I would like to use spring transaction management capabilities within a prototype bean. I did the following:
I've used javax.inject.Provider to create my prototype bean.
I've annotated the method of the prototyped bean with the #Transactional annotation.
Is this the right way of doing it?
#Service
public class SomeService {
#Autowired
private Provider<SomePrototype> myPrototypeProvider;
public void execute() {
SomePrototype somePrototype = myPrototypeProvider.get();
somePrototype.someMethod();
}
}
#Component
#Scope(BeanDefinition.SCOPE_PROTOTYPE)
public class SomePrototype {
#Autowired
private SomeSpringBean someSpringBean;
#Autowired
private SomeRepository someRepository;
#Transactional(propagation = Propagation.REQUIRED)
public void someMethod() {
Result result = someSpringBean.doSomething();
someRepository.save(result);
}
}
The initialisation of transaction-scoped bean requires a proxy. Therefore, if we define a transactional bean as prototype, every that bean is requested, a new proxy is created, and that is not efficient.
What is reason behind this requirement (to have transactional prototype bean)
Note: This is intended to be a canonical answer for a common problem.
I have a Spring #Service class (MileageFeeCalculator) that has an #Autowired field (rateService), but the field is null when I try to use it. The logs show that both the MileageFeeCalculator bean and the MileageRateService bean are being created, but I get a NullPointerException whenever I try to call the mileageCharge method on my service bean. Why isn't Spring autowiring the field?
Controller class:
#Controller
public class MileageFeeController {
#RequestMapping("/mileage/{miles}")
#ResponseBody
public float mileageFee(#PathVariable int miles) {
MileageFeeCalculator calc = new MileageFeeCalculator();
return calc.mileageCharge(miles);
}
}
Service class:
#Service
public class MileageFeeCalculator {
#Autowired
private MileageRateService rateService; // <--- should be autowired, is null
public float mileageCharge(final int miles) {
return (miles * rateService.ratePerMile()); // <--- throws NPE
}
}
Service bean that should be autowired in MileageFeeCalculator but it isn't:
#Service
public class MileageRateService {
public float ratePerMile() {
return 0.565f;
}
}
When I try to GET /mileage/3, I get this exception:
java.lang.NullPointerException: null
at com.chrylis.example.spring_autowired_npe.MileageFeeCalculator.mileageCharge(MileageFeeCalculator.java:13)
at com.chrylis.example.spring_autowired_npe.MileageFeeController.mileageFee(MileageFeeController.java:14)
...
The field annotated #Autowired is null because Spring doesn't know about the copy of MileageFeeCalculator that you created with new and didn't know to autowire it.
The Spring Inversion of Control (IoC) container has three main logical components: a registry (called the ApplicationContext) of components (beans) that are available to be used by the application, a configurer system that injects objects' dependencies into them by matching up the dependencies with beans in the context, and a dependency solver that can look at a configuration of many different beans and determine how to instantiate and configure them in the necessary order.
The IoC container isn't magic, and it has no way of knowing about Java objects unless you somehow inform it of them. When you call new, the JVM instantiates a copy of the new object and hands it straight to you--it never goes through the configuration process. There are three ways that you can get your beans configured.
I have posted all of this code, using Spring Boot to launch, at this GitHub project; you can look at a full running project for each approach to see everything you need to make it work. Tag with the NullPointerException: nonworking
Inject your beans
The most preferable option is to let Spring autowire all of your beans; this requires the least amount of code and is the most maintainable. To make the autowiring work like you wanted, also autowire the MileageFeeCalculator like this:
#Controller
public class MileageFeeController {
#Autowired
private MileageFeeCalculator calc;
#RequestMapping("/mileage/{miles}")
#ResponseBody
public float mileageFee(#PathVariable int miles) {
return calc.mileageCharge(miles);
}
}
If you need to create a new instance of your service object for different requests, you can still use injection by using the Spring bean scopes.
Tag that works by injecting the #MileageFeeCalculator service object: working-inject-bean
Use #Configurable
If you really need objects created with new to be autowired, you can use the Spring #Configurable annotation along with AspectJ compile-time weaving to inject your objects. This approach inserts code into your object's constructor that alerts Spring that it's being created so that Spring can configure the new instance. This requires a bit of configuration in your build (such as compiling with ajc) and turning on Spring's runtime configuration handlers (#EnableSpringConfigured with the JavaConfig syntax). This approach is used by the Roo Active Record system to allow new instances of your entities to get the necessary persistence information injected.
