Optimize VirtualZipDataBlock

Add some optimizations to `VirtualZipDataBlock` that help when
sequentially reading the block from a JarInputStream.

Closes gh-40125

Author: philwebb

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/zip/VirtualDataBlock.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -19,7 +19,6 @@
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.Collection;
-import java.util.List;
 
 /**
  * A virtual {@link DataBlock} build from a collection of other {@link DataBlock}
@@ -29,10 +28,14 @@
  */
 class VirtualDataBlock implements DataBlock {
 
-	private List<DataBlock> parts;
+	private DataBlock[] parts;
+
+	private long[] offsets;
 
 	private long size;
 
+	private volatile int lastReadPart = 0;
+
 	/**
 	 * Create a new {@link VirtualDataBlock} instance. The {@link #setParts(Collection)}
 	 * method must be called before the data block can be used.
@@ -55,12 +58,16 @@ protected VirtualDataBlock() {
 	 * @throws IOException on I/O error
 	 */
 	protected void setParts(Collection<? extends DataBlock> parts) throws IOException {
-		this.parts = List.copyOf(parts);
+		this.parts = parts.toArray(DataBlock[]::new);
+		this.offsets = new long[parts.size()];
 		long size = 0;
+		int i = 0;
 		for (DataBlock part : parts) {
+			this.offsets[i++] = size;
 			size += part.size();
 		}
 		this.size = size;
+
 	}
 
 	@Override
@@ -73,20 +80,30 @@ public int read(ByteBuffer dst, long pos) throws IOException {
 		if (pos < 0 || pos >= this.size) {
 			return -1;
 		}
+		int lastReadPart = this.lastReadPart;
+		int partIndex = 0;
 		long offset = 0;
 		int result = 0;
-		for (DataBlock part : this.parts) {
+		if (pos >= this.offsets[lastReadPart]) {
+			partIndex = lastReadPart;
+			offset = this.offsets[lastReadPart];
+		}
+		while (partIndex < this.parts.length) {
+			DataBlock part = this.parts[partIndex];
 			while (pos >= offset && pos < offset + part.size()) {
 				int count = part.read(dst, pos - offset);
 				result += Math.max(count, 0);
 				if (count <= 0 || !dst.hasRemaining()) {
+					this.lastReadPart = partIndex;
 					return result;
 				}
 				pos += count;
 			}
 			offset += part.size();
+			partIndex++;
 		}
 		return result;
+
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/zip/VirtualZipDataBlock.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -76,12 +76,13 @@ private long addToCentral(List<DataBlock> parts, ZipCentralDirectoryFileHeaderRe
 			.withOffsetToLocalHeader(offsetToLocalHeader);
 		int originalExtraFieldLength = Short.toUnsignedInt(originalRecord.extraFieldLength());
 		int originalFileCommentLength = Short.toUnsignedInt(originalRecord.fileCommentLength());
-		DataBlock extraFieldAndComment = new DataPart(
-				originalRecordPos + originalRecord.size() - originalExtraFieldLength - originalFileCommentLength,
-				originalExtraFieldLength + originalFileCommentLength);
+		int extraFieldAndCommentSize = originalExtraFieldLength + originalFileCommentLength;
 		parts.add(new ByteArrayDataBlock(record.asByteArray()));
 		parts.add(name);
-		parts.add(extraFieldAndComment);
+		if (extraFieldAndCommentSize > 0) {
+			parts.add(new DataPart(originalRecordPos + originalRecord.size() - extraFieldAndCommentSize,
+					extraFieldAndCommentSize));
+		}
 		return record.size();
 	}
 
@@ -93,7 +94,9 @@ private long addToLocal(List<DataBlock> parts, ZipCentralDirectoryFileHeaderReco
 		int extraFieldLength = Short.toUnsignedInt(originalRecord.extraFieldLength());
 		parts.add(new ByteArrayDataBlock(record.asByteArray()));
 		parts.add(name);
-		parts.add(new DataPart(originalRecordPos + originalRecord.size() - extraFieldLength, extraFieldLength));
+		if (extraFieldLength > 0) {
+			parts.add(new DataPart(originalRecordPos + originalRecord.size() - extraFieldLength, extraFieldLength));
+		}
 		parts.add(content);
 		if (dataDescriptorRecord != null) {
 			parts.add(new ByteArrayDataBlock(dataDescriptorRecord.asByteArray()));

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/zip/VirtualZipPerformanceTests.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2012-2024 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.boot.loader.zip;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Path;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+import java.util.zip.ZipOutputStream;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Performance tests for {@link ZipContent} that creates a {@link VirtualZipDataBlock}.
+ *
+ * @author Phillip Webb
+ */
+@Disabled("Only used for manual testing")
+public class VirtualZipPerformanceTests {
+
+	@TempDir
+	Path temp;
+
+	@Test
+	void sequentialReadPerformace() throws IOException {
+		File file = createZipWithLargeEntries();
+		long start = System.nanoTime();
+		try (ZipContent zipContent = ZipContent.open(file.toPath(), "test/")) {
+			try (InputStream in = zipContent.openRawZipData().asInputStream()) {
+				ZipInputStream zip = new ZipInputStream(in);
+				ZipEntry entry = zip.getNextEntry();
+				while (entry != null) {
+					entry = zip.getNextEntry();
+				}
+			}
+		}
+		System.out.println(TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start));
+	}
+
+	private File createZipWithLargeEntries() throws IOException {
+		byte[] bytes = new byte[1024 * 1024];
+		new Random().nextBytes(bytes);
+		File file = this.temp.resolve("test.zip").toFile();
+		try (ZipOutputStream out = new ZipOutputStream(new FileOutputStream(file))) {
+			out.putNextEntry(new ZipEntry("test/"));
+			out.closeEntry();
+			for (int i = 0; i < 50; i++) {
+				out.putNextEntry(new ZipEntry("test/" + i + ".dat"));
+				out.write(bytes);
+				out.closeEntry();
+			}
+		}
+		return file;
+	}
+
+}