BLZT-71 add PostConstruct functionality

* BLZT-71 add annotation

* BLZT-71 add PostConstruct functionality

* BLZT-71 refactoring

* BLZT-71 add documentation

* BLZT-71 fix imports in ReflectionUtils

* BLZT-71 fixes

Core.md

@@ -22,14 +22,14 @@ It initializes the list with default post-processors such as the ScheduleBeanPos
 If we need diagram classes we should use Wiki and add link to it.
 
  - Dependency Injection
-   - [Constructor](core/Constructor.md)
-   - [Setter](core/Setter.md)
-   - [Field](core/Field.md)
+   - [Constructor](/features/core/Constructor.md)
+   - [Setter](/features/core/Setter.md)
+   - [Field](/features/core/Field.md)
    - Collections
    - @Primary
    - @Qualifier
    - @Order
-   - [@Value](core/Value.md)
+   - [@Value](/features/core/Value.md)
    - Prototype Beans into a Singleton
 
 
@@ -40,15 +40,15 @@ If we need diagram classes we should use Wiki and add link to it.
 
 
 - Dependency Injection exceptions
-  - [Circular Dependencies](core/CircularDependencies.md)
+  - [Circular Dependencies](/features/core/CircularDependencies.md)
   - No such bean exception
   - No unique bean exception
   - No constructor with Autowired annotation
   - etc
 
 
 - addition items:
-  - [Scheduling](core/Scheduling.md)
+  - [Scheduling](/features/core/Scheduling.md)
   - Properties file support 
 
 
@@ -60,6 +60,6 @@ If we need diagram classes we should use Wiki and add link to it.
 
 
   - [Logging](/features/core/Logging.md)
-  - PostConstruct
+  - [@PostConstruct](/features/core/PostConstruct.md)
   - PreDestroy
   - Logo

core/src/main/java/com/bobocode/bring/core/annotation/PostConstruct.java

@@ -0,0 +1,58 @@
+package com.bobocode.bring.core.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * <p>The {@code PostConstruct} annotation is used on a method that needs
+ * to be executed after dependency injection is done to perform any
+ * initialization. This method is called immediately after the bean's
+ * properties have been set and the bean has been placed into the
+ * Bring container.</p>
+ *
+ * <p>Methods annotated with {@code @PostConstruct} are invoked only once
+ * in the bean's lifecycle, and they provide a convenient way to
+ * initialize resources or perform any setup logic that is required
+ * before the bean is ready for use.</p>
+ *
+ * <p>The method annotated with {@code @PostConstruct} must be non-static
+ * and should not have any parameters, as it is meant to be an
+ * initialization callback method for the bean instance. If multiple
+ * methods are annotated with {@code @PostConstruct} within a single
+ * class, the order of execution is not guaranteed.</p>
+ *
+ * <p>Example:</p>
+ * <pre>
+ * {@code
+ * import com.bobocode.bring.core.annotation.PostConstruct;
+ *
+ * public class ExampleBean {
+ *
+ *     private String message;
+ *
+ *     @PostConstruct
+ *     public void init() {
+ *         message = "Hello, this is an example!";
+ *         // Additional initialization logic
+ *     }
+ *
+ *     public String getMessage() {
+ *         return message;
+ *     }
+ * }
+ * }
+ * </pre>
+ *
+ * <p>In this example, the {@code init} method will be automatically
+ * invoked after the {@code ExampleBean} is constructed, providing a
+ * way to perform custom initialization logic.</p>
+ *
+ * @author Blyzhnytsia Team
+ * @since 1.0
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+public @interface PostConstruct {
+}

core/src/main/java/com/bobocode/bring/core/bpp/impl/PostConstructBeanPostProcessor.java

@@ -0,0 +1,28 @@
+package com.bobocode.bring.core.bpp.impl;
+
+import com.bobocode.bring.core.annotation.BeanProcessor;
+import com.bobocode.bring.core.annotation.PostConstruct;
+import com.bobocode.bring.core.bpp.BeanPostProcessor;
+import com.bobocode.bring.core.exception.PostConstructException;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+
+import static com.bobocode.bring.core.utils.ReflectionUtils.processBeanPostProcessorAnnotation;
+
+
+@BeanProcessor
+public class PostConstructBeanPostProcessor implements BeanPostProcessor {
+
+    @Override
+    public Object postProcessInitialization(Object bean, String beanName) {
+        Method[] declaredMethods = bean.getClass().getMethods();
+        try {
+            processBeanPostProcessorAnnotation(bean, declaredMethods, PostConstruct.class);
+        } catch (Exception exception) {
+            throw new PostConstructException(exception);
+        }
+
+        return BeanPostProcessor.super.postProcessInitialization(bean, beanName);
+    }
+}

core/src/main/java/com/bobocode/bring/core/exception/PostConstructException.java

@@ -0,0 +1,8 @@
+package com.bobocode.bring.core.exception;
+
+public class PostConstructException extends RuntimeException {
+    public static String POST_CONSTRUCT_EXCEPTION_MESSAGE ="@PostConstruct should be added to method without parameters";
+    public PostConstructException(Throwable cause) {
+        super(POST_CONSTRUCT_EXCEPTION_MESSAGE, cause);
+    }
+}

core/src/main/java/com/bobocode/bring/core/utils/ReflectionUtils.java

@@ -143,6 +143,16 @@ public static Supplier<Object> createNewInstance(Constructor<?> constructor, Obj
         };
     }
 
