImpl();
impl.findOnlyActive();
}
#Autowired
OtherRepository otherRepo;
}
Problem statrement:
when impl.findOnlyActive(); is executed, it should inject all the required beans inside OverlayServiceImpl. In the same class I have two beans which are autowired, it seems none of them injected, this is the reaosn that every time I am encountering Nullpointer exception. so my question is how do I make it work, what are the steps and action I need to take so that spring will inject the dependencies in non managed object i,e OverlayServiceImpl.
I have an interface and service implements it. It has some void methods.
I am using spring java bean configuration. But unable to create bean object because of void methods.How to handle this problem.
I tried to use #PostConstruct instead of #Bean after reading some blogs, but it didn't work out.
public interface MyInterface {
void someData(List<MyClass> list, String somedata);
}
#Service("myInterface")
public DummyClass implements MyInterface {
public void someData(List<MyClass> list, String somedata){
// my business logic
}
}
public AppConfig {
#Bean
public MyInterface myInterface {
return new DummyClass(); // but gives error void cannot return value
}
}
My Junit looks like this
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(
classes = {AppConfig.class},
loader = AnnotationConfigContextLoader.class
)
public class MyTest {
#Autowired
DummyClass dummyClass;
// If I don't use AppConfig and simply autowire then I get
"Error creating bean name, unsatisfied dependency
}
How do I achieve dependency injection here?
Use #Configuration annotation on AppConfig class, with this all the beans defined on this class will be loaded on spring context.
If you use #Service annotation on DummyClass, you do not need to declare #Bean annotation because you are already saying to spring to detect this class for dependency injection. On the other hand use #Bean annotation to specify the instantiation of the class. Normally I let the #Bean to complex classes for dependency injection or to override configurations.
I'm a little confused as to how the inversion of control (IoC) works in Spring.
Say I have a service class called UserServiceImpl that implements UserService interface.
How would this be #Autowired?
And in my Controllers, how would I instantiate an instance of this service?
Would I just do the following?
UserService userService = new UserServiceImpl();
First, and most important - all Spring beans are managed - they "live" inside a container, called "application context".
Second, each application has an entry point to that context. Web applications have a Servlet, JSF uses a el-resolver, etc. Also, there is a place where the application context is bootstrapped and all beans - autowired. In web applications this can be a startup listener.
Autowiring happens by placing an instance of one bean into the desired field in an instance of another bean. Both classes should be beans, i.e. they should be defined to live in the application context.
What is "living" in the application context? This means that the context instantiates the objects, not you. I.e. - you never make new UserServiceImpl() - the container finds each injection point and sets an instance there.
In your controllers, you just have the following:
#Controller // Defines that this class is a spring bean
#RequestMapping("/users")
public class SomeController {
// Tells the application context to inject an instance of UserService here
#Autowired
private UserService userService;
#RequestMapping("/login")
public void login(#RequestParam("username") String username,
#RequestParam("password") String password) {
// The UserServiceImpl is already injected and you can use it
userService.login(username, password);
}
}
A few notes:
In your applicationContext.xml you should enable the <context:component-scan> so that classes are scanned for the #Controller, #Service, etc. annotations.
The entry point for a Spring-MVC application is the DispatcherServlet, but it is hidden from you, and hence the direct interaction and bootstrapping of the application context happens behind the scene.
UserServiceImpl should also be defined as bean - either using <bean id=".." class=".."> or using the #Service annotation. Since it will be the only implementor of UserService, it will be injected.
Apart from the #Autowired annotation, Spring can use XML-configurable autowiring. In that case all fields that have a name or type that matches with an existing bean automatically get a bean injected. In fact, that was the initial idea of autowiring - to have fields injected with dependencies without any configuration. Other annotations like #Inject, #Resource can also be used.
Depends on whether you want the annotations route or the bean XML definition route.
Say you had the beans defined in your applicationContext.xml:
<beans ...>
<bean id="userService" class="com.foo.UserServiceImpl"/>
<bean id="fooController" class="com.foo.FooController"/>
</beans>
The autowiring happens when the application starts up. So, in fooController, which for arguments sake wants to use the UserServiceImpl class, you'd annotate it as follows:
public class FooController {
// You could also annotate the setUserService method instead of this
#Autowired
private UserService userService;
// rest of class goes here
}
When it sees #Autowired, Spring will look for a class that matches the property in the applicationContext, and inject it automatically. If you have more than one UserService bean, then you'll have to qualify which one it should use.
If you do the following:
UserService service = new UserServiceImpl();
It will not pick up the #Autowired unless you set it yourself.
#Autowired is an annotation introduced in Spring 2.5, and it's used only for injection.
For example:
class A {
private int id;
// With setter and getter method
}
class B {
private String name;
#Autowired // Here we are injecting instance of Class A into class B so that you can use 'a' for accessing A's instance variables and methods.
A a;
// With setter and getter method
public void showDetail() {
System.out.println("Value of id form A class" + a.getId(););
}
}
How does #Autowired work internally?
