(NEW) Module "retry"

(NEW) Illustrative classes:
      - App: simulates a production application
      - BusinessOperation<T>: abstraction over any operation that can
        potentially fail
      - FindCustomer <: BusinessOperation<String>: illustrative
        operation that can throw an error
      - Retry <: BusinessOperation<T>: transparently implements the
        retry mechanism
      - Several "business" exceptions:
        - BusinessException: top-level
        - CustomerNotFoundException: can be ignored
        - DatabaseNotAvailableException: fatal error
(NEW) .puml and .png for UML

retry/src/test/java/com/iluwatar/retry/FindCustomerTest.java

@@ -0,0 +1,91 @@
+/*
+ * The MIT License (MIT)
+ * 
+ * Copyright (c) 2014-2016 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.retry;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.*;
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link FindCustomer}.
+ *
+ * @author George Aristy (george.aristy@gmail.com)
+ * @since 1.17.0
+ */
+public class FindCustomerTest {
+  /**
+   * Returns the given result with no exceptions.
+   * 
+   * @since 1.17.0
+   */
+  @Test
+  public void noExceptions() throws Exception {
+    assertThat(
+        new FindCustomer("123").perform(),
+        is("123")
+    );
+  }
+
+  /**
+   * Throws the given exception.
+   * 
+   * @throws Exception the expected exception
+   * @since 1.17.0
+   */
+  @Test(expected = BusinessException.class)
+  public void oneException() throws Exception {
+    new FindCustomer("123", new BusinessException("test")).perform();
+  }
+
+  /**
+   * Should first throw the given exceptions, then return the given result.
+   * 
+   * @throws Exception not an expected exception
+   * @since 1.17.0
+   */
+  @Test
+  public void resultAfterExceptions() throws Exception {
+    final BusinessOperation<String> op = new FindCustomer(
+        "123", 
+        new CustomerNotFoundException("not found"),
+        new DatabaseNotAvailableException("not available")
+    );
+    try {
+      op.perform();
+    } catch (CustomerNotFoundException e) {
+      //ignore
+    }
+    try {
+      op.perform();
+    } catch (DatabaseNotAvailableException e) {
+      //ignore
+    }
+
+    assertThat(
+        op.perform(),
+        is("123")
+    );
+  }
+}

retry/src/test/java/com/iluwatar/retry/RetryTest.java

@@ -0,0 +1,117 @@
+/*
+ * The MIT License (MIT)
+ * 
+ * Copyright (c) 2014-2016 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.retry;
+
+import static org.hamcrest.CoreMatchers.hasItem;
+import static org.hamcrest.CoreMatchers.is;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ * Unit tests for {@link Retry}.
+ *
+ * @author George Aristy (george.aristy@gmail.com)
+ * @since 1.17.0
+ */
+public class RetryTest {
+  /**
+   * Should contain all errors thrown.
+   * 
+   * @since 1.17.0
+   */
+  @Test
+  public void errors() throws Exception {
+    final BusinessException e = new BusinessException("unhandled");
+    final Retry<String> retry = new Retry<>(
+        () -> { throw e; },
+        2,
+        0
+    );
+    try {
+      retry.perform();
+    } catch (BusinessException ex) {
+      //ignore
+    }
+
+    assertThat(
+        retry.errors(),
+        hasItem(e)
+    );
+  }
+
+  /**
+   * No exceptions will be ignored, hence final number of attempts should be 1 even if we're asking
+   * it to attempt twice.
+   * 
+   * @since 1.17.0
+   */
+  @Test
+  public void attempts() {
+    final BusinessException e = new BusinessException("unhandled");
+    final Retry<String> retry = new Retry<>(
+        () -> { throw e; },
+        2,
+        0
+    );
+    try {
+      retry.perform();
+    } catch (BusinessException ex) {
+      //ignore
+    }
+
+    assertThat(
+        retry.attempts(),
+        is(1)
+    );
+  }
+
+  /**
+   * Final number of attempts should be equal to the number of attempts asked because we are 
+   * asking it to ignore the exception that will be thrown.
+   * 
+   * @since 1.17.0
+   */
+  @Test
+  public void ignore() throws Exception {
+    final BusinessException e = new CustomerNotFoundException("customer not found");
+    final Retry<String> retry = new Retry<>(
+        () -> { throw e; },
+        2,
+        0,
+        ex -> CustomerNotFoundException.class.isAssignableFrom(ex.getClass())
+    );
+    try {
+      retry.perform();
+    } catch (BusinessException ex) {
+      //ignore
+    }
+
+    assertThat(
+        retry.attempts(),
+        is(2)
+    );
+  }
+
+}