i am kind of stuck on a problem with creating beans, or probably i got the wrong intention.. Maybe you can help me solve it:
I got a application which takes in requests for batch processing. For every batch i need to create an own context depending on the parameters issued by the request.
I will try to simplyfy it with the following example:
I receive a request to process in a batch FunctionA which is a implementation for my Function_I interface and has sub-implementation FunctionA_DE and FunctionA_AT
Something like this:
public interface Function_I {
String doFunctionStuff()
}
public abstract class FunctionA implements Function_I {
FunctionConfig funcConfig;
public FunctionA(FunctionConfig funcConfig) {
this.funcConfig = funcConfig;
}
public String doFunctionStuff() {
// some code
String result = callSpecificFunctionStuff();
// more code
return result;
}
protected abstract String callSpecificFunctionStuff();
}
public class FunctionA_DE extends FunctionA {
public FunctionA_DE(FunctionConfig funcConf) {
super(funcConf)
}
protected String callSpecifiFunctionStuff() {
//do some specificStuff
return result;
}
}
public class FunctionA_AT extends FunctionA {
public FunctionA_AT(FunctionConfig funcConf) {
super(funcConf)
}
protected String callSpecifiFunctionStuff() {
//do some specificStuff
return result;
}
}
what would be the Spring-Boot-Way of creating a instance for FunctionA_DE to get it as Function_I for the calling part of the application, and what should it look like when i add FunctionB with FunctionB_DE / FunctionB_AT to my classes..
I thought it could be something like:
PSEUDO CODE
#Configuration
public class FunctionFactory {
#Bean(SCOPE=SCOPE_PROTOTYPE) // i need a new instance everytime i call it
public Function_I createFunctionA(FunctionConfiguration funcConfig) {
// create Function depending on the funcConfig so either FunctionA_DE or FunctionA_AT
}
}
and i would call it by Autowiring the FunctionFactory into my calling class and use it with
someSpringFactory.createFunction(functionConfiguration);
but i cant figure it out to create a Prototype-Bean for the function with passing a parameter.. And i cant really find a solution to my question by browsing through SO, but maybe i just got the wrong search terms.. Or my approach to solve this issue i totally wrong (maybe stupid), nobody would solve it the spring-boot-way but stick to Factories.
Appreciate your help!
You could use Springs's application context. Create a bean for each of the interfaces but annotate it with a specific profile e.g. "Function-A-AT". Now when you have to invoke it, you can simply set the application context of spring accordingly and the right bean should be used by Spring.
Hello everyone and thanks for reading my question.
after a discussion with a friend who is well versed in the spring framework i came to the conclusion that my approach or my favoured solution was not what i was searching for and is not how spring should be used. Because the Function_I-Instance depends on the for the specific batch loaded configuration it is not recommended to manage all these instances as #Beans.
In the end i decided to not manage the instances for my Function_I with spring. but instead i build a Controller / Factory which is a #Controller-Class and let this class build the instance i need with the passed parameters for decision making on runtime.
This is how it looks (Pseudo-Code)
#Controller
public class FunctionController {
SomeSpringManagedClass ssmc;
public FunctionController(#Autowired SomeSpringManagedClass ssmc) {
this.ssmc = ssmc;
}
public Function_I createFunction(FunctionConfiguration funcConf) {
boolean funcA, cntryDE;
// code to decide the function
if(funcA && cntryDE) {
return new FunctionA_DE(funcConf);
} else if(funB && cntryDE) {
return new FunctionB_DE(funcConf);
} // maybe more else if...
}
}
Related
#Configuration
public class Product {
#Bean("xyz")
public String getMethod() {
return "abc";
}
}
#Component
public class Test {
String b;
Test(String xyz) {
this.b = xyz;
}
}
Is this any harm with this approach? I am trying to make change in the existing code where I am replacing the #Value with the getter as the method parameter. As I don't want to change the structure of the existing code I am trying to inject the method as bean as a replacement to #Value.
I suggest you to keep the #Value annotation instead of the whole #Bean configurations.
Why?
What if the getMethod()'s returned value needs to be changed very often? Everytime when you're changing something in the Product class, during build time it needs to be recompiled. What happens if the project is getting bigger and you're using this approach? It leads to longer build time and the more important thing is that this solution is not intuitive and it's hard to keep it clean. Don't think about complex solutions only to make the code look fancy. When you need to inject String values, the easiest approach is to create properties files (which won't get recompiled) and use the #Value annotation.