Example:
class EnglishGreeting {
private Greeting greeting;
//setter and getter
}
class Greeting {
private String message;
//setter and getter
}
.xml file it will look alike if not using #Autowired:
<bean id="englishGreeting" class="com.bean.EnglishGreeting">
<property name="greeting" ref="greeting"/>
</bean>
<bean id="greeting" class="com.bean.Greeting">
<property name="message" value="Hello World"/>
</bean>
If you are using #Autowired then:
class EnglishGreeting {
#Autowired //so automatically based on the name it will identify the bean and inject.
private Greeting greeting;
//setter and getter
}
.xml file it will look alike if not using #Autowired:
<bean id="englishGreeting" class="com.bean.EnglishGreeting"></bean>
<bean id="greeting" class="com.bean.Greeting">
<property name="message" value="Hello World"/>
</bean>
If still have some doubt then go through below live demo
How does #Autowired work internally ?
You just need to annotate your service class UserServiceImpl with annotation:
#Service("userService")
Spring container will take care of the life cycle of this class as it register as service.
Then in your controller you can auto wire (instantiate) it and use its functionality:
#Autowired
UserService userService;
Spring dependency inject help you to remove coupling from your classes.
Instead of creating object like this:
UserService userService = new UserServiceImpl();
You will be using this after introducing DI:
#Autowired
private UserService userService;
For achieving this you need to create a bean of your service in your ServiceConfiguration file. After that you need to import that ServiceConfiguration class to your WebApplicationConfiguration class so that you can autowire that bean into your Controller like this:
public class AccController {
#Autowired
private UserService userService;
}
You can find a java configuration based POC here
example.
There are 3 ways you can create an instance using #Autowired.
1. #Autowired on Properties
The annotation can be used directly on properties, therefore eliminating the need for getters and setters:
#Component("userService")
public class UserService {
public String getName() {
return "service name";
}
}
#Component
public class UserController {
#Autowired
UserService userService
}
In the above example, Spring looks for and injects userService when UserController is created.
2. #Autowired on Setters
The #Autowired annotation can be used on setter methods. In the below example, when the annotation is used on the setter method, the setter method is called with the instance of userService when UserController is created:
public class UserController {
private UserService userService;
#Autowired
public void setUserService(UserService userService) {
this.userService = userService;
}
}
3. #Autowired on Constructors
The #Autowired annotation can also be used on constructors. In the below example, when the annotation is used on a constructor, an instance of userService is injected as an argument to the constructor when UserController is created:
public class UserController {
private UserService userService;
#Autowired
public UserController(UserService userService) {
this.userService= userService;
}
}
In simple words Autowiring, wiring links automatically, now comes the question who does this and which kind of wiring.
Answer is: Container does this and Secondary type of wiring is supported, primitives need to be done manually.
Question: How container know what type of wiring ?
Answer: We define it as byType,byName,constructor.
Question: Is there are way we do not define type of autowiring ?
Answer: Yes, it's there by doing one annotation, #Autowired.
Question: But how system know, I need to pick this type of secondary data ?
Answer: You will provide that data in you spring.xml file or by using sterotype annotations to your class so that container can themselves create the objects for you.
Standard way:
#RestController
public class Main {
UserService userService;
public Main(){
userService = new UserServiceImpl();
}
#GetMapping("/")
public String index(){
return userService.print("Example test");
}
}
User service interface:
public interface UserService {
String print(String text);
}
UserServiceImpl class:
public class UserServiceImpl implements UserService {
#Override
public String print(String text) {
return text + " UserServiceImpl";
}
}
Output: Example test UserServiceImpl
That is a great example of tight coupled classes, bad design example and there will be problem with testing (PowerMockito is also bad).
Now let's take a look at SpringBoot dependency injection, nice example of loose coupling:
Interface remains the same,
Main class:
#RestController
public class Main {
UserService userService;
#Autowired
public Main(UserService userService){
this.userService = userService;
}
#GetMapping("/")
public String index(){
return userService.print("Example test");
}
}
ServiceUserImpl class:
#Component
public class UserServiceImpl implements UserService {
#Override
public String print(String text) {
return text + " UserServiceImpl";
}
}
Output: Example test UserServiceImpl
and now it's easy to write test:
#RunWith(MockitoJUnitRunner.class)
public class MainTest {
#Mock
UserService userService;
#Test
public void indexTest() {
when(userService.print("Example test")).thenReturn("Example test UserServiceImpl");
String result = new Main(userService).index();
assertEquals(result, "Example test UserServiceImpl");
}
}
I showed #Autowired annotation on constructor but it can also be used on setter or field.
The whole concept of inversion of control means you are free from a chore to instantiate objects manually and provide all necessary dependencies.
When you annotate class with appropriate annotation (e.g. #Service) Spring will automatically instantiate object for you. If you are not familiar with annotations you can also use XML file instead. However, it's not a bad idea to instantiate classes manually (with the new keyword) in unit tests when you don't want to load the whole spring context.
