Accept default value in placeholders for unresolved property values

src/main/java/org/codehaus/mojo/properties/DefaultValuesAwareExpansionBufferImpl.java

@@ -0,0 +1,72 @@
+package org.codehaus.mojo.properties;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/**
+ * ExpansionBuffer implementation that allows processing of default values within property placeholders
+ *
+ * @author tdiamantis
+ */
+public class DefaultValuesAwareExpansionBufferImpl extends ExpansionBuffer {
+    public DefaultValuesAwareExpansionBufferImpl(String unresolved) {
+        super(unresolved);
+    }
+
+    public KeyAndDefaultValue extractPropertyKeyAndDefaultValue()
+    {
+        advanceToNextPrefix();
+
+        discardPrefix();
+
+        String key = beforeNextSuffix();
+
+        String defaultValue = defaultValue();
+
+        discardToAfterNextSuffix();
+
+        return new KeyAndDefaultValue(key, defaultValue);
+    }
+
+    protected String beforeNextSuffix()
+    {
+        int defValuePos = unresolved.indexOf(":");
+        int propertySuffixPos = unresolved.indexOf("}");
+
+        //check default value separator only if before next suffix
+        if (defValuePos != -1 && propertySuffixPos != -1 && defValuePos < propertySuffixPos)
+        {
+            return unresolved.substring( 0, defValuePos );
+        }
+
+        return unresolved.substring( 0, propertySuffixPos );
+    }
+
+    private String defaultValue()
+    {
+        int defValuePos = unresolved.indexOf( ":" );
+        int propertySuffixPos = unresolved.indexOf( "}" );
+        if (defValuePos != -1 && propertySuffixPos != -1 && (defValuePos+1) < propertySuffixPos)
+        {
+            return unresolved.substring( defValuePos+1, propertySuffixPos );
+        }
+
+        return null;
+    }
+}

src/main/java/org/codehaus/mojo/properties/ExpansionBuffer.java

@@ -19,7 +19,7 @@
  * under the License.
  */
 
-class ExpansionBuffer
+abstract class ExpansionBuffer
 {
     public final StringBuilder resolved = new StringBuilder();
     public String unresolved;
@@ -35,18 +35,7 @@ public boolean hasMoreLegalPlaceholders()
         return prefixPos >= 0 && suffixPos >= 0;
     }
 
-    public String extractPropertyKey()
-    {
-        advanceToNextPrefix();
-
-        discardPrefix();
-
-        String key = beforeNextSuffix();
-
-        discardToAfterNextSuffix();
-
-        return key;
-    }
+    public abstract KeyAndDefaultValue extractPropertyKeyAndDefaultValue();
 
     public String toString() {
         return resolved.append(unresolved).toString();
@@ -79,16 +68,16 @@ private void skipUnresolvedPlaceholder(String newKey)
         resolved.append( "${" ).append(newKey).append( "}" );
     }
 
-    private void discardToAfterNextSuffix() {
+    protected void discardToAfterNextSuffix() {
         int propertySuffixPos = unresolved.indexOf( "}" );
         unresolved = unresolved.substring(propertySuffixPos + 1);
     }
 
-    private void advanceToNextPrefix() {
+    protected void advanceToNextPrefix() {
         resolved.append( beforePrefix() );
     }
 
-    private void discardPrefix() {
+    protected void discardPrefix() {
         int propertyPrefixPos = unresolved.indexOf( "${" );
         unresolved = unresolved.substring(propertyPrefixPos + 2);
     }
@@ -99,9 +88,5 @@ private String beforePrefix()
         return unresolved.substring( 0, propertyPrefixPos );
     }
 
-    private String beforeNextSuffix()
-    {
-        int propertySuffixPos = unresolved.indexOf( "}" );
-        return unresolved.substring( 0, propertySuffixPos );
-    }
+    protected abstract String beforeNextSuffix();
 }

src/main/java/org/codehaus/mojo/properties/ExpansionBufferImpl.java

@@ -0,0 +1,50 @@
+package org.codehaus.mojo.properties;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/**
+ * Default implementation of the ExpansionBuffer class
+ *
+ * @author tdiamantis
+ */
+public class ExpansionBufferImpl extends ExpansionBuffer {
+    public ExpansionBufferImpl(String unresolved) {
+        super(unresolved);
+    }
+
+    public KeyAndDefaultValue extractPropertyKeyAndDefaultValue()
+    {
+        advanceToNextPrefix();
+
+        discardPrefix();
+
+        String key = beforeNextSuffix();
+
+        discardToAfterNextSuffix();
+
+        return new KeyAndDefaultValue(key, null);
+    }
+
+    protected String beforeNextSuffix()
+    {
+        int propertySuffixPos = unresolved.indexOf( "}" );
+        return unresolved.substring( 0, propertySuffixPos );
+    }
+}

