I'm creating a Spring Starter project and need to get all classes which are marked with a custom annotation. The annotated class is not a spring bean.
My current solution is to use the ClassPathScanningCandidateComponentProvider to find the required classes.
ClassPathScanningCandidateComponentProvider scanner =
new ClassPathScanningCandidateComponentProvider(false);
scanner.addIncludeFilter(new AnnotationTypeFilter(CustomAnnotation.class));
candidates = scanner.findCandidateComponents("THE MISSING PACKAGE NAME");
The problem is that I'm currently provide an empty package String so that all packages/classes are scanned which slows the startup down.
I need to access the packages which are scanned by Spring to avoid the scanning of all packages and classes.
Is there a way to retrieve all packages programmatically which are scanned by Spring or is there an alternative solution to retrieve custom annotated classes which are not Spring beans.
Greets
One solution without the need to make a full classpath scan is to use the AutowiredAnnotationBeanPostProcessor:
private List<Class<?>> candidates = new ArrayList<>();
#Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
if(beanClass.isAnnotationPresent(YourAnnotation.class)){
candiates.add(beanClass));
System.out.println(beanClass);
return new Object();
}
}
#Bean
public CandiateHolder candidates() {
return new CandidateHolder(candidates);
}
You can check if the bean class which should be instantiated has the required annotation. If its the case you add the class to a property to expose it later as a bean. Instead of returning null you have to return an instance of a new Object. The returned object can be used to wrap the class in a proxy. Cause I don't need an instance I will return a simple new object. Its maybe a dirty hack but it works.
I have to use this kind of hack cause an instantiation of the needed object will result in an runtime error cause it has to be instantiated in the framework I use.
Related
I am using spring framework.
I am using objectMapper to desiriale store.json file:
service:
objectMapper.readValue(new File(jsonFilePath), Store.class)
store.json:
{
"type": "Store",
"name": "myStore",
}
Store.class:
#Value("${store.size:1000}")
private Integer sroreSize;
#autowire
private storePersistency storePersistency;
public Store(#JsonProperty("name") String name) {
super(name);
}
I am trying find out how to #autowire beans and #value properties in store.class, beans and properties that exist in applicationContext.
In current example sroreSize and storePersistency still null.
I know that I can inject fields to object mapper and then use #JacksonInject annotation but I have a lot of field to inject - not a good option for me.
Custom desirializer also not a good option for me.
Is there any way not to use custom desirializer or not to inject every bean/property that I need in store.class?
Something that injects all the beans and properties and I simply can use it in Store.class.
So you want some Store fields like storePersistency and sroreSize to be initialized once at application startup (which is when Spring will setup the application context) and then at runtime create multiple different Store objects differing in some fields as name that are initialized by Jackson.
I suggest annotating Store with #Component to get Spring to initialize #Value and #Autowired fields. The #Scope annotation will cause a new independent Store instance to be created each time. Simplified example:
#Component
#Scope(SCOPE_PROTOTYPE)
class Store {
private String name;
#Value("${store.size:1000}")
private Integer sroreSize;
}
Then the key is method readerForUpdating where you can pass an existing instance of Store and Jackson will update that instead of creating a new one as usually:
Store store = context.getBean(Store.class);
objectMapper.readerForUpdating(store).readValue("{\"name\":\"myStore\"}");
Where context is a Spring ApplicationContext reference that I autowired in a test class. You don't need to use the return value of readValue in this case, just inspect the existing store variable and name will be updated.
This question already has answers here:
Why is my Spring #Autowired field null?
(21 answers)
Closed 6 years ago.
I was able to use RestTemplate and autowire it. However I want to move my rest template related part of code into another class as follows:
public class Bridge {
private final String BASE_URL = "http://localhost:8080/u";
#Autowired
RestTemplate restTemplate;
public void addW() {
Map<String, String> x = new HashMap<String, String>();
W c = restTemplate.getForObject(BASE_URL + "/device/yeni", W.class, x);
System.out.println("Here!");
}
}
And at another class I call it:
...
Bridge wb = new Bridge();
wb.addW();
...
I am new to Spring and Dependency Injection terms. My restTemplate variable is null and throws an exception. What can I do it how to solve it(I don't know is it related to I use new keyword)?
Using Bridge wb = new Bridge() does not work with dependency injection. Your restTemplate is not injected, because wb in not managed by Spring.
You have to make your Bridge a Spring bean itself, e.g. by annotation:
#Service
public class Bridge {
// ...
}
or by bean declaration:
<bean id="bridge" class="Bridge"/>
Just to add further to Jeha's correct answer.
Currently, by doing
Bridge wb = new Bridge();
Means that, that object instance is not "Spring Managed" - I.e. Spring does not know anything about it. So how can it inject a dependency it knows nothing about.
So as Jeha said. Add the #Service annotation or specify it in your application context xml config file (Or if you are using Spring 3 you #Configuration object)
Then when the Spring context starts up, there will be a Singleton (default behavior) instance of the Bridge.class in the BeanFactory. Either inject that into your other Spring-Managed objects, or pull it out manually e.g.
Bridge wb = (Bridge) applicationContext.getBean("bridge"); // Name comes from the default of the class
Now it will have the dependencies wired in.
If you want to use new operator and still all dependency injected, then rather than making this a spring component (by annotating this with #Service), make it a #Configurable class.
This way even object is instantiated by new operator dependencies will be injected.
Few configuration is also required. A detailed explanation and sample project is here.
http://spring-framework-interoperability.blogspot.in/2012/07/spring-managed-components.html
I have to use company's custom made libraries with Spring Boot and wondering if I'm able to create bean like this in runtime and add it to Spring application context.
