Fallback

fallback/etc/fallback.urm.puml

@@ -0,0 +1,173 @@
+@startuml
+package fallback {
+  class App {
+    - TIMEOUT : int {static}
+    - MAX_ATTEMPTS : int {static}
+    - RETRY_DELAY : int {static}
+    - DEFAULT_API_URL : String {static}
+    - circuitBreaker : CircuitBreaker
+    - executor : ExecutorService
+    - fallbackService : Service
+    - primaryService : Service
+    - state : ExecutionState
+    - LOGGER : Logger {static}
+    + App()
+    + App(primaryService : Service, fallbackService : Service, circuitBreaker : CircuitBreaker)
+    + executeWithFallback() : String
+    - getFallbackData() : String
+    - updateFallbackCache(result : String)
+    + shutdown()
+    + main(args : String[]) {static}
+  }
+
+  interface Service {
+    + getData() : String
+  }
+
+  interface CircuitBreaker {
+    + isOpen() : boolean
+    + allowRequest() : boolean
+    + recordFailure()
+    + recordSuccess()
+    + reset()
+    + getState() : CircuitState
+  }
+
+  class DefaultCircuitBreaker {
+    - RESET_TIMEOUT : long {static}
+    - MIN_HALF_OPEN_DURATION : Duration {static}
+    - state : State
+    - failureThreshold : int
+    - lastFailureTime : long
+    - failureTimestamps : Queue<Long>
+    - windowSize : Duration
+    - halfOpenStartTime : Instant
+    + DefaultCircuitBreaker(failureThreshold : int)
+    + isOpen() : boolean
+    + allowRequest() : boolean
+    + recordFailure()
+    + recordSuccess()
+    + reset()
+    + getState() : CircuitState
+    - transitionToHalfOpen()
+    - enum State { CLOSED, OPEN, HALF_OPEN }
+  }
+
+  class FallbackService {
+    - {static} MAX_RETRIES : int = 3
+    - {static} RETRY_DELAY_MS : long = 1000
+    - {static} TIMEOUT : int = 2
+    - {static} MIN_SUCCESS_RATE : double = 0.6
+    - {static} MAX_REQUESTS_PER_MINUTE : int = 60
+    - {static} LOGGER : Logger
+    - primaryService : Service
+    - fallbackService : Service
+    - circuitBreaker : CircuitBreaker
+    - executor : ExecutorService
+    - healthChecker : ScheduledExecutorService
+    - monitor : ServiceMonitor
+    - rateLimiter : RateLimiter
+    - state : ServiceState
+    + FallbackService(primaryService : Service, fallbackService : Service, circuitBreaker : CircuitBreaker)
+    + getData() : String
+    - executeWithTimeout(task : Callable<String>) : String
+    - executeFallback() : String
+    - updateFallbackCache(result : String)
+    - startHealthChecker()
+    + close()
+    + getMonitor() : ServiceMonitor
+    + getState() : ServiceState
+    - enum ServiceState { STARTING, RUNNING, DEGRADED, CLOSED }
+  }
+
+  class LocalCacheService {
+    - cache : Cache<String, String>
+    - refreshExecutor : ScheduledExecutorService
+    - {static} CACHE_EXPIRY_MS : long = 300000
+    - {static} CACHE_REFRESH_INTERVAL : Duration = Duration.ofMinutes(5)
+    - {static} LOGGER : Logger
+    + LocalCacheService()
+    + getData() : String
+    + updateCache(key : String, value : String)
+    + close() : void
+    - initializeDefaultCache()
+    - scheduleMaintenanceTasks()
+    - cleanupExpiredEntries()
+    - enum FallbackLevel { PRIMARY, SECONDARY, TERTIARY }
+    - class Cache<K, V> {
+      - map : ConcurrentHashMap<K, CacheEntry<V>>
+      - expiryMs : long
+      + Cache(expiryMs : long)
+      + get(key : K) : V
+      + put(key : K, value : V)
+      + cleanup()
+      - record CacheEntry<V>(value : V, expiryTime : long) { + isExpired() : boolean }
+    }
+
+
+  class RemoteService {
+    - apiUrl : String
+    - httpClient : HttpClient
+    - {static} TIMEOUT_SECONDS : int = 2
+    + RemoteService(apiUrl : String, httpClient : HttpClient)
+    + getData() : String
+  }
+
+  class ServiceMonitor {
+    - successCount : AtomicInteger
+    - fallbackCount : AtomicInteger
+    - errorCount : AtomicInteger
+    - lastSuccessTime : AtomicReference<Instant>
+    - lastFailureTime : AtomicReference<Instant>
+    - lastResponseTime : AtomicReference<Duration>
+    - metrics : Queue<ServiceMetric>
+    - fallbackWeight : double
+    - metricWindow : Duration
+    + ServiceMonitor()
+    + ServiceMonitor(fallbackWeight : double, metricWindow : Duration)
+    + recordSuccess(responseTime : Duration)
+    + recordFallback()
+    + recordError()
+    + getSuccessCount() : int
+    + getFallbackCount() : int
+    + getErrorCount() : int
+    + getLastSuccessTime() : Instant
+    + getLastFailureTime() : Instant
+    + getLastResponseTime() : Duration
+    + getSuccessRate() : double
+    + reset()
+    - pruneOldMetrics()
+    - record ServiceMetric(timestamp : Instant, type : MetricType, responseTime : Duration)
+    - enum MetricType { SUCCESS, FALLBACK, ERROR }
+  }
+
+  class RateLimiter {
+    - maxRequests : int
+    - window : Duration
+    - requestTimestamps : Queue<Long>
+    + RateLimiter(maxRequests : int, window : Duration)
+    + tryAcquire() : boolean
+  }
+
+  class ServiceException {
+    + ServiceException(message : String)
+    + ServiceException(message : String, cause : Throwable)
+  }
+}
+  ' Relationships
+  App --> CircuitBreaker
+  App --> Service : primaryService
+  App --> Service : fallbackService
+  DefaultCircuitBreaker ..|> CircuitBreaker 
+  LocalCacheService ..|> Service 
+  RemoteService ..|> Service 
+  FallbackService ..|> Service
+  FallbackService ..|> AutoCloseable
+  FallbackService --> Service : primaryService
+  FallbackService --> Service : fallbackService
+  FallbackService --> CircuitBreaker
+  FallbackService --> ServiceMonitor
+  FallbackService --> RateLimiter
+  ServiceException --|> Exception
+}
+@enduml

fallback/pom.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+
+    The MIT License
+    Copyright © 2014-2022 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<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>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.26.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>fallback</artifactId>
+
+    <properties>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+    <dependencies>
+    <dependency>
+        <groupId>org.junit.jupiter</groupId>
+        <artifactId>junit-jupiter-engine</artifactId>
+        <version>5.8.2</version>
+        <scope>test</scope>
+    </dependency>
+    <dependency>
+        <groupId>org.junit.jupiter</groupId>
+        <artifactId>junit-jupiter-api</artifactId>
+        <version>5.8.2</version>
+        <scope>test</scope>
+    </dependency>
+            <dependency>
+                <groupId>org.junit.jupiter</groupId>
+                <artifactId>junit-jupiter</artifactId>
+                <version>5.8.2</version>
+                <scope>test</scope>
+            </dependency>
+            <dependency>
+                <groupId>org.mockito</groupId>
+                <artifactId>mockito-core</artifactId>
+                <version>4.5.1</version>
+                <scope>test</scope>
+            </dependency>
+
+        </dependencies>
+</project>