fixes #181: Support dependency ordering

src/it/projects/order-dependency-simple/pom.xml

@@ -0,0 +1,33 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.codehaus.mojo.flatten.its</groupId>
+    <artifactId>flatten-dependency-all-simple</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.codehaus.mojo.flatten.its</groupId>
+            <artifactId>dep</artifactId>
+            <version>1.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.mojo.flatten.its</groupId>
+            <artifactId>test</artifactId>
+            <version>2.0</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <defaultGoal>verify</defaultGoal>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>flatten-maven-plugin</artifactId>
+                <configuration>
+                    <orderDependencies>true</orderDependencies>
+                    <flattenDependencyMode>all</flattenDependencyMode>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

src/it/projects/order-dependency-simple/verify.groovy

@@ -0,0 +1,29 @@
+/*
+ * 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.
+ */
+File flattendPom = new File( basedir, '.flattened-pom.xml' )
+assert flattendPom.exists()
+
+def flattendProject = new XmlSlurper().parse( flattendPom )
+assert 1 ==  flattendProject.dependencies.size()
+assert 2 ==  flattendProject.dependencies.dependency.size()
+
+assert "dep" == flattendProject.dependencies.dependency[0].artifactId.text()
+assert "test" == flattendProject.dependencies.dependency[1].artifactId.text()
+
+

src/main/java/org/codehaus/mojo/flatten/DependencyComparator.java

@@ -0,0 +1,23 @@
+package org.codehaus.mojo.flatten;
+
+import org.apache.maven.model.Dependency;
+
+import java.util.Comparator;
+
+/**
+ * Orders a {@link Dependency} through its groupId and artifactId.
+ */
+public class DependencyComparator implements Comparator<Dependency>
+{
+    @Override
+    public int compare( Dependency o1, Dependency o2 )
+    {
+        int c = o1.getGroupId().compareTo( o2.getGroupId() );
+        if ( c == 0 )
+        {
+            // Same groupId
+            c = o1.getArtifactId().compareTo( o2.getArtifactId() );
+        }
+        return c;
+    }
+}

src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java

@@ -295,7 +295,7 @@ public class FlattenMojo
      * </tr>
      * <tr>
      * <td>resolveCiFriendliesOnly</td>
-     * <td>Only resolves variables revision, sha1 and changelist. Keeps everything else. 
+     * <td>Only resolves variables revision, sha1 and changelist. Keeps everything else.
      * See <a href="https://maven.apache.org/maven-ci-friendly.html">Maven CI Friendly</a> for further details.</td>
      * </tr>
      * </tbody>
@@ -329,6 +329,12 @@ public class FlattenMojo
     @Parameter( property = "flatten.dependency.mode", required = false )
     private FlattenDependencyMode flattenDependencyMode;
 
+    /**
+     * Order dependencies by their groupId and artifactId after they are flattened
+     */
+    @Parameter( defaultValue = "false" )
+    private boolean orderDependencies;
+
     /**
      * The ArtifactFactory required to resolve POM using {@link #modelBuilder}.
      */
@@ -341,7 +347,7 @@ public class FlattenMojo
      */
     @Component( role = ModelInterpolator.class )
     private ModelInterpolator modelInterpolator;
-    
+
     /**
      * The {@link ModelInterpolator} used to resolve variables.
      */
@@ -387,6 +393,11 @@ public void execute()
         Model flattenedPom = createFlattenedPom( originalPomFile );
         String headerComment = extractHeaderComment( originalPomFile );
 
+        if ( orderDependencies )
+        {
+            Collections.sort( flattenedPom.getDependencies(), new DependencyComparator() );
+        }
+
         File flattenedPomFile = getFlattenedPomFile();
         writePom( flattenedPom, flattenedPomFile, headerComment );
 

src/test/java/org/codehaus/mojo/flatten/DependencyComparatorTest.java

@@ -0,0 +1,38 @@
+package org.codehaus.mojo.flatten;
+
+import org.apache.maven.model.Dependency;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DependencyComparatorTest
+{
+    private final DependencyComparator comparator = new DependencyComparator();
+
+    @Test
+    public void shouldOrder()
+    {
+        List<Dependency> dependencies = new ArrayList<>();
+        dependencies.add( createDependency( "g", "b", "1" ) );
+        dependencies.add( createDependency( "g", "a", "1" ) );
+        dependencies.add( createDependency( "g", "c", "1" ) );
+        Collections.sort( dependencies, comparator );
+        assertThat( dependencies ).usingComparatorForType( comparator, Dependency.class ).containsExactly(
+                createDependency( "g", "a", "1" ),
+                createDependency( "g", "b", "1" ),
+                createDependency( "g", "c", "1" ) );
+    }
+
+    private Dependency createDependency( String groupId, String artifactId, String version )
+    {
+        Dependency dependency = new Dependency();
+        dependency.setGroupId( groupId );
+        dependency.setArtifactId( artifactId );
+        dependency.setVersion( version );
+        return dependency;
+    }
+}