[MNG-6801] MavenXpp3Writer doesn't retain order of properties (#811)

maven-model/src/main/mdo/reader-ex.vm

@@ -41,6 +41,7 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -273,7 +274,7 @@ public class ${className}
                     ${classLcapName}.${field.name}( ${field.name} );
                     break;
       #elseif ( $field.type == "java.util.Properties" && $field.to == "String" && $field.multiplicity == "*" )
-                    Map<String, String> ${field.name} = new HashMap<>();
+                    Map<String, String> ${field.name} = new LinkedHashMap<>();
                     locations = new HashMap<>();
                     while ( parser.nextTag() == XmlPullParser.START_TAG )
                     {

maven-model/src/main/mdo/reader.vm

@@ -41,6 +41,7 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -297,7 +298,7 @@ public class ${className}
                     ${classLcapName}.${field.name}( ${field.name} );
                     break;
       #elseif ( $field.type == "java.util.Properties" && $field.to == "String" && $field.multiplicity == "*" )
-                    Map<String, String> ${field.name} = new HashMap<>();
+                    Map<String, String> ${field.name} = new LinkedHashMap<>();
                     while ( parser.nextTag() == XmlPullParser.START_TAG )
                     {
                         String key = parser.getName();

maven-model/src/test/java/org/apache/maven/model/v4/ModelXmlTest.java

@@ -0,0 +1,69 @@
+package org.apache.maven.model.v4;
+
+/*
+ * 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.
+ */
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.apache.maven.api.model.Model;
+import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ModelXmlTest
+{
+
+    @Test
+    public void testXmlRoundtripWithProperties() throws Exception
+    {
+        Map<String, String> props = new LinkedHashMap<>();
+        props.put( "javax.version", "3.1.0" );
+        props.put( "mockito.version", "1.10.19" );
+        props.put( "hamcret.version", "2.1" );
+        props.put( "lombok.version", "1.18.6" );
+        props.put( "junit.version", "4.12" );
+        Model model = Model.newBuilder( true )
+                .properties( props )
+                .build();
+        String xml = toXml( model );
+
+        for ( int i = 0; i < 10; i++ )
+        {
+            String newStr = toXml( fromXml( xml ) );
+            assertEquals( newStr, xml );
+        }
+    }
+
+    String toXml( Model model ) throws IOException
+    {
+        StringWriter sw = new StringWriter();
+        new MavenXpp3Writer().write( sw, model );
+        return sw.toString();
+    }
+
+    Model fromXml( String xml ) throws IOException, XmlPullParserException
+    {
+        return new MavenXpp3Reader().read( new StringReader( xml ) );
+    }
+}

maven-settings/src/main/mdo/reader.vm

@@ -41,6 +41,7 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -771,7 +772,7 @@ public class ${className}
                     ${classLcapName}.${field.name}( ${field.name} );
                     break;
       #elseif ( $field.type == "java.util.Properties" && $field.to == "String" && $field.multiplicity == "*" )
-                    Map<String, String> ${field.name} = new HashMap<>();
+                    Map<String, String> ${field.name} = new LinkedHashMap<>();
                     while ( parser.nextTag() == XmlPullParser.START_TAG )
                     {
                         String key = parser.getName();

maven-toolchain-model/src/main/mdo/reader.vm

@@ -41,6 +41,7 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -771,7 +772,7 @@ public class ${className}
                     ${classLcapName}.${field.name}( ${field.name} );
                     break;
       #elseif ( $field.type == "java.util.Properties" && $field.to == "String" && $field.multiplicity == "*" )
-                    Map<String, String> ${field.name} = new HashMap<>();
+                    Map<String, String> ${field.name} = new LinkedHashMap<>();
                     while ( parser.nextTag() == XmlPullParser.START_TAG )
                     {
                         String key = parser.getName();