+    public static void processBeanPostProcessorAnnotation(Object bean,
+                                                          Method[] declaredMethods,
+                                                          Class<? extends Annotation> annotation) throws ReflectiveOperationException {
+        for (Method declaredMethod : declaredMethods) {
+            if (declaredMethod.isAnnotationPresent(annotation)) {
+                declaredMethod.invoke(bean);
+            }
+        }
+    }
+
     private static class QualifierAnnotationParanamer extends AnnotationParanamer {
 
         public QualifierAnnotationParanamer(Paranamer fallback) {

core/src/test/java/com/bobocode/bring/core/bpp/impl/PostConstructBeanPostProcessorTest.java

@@ -0,0 +1,37 @@
+package com.bobocode.bring.core.bpp.impl;
+
+import com.bobocode.bring.core.BringApplication;
+import com.bobocode.bring.core.exception.PostConstructException;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
+import testdata.postconstruct.positive.CustomPostConstruct;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class PostConstructBeanPostProcessorTest {
+
+    @Test
+    void shouldFillMessage_postProcessInitialization() {
+        //given
+        var bringApplicationContext = BringApplication.run("testdata.postconstruct.positive");
+
+        //when
+        var myCustomPostConstruct = bringApplicationContext.getBean(CustomPostConstruct.class);
+
+        //then
+        assertThat(myCustomPostConstruct.getMessage()).isEqualTo("Hello!");
+    }
+
+    @Test
+    void shouldThrowException_postProcessInitialization() {
+        //given
+        var expectedMessage = "@PostConstruct should be added to method without parameters";
+        // when
+        Executable executable = () -> BringApplication.run("testdata.postconstruct.negative");
+
+        // then
+        PostConstructException postConstructException = assertThrows(PostConstructException.class, executable);
+        assertThat(postConstructException.getMessage()).isEqualTo(expectedMessage);
+    }
+}

core/src/test/java/testdata/postconstruct/negative/CustomPostConstruct.java

@@ -0,0 +1,17 @@
+package testdata.postconstruct.negative;
+
+import com.bobocode.bring.core.annotation.Component;
+import com.bobocode.bring.core.annotation.PostConstruct;
+import lombok.Getter;
+
+@Getter
+@Component
+public class CustomPostConstruct {
+
+    private String message;
+
+    @PostConstruct
+    public void fillMessage(String invalidParam) {
+        message = "Hello!";
+    }
+}

core/src/test/java/testdata/postconstruct/positive/CustomPostConstruct.java

@@ -0,0 +1,17 @@
+package testdata.postconstruct.positive;
+
+import com.bobocode.bring.core.annotation.Component;
+import com.bobocode.bring.core.annotation.PostConstruct;
+import lombok.Getter;
+
+@Component
+@Getter
+public class CustomPostConstruct {
+
+    private String message;
+
+    @PostConstruct
+    public void fillMessage() {
+        message = "Hello!";
+    }
+}

features/core/PostConstruct.md

@@ -0,0 +1,66 @@
+# @PostConstruct
+
+## Introduction
+
+In the Bring framework, `@PostConstruct` is a method-level annotation used to indicate that a method should be invoked immediately after an instance of the bean is constructed, and before any other initialization logic occurs.
+## Usage
+
+To use `@PostConstruct`, follow these steps:
+
+1. **Add the Annotation**: Place the `@PostConstruct` annotation on a method within your Bring bean class.
+
+    ```java
+    import com.bobocode.bring.core.annotation.PostConstruct;
+
+    public class MyBean {
+
+        @PostConstruct
+        public void init() {
+            // Initialization logic here
+            // This method will be called after bean instantiation.
+        }
+    }
+    ```
+
+
+2. **Invoke the Bring Container**: Make sure that you obtain the bean from the Bring container. The `@PostConstruct` annotated method will be automatically invoked.
+
+    ```java
+    import com.bobocode.bring.core.BringApplication;
+
+    public class MyApp {
+        public static void main(String[] args) {
+             var bringApplicationContext = BringApplication.run("your.path");
+             var myBean = bringApplicationContext.getBean(CustomPostConstruct.class);
+                // Your bean is now initialized, and @PostConstruct method has been called.
+            }
+        }
+    ```
+
+## Important Points
+
+- The method annotated with `@PostConstruct` must not have any parameters.
+- This annotation is generally used in conjunction with the `@Component` stereotype annotations (e.g., `@Service`, `@Repository`, `@Controller`) or in configuration classes.
+- The `@PostConstruct` method will be invoked after the bean has been constructed and before any custom initialization logic specified in the bean definition.
+
+## Example
+
+Here is a simple example of a class using `@PostConstruct`:
+
+```java
+import com.bobocode.bring.core.annotation.PostConstruct;
+
+public class ExampleBean {
+
+    private String message;
+
+    @PostConstruct
+    public void init() {
+        message = "Hello, this is an example!";
+        // Additional initialization logic
+    }
+
+    public String getMessage() {
+        return message;
+    }
+}