java文件序列化_通过快速Java和文件序列化加快速度

java文件序列化

从Java的第一个版本开始，许多开发人员每天都在努力实现至少与C / C ++一样好的性能。 JVM供应商正在通过实现一些新的JIT算法来尽力而为，但仍有许多工作要做，尤其是在我们如何使用Java方面。

例如，对象<->文件序列化有很多优势，尤其是在写入/读取可以轻松放入内存的对象方面。我将尝试阐明该主题。

所有测试都在下面显示的简单对象上执行：

public class TestObject implements Serializable {private long longVariable;private long[] longArray;private String stringObject;private String secondStringObject; //just for testing nulls/* getters and setters */
}

为了更简洁，我将仅显示write方法（尽管另一种方法也非常相似）。完整的源代码可在我的GitHub（http://github.com/jkubrynski/serialization-tests）上找到。

最标准的Java序列化（我们都从这里开始）如下所示：

public void testWriteBuffered(TestObject test, String fileName) throws IOException {ObjectOutputStream objectOutputStream = null;try {FileOutputStream fos = new FileOutputStream(fileName);BufferedOutputStream bos = new BufferedOutputStream(fos);objectOutputStream = new ObjectOutputStream(bos);objectOutputStream.writeObject(test);} finally {if (objectOutputStream != null) {objectOutputStream.close();}}
}

加快标准序列化的最简单方法是使用RandomAccessFile对象：

public void testWriteBuffered(TestObject test, String fileName) throws IOException {ObjectOutputStream objectOutputStream = null;try {RandomAccessFile raf = new RandomAccessFile(fileName, "rw");FileOutputStream fos = new FileOutputStream(raf.getFD());objectOutputStream = new ObjectOutputStream(fos);objectOutputStream.writeObject(test);} finally {if (objectOutputStream != null) {objectOutputStream.close();}      
}

更复杂的技术是使用Kryo框架。新旧版本之间的差异很大。我都检查了。因为性能比较没有发现任何明显的不同，所以我将重点介绍第二个版本，因为它更加用户友好，甚至更快。

private static Kryo kryo = new Kryo(); // version 2.xpublic void testWriteBuffered(TestObject test, String fileName) throws IOException {Output output = null;try {RandomAccessFile raf = new RandomAccessFile(fileName, "rw");output = new Output(new FileOutputStream(raf.getFD()), MAX_BUFFER_SIZE);kryo.writeObject(output, test);} finally {if (output != null) {output.close();}}
}

最后一个选择是受Martin Thompson文章启发的解决方案。它显示了如何以C ++方式和Java处理内存

public void testWriteBuffered(TestObject test, String fileName) throws IOException {RandomAccessFile raf = null;try {MemoryBuffer memoryBuffer = new MemoryBuffer(MAX_BUFFER_SIZE);raf = new RandomAccessFile(fileName, "rw");test.write(memoryBuffer);raf.write(memoryBuffer.getBuffer());} catch (IOException e) {if (raf != null) {raf.close();}}
}

TestObject的写入方法如下所示：

public void write(MemoryBuffer unsafeBuffer) {unsafeBuffer.putLong(longVariable);unsafeBuffer.putLongArray(longArray);// we support nullsboolean objectExists = stringObject != null;unsafeBuffer.putBoolean(objectExists);if (objectExists) {unsafeBuffer.putCharArray(stringObject.toCharArray());}objectExists = secondStringObject != null;unsafeBuffer.putBoolean(objectExists);if (objectExists) {unsafeBuffer.putCharArray(secondStringObject.toCharArray());}
}

直接内存缓冲区类（简称，只是为了展示这个主意）：

public class MemoryBuffer {// getting Unsafe by reflectionpublic static final Unsafe unsafe = UnsafeUtil.getUnsafe();private final byte[] buffer;private static final long byteArrayOffset = unsafe.arrayBaseOffset(byte[].class);private static final long longArrayOffset = unsafe.arrayBaseOffset(long[].class);// other offsets private static final int SIZE_OF_LONG = 8;// other sizes private long pos = 0;public MemoryBuffer(int bufferSize) {this.buffer = new byte[bufferSize];}public final byte[] getBuffer() {return buffer;}public final void putLong(long value) {unsafe.putLong(buffer, byteArrayOffset + pos, value);pos += SIZE_OF_LONG;}public final long getLong() {long result = unsafe.getLong(buffer, byteArrayOffset + pos);pos += SIZE_OF_LONG;return result;}public final void putLongArray(final long[] values) {putInt(values.length);long bytesToCopy = values.length << 3;unsafe.copyMemory(values, longArrayOffset, buffer, byteArrayOffset + pos, bytesToCopy);pos += bytesToCopy;}public final long[] getLongArray() {int arraySize = getInt();long[] values = new long[arraySize];long bytesToCopy = values.length << 3;unsafe.copyMemory(buffer, byteArrayOffset + pos, values, longArrayOffset, bytesToCopy);pos += bytesToCopy;return values;}/* other methods */
}

卡尺运行多个小时的结果如下所示：