The pattern Role object (#1031)

* init repo for role object

* add to init

*  add to init

*  add first impl

*  add pattern

*  add license

*  add changes

role-object/README.md

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+---
+layout: pattern
+title: Role object
+folder: Migration
+permalink: /patterns/role-object/
+categories: Structural
+tags:
+ - Java
+ - Difficulty-Medium
+ - Handle Body Pattern
+---
+
+## Also known as
+Post pattern, Extension Object pattern
+
+## Intent
+Adapt an object to different client’s needs through transparently attached role objects, each one representing a role
+the object has to play in that client’s context. The object manages its role set dynamically. By representing roles as
+individual objects, different contexts are kept separate and system configuration is simplified.
+
+## Applicability
+Use the Role Object pattern, if:
+- you want to handle a key abstraction in different contexts and you do not want to put the resulting context specific interfaces into the same class interface.
+- you want to handle the available roles dynamically so that they can be attached and removed on demand, that is at runtime, rather than fixing them statically at compile-time.
+- you want to treat the extensions transparently and need to preserve the logical object identity of the resultingobject conglomerate.
+- you want to keep role/client pairs independent from each other so that changes to a role do not affect clients that are not interested in that role.
+
+## Credits
+- [Hillside - Role object pattern](https://hillside.net/plop/plop97/Proceedings/riehle.pdf)
+- [Role object](http://wiki.c2.com/?RoleObject)
+- [Fowler - Dealing with roles](https://martinfowler.com/apsupp/roles.pdf)

role-object/pom.xml

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+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 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 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.22.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>role-object</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+</project>

role-object/src/main/java/com/iluwatar/roleobject/ApplicationRoleObject.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.
+ */
+package com.iluwatar.roleobject;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static com.iluwatar.roleobject.Role.*;
+
+/**
+ * The Role Object pattern suggests to model context-specific views
+ * of an object as separate role objects which are
+ * dynamically attached to and removed from the core object.
+ * We call the resulting composite object structure,
+ * consisting of the core and its role objects, a subject.
+ * A subject often plays several roles and the same role is likely to
+ * be played by different subjects.
+ * As an example consider two different customers playing the role of borrower and
+ * investor, respectively. Both roles could as well be played by a single {@link Customer} object.
+ * The common superclass for customer-specific roles is provided by {@link CustomerRole},
+ * which also supports the {@link Customer} interface.
+ * <p>
+ * The {@link CustomerRole} class is abstract and not meant to be instantiated.
+ * Concrete subclasses of {@link CustomerRole}, for example {@link BorrowerRole} or {@link InvestorRole},
+ * define and implement the interface for specific roles. It is only
+ * these subclasses which are instantiated at runtime.
+ * The {@link BorrowerRole}  class defines the context-specific view of {@link Customer}  objects as needed by the loan department.
+ * It defines additional operations to manage the customer’s
+ * credits and securities. Similarly, the {@link InvestorRole} class adds operations specific
+ * to the investment department’s view of customers.
+ * A client like the loan application may either work with objects of the {@link CustomerRole} class, using the interface class
+ * {@link Customer}, or with objects of concrete  {@link CustomerRole} subclasses. Suppose the loan application knows a particular
+ * {@link Customer} instance through its {@link Customer} interface. The loan application may want to check whether the {@link Customer}
+ * object plays the role of Borrower.
+ * To this end it calls {@link Customer#hasRole(Role)} with a suitable role specification. For the purpose of
+ * our example, let’s assume we can name roles with enum.
+ * If the {@link Customer} object can play the role named “Borrower,” the loan application will ask it
+ * to return a reference to the corresponding object.
+ * The loan application may now use this reference to call Borrower-specific operations.
+ */
+public class ApplicationRoleObject {
+
+    private static final Logger logger = LoggerFactory.getLogger(Role.class);
+
+    public static void main(String[] args) {
+        Customer customer = Customer.newCustomer(Borrower, Investor);
+
+        logger.info(" the new customer created : {}", customer);
+
+        boolean hasBorrowerRole = customer.hasRole(Borrower);
+        logger.info(" customer has a borrowed role - {}", hasBorrowerRole);
+        boolean hasInvestorRole = customer.hasRole(Investor);
+        logger.info(" customer has an investor role - {}", hasInvestorRole);
+
+        customer.getRole(Investor, InvestorRole.class)
+                .ifPresent(inv -> {
+                    inv.setAmountToInvest(1000);
+                    inv.setName("Billy");
+                });
+        customer.getRole(Borrower, BorrowerRole.class)
+                .ifPresent(inv -> inv.setName("Johny"));
+
+        customer.getRole(Investor, InvestorRole.class)
+                .map(InvestorRole::invest)
+                .ifPresent(logger::info);
+
+        customer.getRole(Borrower, BorrowerRole.class)
+                .map(BorrowerRole::borrow)
+                .ifPresent(logger::info);
+    }
+
+
+}