src/main/java/org/codehaus/mojo/properties/KeyAndDefaultValue.java

@@ -0,0 +1,49 @@
+package org.codehaus.mojo.properties;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/**
+ * @author tdiamantis
+ */
+public class KeyAndDefaultValue {
+    private String key;
+    private String defaultValue;
+
+    public KeyAndDefaultValue(String key, String defaultValue) {
+        this.key = key;
+        this.defaultValue = defaultValue;
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public void setKey(String key) {
+        this.key = key;
+    }
+
+    public String getDefaultValue() {
+        return defaultValue;
+    }
+
+    public void setDefaultValue(String defaultValue) {
+        this.defaultValue = defaultValue;
+    }
+}

src/main/java/org/codehaus/mojo/properties/PropertyResolver.java

@@ -40,19 +40,40 @@ class PropertyResolver {
      * @return resolved property value
      * @throws IllegalArgumentException when properties are circularly defined
      */
-    public String getPropertyValue( String key, Properties properties, Properties environment )
+    public String getPropertyValue( String key, Properties properties, Properties environment ) {
+        return getPropertyValue(key, properties, environment, false);
+    }
+
+    /**
+     * Same as the previous method. Accepts an extra flag to indicate whether default values should be
+     * processed within property placeholders or not.
+     *
+     * @param key           property key
+     * @param properties           project properties
+     * @param environment environment variables
+     * @param useDefaultValues    process default values flag
+     * @return resolved property value
+     * @throws IllegalArgumentException when properties are circularly defined
+     */
+    public String getPropertyValue( String key, Properties properties, Properties environment, boolean useDefaultValues )
     {
         String value = properties.getProperty(key);
 
-        ExpansionBuffer buffer = new ExpansionBuffer(value);
+        ExpansionBuffer buffer;
+        if ( useDefaultValues ) {
+            buffer = new DefaultValuesAwareExpansionBufferImpl(value);
+        } else {
+            buffer = new ExpansionBufferImpl(value);
+        }
 
         CircularDefinitionPreventer circularDefinitionPreventer =
                 new CircularDefinitionPreventer().visited( key, value);
 
         while ( buffer.hasMoreLegalPlaceholders() )
         {
-            String newKey = buffer.extractPropertyKey();
-            String newValue = fromPropertiesThenSystemThenEnvironment( newKey, properties, environment );
+            KeyAndDefaultValue kv = buffer.extractPropertyKeyAndDefaultValue();
+            String newKey = kv.getKey();
+            String newValue = fromPropertiesThenSystemThenEnvironment( newKey, kv.getDefaultValue(), properties, environment );
 
             circularDefinitionPreventer.visited(newKey, newValue);
 
@@ -62,7 +83,7 @@ public String getPropertyValue( String key, Properties properties, Properties en
         return buffer.toString();
     }
 
-    private String fromPropertiesThenSystemThenEnvironment(String key, Properties properties, Properties environment)
+    private String fromPropertiesThenSystemThenEnvironment(String key, String defaultValue, Properties properties, Properties environment)
     {
         String value = properties.getProperty( key );
 
@@ -78,6 +99,12 @@ private String fromPropertiesThenSystemThenEnvironment(String key, Properties pr
             value = environment.getProperty( key.substring( 4 ) );
         }
 
+        // try default value
+        if ( value == null )
+        {
+            value = defaultValue;
+        }
+
         return value;
     }
 }

src/main/java/org/codehaus/mojo/properties/ReadPropertiesMojo.java

@@ -108,6 +108,13 @@ public void setUrls(String[] urls)
      */
     private boolean quiet;
 
+    /**
+     * If the plugin should process default values within property placeholders
+     *
+     * @parameter default-value="false"
+     */
+    private boolean useDefaultValues;
+
     /**
      * Used for resolving property placeholders.
      */
@@ -246,7 +253,7 @@ private Properties loadSystemEnvironmentPropertiesWhenDefined() throws MojoExecu
     private String getPropertyValue( String k, Properties p, Properties environment ) throws MojoFailureException
     {
         try {
-            return resolver.getPropertyValue(k, p, environment);
+            return resolver.getPropertyValue(k, p, environment, useDefaultValues);
         } catch (IllegalArgumentException e) {
             throw new MojoFailureException(e.getMessage());
         }
@@ -270,6 +277,14 @@ void setQuiet(boolean quiet)
         this.quiet = quiet;
     }
 
+    /**
+     * @param useDefaultValues set to <code>true</code> if default values need to be processed within property placeholders
+     */
+    public void setUseDefaultValues(boolean useDefaultValues)
+    {
+        this.useDefaultValues = useDefaultValues;
+    }
+
     /**
      * Default scope for test access.
      * @param project The test project.
@@ -279,6 +294,14 @@ void setProject(MavenProject project)
         this.project = project;
     }
 
+    /**
+     * For test access.
+     * @return The test project
+     */
+    public MavenProject getProject() {
+        return project;
+    }
+
     private static abstract class Resource
     {
         private InputStream stream;