[MSHADE-431] Use a caching output stream (#158)

Use a caching output stream to avoid overwriting the file if not needed

Author: gnodet

src/main/java/org/apache/maven/plugins/shade/DefaultShader.java

@@ -22,7 +22,6 @@
 import java.io.BufferedOutputStream;
 import java.io.ByteArrayInputStream;
 import java.io.File;
-import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
@@ -62,6 +61,7 @@
 import org.apache.maven.plugins.shade.resource.ReproducibleResourceTransformer;
 import org.apache.maven.plugins.shade.resource.ResourceTransformer;
 import org.codehaus.plexus.util.IOUtil;
+import org.codehaus.plexus.util.io.CachingOutputStream;
 import org.objectweb.asm.ClassReader;
 import org.objectweb.asm.ClassVisitor;
 import org.objectweb.asm.ClassWriter;
@@ -116,7 +116,8 @@ public void shade( ShadeRequest shadeRequest )
         shadeRequest.getUberJar().getParentFile().mkdirs();
 
         try ( JarOutputStream out  =
-                  new JarOutputStream( new BufferedOutputStream( new FileOutputStream( shadeRequest.getUberJar() ) ) ) )
+                  new JarOutputStream( new BufferedOutputStream(
+                          new CachingOutputStream( shadeRequest.getUberJar() ) ) ) )
         {
             goThroughAllJarEntriesForManifestTransformer( shadeRequest, resources, manifestTransformer, out );
 

src/test/java/org/apache/maven/plugins/shade/DefaultShaderTest.java

@@ -28,6 +28,9 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.attribute.FileTime;
+import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -343,6 +346,44 @@ public void testShaderWithNestedJar() throws Exception
 
         final String innerJarFileName = "inner.jar";
 
+        temporaryFolder.create();
+        File innerJar = temporaryFolder.newFile( innerJarFileName );
+        try ( JarOutputStream jos = new JarOutputStream( Files.newOutputStream( innerJar.toPath() ) ) )
+        {
+            jos.putNextEntry( new JarEntry( "foo.txt" ) );
+            jos.write( "c1".getBytes( StandardCharsets.UTF_8 ) );
+            jos.closeEntry();
+        }
+
+        ShadeRequest shadeRequest = new ShadeRequest();
+        shadeRequest.setJars( new LinkedHashSet<>( Collections.singleton( innerJar ) ) );
+        shadeRequest.setFilters( Collections.emptyList() );
+        shadeRequest.setRelocators( Collections.emptyList() );
+        shadeRequest.setResourceTransformers( Collections.emptyList() );
+        File shadedFile = temporaryFolder.newFile( "shaded.jar" );
+        shadeRequest.setUberJar( shadedFile );
+
+        DefaultShader shader = newShader();
+        shader.shade( shadeRequest );
+
+        FileTime lastModified = FileTime.from( Files.getLastModifiedTime( shadedFile.toPath() ).toInstant()
+                .minus( 5, ChronoUnit.SECONDS ) );
+
+        Files.setLastModifiedTime( shadedFile.toPath(), lastModified );
+
+        shader.shade(shadeRequest);
+        assertEquals( lastModified, Files.getLastModifiedTime( shadedFile.toPath() ) );
+
+        temporaryFolder.delete();
+    }
+
+    @Test
+    public void testShaderNoOverwrite() throws Exception
+    {
+        TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+        final String innerJarFileName = "inner.jar";
+
         temporaryFolder.create();
         File innerJar = temporaryFolder.newFile( innerJarFileName );
         try ( JarOutputStream jos = new JarOutputStream( new FileOutputStream( innerJar ) ) )