Develop Reference

Unable to Autowire through constructor

I am trying to Autowire a class through constructor.
#Component
public class Test<T extends Something>{
#Autowired
public Test(Class<T> entity)
doSomething(enity);
}
...
When I run the code I keep get the error message
Parameter 0 of constructor in com.test.Test required a bean of type 'java.lang.Class' that could not be found.
Action:
Consider defining a bean of type 'java.lang.Class' in your configuration.
Could someone please tell me where I am going wrong here. Thanks.

It says you that it could not find Class class marked as Bean etc
So you need to have a class wanted to be injected declared as #Bean ,#Component etc.
Here is an example:
#Configuration
public class Config {
#Bean
public<T> Class<T> tClass(){
return (some class to be returned);// you need to generify or pass some type of class which you want
}
}
//Here is injecting with no problems
#Component
public class Test<T> {
private Class<T> tClass;
#Autowired
public Test(Class<T> tClass) {
this.tClass = tClass;
}
}
Some how its better do define such architecture which would be better in this case:
public interface Foo<T> {
Class<T> getClassFromType();
}
#Component
public class FooIntegerImpl implements Foo<Integer>{
#Override
public Class<Integer> getClassFromType() {
return Integer.class;
}
}
#Component
public class FooStringImpl implements Foo<String>{
#Override
public Class<String> getClassFromType() {
return String.class;
}
}
#Component
public class Test {
private List<Foo> foo;
#Autowired
public Test(List<Foo> foo) {
this.foo = foo;
}
}
For such purposes for example you can define generic API which would be common for all cases , actually you can define AbstractCrudOperations and define crud things when someone need to inherit it would define type of object which need to be in and will have some methods defined
Actually in your case i dont know the logic what you want to implement but basic error is that Class could not be found as bean
I think this is helpful for you

Get a List of Beans for a certain type

I have a certain type of class that can provide data and a registry where the different data providers are registered. I am looking for an elegant way to implement this in spring boot.
My current implementation looks like this (code is shortened for brevity):
public interface DataProvider{
Data getSomeData();
}
public class Registry{
public register(DataProvider provider){
//add to internal list
};
public List<DataProvider> getProviders(){
//return providers
}
public Data someAggregatedOperation(){ ... }
}
public class Provider1 implements DataProvider { ... }
public class Provider2 implements DataProvider { ... }
Now for the wiring part, and this is the part I want to change to something more elegant:
#Configuration
public class MyAppConfiguration{
#Bean
public Registry providerRegistry(){
Registry reg = new Registry();
reg.register(new Provider1());
reg.register(new Provider2());
return reg;
}
}
Then I can inject the registry into other classes that need to operate on the services.
I know that DI is for providing different implementation for a single type but one at a time. So DI most probably is not the right tool, my question is more about spring if there's a good way I don't know to achieve this.
As example Annotate them with a Qualifier and then resolve all Beans with that qualifier in the registry.
The way I would not want to take is using a custom Annotation and then resolving all the classes via reflection, instantiate them and put them in the registry. But at the moment it's the only way I can see so I don't have to modify the config and handwire the services.

If you want all of them to be autowired, you can just autowire a list of your interface implementations.
#Bean
public class Provider1 implements DataProvider { ... }
#Bean
public class Provider2 implements DataProvider { ... }
#Bean
public class Registry{
#Autowired
private List<DataProvider> providers;
public List<DataProvider> getProviders(){
//return providers
}
public Data someAggregatedOperation(){ ... }
}
In case you want to keep using a configuration class you could do something like:
#Bean
public class Provider1 implements DataProvider { ... }
#Bean
public class Provider2 implements DataProvider { ... }
public class Registry{
private List<DataProvider> providers;
public Registry(final List<DataProvider> providers) {
this.providers = providers;
}
public List<DataProvider> getProviders(){
//return providers
}
public Data someAggregatedOperation(){ ... }
}
#Configuration
public class MyAppConfiguration{
#Bean
#Autowired
public Registry providerRegistry(final List<DataProvider> providers){
return new Registry(providers);
}
}

Changing a class annotated #Component to #Bean annotated method

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.

How to extend #Service?

Here is a sample class below:
#Service("testService")
public class TestService {
public String something() {
return "abc";
}
}
I want to extend the class and let the container know that it needs to pick up my extended class from now.
#Service("extendedTestService")
public class ExtendedTestServiceMock extends TestService {
#Override
public String something() {
return "xyz";
}
}
Test class:
public class TestClass extends SpringTest {
#Autowired
#Qualifier("extendedTestService")
private ExtendedTestService testService;
public void testMethod() {
......
}
}
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [TestService] is defined: expected single matching bean but found 2: ExtendedTestServiceMock,testService
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:865) ~[spring-beans-3.2.8.RELEASE.jar:3.2.8.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:770) ~[spring-beans-3.2.8.RELEASE.jar:3.2.8.RELEASE]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:489) ~[spring-beans-3.2.8.RELEASE.jar:3.2.8.RELEASE]
... 91 common frames omitted
How to resolve it?

Try using interfaces.
public interface TestService {
String something();
}
Implementations:
#Service
#Qualifier("testService")
public class TestServiceImpl implements TestService { ... }
#Service
#Qualifier("testServiceMock")
public class TestServiceMockImpl implements TestService { ... }
And the test class:
public class TestClass extends SpringTest {
#Autowired
#Qualifier("extendedTestService")
private TestService testService;
...
}

One solution that would work in your case is the #Primary annotation.
Your TestServiceMockImpl would look like:
#Service("extendedTestService ")
#Primary
public class ExtendedTestServiceMock extends TestService {
#override
public String something() {
return "xyz";
}
}
Check out this for more details on #Primary
I however suggest that you don't follow the above solution (since this will get out of hand very quick if you start using #Primary everywhere), that you instead take a look at Spring Profiles
There are a lot of way you could create your Spring configuration using profiles, but regardless of how you end up configuring the beans, the end result would be a more clean design.

If you have an identifier to help you decide which service to initialize, then you can use ConditionlOnProperty annotation
Ex:
#Service
#ConditionlOnProperty(value = "test.service.extension.enabled")
public class TestService {
}
#Service
#ConditionlOnProperty(value = "test.service.extension.enabled", havingValue = "false")
public class ExtendedTestServiceMock extends TestService {
}
If you want to use the extended test service, you can set the property test.service.extension.enabled=true in your application.properties

It depends on your definition order if your service define on the xml file.
Otherwise, you could use a BeanFactoryPostProcessor to do this, which is only registered in the test scenarios that you want this mocked.
public class SystemTestBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
#Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory factory) throws BeansException {
// put your custom code in here
}
}
Or you can use #DependsOn to make sure the parent bean should be deploy firstly then your extend bean
#Service("testService")
#DependsOn("testService")
public class ExtendedTestService extends TestService {
}
Hope this helps.

Spring 3.2 Autowire generic types

So I have a number of generics in Spring 3.2 and ideally my architecture would look something like this.
class GenericDao<T>{}
class GenericService<T, T_DAO extends GenericDao<T>>
{
// FAILS
#Autowired
T_DAO;
}
#Component
class Foo{}
#Repository
class FooDao extends GenericDao<Foo>{}
#Service
FooService extends GenericService<Foo, FooDao>{}
Unfortunately with multiple implementations of the generics the autowiring throws an error about multiple matching bean definitions. I assume this is because #Autowired processes before type erasure. Every solution I've found or come up with looks ugly to me or just inexplicably refuses to work. What is the best way around this problem?

How about adding a constructor to the GenericService and move the autowiring to the extending class, e.g.
class GenericService<T, T_DAO extends GenericDao<T>> {
private final T_DAO tDao;
GenericService(T_DAO tDao) {
this.tDao = tDao;
}
}
#Service
FooService extends GenericService<Foo, FooDao> {
#Autowired
FooService(FooDao fooDao) {
super(fooDao);
}
}
Update:
As of Spring 4.0 RC1, it is possible to autowire based on generic type, which means that you can write a generic service like
class GenericService<T, T_DAO extends GenericDao<T>> {
#Autowired
private T_DAO tDao;
}
and create multiple different Spring beans of it like:
#Service
class FooService extends GenericService<Foo, FooDao> {
}

Here is a closest solution. The specialized DAOs are annotated at the business layer. As in the question from OP, the best effort would be having an annotated DAO in the EntityDAO generic template itself. Type erasure seems to be not allowing the specialized type information to get passed onto the spring factories [resulting in reporting matching beans from all the specialized DAOs]
The Generic Entity DAO template
public class EntityDAO<T>
{
#Autowired
SessionFactory factory;
public Session getCurrentSession()
{
return factory.getCurrentSession();
}
public void create(T record)
{
getCurrentSession().save(record);
}
public void update(T record)
{
getCurrentSession().update(record);
}
public void delete(T record)
{
getCurrentSession().delete(record);
}
public void persist(T record)
{
getCurrentSession().saveOrUpdate(record);
}
public T get(Class<T> clazz, Integer id)
{
return (T) getCurrentSession().get(clazz, id);
}
}
The Generic Entity Based Business Layer Template
public abstract class EntityBusinessService<T>
implements Serializable
{
public abstract EntityDAO<T> getDAO();
//Rest of code.
}
An Example Specialized Entity DAO
#Transactional
#Repository
public class UserDAO
extends EntityDAO<User>
{
}
An Example Specialized Entity Business Class
#Transactional
#Service
#Scope("prototype")
public class UserBusinessService
extends EntityBusinessService<User>
{
#Autowired
UserDAO dao;
#Override
public EntityDAO<User> getDAO()
{
return dao;
}
//Rest of code
}

