Avoid overwriting descriptors if the content is the same

plexus-component-metadata/src/main/java/org/codehaus/plexus/metadata/CachingWriter.java

@@ -0,0 +1,56 @@
+package org.codehaus.plexus.metadata;
+
+/*
+ * Copyright (c) 2022, Codehaus.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute,
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
+ * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class CachingWriter extends StringWriter
+{
+    private final Path path;
+    private final Charset charset;
+
+    public CachingWriter( Path path, Charset charset )
+    {
+        this.path = Objects.requireNonNull( path );
+        this.charset = Objects.requireNonNull( charset );
+    }
+
+    @Override
+    public void close() throws IOException
+    {
+        byte[] data = getBuffer().toString().getBytes( charset );
+        if ( Files.exists( path ) && Files.size( path ) == data.length )
+        {
+            byte[] ba = Files.readAllBytes( path );
+            if ( Arrays.equals( data, ba ) )
+            {
+                return;
+            }
+        }
+        Files.write( path, data );
+    }
+
+}

plexus-component-metadata/src/main/java/org/codehaus/plexus/metadata/DefaultMetadataGenerator.java

@@ -25,6 +25,8 @@
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -185,7 +187,7 @@ private void writeDescriptor( ComponentSetDescriptor desc, File outputFile )
 
         FileUtils.forceMkdir( outputFile.getParentFile() );
 
-        BufferedWriter output = new BufferedWriter( new OutputStreamWriter( new FileOutputStream( outputFile ), "UTF-8" ) );
+        Writer output = new CachingWriter( outputFile.toPath(), StandardCharsets.UTF_8 );
 
         try
         {

plexus-component-metadata/src/main/java/org/codehaus/plexus/metadata/merge/AbstractMerger.java

@@ -26,8 +26,10 @@
 import java.io.IOException;
 import java.io.OutputStreamWriter;
 import java.io.Writer;
+import java.nio.charset.StandardCharsets;
 import java.util.List;
 
+import org.codehaus.plexus.metadata.CachingWriter;
 import org.codehaus.plexus.util.IOUtil;
 import org.jdom2.Document;
 import org.jdom2.JDOMException;
@@ -61,7 +63,7 @@ public void writeMergedDocument( Document mergedDocument, File file )
         Writer fw = null;
         try
         {
-            fw = new OutputStreamWriter( new FileOutputStream( file ), "UTF-8" );
+            fw = new CachingWriter( file.toPath(), StandardCharsets.UTF_8 );
             out.output( mergedDocument, fw );
         }
         finally