role-object/src/main/java/com/iluwatar/roleobject/BorrowerRole.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.
+ */
+package com.iluwatar.roleobject;
+
+public class BorrowerRole extends CustomerRole{
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String borrow(){
+        return String.format("Borrower %s wants to get some money.",name);
+    }
+
+}

role-object/src/main/java/com/iluwatar/roleobject/Customer.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.
+ */
+package com.iluwatar.roleobject;
+
+import java.util.Optional;
+
+/**
+ * The main abstraction to work with Customer.
+ */
+public abstract class Customer {
+
+    /**
+     * Add specific role @see {@link Role}
+     *
+     * @param role to add
+     * @return true if the operation has been successful otherwise false
+     */
+    public abstract boolean addRole(Role role);
+
+    /**
+     * Check specific role @see {@link Role}
+     *
+     * @param role to check
+     * @return true if the role exists otherwise false
+     */
+
+    public abstract boolean hasRole(Role role);
+
+    /**
+     * Remove specific role @see {@link Role}
+     *
+     * @param role to remove
+     * @return true if the operation has been successful otherwise false
+     */
+    public abstract boolean remRole(Role role);
+
+    /**
+     * Get specific instance associated with this role @see {@link Role}
+     *
+     * @param role         to get
+     * @param expectedRole instance class expected to get
+     * @return optional with value if the instance exists and corresponds expected class
+     */
+    public abstract <T extends Customer> Optional<T> getRole(Role role, Class<T> expectedRole);
+
+
+    public static Customer newCustomer() {
+        return new CustomerCore();
+    }
+
+    public static Customer newCustomer(Role... role) {
+        Customer customer = newCustomer();
+        for (Role r : role) {
+            customer.addRole(r);
+        }
+        return customer;
+    }
+
+}

role-object/src/main/java/com/iluwatar/roleobject/CustomerCore.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.
+ */
+package com.iluwatar.roleobject;
+
+import java.util.*;
+
+/**
+ * Core class to store different customer roles
+ *
+ * @see CustomerRole
+ * Note: not thread safe
+ */
+public class CustomerCore extends Customer {
+
+    private Map<Role, CustomerRole> roles;
+
+    public CustomerCore() {
+        roles = new HashMap<>();
+    }
+
+    @Override
+    public boolean addRole(Role role) {
+        return role
+                .instance()
+                .map(inst -> {
+                    roles.put(role, inst);
+                    return true;
+                })
+                .orElse(false);
+    }
+
+    @Override
+    public boolean hasRole(Role role) {
+        return roles.containsKey(role);
+    }
+
+    @Override
+    public boolean remRole(Role role) {
+        return Objects.nonNull(roles.remove(role));
+    }
+
+    @Override
+    public <T extends Customer> Optional<T> getRole(Role role, Class<T> expectedRole) {
+        return Optional
+                .ofNullable(roles.get(role))
+                .filter(expectedRole::isInstance)
+                .map(expectedRole::cast);
+    }
+
+    @Override
+    public String toString() {
+        String roles = Arrays.toString(this.roles.keySet().toArray());
+        return "Customer{roles=" + roles + "}";
+    }
+}

role-object/src/main/java/com/iluwatar/roleobject/CustomerRole.java

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+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.
+ */
+package com.iluwatar.roleobject;
+
+/**
+ * Key abstraction for segregated roles
+ */
+public abstract class CustomerRole extends CustomerCore{}