enhancement: iluwatar#1947 implement chain of responsibilities with java stream (iluwatar#2123)

Author: JanFidor

chain-of-responsibility/README.md

@@ -118,18 +118,24 @@ The Orc King gives the orders and forms the chain.
 
 ```java
 public class OrcKing {
-  RequestHandler chain;
+
+  private List<RequestHandler> handlers;
 
   public OrcKing() {
     buildChain();
   }
 
   private void buildChain() {
-    chain = new OrcCommander(new OrcOfficer(new OrcSoldier(null)));
+    handlers = Arrays.asList(new OrcCommander(), new OrcOfficer(), new OrcSoldier());
   }
 
   public void makeRequest(Request req) {
-    chain.handleRequest(req);
+    handlers
+        .stream()
+        .sorted(Comparator.comparing(RequestHandler::getPriority))
+        .filter(handler -> handler.canHandleRequest(req))
+        .findFirst()
+        .ifPresent(handler -> handler.handle(req));
   }
 }
 ```

chain-of-responsibility/etc/chain-of-responsibility.urm.png

@@ -5,25 +5,34 @@ package com.iluwatar.chain {
     + main(args : String[]) {static}
   }
   class OrcCommander {
-    + OrcCommander(handler : RequestHandler)
-    + handleRequest(req : Request)
-    + toString() : String
+    - LOGGER : Logger {static}
+    + OrcCommander()
+    + canHandleRequest(req : Request) : boolean
+    + getPriority() : int
+    + handle(req : Request)
+    + name() : String
   }
   class OrcKing {
-    - chain : RequestHandler
+    - handlers : List<RequestHandler>
     + OrcKing()
     - buildChain()
     + makeRequest(req : Request)
   }
   class OrcOfficer {
-    + OrcOfficer(handler : RequestHandler)
-    + handleRequest(req : Request)
-    + toString() : String
+    - LOGGER : Logger {static}
+    + OrcOfficer()
+    + canHandleRequest(req : Request) : boolean
+    + getPriority() : int
+    + handle(req : Request)
+    + name() : String
   }
   class OrcSoldier {
-    + OrcSoldier(handler : RequestHandler)
-    + handleRequest(req : Request)
-    + toString() : String
+    - LOGGER : Logger {static}
+    + OrcSoldier()
+    + canHandleRequest(req : Request) : boolean
+    + getPriority() : int
+    + handle(req : Request)
+    + name() : String
   }
   class Request {
     - handled : boolean
@@ -36,13 +45,11 @@ package com.iluwatar.chain {
     + markHandled()
     + toString() : String
   }
-  abstract class RequestHandler {
-    - LOGGER : Logger {static}
-    - next : RequestHandler
-    + RequestHandler(next : RequestHandler)
-    + handleRequest(req : Request)
-    # printHandling(req : Request)
-    + toString() : String {abstract}
+  interface RequestHandler {
+    + canHandleRequest(Request) : boolean {abstract}
+    + getPriority() : int {abstract}
+    + handle(Request) {abstract}
+    + name() : String {abstract}
   }
   enum RequestType {
     + COLLECT_TAX {static}
@@ -52,10 +59,9 @@ package com.iluwatar.chain {
     + values() : RequestType[] {static}
   }
 }
-OrcKing -->  "-chain" RequestHandler
-RequestHandler -->  "-next" RequestHandler
+OrcKing -->  "-handlers" RequestHandler
 Request -->  "-requestType" RequestType
-OrcCommander --|> RequestHandler 
-OrcOfficer --|> RequestHandler 
-OrcSoldier --|> RequestHandler 
+OrcCommander ..|> RequestHandler 
+OrcOfficer ..|> RequestHandler 
+OrcSoldier ..|> RequestHandler 
 @enduml

chain-of-responsibility/etc/chain-of-responsibility.urm.puml

@@ -24,27 +24,31 @@
  */
 package com.iluwatar.chain;
 
+import lombok.extern.slf4j.Slf4j;
+
 /**
  * OrcCommander.
  */
-public class OrcCommander extends RequestHandler {
+@Slf4j
+public class OrcCommander implements RequestHandler {
+  @Override
+  public boolean canHandleRequest(Request req) {
+    return req.getRequestType() == RequestType.DEFEND_CASTLE;
+  }
 
-  public OrcCommander(RequestHandler handler) {
-    super(handler);
+  @Override
+  public int getPriority() {
+    return 2;
   }
 
   @Override
-  public void handleRequest(Request req) {
-    if (RequestType.DEFEND_CASTLE == req.getRequestType()) {
-      printHandling(req);
-      req.markHandled();
-    } else {
-      super.handleRequest(req);
-    }
+  public void handle(Request req) {
+    req.markHandled();
+    LOGGER.info("{} handling request \"{}\"", name(), req);
   }
 
