Merge pull request #75 from eugenp/master

update

algorithms-miscellaneous-1/README.md

@@ -10,4 +10,4 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Introduction to Minimax Algorithm](https://www.baeldung.com/java-minimax-algorithm)
 - [How to Calculate Levenshtein Distance in Java?](https://www.baeldung.com/java-levenshtein-distance)
 - [How to Find the Kth Largest Element in Java](https://www.baeldung.com/java-kth-largest-element)
-- More articles: [[next -->]](/../algorithms-miscellaneous-2)
+- More articles: [[next -->]](/algorithms-miscellaneous-2)

algorithms-miscellaneous-2/README.md

@@ -14,4 +14,4 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Displaying Money Amounts in Words](https://www.baeldung.com/java-money-into-words)
 - [A Collaborative Filtering Recommendation System in Java](https://www.baeldung.com/java-collaborative-filtering-recommendations)
 - [Implementing A* Pathfinding in Java](https://www.baeldung.com/java-a-star-pathfinding)
-- More articles: [[<-- prev]](/../algorithms-miscellaneous-1) [[next -->]](/../algorithms-miscellaneous-3)
+- More articles: [[<-- prev]](/algorithms-miscellaneous-1) [[next -->]](/algorithms-miscellaneous-3)

algorithms-miscellaneous-5/README.md

@@ -15,5 +15,5 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Maximum Subarray Problem](https://www.baeldung.com/java-maximum-subarray)
 - [How to Merge Two Sorted Arrays](https://www.baeldung.com/java-merge-sorted-arrays)
 - [Median of Stream of Integers using Heap](https://www.baeldung.com/java-stream-integers-median-using-heap)
-- More articles: [[<-- prev]](/../algorithms-miscellaneous-4) [[next -->]](/../algorithms-miscellaneous-6)
+- More articles: [[<-- prev]](/algorithms-miscellaneous-4) [[next -->]](/algorithms-miscellaneous-6)
 

algorithms-miscellaneous-6/README.md

@@ -10,4 +10,4 @@
 - [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
 - [Finding Top K Elements in an Array](https://www.baeldung.com/java-array-top-elements)
 - [Reversing a Linked List in Java](https://www.baeldung.com/java-reverse-linked-list)
-- More articles: [[<-- prev]](/../algorithms-miscellaneous-5)
+- More articles: [[<-- prev]](/algorithms-miscellaneous-5)

apache-spark/README.md

@@ -8,3 +8,4 @@ This module contains articles about Apache Spark
 - [Building a Data Pipeline with Kafka, Spark Streaming and Cassandra](https://www.baeldung.com/kafka-spark-data-pipeline)
 - [Machine Learning with Spark MLlib](https://www.baeldung.com/spark-mlib-machine-learning)
 - [Introduction to Spark Graph Processing with GraphFrames](https://www.baeldung.com/spark-graph-graphframes)
+- [Apache Spark: Differences between Dataframes, Datasets and RDDs](https://www.baeldung.com/java-spark-dataframe-dataset-rdd)

core-java-modules/core-java-9-jigsaw/src/modules/com.baeldung.student.service.dbimpl/com/baeldung/student/service/dbimpl/StudentDbService.java

@@ -19,12 +19,12 @@ public class StudentDbService implements StudentService {
     }
 
     public Student update(Student student) {
-        logger.log(Level.INFO, "Updating sutdent in DB...");
+        logger.log(Level.INFO, "Updating student in DB...");
         return student;
     }
 
     public String delete(String registrationId) {
-        logger.log(Level.INFO, "Deleteing sutdent in DB...");
+        logger.log(Level.INFO, "Deleting student in DB...");
         return registrationId;
     }
 }

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/removeallperformance/HashSetBenchmark.java

@@ -33,11 +33,15 @@ public class HashSetBenchmark {
         private List<Employee> employeeList1 = new ArrayList<>();
         private Set<Employee> employeeSet2 = new HashSet<>();
         private List<Employee> employeeList2 = new ArrayList<>();
+        private Set<Employee> employeeSet3 = new HashSet<>();
+        private Set<Employee> employeeSet4 = new HashSet<>();
 
         private long set1Size = 60000;
         private long list1Size = 50000;
         private long set2Size = 50000;
         private long list2Size = 60000;
+        private long set3Size = 50000;
+        private long set4Size = 60000;
 
