password generator added

SVN: 3817

common/source/java/ch/systemsx/cisd/common/utilities/PasswordGenerator.java

+/*
+ * Copyright 2008 ETH Zuerich, CISD
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package ch.systemsx.cisd.common.utilities;
+
+import java.util.Random;
+
+/**
+ * Generator for human pronounceable passwords
+ *
+ * @author Franz-Josef Elmer
+ */
+public class PasswordGenerator
+{
+    private enum State
+    {
+        DIGIT()
+        {
+            @Override
+            State nextState(Random random)
+            {
+                return random.nextBoolean() ? CONSONANT : VOWEL;
+            }
+
+            @Override
+            String getCharacters()
+            {
+                return "0123456789";
+            }
+        },
+        
+        CONSONANT()
+        {
+            @Override
+            State nextState(Random random)
+            {
+                return random.nextBoolean() ? DIGIT : VOWEL;
+            }
+
+            @Override
+            String getCharacters()
+            {
+                return "bdcfghjklmnpqrstvwxzBCDFGHJKLMNPQRSTVWXZ";
+            }
+            
+        },
+        
+        VOWEL()
+        {
+            @Override
+            State nextState(Random random)
+            {
+                return random.nextBoolean() ? CONSONANT : DIGIT;
+            }
+
+            @Override
+            String getCharacters()
+            {
+                return "aeiouyAEIOUY";
+            }
+        };
+        
+        State nextState(Random random)
+        {
+            return this;
+        }
+        
+        void appendCharacterTo(StringBuilder builder, Random random)
+        {
+            String characters = getCharacters();
+            builder.append(characters.charAt(random.nextInt(characters.length())));
+        }
+        
+        abstract String getCharacters();
+    }
+    
+    private final Random random;
+    
+    /**
+     * Creates an instance based on the default constructor of {@link Random}.
+     */
+    public PasswordGenerator()
+    {
+        this(new Random());
+    }
+
+    /**
+     * Creates an instance which uses the specified random number generator.
+     */
+    public PasswordGenerator(Random random)
+    {
+        assert random != null : "Unspecified random number generator.";
+        this.random = random;
+    }
+    
+    /**
+     * Creates a password of specified length.
+     */
+    public String generatePassword(int length)
+    {
+        State state = State.DIGIT;
+        StringBuilder builder = new StringBuilder();
+        for (int i = 0; i < length; i++)
+        {
+            state = state.nextState(random);
+            state.appendCharacterTo(builder, random);
+        }
+        return builder.toString();
+    }
+}