#Bean(name = {"customConnectionFactory"})
public ConnFactory connector() {
return new SimpleConnFactory(configuration(), "prefix");
}
So this worked fine when I was allowed to wire beans normally when starting the application. Now requirements have changed and I should be able to do this dynamically runtime. I've done some research and it seems that it's possible to add class to spring context runtime, but how about running method which returns new object?
Could be something like this
DefaultListableBeanFactory beanFactory = //get and store the factory somewhere
MyBean newBean = new MyBean();
beanFactory.initializeBean(newBean,"TheBeanName"); //could be class' canonical name
beanFactory.autowireBeanProperties(newBean, AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE, true);
beanFactory.registerSingleton("TheBeanName", newBean);
Spring provides bean scope as "Prototype". Means whenever bean is required in application, Spring container will create a fresh/new instance of bean.
Does is follow prototype design pattern also?
Does it create object only once and in subsequent request calls clone() method on created object to create new object?
Also if someone can provide example of prototype in JDK, Spring, Hibernate or any J2EE framework.
No spring does not use cloning to create prototype scoped instances.
Below is the code snippet taken from AbstractBeanFactory.doGetBean() function:
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
#Override
public Object getObject() throws BeansException {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
The createBean method call boils down to below code:
BeanUtils.instantiateClass(constructorToUse);
Spring does not use the Prototype Pattern, it uses reflection.
Plus, in order to use clone() it would have to subclass somehow a bean, because clone() is protected, so it does not use clone() either.
Here is a code fragment from
org.springframework.beans.factory.support.SimpleInstantiationStrategy
where you can see the use of java.lang.reflect.Constructor and java.lang.Class reflection method:
public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
if (beanDefinition.getMethodOverrides().isEmpty()) {
Constructor<?> constructorToUse;
synchronized (beanDefinition.constructorArgumentLock) {
constructorToUse = (Constructor<?>) beanDefinition.resolvedConstructorOrFactoryMethod;
...
constructorToUse = clazz.getDeclaredConstructor((Class[]) null);
...
}
...
}
...
}
So the term prototype is used to suggest that at every call to getBean, you'll get a new instance with the same properties. This is more than a simple call to a constructor however, because you'll get a bean with all dependencies wired and other properties set, so in a sense it is a prototype. Or at least it fits the concept very well.
I have not dug into Spring source code, but I think Beans with prototype scope in Spring are not created using clone() method because it is not mandatory to implement the Cloneable interface for those beans.
Moreover, suppose it is creating them using clone(). It would then be dangerous if someone is expecting deep copy instead of shallow copy.
You can always test it and find the answer.
No. Spring scopes such as prototype or singletone do not follow strictly design patterns. The naming of scopes was used to intuitively suggest behavior container provides.
This way you can have a "singleton" pattern within the container and create another object outside of the container. Similarly "prototype" pattern does not have to implement "clone" functionality.
You may want to look into this link as well: Singleton design pattern vs Singleton beans in Spring container
More elaborate explanations here:
https://springframework.guru/gang-of-four-design-patterns/prototype-pattern/
I have a Grails application that needs to run a strategy that will likely be swapped out over time. I know Spring underlies Grails, so I was wondering if I had access to Spring's IoC container so that I could externalize the actual dependency in an xml file (note: I have never actually done this, but just know of it, so I may be missing something). My goal is to be able to do something like the following:
class SchemaUpdateService {
public int calculateSomething(){
ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
IStrategy strat = (IStrategy) ctx.getBean("mystrat");
}
}
And then map the appropriate implementation in the beans.xml file. I assume this is supported in Grails. Does anyone have any documentation on how this would work? Do I really just need the Spring IoC library and it will just work? Thanks!
You define your beans in resources.xml or resources.groovy. The grails documentation is very clear about how to access the Spring application context.
You can access the application context from any Grails artefact using
ApplicationContext ctx = grailsApplication.mainContext
You can then use this to retrieve whichever beans you're interested in:
IStrategy strat = (IStrategy) ctx.getBean("mystrat")
In classes that don't have access to grailsApplication, you could use a helper such as the following to access the application context and the beans therein
class SpringUtils {
static getBean(String name) {
applicationContext.getBean(name)
}
static <T> T getBean(String name, Class<T> requiredType) {
applicationContext.getBean(name, requiredType)
}
static ApplicationContext getApplicationContext() {
ApplicationHolder.application.mainContext
}
}
However, this should only be necessary if you need to retrieve different implementations of the same bean at runtime. If the required bean is known at compile-time, just wire the beans together in resources.xml or resources.groovy
First of all, you want to define your strategy in your grails-app/conf/spring/resources.groovy:
beans = {
myStrat(com.yourcompany.StrategyImpl) {
someProperty = someValue
}
}
Then, you simply def the a property with the same name into your service:
class SomeGrailsService {
def myStrat
def someMethod() {
return myStrat.doSomething()
}
}
In any Grails artefact (such as services and domain classes), Grails will automatically give the myStrat property the correct value. But don't forget, in a unit test you'll have to give it a value manually as the auto-wiring does not happen in unit tests.
Outside of a Grails artefact, you can use something like:
def myStrat = ApplicationHolder.application.mainContext.myStrat
In Grails 2.0, Graeme et al are deprecating the use of the *Holder classes (such as ApplicationHolder and ConfigurationHolder), so I'm not quite sure what the Grails 2.0 approach would be...