         @Setup(Level.Trial)
         public void setUp() {
@@ -57,6 +61,14 @@ public class HashSetBenchmark {
             for (long i = 0; i < list2Size; i++) {
                 employeeList2.add(new Employee(i, RandomStringUtils.random(7, true, false)));
             }
+            
+            for (long i = 0; i < set3Size; i++) {
+                employeeSet3.add(new Employee(i, RandomStringUtils.random(7, true, false)));
+            }
+
+            for (long i = 0; i < set4Size; i++) {
+                employeeSet4.add(new Employee(i, RandomStringUtils.random(7, true, false)));
+            }
 
         }
 
@@ -71,6 +83,11 @@ public class HashSetBenchmark {
     public boolean given_SizeOfHashsetSmallerThanSizeOfCollection_When_RemoveAllFromHashSet_Then_BadPerformance(MyState state) {
         return state.employeeSet2.removeAll(state.employeeList2);
     }
+    
+    @Benchmark
+    public boolean given_SizeOfHashsetSmallerThanSizeOfAnotherHashSet_When_RemoveAllFromHashSet_Then_GoodPerformance(MyState state) {
+        return state.employeeSet3.removeAll(state.employeeSet4);
+    }
 
     public static void main(String[] args) throws Exception {
         Options options = new OptionsBuilder().include(HashSetBenchmark.class.getSimpleName())

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/deadlockAndLivelock/LivelockExample.java

@@ -73,7 +73,7 @@ public class LivelockExample {
 
     public void tryLock(Lock lock, long millis) {
         try {
-            lock.tryLock(10, TimeUnit.MILLISECONDS);
+            lock.tryLock(millis, TimeUnit.MILLISECONDS);
         } catch (InterruptedException e) {
             e.printStackTrace();
         }

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Animal.java

@@ -0,0 +1,6 @@
+package com.baeldung.exceptions.classcastexception;
+
+public interface Animal {
+
+    String getName();
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Box.java

@@ -0,0 +1,14 @@
+package com.baeldung.exceptions.classcastexception;
+
+public class Box<T> {
+
+    private T content;
+
+    public T getContent() {
+        return content;
+    }
+
+    public void setContent(T content) {
+        this.content = content;
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Frog.java

@@ -0,0 +1,9 @@
+package com.baeldung.exceptions.classcastexception;
+
+public class Frog extends Reptile {
+
+    @Override
+    public String getName() {
+        return super.getName() + ": Frog";
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Mammal.java

@@ -0,0 +1,9 @@
+package com.baeldung.exceptions.classcastexception;
+
+public class Mammal implements Animal {
+
+    @Override
+    public String getName() {
+        return "Mammal";
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Reptile.java

@@ -0,0 +1,9 @@
+package com.baeldung.exceptions.classcastexception;
+
+public class Reptile implements Animal {
+
+    @Override
+    public String getName() {
+        return "Reptile";
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/CheckedCastsUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.exceptions.classcastexception;
+
+import org.junit.Test;
+
+import java.io.Serializable;
+
+public class CheckedCastsUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenBaseTypeVariableReferencingChildInstance_whenCastToIncompatibleSubtype_thenClassCastException() {
+        Animal animal = new Frog();
+
+        //A checked downcast to Mammal is incompatible from Frog because Frog is not a subtype of Mammal.
+        Mammal mammal = (Mammal) animal;
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenBaseTypeVariableReferencingChildInstance_whenCastToIncompatibleInterface_thenClassCastException() {
+        Animal animal = new Frog();
+
+        //A checked cast to Serializable is incompatible from Frog because Frog is not a subtype of Serializable.
+        Serializable serial = (Serializable) animal;
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenObjectVariableReferencingPrimitiveArray_whenCastToBoxedTypeArray_thenClassCastException() {
+        Object primitives = new int[1];
+
+        //A checked cast to Integer[] is incompatible from primitive arrays. Auto-boxing does not work for arrays.
+        Integer[] integers = (Integer[]) primitives;
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenObjectVariableReferencingPrimitiveArray_whenCastToPromotedTypeArray_thenClassCastException() {
+        Object primitives = new int[1];
+
+        //A checked cast to long[] is incompatible from int[]. Type promotion does not work for arrays.
+        long[] longs = (long[]) primitives;
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/GenericConversionUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.exceptions.classcastexception;
+
+import org.junit.Test;
+
+public class GenericConversionUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenIncompatibleType_whenConvertInstanceOfObject_thenClassCastException() {
+        // Should have been null, but due to type erasure, inside convertInstanceOfObject,
+        // it will attempt to cast to Object instead of String, so it casts to Object, which is always possible.
+        String shouldBeNull = convertInstanceOfObject(123);
+    }
+
+    public static <T> T convertInstanceOfObject(Object o) {
+        try {
+            return (T) o; // Casts to Object due to type erasure
+        } catch (ClassCastException e) {
+            return null; // Will never reach this
+        }
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/UncheckedConversionUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.exceptions.classcastexception;
+
+import org.junit.Test;
+
+public class UncheckedConversionUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenPollutedGenericType_whenGetProperty_thenClassCastException() {
+        Box<Long> originalBox = new Box<>();
+        Box raw = originalBox;
+        raw.setContent(2.5);
+        Box<Long> bound = (Box<Long>) raw;
+
+        //An incompatible element was found in the raw box.
+        Long content = bound.getContent();
+    }
+}