Now, if you want to add new methods without changing the structure of the existing code there are some patterns which you can apply like decorator pattern.
The main idea is simple: you're creating a decorator class which has an object of the type you need.
The easiest example (which you'll find everywhere on the internet) is the classic Shape example:
public interface Shape {
String someMethod();
}
#Component
public class CustomShape implements Shape { //implement the method here }
And here is the decorator:
public interface ShapeDecorator {
String someMethodExtended();
void someExtraMethod();
}
#Component
public class CustomShapeDecorator implements ShapeDecorator{
#Autowired
// #Qualifier - optional (only if you have more Shape implementations)
private Shape shape;
// now you can either:
// 1. provide new methods
#Override
public void someExtraMethod(){
System.out.println("Hello world!");
}
// 2. or you can EXTEND the Shape's "someMethod()" implementation
#Override
public String someMethodExtended(){
String oldString = this.shape.someMethod();
return oldString + " EXTENDED";
}
}
I'm trying to implement my #secured annotation similar to Spring's, but generalized to any project and I'm having problems.
I looked at a lot of documentation but my internet is really restringed and need an answer. My idea is that the code to use it is like this:
public class a {
#secured (access> 3)
private void a() {}
}
The controller:
public class SecuredProvider {
private void check () {
if (accessLevesOfMethod> registerUser.getAccesLevel ()) {
// execute method
} else {
throw new exception ();
}
}
in the main
new A (). a ();
And if the logged user have an access level < 3 throws an exception, any other case they method is executed normally.
Thanks in advance.
Solved with AOP, using Dependency injection with google's GUICE an intercepting every method with #Secure
I want to return multiple spring beans based on the condition in the factory class.
Is this a good practice?
Any better ways to write the following piece of code?.
Any other design patterns suitable here?
Below is the code snippet:
package com.test;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
#Component
public class InstanceFactory {
#Resource(name = "instance1")
private Instance instance1;
#Resource(name = "instance2")
private Instance instance2;
public Instance getService(Condition condition) {
if (condition.one() && condition.two()) {
return instance2;
} else {
return instance1;
}
}
}
It depends on what you want to achieve. Factory Pattern is meant to create objects but what you are returning are objects already create somewhere else (Spring in this case). If you want to create beans that will be managed by Spring there are several ways:
#Conditional(YourConditionImplementation.class): This annotation added on a method of a #Configuration annotated class will allow you to create a bean when the given condition is fullfilled. Example here: https://javapapers.com/spring/spring-conditional-annotation/
You can uses as well BeanFactory to inject the definition of your bean (DefinitionBean) into the container. Example here: https://www.logicbig.com/tutorials/spring-framework/spring-core/bean-definition.html
Now, if you want an object that determine what object of type Instance fits better for some need then your approach is ok, but it is not technically a factory :)
When designing something like that I would face that solution considering two design patterns:
Strategy pattern: In order to replace repetitive if else every time you need to evaluate more instances.
Decorator pattern: Trying to make every condition as configurable as possible. They can be composed (decorated) for one or more predicates.
Considering these two pattens you might achieve something like this:
First, define which conditions will identify a given instance:
public enum InstanceType {
INSTANCE_TYPE_1(Condition::isOne, Condition::isTwo),
INSTANCE_TYPE_2(Condition::isOne, Condition::isThree),
...;
private List<Predicate<Condition>> evaluators;
#SafeVarargs
InstanceType(final Predicate<Condition>... evaluators) {
this.evaluators = Arrays.asList(evaluators);
}
public boolean evaluate(final Condition condition) {
return evaluators.stream().allMatch(it -> it.test(condition));
}
}
Then, you should link every instance implementation to an specific instance type:
#Component
public class InstanceOne implements Instance {
#Override
public InstanceType getType() {
return InstanceType.INSTANCE_TYPE_1;
}
}
Finally, a class to config where defining the relation between types and instances as EnumMap
#Configuration
public class InstanceFactoryConfig {
#Autowired
private List<Instance> instances;
#Bean
public EnumMap<InstanceType, Instance> instancesMap() {
EnumMap<InstanceType, Instance> instanceEnumMap = new EnumMap<>(InstanceType.class);
instances.forEach(i -> instanceEnumMap.put(i.getType(), i));
return instanceEnumMap;
}
}
Thus, you InstanceFactory can be replaced to something like this:
public class InstanceFactory {
#Autowire
private final EnumMap<InstanceType, Instance> instancesMap;
public void getInstance(Condition condition) {
instancesMap.get(getInstanceType(condition)).doSomething();
}
private InstanceType getInstanceType(Condition condition) {
return Arrays.stream(InstancesType.values())
.filter(evaluator -> evaluator.evaluate(condition))
.findFirst().orElseThrow(() -> new RuntimeException("Instance type not found"));
}
}
As you can see, you InstanceFactory is less prone to be modified. This means, every time you need you add a new instance implementation you only need to modify the InstanceType enum. Hope this is helps.
