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

@@ -19,11 +19,11 @@
  * under the License.
  */
 
-class ExpansionBuffer
+abstract class ExpansionBuffer
 {
     private final StringBuilder resolved = new StringBuilder();
 
-    private String unresolved;
+    protected String unresolved;
 
     public ExpansionBuffer( String unresolved )
     {
@@ -37,18 +37,7 @@ 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()
     {
@@ -82,18 +71,18 @@ 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 );
@@ -105,9 +94,5 @@ 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

@@ -38,19 +38,40 @@ 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 );
 
@@ -60,7 +81,7 @@ 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 );
 
@@ -76,6 +97,12 @@ private String fromPropertiesThenSystemThenEnvironment( String key, Properties p
             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

@@ -85,7 +85,7 @@ public void setFiles( File[] files )
 
     /**
      * Default scope for test access.
-     * 
+     *
      * @param urls The URLs to set for tests.
      */
     public void setUrls( String[] urls )
@@ -122,6 +122,14 @@ public void setKeyPrefix( String keyPrefix )
     @Parameter( defaultValue = "false", property = "prop.skipLoadProperties" )
     private boolean skipLoadProperties;
 
+    /**
+     * If the plugin should process default values within property placeholders
+     *
+     * @parameter default-value="false"
+     */
+    @Parameter( defaultValue = "false" )
+    private boolean useDefaultValues;
+
     /**
      * Used for resolving property placeholders.
      */
@@ -278,7 +286,7 @@ private String getPropertyValue( String k, Properties p, Properties environment
     {
         try
         {
-            return resolver.getPropertyValue( k, p, environment );
+            return resolver.getPropertyValue( k, p, environment , useDefaultValues);
         }
         catch ( IllegalArgumentException e )
         {
@@ -288,7 +296,7 @@ private String getPropertyValue( String k, Properties p, Properties environment
 
     /**
      * Override-able for test purposes.
-     * 
+     *
      * @return The shell environment variables, can be empty but never <code>null</code>.
      * @throws IOException If the environment variables could not be queried from the shell.
      */
@@ -300,7 +308,7 @@ Properties getSystemEnvVars()
 
     /**
      * Default scope for test access.
-     * 
+     *
      * @param quiet Set to <code>true</code> if missing files can be skipped.
      */
     void setQuiet( boolean quiet )
@@ -317,16 +325,32 @@ void setSkipLoadProperties( boolean skipLoadProperties )
         this.skipLoadProperties = skipLoadProperties;
     }
 
+    /**
+     * @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.
      */
     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;