#Service
#Configurable
public class MileageFeeCalculator {
#Autowired
private MileageRateService rateService;
public float mileageCharge(final int miles) {
return (miles * rateService.ratePerMile());
}
}
Tag that works by using #Configurable on the service object: working-configurable
Manual bean lookup: not recommended
This approach is suitable only for interfacing with legacy code in special situations. It is nearly always preferable to create a singleton adapter class that Spring can autowire and the legacy code can call, but it is possible to directly ask the Spring application context for a bean.
To do this, you need a class to which Spring can give a reference to the ApplicationContext object:
#Component
public class ApplicationContextHolder implements ApplicationContextAware {
private static ApplicationContext context;
#Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
context = applicationContext;
}
public static ApplicationContext getContext() {
return context;
}
}
Then your legacy code can call getContext() and retrieve the beans it needs:
#Controller
public class MileageFeeController {
#RequestMapping("/mileage/{miles}")
#ResponseBody
public float mileageFee(#PathVariable int miles) {
MileageFeeCalculator calc = ApplicationContextHolder.getContext().getBean(MileageFeeCalculator.class);
return calc.mileageCharge(miles);
}
}
Tag that works by manually looking up the service object in the Spring context: working-manual-lookup
If you are not coding a web application, make sure your class in which #Autowiring is done is a spring bean. Typically, spring container won't be aware of the class which we might think of as a spring bean. We have to tell the Spring container about our spring classes.
This can be achieved by configuring in appln-contxt or the better way is to annotate class as #Component and please do not create the annotated class using new operator.
Make sure you get it from Appln-context as below.
#Component
public class MyDemo {
#Autowired
private MyService myService;
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("test");
ApplicationContext ctx=new ClassPathXmlApplicationContext("spring.xml");
System.out.println("ctx>>"+ctx);
Customer c1=null;
MyDemo myDemo=ctx.getBean(MyDemo.class);
System.out.println(myDemo);
myDemo.callService(ctx);
}
public void callService(ApplicationContext ctx) {
// TODO Auto-generated method stub
System.out.println("---callService---");
System.out.println(myService);
myService.callMydao();
}
}
Actually, you should use either JVM managed Objects or Spring-managed Object to invoke methods.
from your above code in your controller class, you are creating a new object to call your service class which has an auto-wired object.
MileageFeeCalculator calc = new MileageFeeCalculator();
so it won't work that way.
The solution makes this MileageFeeCalculator as an auto-wired object in the Controller itself.
Change your Controller class like below.
#Controller
public class MileageFeeController {
#Autowired
MileageFeeCalculator calc;
#RequestMapping("/mileage/{miles}")
#ResponseBody
public float mileageFee(#PathVariable int miles) {
return calc.mileageCharge(miles);
}
}
I once encountered the same issue when I was not quite used to the life in the IoC world. The #Autowired field of one of my beans is null at runtime.
The root cause is, instead of using the auto-created bean maintained by the Spring IoC container (whose #Autowired field is indeed properly injected), I am newing my own instance of that bean type and using it. Of course this one's #Autowired field is null because Spring has no chance to inject it.
Your problem is new (object creation in java style)
MileageFeeCalculator calc = new MileageFeeCalculator();
With annotation #Service, #Component, #Configuration beans are created in the
application context of Spring when server is started. But when we create objects
using new operator the object is not registered in application context which is already created. For Example Employee.java class i have used.
Check this out:
public class ConfiguredTenantScopedBeanProcessor implements BeanFactoryPostProcessor {
#Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
String name = "tenant";
System.out.println("Bean factory post processor is initialized");
beanFactory.registerScope("employee", new Employee());
Assert.state(beanFactory instanceof BeanDefinitionRegistry,
"BeanFactory was not a BeanDefinitionRegistry, so CustomScope cannot be used.");
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
for (String beanName : beanFactory.getBeanDefinitionNames()) {
BeanDefinition definition = beanFactory.getBeanDefinition(beanName);
if (name.equals(definition.getScope())) {
BeanDefinitionHolder proxyHolder = ScopedProxyUtils.createScopedProxy(new BeanDefinitionHolder(definition, beanName), registry, true);
registry.registerBeanDefinition(beanName, proxyHolder.getBeanDefinition());
}
}
}
}
I'm new to Spring, but I discovered this working solution. Please tell me if it's a deprecable way.