You can use spring existing FactoryBean interface and implement your own logic
It’s one of the best approaches to create beans in spring framework
Here is the link with example :
https://www.baeldung.com/spring-factorybean
See:
Spring Profile
The active profile is set by properties and based on the value you assign to the profile, Spring will load different beans for the same interface.
So it might be exactly what you need.
I am working on a REST API where I have an interface that defines a list of methods which are implemented by 4 different classes, with the possibility of adding many more in the future.
When I receive an HTTP request from the client there is some information included in the URL which will determine which implementation needs to be used.
Within my controller, I would like to have the end-point method contain a switch statement that checks the URL path variable and then uses the appropriate implementation.
I know that I can define and inject the concrete implementations into the controller and then insert which one I would like to use in each particular case in the switch statement, but this doesn't seem very elegant or scalable for 2 reasons:
I now have to instantiate all of the services, even though I only need to use one.
The code seems like it could be much leaner since I am literally calling the same method that is defined in the interface with the same parameters and while in the example it is not really an issue, but in the case that the list of implementations grows ... so does the number of cases and redundant code.
Is there a better solution to solve this type of situation? I am using SpringBoot 2 and JDK 10, ideally, I'd like to implement the most modern solution.
My Current Approach
#RequestMapping(Requests.MY_BASE_API_URL)
public class MyController {
//== FIELDS ==
private final ConcreteServiceImpl1 concreteService1;
private final ConcreteServiceImpl2 concreteService2;
private final ConcreteServiceImpl3 concreteService3;
//== CONSTRUCTORS ==
#Autowired
public MyController(ConcreteServiceImpl1 concreteService1, ConcreteServiceImpl2 concreteService2,
ConcreteServiceImpl3 concreteService3){
this.concreteService1 = concreteService1;
this.concreteService2 = concreteService2;
this.concreteService3 = concreteService3;
}
//== REQUEST MAPPINGS ==
#GetMapping(Requests.SPECIFIC_REQUEST)
public ResponseEntity<?> handleSpecificRequest(#PathVariable String source,
#RequestParam String start,
#RequestParam String end){
source = source.toLowerCase();
if(MyConstants.SOURCES.contains(source)){
switch(source){
case("value1"):
concreteService1.doSomething(start, end);
break;
case("value2"):
concreteService2.doSomething(start, end);
break;
case("value3"):
concreteService3.doSomething(start, end);
break;
}
}else{
//An invalid source path variable was recieved
}
//Return something after additional processing
return null;
}
}
In Spring you can get all implementations of an interface (say T) by injecting a List<T> or a Map<String, T> field. In the second case the names of the beans will become the keys of the map. You could consider this if there are a lot of possible implementations or if they change often. Thanks to it you could add or remove an implementation without changing the controller.
Both injecting a List or a Map have some benefits and drawbacks in this case. If you inject a List you would probably need to add some method to map the name and the implementation. Something like :
interface MyInterface() {
(...)
String name()
}
This way you could transform it to a Map<String, MyInterface>, for example using Streams API. While this would be more explicit, it would polute your interface a bit (why should it be aware that there are multiple implementations?).
When using the Map you should probably name the beans explicitly or even introduce an annotation to follow the principle of least astonishment. If you are naming the beans by using the class name or the method name of the configuration class you could break the app by renaming those (and in effect changing the url), which is usually a safe operation to do.