Keep in mind that you must enable the #Autowired annotation by adding element <context:annotation-config/> into the spring configuration file. This will register the AutowiredAnnotationBeanPostProcessor which takes care the processing of annotation.
And then you can autowire your service by using the field injection method.
public class YourController{
#Autowired
private UserService userService;
}
I found this from the post Spring #autowired annotation
i am really confused with spring annotations.
where to use # Autowired, where class is # Bean or # Component,
i understand we cannot use
Example example=new Example("String");
in Spring
but how alone
#Autowired
Example example;
will solve the purpose?
what about Example Constructor ,how spring will provide String value to Example Constructor?
i went through one of the article but it does not make much sense to me.
it would be great if some one can give me just brief and simple explanation.
Spring doesn't say you can't do Example example = new Example("String"); That is still perfectly legal if Example does not need to be a singleton bean. Where #Autowired and #Bean come into play is when you want to instantiate a class as a singleton. In Spring, any bean you annotate with #Service, #Component or #Repository would get automatically registered as a singleton bean as long as your component scanning is setup correctly. The option of using #Bean allows you to define these singletons without annotating the classes explicitly. Instead you would create a class, annotate it with #Configuration and within that class, define one or more #Bean definitions.
So instead of
#Component
public class MyService {
public MyService() {}
}
You could have
public class MyService {
public MyService() {}
}
#Configuration
public class Application {
#Bean
public MyService myService() {
return new MyService();
}
#Autowired
#Bean
public MyOtherService myOtherService(MyService myService) {
return new MyOtherService();
}
}
The trade-off is having your beans defined in one place vs annotating individual classes. I typically use both depending on what I need.
You will first define a bean of type example:
<beans>
<bean name="example" class="Example">
<constructor-arg value="String">
</bean>
</beans>
or in Java code as:
#Bean
public Example example() {
return new Example("String");
}
Now when you use #Autowired the spring container will inject the bean created above into the parent bean.
Default constructor + #Component - Annotation is enough to get #Autowired work:
#Component
public class Example {
public Example(){
this.str = "string";
}
}
You should never instantiate a concrete implementation via #Bean declaration. Always do something like this:
public interface MyApiInterface{
void doSomeOperation();
}
#Component
public class MyApiV1 implements MyApiInterface {
public void doSomeOperation() {...}
}
And now you can use it in your code:
#Autowired
private MyApiInterface _api; // spring will AUTOmaticaly find the implementation
I have several classes in a Spring Boot project, some work with #Autowired, some do not. Here my code follows:
Application.java (#Autowired works):
package com.example.myproject;
#ComponentScan(basePackages = {"com.example.myproject"})
#Configuration
#EnableAutoConfiguration
#EnableJpaRepositories(basePackages = "com.example.myproject.repository")
#PropertySource({"classpath:db.properties", "classpath:soap.properties"})
public class Application {
#Autowired
private Environment environment;
public static void main(String[] args) {
SpringApplication.run(Application.class);
}
#Bean
public SOAPConfiguration soapConfiguration() {
SOAPConfiguration SOAPConfiguration = new SOAPConfiguration();
SOAPConfiguration.setUsername(environment.getProperty("SOAP.username"));
SOAPConfiguration.setPassword(environment.getProperty("SOAP.password"));
SOAPConfiguration.setUrl(environment.getProperty("SOAP.root"));
return SOAPConfiguration;
}
HomeController (#Autowired works):
package com.example.myproject.controller;
#Controller
class HomeController {
#Resource
MyRepository myRepository;
MyService (#Autowired does not work):
package com.example.myproject.service;
#Service
public class MyServiceImpl implements MyService {
#Autowired
public SOAPConfiguration soapConfiguration; // is null
private void init() {
log = LogFactory.getLog(MyServiceImpl.class);
log.info("starting init, soapConfiguration: " + soapConfiguration);
url = soapConfiguration.getUrl(); // booom -> NullPointerException
I do not get the SOAPConfiguration but my application breaks with a null pointer exception when I try to access it.
I have already read many Threads here and googled around, but did not find a solution yet. I tried to deliver all necessary information, please let me know if anything misses.
I guess you call init() before the autowiring takes place. Annotate init() with #PostConstruct to make it call automatically after all the spring autowiring.
EDIT: after seeing your comment, I guess you are creating it using new MyServiceImpl(). This takes away the control of the MyServiceImpl from Spring and gives it to you. Autowiring won't work in those case
Did you created a bean for the class SOAPConfiguration in any of your configuration classes? If you want to autowire a class in your project, you need to create a bean for it. For example,
#Configuration
public class SomeConfiguration{
#Bean
public SOAPConfiguration createSOAPConfiguration(){
return new SOAPConfiguration();
}
}
public class SomeOtherClass{
#Autowired
private SOAPConfiguration soapConfiguration;
}