I make Spring inject applicationContext in this bean:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;
#Component
public class SpringUtils {
public static ApplicationContext ctx;
/**
* Make Spring inject the application context
* and save it on a static variable,
* so that it can be accessed from any point in the application.
*/
#Autowired
private void setApplicationContext(ApplicationContext applicationContext) {
ctx = applicationContext;
}
}
You can put this code also in the main application class if you want.
Other classes can use it like this:
MyBean myBean = (MyBean)SpringUtils.ctx.getBean(MyBean.class);
In this way any bean can be obtained by any object in the application (also intantiated with new) and in a static way.
It seems to be rare case but here is what happened to me:
We used #Inject instead of #Autowired which is javaee standard supported by Spring. Every places it worked fine and the beans injected correctly, instead of one place. The bean injection seems the same
#Inject
Calculator myCalculator
At last we found that the error was that we (actually, the Eclipse auto complete feature) imported com.opensymphony.xwork2.Inject instead of javax.inject.Inject !
So to summarize, make sure that your annotations (#Autowired, #Inject, #Service ,... ) have correct packages!
What hasn't been mentioned here is described in this article in the paragraph "Order of execution".
After "learning" that I had to annotate a class with #Component or the derivatives #Service or #Repository (I guess there are more), to autowire other components inside them, it struck me that these other components still were null inside the constructor of the parent component.
Using #PostConstruct solves that:
#SpringBootApplication
public class Application {
#Autowired MyComponent comp;
}
and:
#Component
public class MyComponent {
#Autowired ComponentDAO dao;
public MyComponent() {
// dao is null here
}
#PostConstruct
public void init() {
// dao is initialized here
}
}
One of the below will work :
The class where you are using #Autowired is not a Bean (You may have used new() somewhere I am sure).
Inside the SpringConfig class you have not mentioned the packages the Spring should look for #Component ( I am talking about #ComponentScan(basePackages"here") )
If above two don't work .... start putting System.out.println() and figure out where it is going wrong.
If this is happening in a test class, make sure you haven't forgotten to annotate the class.
For example, in Spring Boot:
#RunWith(SpringRunner.class)
#SpringBootTest
public class MyTests {
....
Some time elapses...
Spring Boot continues to evolve. It is no longer required to use #RunWith if you use the correct version of JUnit.
For #SpringBootTest to work stand alone, you need to use #Test from JUnit5 instead of JUnit4.
//import org.junit.Test; // JUnit4
import org.junit.jupiter.api.Test; // JUnit5
#SpringBootTest
public class MyTests {
....
If you get this configuration wrong your tests will compile, but #Autowired and #Value fields (for example) will be null. Since Spring Boot operates by magic, you may have few avenues for directly debugging this failure.
In simple words there are mainly two reasons for an #Autowired field to be null
YOUR CLASS IS NOT A SPRING BEAN.
The class in which you define the #Autowire anotation is not a spring bean. Thus spring will not auto wire the members.
THE FIELD IS NOT A BEAN.
There is no bean with the type or type in hierarchy you specified in the #Autowired field is not yet present in the spring application context or registry
Another solution would be to put a call of
SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this)
to MileageFeeCalculator constructor like this:
#Service
public class MileageFeeCalculator {
#Autowired
private MileageRateService rateService; // <--- will be autowired when constructor is called
public MileageFeeCalculator() {
SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this)
}
public float mileageCharge(final int miles) {
return (miles * rateService.ratePerMile());
}
}
I think you have missed to instruct spring to scan classes with annotation.
You can use #ComponentScan("packageToScan") on the configuration class of your spring application to instruct spring to scan.
#Service, #Component etc annotations add meta description.
Spring only injects instances of those classes which are either created as bean or marked with annotation.
Classes marked with annotation need to be identified by spring before injecting, #ComponentScan instruct spring look for the classes marked with annotation. When Spring finds #Autowired it searches for the related bean, and injects the required instance.
Adding annotation only, does not fix or facilitate the dependency injection, Spring needs to know where to look for.
This is the culprit of giving NullPointerException MileageFeeCalculator calc = new MileageFeeCalculator(); We are using Spring - don't need to create object manually. Object creation will be taken care of by IoC container.