A simplistic implementation in Spring Boot could look like this:
#SpringBootApplication
public class DynamicDependencyInjectionForMultipleImplementationsApplication {
public static void main(String[] args) {
SpringApplication.run(DynamicDependencyInjectionForMultipleImplementationsApplication.class, args);
}
interface MyInterface {
Object getStuff();
}
class Implementation1 implements MyInterface {
#Override public Object getStuff() {
return "foo";
}
}
class Implementation2 implements MyInterface {
#Override public Object getStuff() {
return "bar";
}
}
#Configuration
class Config {
#Bean("getFoo")
Implementation1 implementation1() {
return new Implementation1();
}
#Bean("getBar")
Implementation2 implementation2() {
return new Implementation2();
}
}
#RestController
class Controller {
private final Map<String, MyInterface> implementations;
Controller(Map<String, MyInterface> implementations) {
this.implementations = implementations;
}
#GetMapping("/run/{beanName}")
Object runSelectedImplementation(#PathVariable String beanName) {
return Optional.ofNullable(implementations.get(beanName))
.orElseThrow(UnknownImplementation::new)
.getStuff();
}
#ResponseStatus(BAD_REQUEST)
class UnknownImplementation extends RuntimeException {
}
}
}
It passes the following tests:
#RunWith(SpringRunner.class)
#SpringBootTest
#AutoConfigureMockMvc
public class DynamicDependencyInjectionForMultipleImplementationsApplicationTests {
#Autowired
private MockMvc mockMvc;
#Test
public void shouldCallImplementation1() throws Exception {
mockMvc.perform(get("/run/getFoo"))
.andExpect(status().isOk())
.andExpect(content().string(containsString("foo")));
}
#Test
public void shouldCallImplementation2() throws Exception {
mockMvc.perform(get("/run/getBar"))
.andExpect(status().isOk())
.andExpect(content().string(containsString("bar")));
}
#Test
public void shouldRejectUnknownImplementations() throws Exception {
mockMvc.perform(get("/run/getSomethingElse"))
.andExpect(status().isBadRequest());
}
}
Regarding two of your doubts :
1. Instantiating the service object should not be an issue as this is one time job and controller gonna need them to serve all type of request.
2. You can use the exact Path mapping to get rid of switch case. For e.g. :
#GetMapping("/specificRequest/value1")
#GetMapping("/specificRequest/value2")
#GetMapping("/specificRequest/value3")
All of the above mapping will be on separate method which would deal with specific source value and invoke respective service method.
Hope this will help to make code more cleaner and elegant.
There is one more option of separating this on service layer and having only one endpoint to serve all types of source but as you said there is different implementation for each source value then it says that source is nothing but a resource for your application and having separate URI/separate method makes the perfect sense here. Few advantages that I see here with this are :
Makes it easy to write the test cases.
Scaling the same without impacting any other source/service.
Your code dealing the each source as separate entity from other sources.
The above approach should be fine when you have limited source values. If you have no control over source value then we need further redesign here by making source value differentiate by one more value like sourceType etc. and then having separate controller for each group type of source.
I write simple application. I don't want to use any frameworks. Please suggest me right place to hold annotation processing.
I have a few lines in main method:
String myString = (#NonNull String)list;
And I created #interface:
#Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
public #interface NonNull {
}
Which step should I take next? Can I work with annotations without using reflection? Could you expose for me samples of such annotation processing code?
There is no way (AFAIK) to work with annotations without reflection.
If you don't want to use any framework, first step is to write kind of proxy class handling the method requests. It is an example of method processing with annotation use over method:
public class MyProxy {
private <T> T getProxy(T t) {
return (T) Proxy.newProxyInstance(t.getClass().getClassLoader(), new Class<?>[]{MyClass.class}, new MyInvocationHandler(t));
}
}
And then implement InvocationHandler:
public class MyInvocationHandler implements InvocationHandler {
private Object obj;
MyInvocationHandler (Object obj) {
this.obj = obj;
}
#Override
public Object invoke(Object proxy, final Method method, final Object[] args) throws Throwable {
boolean isNotNull = method.isAnnotationPresent(NotNull.class);
if (isNotNull) {
/* process annotated method. Or go through proxy object fields etc.. */
}
}
}
I hope it will help you.
You didn't say what kind of annotation processing you want to do.
Do you want to add a run-time check that will cause your code to crash if list is ever null at run time? For this, reflection will work.
Do you want to add a compile-time check that will reject your code if it cannot prove that list is never null at run time? For this, an annotation processor such as the Checker Framework will work.
Your question does not explain why you don't want to use a framework. Doing so will save you from re-implementing a lot of functionality that others have already created.