我在将代码从Linux（Ubuntu LTS 12.4）环境移植到Windows Server 2008的过程中遇到了一个问题。
我需要使用内存映射文件，但我无法阻止Windows下面的错误。
此问题在以下单元测试中重现。这两项测试在Linux上取得了成功，但在Windows上测试 testWithRandowmAccessFile 失败，底部有堆栈跟踪。
testWithRandowmAccessFile 测试失败的根本原因是什么？
我该如何在Windows上实现它？
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
import org.apache.commons.io.IOUtils;
import org.junit.Test;
public class TestIOOnWindows {
@Test
public void testWithRandowmAccessFile() throws IOException {
final File sourceFile = new File("source.txt");
final File manipulatedFile = new File("manipulated.txt");
final File targetFile = new File("target.txt");
try
(
FileInputStream sourceInputStream = new FileInputStream(sourceFile);
RandomAccessFile manipulated = new RandomAccessFile(manipulatedFile, "rw");
FileChannel fcOut = manipulated.getChannel()
)
{
byte[] sourceBytes = new byte[Long.valueOf(sourceFile.length()).intValue()];
IOUtils.read(sourceInputStream, sourceBytes);
final int length = sourceBytes.length;
// ========= with this single line on Windows, the move fails ======
MappedByteBuffer byteBuffer = fcOut.map(FileChannel.MapMode.READ_WRITE, 0, length);
// commenting this line would not prevent the error on Windows
byteBuffer.put(sourceBytes, 0, length);
}
Files.move(
Paths.get(manipulatedFile.getAbsolutePath()),
Paths.get(targetFile.getAbsolutePath()),
StandardCopyOption.REPLACE_EXISTING);
}
@Test
public void testWithFileOutputStream() throws IOException {
final File sourceFile = new File("source.txt");
final File manipulatedFile = new File("manipulated.txt");
final File targetFile = new File("target.txt");
try
(
FileInputStream sourceInputStream = new FileInputStream(sourceFile);
FileOutputStream manipulatedOutputStream = new FileOutputStream(manipulatedFile);
FileChannel fcIn = sourceInputStream.getChannel();
FileChannel fcOut = manipulatedOutputStream.getChannel()
)
{
final long length = sourceFile.length();
// ========= with this single line on Windows, the move succeed ====
fcIn.transferTo(0, length, fcOut);
}
Files.move(
Paths.get(manipulatedFile.getAbsolutePath()),
Paths.get(targetFile.getAbsolutePath()),
StandardCopyOption.REPLACE_EXISTING);
}
}
添加在Windows上从命令提示符运行单元测试时得到的粘性跟踪。
There was 1 failure:
1) testWithRandowmAccessFile(TestIOOnWindows) java.nio.file.FileSystemException: C:\Users\Administrator\AppData\Local\Temp\manipulated.txt -> C:\Users\Administrator\AppData\Local\Temp\target.txt: The process cannot access the file because it is being used by another process.
at sun.nio.fs.WindowsException.translateToIOException(Unknown Source)
at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
at sun.nio.fs.WindowsFileCopy.move(Unknown Source)
at sun.nio.fs.WindowsFileSystemProvider.move(Unknown Source)
at java.nio.file.Files.move(Unknown Source)
===> at TestIOOnWindows.testWithRandowmAccessFile(TestIOOnWindows.java:40) <===
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:24)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
at org.junit.runner.JUnitCore.run(JUnitCore.java:136)
at org.junit.runner.JUnitCore.run(JUnitCore.java:117)
at org.junit.runner.JUnitCore.runMain(JUnitCore.java:98)
at org.junit.runner.JUnitCore.runMainAndExit(JUnitCore.java:53)
at org.junit.runner.JUnitCore.main(JUnitCore.java:45)
FAILURES!!!
Tests run: 2, Failures: 1
答案 0 :(得分：2)
在Java中，文件映射是垃圾收集的，并且没有强制销毁映射的支持方法。
来自FileChannel.map()文档：
缓冲区及其表示的映射将一直有效，直到 缓冲区本身是垃圾收集。
映射一旦建立，就不依赖于文件通道 那是用来创造它的。特别是关闭频道 对映射的有效性没有影响。
在Sun的JDK中，您可以通过在执行文件移动之前强行销毁映射来测试这确实是罪魁祸首：
import sun.nio.ch.DirectBuffer;
import sun.misc.Cleaner;
[...]
if (byteBuffer.isDirect()) {
Cleaner cleaner = ((DirectBuffer) byteBuffer).cleaner();
cleaner.clean();
}
// move file
答案 1 :(得分：1)
错误消息说明了一切。 Windows无法像任何Unix一样删除或重命名打开的文件，而您正在打开workFile，然后立即尝试重命名它。你必须先关闭流。