[BAEL-13506] - Split or move core-java-8 module (#7790)

core-java-modules/core-java-annotations/README.md

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+=========
+
+## Core Java 8 Cookbooks and Examples
+
+### Relevant Articles: 
+- [Java @Override Annotation](https://www.baeldung.com/java-override)
+- [Java @SuppressWarnings Annotation](https://www.baeldung.com/java-suppresswarnings)
+- [Java @SafeVarargs Annotation](https://www.baeldung.com/java-safevarargs)
+- [Java @Deprecated Annotation](https://www.baeldung.com/java-deprecated)
+- [Overview of Java Built-in Annotations](https://www.baeldung.com/java-default-annotations)
+- [Creating a Custom Annotation in Java](https://www.baeldung.com/java-custom-annotation)

core-java-modules/core-java-annotations/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-annotations</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-annotations</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-bytecode</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-annotations</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+        <asspectj.version>1.8.9</asspectj.version>
+        <jmh-core.version>1.19</jmh-core.version>
+        <jmh-generator.version>1.19</jmh-generator.version>
+        <!-- plugins -->
+        <maven-surefire-plugin.version>2.22.1</maven-surefire-plugin.version>
+    </properties>
+</project>

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/ClassWithAnnotation.java

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+package com.baeldung.annotations;
+
+@Deprecated
+class ClassWithAnnotation {
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/ClassWithDeprecatedMethod.java

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+package com.baeldung.annotations;
+
+class ClassWithDeprecatedMethod {
+
+    @Deprecated
+    static void deprecatedMethod() {
+
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/ClassWithSafeVarargs.java

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+package com.baeldung.annotations;
+
+class ClassWithSafeVarargs<T> {
+
+    @SafeVarargs
+    final void iterateOverVarargs(T... args) {
+        for (T x : args) {
+            // do stuff with x
+        }
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/ClassWithSuppressWarnings.java

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+package com.baeldung.annotations;
+
+class ClassWithSuppressWarnings {
+
+    @SuppressWarnings("deprecation")
+    void useDeprecatedMethod() {
+        ClassWithDeprecatedMethod.deprecatedMethod(); // no warning is generated here
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/IntConsumer.java

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+package com.baeldung.annotations;
+
+@FunctionalInterface
+interface IntConsumer {
+
+    void accept(Integer number);
+
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/Interval.java

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+package com.baeldung.annotations;
+
+import java.lang.annotation.Repeatable;
+
+@Repeatable(Intervals.class)
+@interface Interval {
+    int hour() default 1;
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/IntervalUsage.java

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+package com.baeldung.annotations;
+
+public class IntervalUsage {
+
+    @Interval(hour = 17)
+    @Interval(hour = 13)
+    void doPeriodicCleanup() {
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/Intervals.java

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+package com.baeldung.annotations;
+
+@interface Intervals {
+    Interval[] value();
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/MyAnnotation.java

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+package com.baeldung.annotations;
+
+import java.lang.annotation.*;
+
+@Inherited
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.LOCAL_VARIABLE, ElementType.FIELD})
+@interface MyAnnotation {
+
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/MyAnnotationTarget.java

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+package com.baeldung.annotations;
+
+class MyAnnotationTarget {
+
+    // this is OK
+    @MyAnnotation
+    String someField;
+
+    // @MyAnnotation <- this is invalid usage!
+    void doSomething() {
+
+        // this also works
+        @MyAnnotation
+        String localVariable;
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/MyOperation.java

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+package com.baeldung.annotations;
+
+interface MyOperation {
+
+    void perform();
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/MyOperationImpl.java

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+package com.baeldung.annotations;
+
+class MyOperationImpl implements MyOperation {
+
+    @Override
+    public void perform() {
+
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/Init.java

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+package com.baeldung.customannotations;
+
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+@Retention(RUNTIME)
+@Target(METHOD)
+public @interface Init {
+
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/JsonElement.java

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+package com.baeldung.customannotations;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+@Retention(RUNTIME)
+@Target({ FIELD })
+public @interface JsonElement {
+    public String key() default "";
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/JsonSerializable.java

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+package com.baeldung.customannotations;
+
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+@Retention(RUNTIME)
+@Target(TYPE)
+public @interface JsonSerializable {
+
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/JsonSerializationException.java