core-java-modules/core-java-lang-3/README.md

@@ -7,4 +7,5 @@ This module contains articles about core features in the Java language
 - [When are Static Variables Initialized in Java?](https://www.baeldung.com/java-static-variables-initialization)
 - [Checking if a Class Exists in Java](https://www.baeldung.com/java-check-class-exists)
 - [The Difference Between a.getClass() and A.class in Java](https://www.baeldung.com/java-getclass-vs-class)
+- [Constants in Java: Patterns and Anti-Patterns](https://www.baeldung.com/java-constants-good-practices)
 - [[<-- Prev]](/core-java-modules/core-java-lang-2)

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/constantspatterns/Calculator.java

@@ -0,0 +1,37 @@
+package com.baeldung.constantspatterns;
+
+public class Calculator {
+    public static final double PI = 3.14159265359;
+    private static final double UPPER_LIMIT = 0x1.fffffffffffffP+1023;
+
+    public enum Operation {
+        ADD, SUBTRACT, DIVIDE, MULTIPLY
+    }
+
+    public double operateOnTwoNumbers(double numberOne, double numberTwo, Operation operation) {
+        if (numberOne > UPPER_LIMIT) {
+            throw new IllegalArgumentException("'numberOne' is too large");
+        }
+        if (numberTwo > UPPER_LIMIT) {
+            throw new IllegalArgumentException("'numberTwo' is too large");
+        }
+        double answer = 0;
+
+        switch (operation) {
+        case ADD:
+            answer = numberOne + numberTwo;
+            break;
+        case SUBTRACT:
+            answer = numberOne - numberTwo;
+            break;
+        case DIVIDE:
+            answer = numberOne / numberTwo;
+            break;
+        case MULTIPLY:
+            answer = numberOne * numberTwo;
+            break;
+        }
+
+        return answer;
+    }
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/constantspatterns/CalculatorConstants.java

@@ -0,0 +1,10 @@
+package com.baeldung.constantspatterns;
+
+public interface CalculatorConstants {
+    double PI = 3.14159265359;
+    double UPPER_LIMIT = 0x1.fffffffffffffP+1023;
+
+    enum Operation {
+        ADD, SUBTRACT, MULTIPLY, DIVIDE
+    };
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/constantspatterns/GeometryCalculator.java

@@ -0,0 +1,32 @@
+package com.baeldung.constantspatterns;
+
+public class GeometryCalculator implements CalculatorConstants {
+    public static final double UPPER_LIMIT = 100000000000000000000.0;
+
+    public double operateOnTwoNumbers(double numberOne, double numberTwo, Operation operation) {
+        if (numberOne > UPPER_LIMIT) {
+            throw new IllegalArgumentException("'numberOne' is too large");
+        }
+        if (numberTwo > UPPER_LIMIT) {
+            throw new IllegalArgumentException("'numberTwo' is too large");
+        }
+        double answer = 0;
+
+        switch (operation) {
+        case ADD:
+            answer = numberOne + numberTwo;
+            break;
+        case SUBTRACT:
+            answer = numberOne - numberTwo;
+            break;
+        case DIVIDE:
+            answer = numberOne / numberTwo;
+            break;
+        case MULTIPLY:
+            answer = numberOne * numberTwo;
+            break;
+        }
+
+        return answer;
+    }
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/constantspatterns/calculations/MathConstants.java

@@ -0,0 +1,16 @@
+package com.baeldung.constantspatterns.calculations;
+
+public final class MathConstants {
+    public static final double PI = 3.14159265359;
+    static final double GOLDEN_RATIO = 1.6180;
+    static final double GRAVITATIONAL_ACCELERATION = 9.8;
+    static final double EULERS_NUMBER = 2.7182818284590452353602874713527;
+
+    public enum Operation {
+        ADD, SUBTRACT, DIVIDE, MULTIPLY
+    }
+
+    private MathConstants() {
+
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/constantspatterns/ConstantPatternUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.constantspatterns;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class ConstantPatternUnitTest {
+    @Test
+    public void givenTwoNumbersAndAdd_whenCallingCalculatorOperatOneTwoNumbers_thenCorrectAnswerReturned() {
+        Calculator calculator = new Calculator();
+        double expected = 4;
+        double answer = calculator.operateOnTwoNumbers(2, 2, Calculator.Operation.ADD);
+        assertEquals(expected, answer);
+    }
+    
+    @Test
+    public void givenTwoNumbersAndAdd_whenCallingGeometryCalculatorOperatOneTwoNumbers_thenCorrectAnswerReturned() {
+        GeometryCalculator calculator = new GeometryCalculator();
+        double expected = 4;
+        double answer = calculator.operateOnTwoNumbers(2, 2, GeometryCalculator.Operation.ADD);
+        assertEquals(expected, answer);
+    }
+}

core-java-modules/core-java-networking-2/README.md

@@ -14,4 +14,5 @@ This module contains articles about networking in Java
 - [Handling java.net.ConnectException](https://www.baeldung.com/java-net-connectexception)
 - [Getting MAC addresses in Java](https://www.baeldung.com/java-mac-address)
 - [Sending Emails with Attachments in Java](https://www.baeldung.com/java-send-emails-attachments)
+- [Finding a Free Port in Java](https://www.baeldung.com/java-free-port)
 - [[<-- Prev]](/core-java-modules/core-java-networking)

core-java-modules/core-java-security-2/src/main/java/com/baeldung/hashing/SHACommonUtils.java

@@ -3,7 +3,7 @@ package com.baeldung.hashing;
 class SHACommonUtils {
 
     public static String bytesToHex(byte[] hash) {
-        StringBuffer hexString = new StringBuffer();
+        StringBuilder hexString = new StringBuilder(2 * hash.length);
         for (byte h : hash) {
             String hex = Integer.toHexString(0xff & h);
             if (hex.length() == 1)

ddd/pom.xml

@@ -104,16 +104,12 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>${maven-surefire-plugin.version}</version>
             </plugin>
         </plugins>
     </build>
 
     <properties>
-        <maven-surefire-plugin.version>2.22.2</maven-surefire-plugin.version>
-
         <joda-money.version>1.0.1</joda-money.version>
 
-        <junit-jupiter.version>5.6.2</junit-jupiter.version>
     </properties>
 </project>

netflix-modules/mantis/pom.xml

@@ -0,0 +1,78 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <artifactId>mantis</artifactId>
+    <name>Mantis</name>
+    <packaging>jar</packaging>
+    <description>Sample project for Netflix Mantis</description>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-boot-2</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-2</relativePath>
+    </parent>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+            <version>2.1.3.RELEASE</version>
+        </dependency>
+
+        <dependency>
+            <groupId>io.mantisrx</groupId>
+            <artifactId>mantis-runtime</artifactId>
+            <version>1.2.63</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.slf4j</groupId>
+                    <artifactId>slf4j-log4j12</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>2.10.2</version>
+        </dependency>
+
+        <dependency>
+            <groupId>net.andreinc.mockneat</groupId>
+            <artifactId>mockneat</artifactId>
+            <version>0.3.8</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.18.12</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-webflux</artifactId>
+            <version>5.0.9.RELEASE</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>io.projectreactor.netty</groupId>
+            <artifactId>reactor-netty</artifactId>
+            <version>0.9.12.RELEASE</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <repositories>
+        <repository>
+            <id>SpringLibReleaseRepo</id>
+            <url>https://repo.spring.io/libs-release/</url>
+        </repository>
+    </repositories>
+
+</project>

netflix-modules/mantis/src/main/java/com/baeldung/netflix/mantis/MantisApplication.java

@@ -0,0 +1,23 @@
+package com.baeldung.netflix.mantis;
+
+import com.baeldung.netflix.mantis.job.LogAggregationJob;
+import io.mantisrx.runtime.executor.LocalJobExecutorNetworked;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@Slf4j
+@SpringBootApplication
+public class MantisApplication implements CommandLineRunner {
+
+    public static void main(String[] args) {
+        SpringApplication.run(MantisApplication.class, args);
+    }
+
+    @Override
+    public void run(String... args) {
+        LocalJobExecutorNetworked.execute(new LogAggregationJob().getJobInstance());
+    }
+
+}

netflix-modules/mantis/src/main/java/com/baeldung/netflix/mantis/job/LogAggregationJob.java

@@ -0,0 +1,37 @@
+package com.baeldung.netflix.mantis.job;
+
+import com.baeldung.netflix.mantis.model.LogAggregate;
+import com.baeldung.netflix.mantis.source.RandomLogSource;
+import com.baeldung.netflix.mantis.stage.CountLogStage;
+import com.baeldung.netflix.mantis.stage.GroupLogStage;
+import com.baeldung.netflix.mantis.stage.TransformLogStage;
+import io.mantisrx.runtime.Job;
+import io.mantisrx.runtime.MantisJob;
+import io.mantisrx.runtime.MantisJobProvider;
+import io.mantisrx.runtime.Metadata;
+import io.mantisrx.runtime.sink.Sink;
+import io.mantisrx.runtime.sink.Sinks;
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
+
+@NoArgsConstructor
+@AllArgsConstructor
+public class LogAggregationJob extends MantisJobProvider<LogAggregate> {
+
+    private Sink<LogAggregate> sink = Sinks.eagerSubscribe(Sinks.sse(LogAggregate::toJsonString));
+
+    @Override
+    public Job<LogAggregate> getJobInstance() {
+
+        return MantisJob
+          .source(new RandomLogSource())
+          .stage(new TransformLogStage(), TransformLogStage.stageConfig())
+          .stage(new GroupLogStage(), GroupLogStage.config())
+          .stage(new CountLogStage(), CountLogStage.config())
+          .sink(sink)
+          .metadata(new Metadata.Builder().build())
+          .create();
+
+    }
+
+}

netflix-modules/mantis/src/main/java/com/baeldung/netflix/mantis/job/LogCollectingJob.java

@@ -0,0 +1,34 @@
+package com.baeldung.netflix.mantis.job;
+
+import com.baeldung.netflix.mantis.model.LogEvent;
+import com.baeldung.netflix.mantis.sink.LogSink;
+import com.baeldung.netflix.mantis.source.RandomLogSource;
+import com.baeldung.netflix.mantis.stage.TransformLogStage;
+import io.mantisrx.runtime.Job;
+import io.mantisrx.runtime.MantisJob;
+import io.mantisrx.runtime.MantisJobProvider;
+import io.mantisrx.runtime.Metadata;
+import io.mantisrx.runtime.ScalarToScalar;
+import io.mantisrx.runtime.sink.Sink;
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
+
+@NoArgsConstructor
+@AllArgsConstructor
+public class LogCollectingJob extends MantisJobProvider<LogEvent> {
+
+    private Sink<LogEvent> sink = new LogSink();
+
+    @Override
+    public Job<LogEvent> getJobInstance() {
+
+        return MantisJob
+          .source(new RandomLogSource())
+          .stage(new TransformLogStage(), new ScalarToScalar.Config<>())
+          .sink(sink)
+          .metadata(new Metadata.Builder().build())
+          .create();
+
+    }
+
+}

netflix-modules/mantis/src/main/java/com/baeldung/netflix/mantis/model/LogAggregate.java

@@ -0,0 +1,28 @@
+package com.baeldung.netflix.mantis.model;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.mantisrx.runtime.codec.JsonType;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@Getter
+@NoArgsConstructor
+@AllArgsConstructor
+public class LogAggregate implements JsonType {
+
+    private static final ObjectMapper mapper = new ObjectMapper();
+
+    private Integer count;
+    private String level;
+
+    public String toJsonString() {
+        try {
+            return mapper.writeValueAsString(this);
+        } catch (JsonProcessingException e) {
+            return null;
+        }
+    }
+
+}