UPDATE: Really smart people were quick to point on this answer, which explains the weirdness, described below
ORIGINAL ANSWER:
I don't know if it helps anyone, but I was stuck with the same problem even while doing things seemingly right. In my Main method, I have a code like this:
ApplicationContext context =
new ClassPathXmlApplicationContext(new String[] {
"common.xml",
"token.xml",
"pep-config.xml" });
TokenInitializer ti = context.getBean(TokenInitializer.class);
and in a token.xml file I've had a line
<context:component-scan base-package="package.path"/>
I noticed that the package.path does no longer exist, so I've just dropped the line for good.
And after that, NPE started coming in. In a pep-config.xml I had just 2 beans:
<bean id="someAbac" class="com.pep.SomeAbac" init-method="init"/>
<bean id="settings" class="com.pep.Settings"/>
and SomeAbac class has a property declared as
#Autowired private Settings settings;
for some unknown reason, settings is null in init(), when <context:component-scan/> element is not present at all, but when it's present and has some bs as a basePackage, everything works well. This line now looks like this:
<context:component-scan base-package="some.shit"/>
and it works. May be someone can provide an explanation, but for me it's enough right now )
Also note that if, for whatever reason, you make a method in a #Service as final, the autowired beans you will access from it will always be null.
You can also fix this issue using #Service annotation on service class and passing the required bean classA as a parameter to the other beans classB constructor and annotate the constructor of classB with #Autowired. Sample snippet here :
#Service
public class ClassB {
private ClassA classA;
#Autowired
public ClassB(ClassA classA) {
this.classA = classA;
}
public void useClassAObjectHere(){
classA.callMethodOnObjectA();
}
}
This is only valid in case of Unit test.
My Service class had an annotation of service and it was #autowired another component class. When I tested the component class was coming null. Because for service class I was creating the object using new
If you are writing unit test make sure you are not creating object using new object(). Use instead injectMock.
This fixed my issue. Here is a useful link
Not entirely related to the question, but if the field injection is null, the constructor based injection will still work fine.
private OrderingClient orderingClient;
private Sales2Client sales2Client;
private Settings2Client settings2Client;
#Autowired
public BrinkWebTool(OrderingClient orderingClient, Sales2Client sales2Client, Settings2Client settings2Client) {
this.orderingClient = orderingClient;
this.sales2Client = sales2Client;
this.settings2Client = settings2Client;
}
In addition, don't inject to a static member, it will be null.
if you are using a private method, it will be null, try to change private to public in controller.
I have the following situation:
#Controller
public class myController {
#Autowired
private IProxy service;
public ModelAndView init(HttpServletRequest request, HttpServletResponse response) throws Exception {
List<String> list = service.getName();
}
}
Then my Service is define as follow:
public interface IProxy {
public List<String> getName();
}
Proxy class is responsible for the lookup to the remote bean
#Service("service")
public class Proxy implements IProxy {
...
public List<String> getName() {
return myClass.getName();
}
And the implementation is the following:
#Interceptors(interceptor.class)
#Stateless
#Resource(name = "java:/db")
#Remote(MyClassRemote.class)
public class MyClassImpl extends MyEjb implements MyClassRemote{
#PersistenceContext(unitName = "db")
private EntityManager em;
#Resource
private SessionContext sctx;
#Autowired
public IMyRepo myRepo;
#Override
public List<String> getName() {
try {
return myRepo.getName(em);
}
catch (Exception ex) {
ex.printStackTrace();
throw ex;
}
finally {}
}
So, the problem is that here myRepo is null. I don't know why because IMyRepo and his implementation are always located within the path scanned by Spring.
Just one clarification: MyRepo class that implements IMyRepo is annotated with #Repository.
Any idea?
you can inject spring beans in EJB using Spring interceptors, as explained here in the official documentation. Basically you'll need to adjust your class as follows:
// added the SpringBeanAutowiringInterceptor class
#Interceptors({ interceptor.class, SpringBeanAutowiringInterceptor.class })
#Stateless
#Resource(name = "java:/db")
#Remote(MyClassRemote.class)
public class MyClassImpl extends MyEjb implements MyClassRemote{
// your code
}
You'll also need to define the context location in a beanRefContext.xml file (with your own application context file):
application-context.xml version
<bean id="context"
class="org.springframework.context.support.ClassPathXmlApplicationContext">
<constructor-arg>
<list>
<value>application-context.xml</value>
</list>
</constructor-arg>
</bean>
Java Configuration version:
<bean id="context"
class="org.springframework.context.annotation.AnnotationConfigApplicationContext">
<constructor-arg>
<list>
<value type="java.lang.Class">com.your.app.Configuration</value>
</list>
</constructor-arg>
</bean>
Spring beans and EJB are two different things, you can't just inject a Spring bean in an EJB, because that EJB is no Spring bean, so Spring doesn't know there is a field which should be injected by Spring (unless you use some fancy AOP stuff, which can enable injection into non-Spring-managed beans).