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+package com.baeldung.customannotations;
+
+public class JsonSerializationException extends RuntimeException {
+
+    private static final long serialVersionUID = 1L;
+
+    public JsonSerializationException(String message) {
+        super(message);
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java

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+package com.baeldung.customannotations;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+public class ObjectToJsonConverter {
+    public String convertToJson(Object object) throws JsonSerializationException {
+        try {
+
+            checkIfSerializable(object);
+            initializeObject(object);
+            return getJsonString(object);
+
+        } catch (Exception e) {
+            throw new JsonSerializationException(e.getMessage());
+        }
+    }
+
+    private void checkIfSerializable(Object object) {
+        if (Objects.isNull(object)) {
+            throw new JsonSerializationException("Can't serialize a null object");
+        }
+
+        Class<?> clazz = object.getClass();
+        if (!clazz.isAnnotationPresent(JsonSerializable.class)) {
+            throw new JsonSerializationException("The class " + clazz.getSimpleName() + " is not annotated with JsonSerializable");
+        }
+    }
+
+    private void initializeObject(Object object) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
+        Class<?> clazz = object.getClass();
+        for (Method method : clazz.getDeclaredMethods()) {
+            if (method.isAnnotationPresent(Init.class)) {
+                method.setAccessible(true);
+                method.invoke(object);
+            }
+        }
+    }
+
+    private String getJsonString(Object object) throws IllegalArgumentException, IllegalAccessException {
+        Class<?> clazz = object.getClass();
+        Map<String, String> jsonElementsMap = new HashMap<>();
+        for (Field field : clazz.getDeclaredFields()) {
+            field.setAccessible(true);
+            if (field.isAnnotationPresent(JsonElement.class)) {
+                jsonElementsMap.put(getKey(field), (String) field.get(object));
+            }
+        }
+
+        String jsonString = jsonElementsMap.entrySet()
+            .stream()
+            .map(entry -> "\"" + entry.getKey() + "\":\"" + entry.getValue() + "\"")
+            .collect(Collectors.joining(","));
+        return "{" + jsonString + "}";
+    }
+
+    private String getKey(Field field) {
+        String value = field.getAnnotation(JsonElement.class)
+            .key();
+        return value.isEmpty() ? field.getName() : value;
+    }
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/customannotations/Person.java

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+package com.baeldung.customannotations;
+
+@JsonSerializable
+public class Person {
+    @JsonElement
+    private String firstName;
+    @JsonElement
+    private String lastName;
+    @JsonElement(key = "personAge")
+    private String age;
+
+    private String address;
+
+    public Person(String firstName, String lastName) {
+        super();
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public Person(String firstName, String lastName, String age) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.age = age;
+    }
+
+    @Init
+    private void initNames() {
+        this.firstName = this.firstName.substring(0, 1)
+            .toUpperCase() + this.firstName.substring(1);
+        this.lastName = this.lastName.substring(0, 1)
+            .toUpperCase() + this.lastName.substring(1);
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public String getAge() {
+        return age;
+    }
+
+    public void setAge(String age) {
+        this.age = age;
+    }
+
+    public String getAddress() {
+        return address;
+    }
+
+    public void setAddress(String address) {
+        this.address = address;
+    }
+
+}

core-java-modules/core-java-annotations/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java-modules/core-java-annotations/src/test/java/com/baeldung/customannotations/JsonSerializerUnitTest.java

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+package com.baeldung.customannotations;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class JsonSerializerUnitTest {
+
+    @Test
+    public void givenObjectNotSerializedThenExceptionThrown() throws JsonSerializationException {
+        Object object = new Object();
+        ObjectToJsonConverter serializer = new ObjectToJsonConverter();
+        assertThrows(JsonSerializationException.class, () -> {
+            serializer.convertToJson(object);
+        });
+    }
+
+    @Test
+    public void givenObjectSerializedThenTrueReturned() throws JsonSerializationException {
+        Person person = new Person("soufiane", "cheouati", "34");
+        ObjectToJsonConverter serializer = new ObjectToJsonConverter();
+        String jsonString = serializer.convertToJson(person);
+        assertEquals("{\"personAge\":\"34\",\"firstName\":\"Soufiane\",\"lastName\":\"Cheouati\"}", jsonString);
+    }
+}

core-java-modules/core-java-annotations/src/test/resources/.gitignore

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+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear