Create new module: Reliability (#154)

* Create new module: Reliability

* Add Throttler

Author: mincong-h

README.md

@@ -34,6 +34,7 @@ Mongo | The MongoDB database
 Mockito | [Mockito](https://site.mockito.org/), the most popular mocking framework for Java unit tests
 OCA | Oracle Certified Associate Java SE 8
 OCP | Oracle Certified Professional Java SE 8
+Reliability | Tips to make production more reliable.
 Rest | RESTful API using [Jersey][jersey].
 Typesafe Config | [Typesafe Config](https://github.com/lightbend/config), configuration library for JVM languages.
 XML | XML serialization, XPath, XSD.

pom.xml

@@ -58,6 +58,7 @@
     <module>guava</module>
     <module>jetty</module>
     <module>protobuf</module>
+    <module>reliability</module>
   </modules>
 
   <dependencyManagement>

reliability/pom.xml

@@ -0,0 +1,32 @@
+<?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">
+  <parent>
+    <artifactId>java-examples-parent</artifactId>
+    <groupId>io.mincong</groupId>
+    <version>1.0.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>java-examples-reliability</artifactId>
+  <name>Java Examples - Reliability</name>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

reliability/src/main/java/io/mincong/reliability/Throttler.java

@@ -0,0 +1,43 @@
+package io.mincong.reliability;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Throttler {
+
+  private final int messageLimit;
+
+  public Throttler(int messageLimit) {
+    this.messageLimit = messageLimit;
+  }
+
+  public ThrottleResult throttle(List<String> messages) {
+    var passed = new ArrayList<String>();
+    var throttled = new ArrayList<String>();
+    var quota = messageLimit;
+
+    for (var message : messages) {
+      if (quota > 0) {
+        passed.add(message);
+        quota--;
+      } else {
+        throttled.add(message);
+      }
+    }
+    /*
+     * You can also add metrics or logs on the output to improve the
+     * observability of the system.
+     */
+    return new ThrottleResult(passed, throttled);
+  }
+
+  public static class ThrottleResult {
+    public final List<String> passed;
+    public final List<String> throttled;
+
+    public ThrottleResult(List<String> passed, List<String> throttled) {
+      this.passed = passed;
+      this.throttled = throttled;
+    }
+  }
+}

reliability/src/test/java/io/mincong/reliability/ThrottlerTest.java

@@ -0,0 +1,29 @@
+package io.mincong.reliability;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class ThrottlerTest {
+
+  @Test
+  void throttle_lessMessagesThanLimit() {
+    var throttler = new Throttler(3);
+
+    var result = throttler.throttle(List.of("1", "2"));
+
+    assertThat(result.passed).containsExactly("1", "2");
+    assertThat(result.throttled).isEmpty();
+  }
+
+  @Test
+  void throttle_moreMessagesThanLimit() {
+    var throttler = new Throttler(3);
+
+    var result = throttler.throttle(List.of("1", "2", "3", "4"));
+
+    assertThat(result.passed).containsExactly("1", "2", "3");
+    assertThat(result.throttled).containsExactly("4");
+  }
+}