I've a Spring web application and I'm trying to add some aspect to my service objects. The goal is to maintain aspect's state only through a single request scope, and to obtain a reference to aspect instance so I can manage state. I've tried 3 different versions of code, making requests via controller:
Same as related code (see below). State is retained through multiple invocations, but the #Autowired TestAspect aspect instance is not the same use by AOP framework.
Adding factory-method="aspectOf" to testAspect bean declaration in beans-context.xml, state is retained as previous case, and the #Autowired TestAspect aspect instance is the same used by AOP framework. Although it works, I want aspect's scope to be a single request, while in this case I have an application-scoped singleton.
Substituting #Aspect with #Aspect("perthis(participateAroundPointcut())") I get the following exception: Caused by: java.lang.IllegalArgumentException: Bean with name 'testAspect' is a singleton, but aspect instantiation model is not singleton, both with factory-method="aspectOf" or without.
How can I get #Autowired TestAspect aspect reference to be the same aspect instance used by AOP framework? Is factory-method="aspectOf" the only one way?
And how can i have a request-scoped aspect instead of a singleton? Why am I getting the exception?
Here is my code.
Service:
#Service
public class TestService {
#Autowired
private TestAspect aspect;
private static final Logger logger = LoggerFactory.getLogger(TestService.class);
public void method(){
logger.debug("Executing method");
}
public void service(){
aspect.initialize();
method();
}
}
Aspect: (without ("perthis(participateAroundPointcut())"))
#Aspect
public class TestAspect {
private static final Logger logger = LoggerFactory.getLogger(ParticipatoryAspect.class);
private boolean initialized=false;
#Pointcut("execution(* org.mose.emergencyalert.TestService.method(..))")
public void participateAroundPointcut(){}
#Around("participateAroundPointcut()")
public void participateAround(ProceedingJoinPoint joinPoint) throws Throwable{
logger.debug("Pre-execution; Initialized: "+initialized);
joinPoint.proceed();
logger.debug("Post-execution");
}
public void initialize(){
this.initialized=true;
logger.debug("Initialized: "+initialized);
}
}
beans-context.xml (without factory-method="aspectOf"):
<aop:aspectj-autoproxy />
<bean id="testAspect" class="org.mose.emergencyalert.aop.aspects.TestAspect"/>
I'm trying to instantiate a generic class in Spring, but I get following exception:
Initialization of bean failed; nested exception is
org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class football.dao.jpa.GenericJpaDAO]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Superclass has no null constructors but no arguments were given:
This is the XML configuration for Spring container:
<bean id="clubDAO" class="football.dao.jpa.GenericJpaDAO">
<constructor-arg type="EntityManagerFactory" ref="entityManagerFactory"/>
<constructor-arg type="Class" value="football.model.entities.ClubEntity"/>
<constructor-arg type="String" value="ClubEntity"/>
</bean>
This is the generic class:
public class GenericJpaDAO <T extends HavingID> {
private EntityManager em;
private Class entityClass;
private String entityName;
public GenericJpaDAO( Class entityClass, String entityName,
EntityManagerFactory emFactory ) {
this.entityClass = entityClass;
this.entityName = entityName;
em = emFactory.createEntityManager();
}
#Transactional
public void create( T entity ) {
em.persist( entity );
}
// more methods
}
I'm not really sure what could be causing this. I would appreciate any ideas.
This problem is not related to generics, it's a limitation of Spring AOP.
If aspects (including #Transactional aspect) are applied to the class using CGLIB proxy (this happens if target class doesn't implement any interfaces or if AOP is configured with proxy-target-class = "true"), no-argument constructor is required:
public class GenericJpaDAO <T extends HavingID> {
...
public GenericJpaDAO() {}
public GenericJpaDAO( Class entityClass, String entityName,
EntityManagerFactory emFactory ) { ... }
...
}
See also:
7.6 Proxying mechanisms