   @Override
-  public String toString() {
+  public String name() {
     return "Orc commander";
   }
 }

chain-of-responsibility/src/main/java/com/iluwatar/chain/OrcCommander.java

@@ -24,23 +24,34 @@
  */
 package com.iluwatar.chain;
 
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+
 /**
  * OrcKing makes requests that are handled by the chain.
  */
 public class OrcKing {
 
-  private RequestHandler chain;
+  private List<RequestHandler> handlers;
 
   public OrcKing() {
     buildChain();
   }
 
   private void buildChain() {
-    chain = new OrcCommander(new OrcOfficer(new OrcSoldier(null)));
+    handlers = Arrays.asList(new OrcCommander(), new OrcOfficer(), new OrcSoldier());
   }
 
+  /**
+   * Handle request by the chain.
+   */
   public void makeRequest(Request req) {
-    chain.handleRequest(req);
+    handlers
+        .stream()
+        .sorted(Comparator.comparing(RequestHandler::getPriority))
+        .filter(handler -> handler.canHandleRequest(req))
+        .findFirst()
+        .ifPresent(handler -> handler.handle(req));
   }
-
 }

chain-of-responsibility/src/main/java/com/iluwatar/chain/OrcKing.java

@@ -24,28 +24,32 @@
  */
 package com.iluwatar.chain;
 
+import lombok.extern.slf4j.Slf4j;
+
 /**
  * OrcOfficer.
  */
-public class OrcOfficer extends RequestHandler {
+@Slf4j
+public class OrcOfficer implements RequestHandler {
+  @Override
+  public boolean canHandleRequest(Request req) {
+    return req.getRequestType() == RequestType.TORTURE_PRISONER;
+  }
 
-  public OrcOfficer(RequestHandler handler) {
-    super(handler);
+  @Override
+  public int getPriority() {
+    return 3;
   }
 
   @Override
-  public void handleRequest(Request req) {
-    if (RequestType.TORTURE_PRISONER == req.getRequestType()) {
-      printHandling(req);
-      req.markHandled();
-    } else {
-      super.handleRequest(req);
-    }
+  public void handle(Request req) {
+    req.markHandled();
+    LOGGER.info("{} handling request \"{}\"", name(), req);
   }
 
   @Override
-  public String toString() {
+  public String name() {
     return "Orc officer";
   }
-
 }
+

chain-of-responsibility/src/main/java/com/iluwatar/chain/OrcOfficer.java

@@ -24,27 +24,31 @@
  */
 package com.iluwatar.chain;
 
+import lombok.extern.slf4j.Slf4j;
+
 /**
  * OrcSoldier.
  */
-public class OrcSoldier extends RequestHandler {
+@Slf4j
+public class OrcSoldier implements RequestHandler {
+  @Override
+  public boolean canHandleRequest(Request req) {
+    return req.getRequestType() == RequestType.COLLECT_TAX;
+  }
 
-  public OrcSoldier(RequestHandler handler) {
-    super(handler);
+  @Override
+  public int getPriority() {
+    return 1;
   }
 
   @Override
-  public void handleRequest(Request req) {
-    if (RequestType.COLLECT_TAX == req.getRequestType()) {
-      printHandling(req);
-      req.markHandled();
-    } else {
-      super.handleRequest(req);
-    }
+  public void handle(Request req) {
+    req.markHandled();
+    LOGGER.info("{} handling request \"{}\"", name(), req);
   }
 
   @Override
-  public String toString() {
+  public String name() {
     return "Orc soldier";
   }
 }

chain-of-responsibility/src/main/java/com/iluwatar/chain/OrcSoldier.java

@@ -24,31 +24,16 @@
  */
 package com.iluwatar.chain;
 
-import lombok.AllArgsConstructor;
-import lombok.extern.slf4j.Slf4j;
-
 /**
  * RequestHandler.
  */
-@Slf4j
-@AllArgsConstructor
-public abstract class RequestHandler {
+public interface RequestHandler {
 
-  private final RequestHandler next;
+  boolean canHandleRequest(Request req);
 
-  /**
-   * Request handler.
-   */
-  public void handleRequest(Request req) {
-    if (next != null) {
-      next.handleRequest(req);
-    }
-  }
+  int getPriority();
 
-  protected void printHandling(Request req) {
-    LOGGER.info("{} handling request \"{}\"", this, req);
-  }
+  void handle(Request req);
 
-  @Override
-  public abstract String toString();
+  String name();
 }