Ensure indexer output is deterministic and repeatable

Closes gh-22383

spring-context-indexer/src/main/java/org/springframework/context/index/processor/PropertiesMarshaller.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,7 +33,7 @@ import java.util.Set;
 abstract class PropertiesMarshaller {
 
 	public static void write(CandidateComponentsMetadata metadata, OutputStream out) throws IOException {
-		Properties props = new Properties();
+		Properties props = new SortedProperties(true);
 		metadata.getItems().forEach(m -> props.put(m.getType(), String.join(",", m.getStereotypes())));
 		props.store(out, "");
 	}

spring-context-indexer/src/main/java/org/springframework/context/index/processor/SortedProperties.java

@@ -0,0 +1,159 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.
+ */
+
+package org.springframework.context.index.processor;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.StringWriter;
+import java.io.Writer;
+import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Enumeration;
+import java.util.Map.Entry;
+import java.util.Properties;
+import java.util.Set;
+import java.util.TreeSet;
+
+/**
+ * Specialization of {@link Properties} that sorts properties alphanumerically
+ * based on their keys.
+ *
+ * <p>This can be useful when storing the {@link Properties} instance in a
+ * properties file, since it allows such files to be generated in a repeatable
+ * manner with consistent ordering of properties.
+ *
+ * <p>Comments in generated properties files can also be optionally omitted.
+ *
+ * @author Sam Brannen
+ * @since 5.2
+ * @see java.util.Properties
+ */
+@SuppressWarnings("serial")
+class SortedProperties extends Properties {
+
+	static final String EOL = System.lineSeparator();
+
+	private static final Comparator<Object> keyComparator = //
+		(key1, key2) -> String.valueOf(key1).compareTo(String.valueOf(key2));
+
+	private static final Comparator<Entry<Object, Object>> entryComparator = //
+		Entry.comparingByKey(keyComparator);
+
+	private final boolean omitComments;
+
+
+	/**
+	 * Construct a new {@code SortedProperties} instance that honors the supplied
+	 * {@code omitComments} flag.
+	 *
+	 * @param omitComments {@code true} if comments should be omitted when
+	 * storing properties in a file
+	 */
+	SortedProperties(boolean omitComments) {
+		this.omitComments = omitComments;
+	}
+
+	/**
+	 * Construct a new {@code SortedProperties} instance with properties populated
+	 * from the supplied {@link Properties} object and honoring the supplied
+	 * {@code omitComments} flag.
+	 *
+	 * <p>Default properties from the supplied {@code Properties} object will
+	 * not be copied.
+	 *
+	 * @param properties the {@code Properties} object from which to copy the
+	 * initial properties
+	 * @param omitComments {@code true} if comments should be omitted when
+	 * storing properties in a file
+	 */
+	SortedProperties(Properties properties, boolean omitComments) {
+		this(omitComments);
+		putAll(properties);
+	}
+
+	@Override
+	public void store(OutputStream out, String comments) throws IOException {
+		ByteArrayOutputStream baos = new ByteArrayOutputStream();
+		super.store(baos, (this.omitComments ? null : comments));
+		String contents = new String(baos.toByteArray(), StandardCharsets.ISO_8859_1);
+		for (String line : contents.split(EOL)) {
+			if (!this.omitComments || !line.startsWith("#")) {
+				out.write((line + EOL).getBytes(StandardCharsets.ISO_8859_1));
+			}
+		}
+	}
+
+	@Override
+	public void store(Writer writer, String comments) throws IOException {
+		StringWriter stringWriter = new StringWriter();
+		super.store(stringWriter, (this.omitComments ? null : comments));
+		String contents = stringWriter.toString();
+		for (String line : contents.split(EOL)) {
+			if (!this.omitComments || !line.startsWith("#")) {
+				writer.write(line + EOL);
+			}
+		}
+	}
+
+	@Override
+	public void storeToXML(OutputStream out, String comments) throws IOException {
+		super.storeToXML(out, (this.omitComments ? null : comments));
+	}
+
+	@Override
+	public void storeToXML(OutputStream out, String comments, String encoding) throws IOException {
+		super.storeToXML(out, (this.omitComments ? null : comments), encoding);
+	}
+
+	/**
+	 * Return a sorted enumeration of the keys in this {@link Properties} object.
+	 * @see #keySet()
+	 */
+	@Override
+	public synchronized Enumeration<Object> keys() {
+		return Collections.enumeration(keySet());
+	}
+
+	/**
+	 * Return a sorted set of the keys in this {@link Properties} object.
+	 * <p>The keys will be converted to strings if necessary using
+	 * {@link String#valueOf(Object)} and sorted alphanumerically according to
+	 * the natural order of strings.
+	 */
+	@Override
+	public Set<Object> keySet() {
+		Set<Object> sortedKeys = new TreeSet<>(keyComparator);
+		sortedKeys.addAll(super.keySet());
+		return Collections.synchronizedSet(sortedKeys);
+	}
+
+	/**
+	 * Return a sorted set of the entries in this {@link Properties} object.
+	 * <p>The entries will be sorted based on their keys, and the keys will be
+	 * converted to strings if necessary using {@link String#valueOf(Object)}
+	 * and compared alphanumerically according to the natural order of strings.
+	 */
+	@Override
+	public Set<Entry<Object, Object>> entrySet() {
+		Set<Entry<Object, Object>> sortedEntries = new TreeSet<>(entryComparator);
+		sortedEntries.addAll(super.entrySet());
+		return Collections.synchronizedSet(sortedEntries);
+	}
+
+}

spring-context-indexer/src/test/java/org/springframework/context/index/processor/PropertiesMarshallerTests.java

@@ -19,6 +19,7 @@ package org.springframework.context.index.processor;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.HashSet;
 
@@ -27,11 +28,11 @@ import org.junit.Test;
 import static org.assertj.core.api.Assertions.assertThat;
 
 
-
 /**
  * Tests for {@link PropertiesMarshaller}.
  *
  * @author Stephane Nicoll
+ * @author Vedran Pavic
  */
 public class PropertiesMarshallerTests {
 
@@ -50,6 +51,19 @@ public class PropertiesMarshallerTests {
 		assertThat(readMetadata.getItems()).hasSize(2);
 	}
 
+	@Test
+	public void metadataIsWrittenDeterministically() throws IOException {
+		CandidateComponentsMetadata metadata = new CandidateComponentsMetadata();
+		metadata.add(createItem("com.b", "type"));
+		metadata.add(createItem("com.c", "type"));
+		metadata.add(createItem("com.a", "type"));
+
+		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+		PropertiesMarshaller.write(metadata, outputStream);
+		String contents = new String(outputStream.toByteArray(), StandardCharsets.ISO_8859_1);
+		assertThat(contents.split(System.lineSeparator())).containsExactly("com.a=type", "com.b=type", "com.c=type");
+	}
+
 	private static ItemMetadata createItem(String type, String... stereotypes) {
 		return new ItemMetadata(type, new HashSet<>(Arrays.asList(stereotypes)));
 	}