You can remove the #autowire annotation and perform delayed “autowire” using #PostConstruct and ServiceLocatorFactoryBean.
Your GenericService will look similar to this
public class GenericService<T, T_DAO extends GenericDao<T>>{
#Autowired
private DaoLocator daoLocatorFactoryBean;
//No need to autowried, autowireDao() will do this for you
T_DAO dao;
#SuppressWarnings("unchecked")
#PostConstruct
protected void autowireDao(){
//Read the actual class at run time
final Type type;
type = ((ParameterizedType) getClass().getGenericSuperclass())
.getActualTypeArguments()[1];
//figure out the class of the fully qualified class name
//this way you can know the bean name to look for
final String typeClass = type.toString();
String daoName = typeClass.substring(typeClass.lastIndexOf('.')+1
,typeClass.length());
daoName = Character.toLowerCase(daoName.charAt(0)) + daoName.substring(1);
this.dao = (T_DAO) daoLocatorFactoryBean.lookup(daoName);
}
daoLocatorFactoryBean does the magic for you.
In order to use it you need to add an interface similar to the one below:
public interface DaoLocator {
public GenericDao<?> lookup(String serviceName);
}
You need to add the following snippet to your applicationContext.xml
<bean id="daoLocatorFactoryBean"
class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean">
<property name="serviceLocatorInterface"
value="org.haim.springframwork.stackoverflow.DaoLocator" />
</bean>
This is a nice trick and it will save you little boilerplate classes.
B.T.W I do not see this boilerplate code as a big issue and the project I working for uses matsev approach.

Why do you want a generic service ? Service classes are meant for specific units of work involving multple entities. You can just inject a repository straight into a controller.
Here is an example of generic repository with constructor argument, you could also make each method Generic instead and have no constructor argument. But each method call would require class as parameter:
public class DomainRepository<T> {
#Resource(name = "sessionFactory")
protected SessionFactory sessionFactory;
public DomainRepository(Class genericType) {
this.genericType = genericType;
}
#Transactional(readOnly = true)
public T get(final long id) {
return (T) sessionFactory.getCurrentSession().get(genericType, id);
}
Example of bean definition for the generic repository - you could have multple different beans, using different contstructor args.
<bean id="tagRepository" class="com.yourcompnay.data.DomainRepository">
<constructor-arg value="com.yourcompnay.domain.Tag"/>
</bean>
Depdncy injection of bean using resource annotation
#Resource(name = "tagRepository")
private DomainRepository<Tag> tagRepository;
And this allows the Domainreposiroty to be subclassed for specific entities/methods, which woul dallow autowiring :
public class PersonRepository extends DomainRepository<Person> {
public PersonRepository(){
super(Person.class);
}
...

You should use autowiring in classes which extends these generics

For this question one needs to understand about what autowire is. In common terms we can say that through autowire we create a object instance/bean at the time of deployment of the web app. So now going with the question if you are declaring autowiring in multiple places with the same name. Then this error comes. Autowiring can be done in multiple ways so if you are using multiple type of autowiring technique, then also one could get this error.

Complete Generic Solution using Spring 4:
Domain Class
#Component
class Foo{
}
#Component
class Bar{
}
DAO Layer
interface GenericDao<T>{
//list of methods
}
class GenericDaoImpl<T> implements GenericDao<T>{
#Autowired
SessionFactory factory;
private Class<T> domainClass; // Get Class Type of <T>
public Session getCurrentSession(){
return factory.getCurrentSession();
}
public DaoImpl() {
this.domainClass = (Class<T>) GenericTypeResolver.resolveTypeArgument(getClass(), DaoImpl.class);
}
//implementation of methods
}
interface FooDao extends GenericDao<Foo>{
//Define extra methods if required
}
interface BarDao extends GenericDao<Bar>{
//Define extra methods if required
}
#Repository
class FooDao extends GenericDaoImpl<Foo> implements FooDao{
//implementation of extra methods
}
#Repository
class BarDao extends GenericDaoImpl<Bar> implements BarDao{
//implementation of extra methods
}
Service Layer
interface GenericService<T>{
//List of methods
}
class GenericServiceImpl<T> implements GenericService<T>{
#Autowire
protected GenericDao<T> dao; //used to access DAO layer
}
class FooService extends GenericService<Foo>{
//Add extra methods of required
}
class BarService extends GenericService<Bar>{
//Add extra methods of required
}
#Service
class FooServiceImpl extends GenericServiceImpl<Foo> implements GenericService<Foo>{
//implementation of extra methods
}
#Service
class BarServiceImpl extends GenericServiceImpl<Bar> implements GenericService<Bar>{
//implementation of extra methods
}