实际文件为0字节时，java.io.File.length（）大于0

什么：

/// Where is the directory that we're compressing onto the USB stick?
File dir = new File(Environment.getExternalStorageDirectory(), "logs");
if (!dir.exists() || !dir.isDirectory()) throw new IOException("Invalid directory.");

/// Where on the USB stick is the logs.zip going to go?
File zip = new File("/storage/FD91-1317/logs.zip");

/// Delete the file if it already exists then recreate it 
if (zip.exists() && !zip.delete()) throw new IOException("Failed to create zip file.");
zip.createNewFile();

/// Using try {} to manage our streams
try (FileOutputStream fileOutputStream = new FileOutputStream(zip); ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)) {
    /// Get the list of files to enumerate through
    File[] files = dir.listFiles();

    // Enumerate through each file to be compressed
    for (File file : files) {
        /// If somehow a file was deleted throw an exception
        if (!file.exists()) throw new FileNotFoundException(file.getPath());

        /// Create the new zip entry
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));

        /// Copy the file into the zip
        try (FileInputStream fileInputStream = new FileInputStream(file)) {
            IOUtils.copy(fileInputStream, zipOutputStream);
        }

        /// Close the zip entry
        zipOutputStream.closeEntry();
    }
}

/// Validate that the zip has been created successfully 
if (zip.length() == 0) throw new IOException("Zip failed to be created!!!!");
Log.v("logs", String.format("Logs collected: %s", zip.length());

我的Android应用程序正在根Android设备（API 25+）上压缩一个目录，并将zip写入一个可移动U盘

问题：

/// Where is the directory that we're compressing onto the USB stick?
File dir = new File(Environment.getExternalStorageDirectory(), "logs");
if (!dir.exists() || !dir.isDirectory()) throw new IOException("Invalid directory.");

/// Where on the USB stick is the logs.zip going to go?
File zip = new File("/storage/FD91-1317/logs.zip");

/// Delete the file if it already exists then recreate it 
if (zip.exists() && !zip.delete()) throw new IOException("Failed to create zip file.");
zip.createNewFile();

/// Using try {} to manage our streams
try (FileOutputStream fileOutputStream = new FileOutputStream(zip); ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)) {
    /// Get the list of files to enumerate through
    File[] files = dir.listFiles();

    // Enumerate through each file to be compressed
    for (File file : files) {
        /// If somehow a file was deleted throw an exception
        if (!file.exists()) throw new FileNotFoundException(file.getPath());

        /// Create the new zip entry
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));

        /// Copy the file into the zip
        try (FileInputStream fileInputStream = new FileInputStream(file)) {
            IOUtils.copy(fileInputStream, zipOutputStream);
        }

        /// Close the zip entry
        zipOutputStream.closeEntry();
    }
}

/// Validate that the zip has been created successfully 
if (zip.length() == 0) throw new IOException("Zip failed to be created!!!!");
Log.v("logs", String.format("Logs collected: %s", zip.length());

Java告诉我这个文件是97993字节，但当我从Android设备中取出U盘并将其插入mac时，mac却说是0字节

代码：

/// Where is the directory that we're compressing onto the USB stick?
File dir = new File(Environment.getExternalStorageDirectory(), "logs");
if (!dir.exists() || !dir.isDirectory()) throw new IOException("Invalid directory.");

/// Where on the USB stick is the logs.zip going to go?
File zip = new File("/storage/FD91-1317/logs.zip");

/// Delete the file if it already exists then recreate it 
if (zip.exists() && !zip.delete()) throw new IOException("Failed to create zip file.");
zip.createNewFile();

/// Using try {} to manage our streams
try (FileOutputStream fileOutputStream = new FileOutputStream(zip); ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)) {
    /// Get the list of files to enumerate through
    File[] files = dir.listFiles();

    // Enumerate through each file to be compressed
    for (File file : files) {
        /// If somehow a file was deleted throw an exception
        if (!file.exists()) throw new FileNotFoundException(file.getPath());

        /// Create the new zip entry
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));

        /// Copy the file into the zip
        try (FileInputStream fileInputStream = new FileInputStream(file)) {
            IOUtils.copy(fileInputStream, zipOutputStream);
        }

        /// Close the zip entry
        zipOutputStream.closeEntry();
    }
}

/// Validate that the zip has been created successfully 
if (zip.length() == 0) throw new IOException("Zip failed to be created!!!!");
Log.v("logs", String.format("Logs collected: %s", zip.length());

更多信息：

/// Where is the directory that we're compressing onto the USB stick?
File dir = new File(Environment.getExternalStorageDirectory(), "logs");
if (!dir.exists() || !dir.isDirectory()) throw new IOException("Invalid directory.");

/// Where on the USB stick is the logs.zip going to go?
File zip = new File("/storage/FD91-1317/logs.zip");

/// Delete the file if it already exists then recreate it 
if (zip.exists() && !zip.delete()) throw new IOException("Failed to create zip file.");
zip.createNewFile();

/// Using try {} to manage our streams
try (FileOutputStream fileOutputStream = new FileOutputStream(zip); ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)) {
    /// Get the list of files to enumerate through
    File[] files = dir.listFiles();

    // Enumerate through each file to be compressed
    for (File file : files) {
        /// If somehow a file was deleted throw an exception
        if (!file.exists()) throw new FileNotFoundException(file.getPath());

        /// Create the new zip entry
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));

        /// Copy the file into the zip
        try (FileInputStream fileInputStream = new FileInputStream(file)) {
            IOUtils.copy(fileInputStream, zipOutputStream);
        }

        /// Close the zip entry
        zipOutputStream.closeEntry();
    }
}

/// Validate that the zip has been created successfully 
if (zip.length() == 0) throw new IOException("Zip failed to be created!!!!");
Log.v("logs", String.format("Logs collected: %s", zip.length());

• 我的应用程序作为系统应用程序运行在

  /system/priv-app/

  目录中
• 我的应用程序具有android.permission.WRITE\u MEDIA\u STORAGE权限
• 如果我在调用

  Log.v（…）

  后的5-10秒内取出U盘，插入mac时U盘上的zip文件仅为0字节。如果我等待的时间超过10秒，它将总是有字节

• Log.v（…）

  也在记录收集的日志：97993

• org.apache.commons.io.FileUtils.readFileToByteArray（zip）

  还返回一个长度为97993的字节数组，该字节数组100%包含数据，并且不是空的

• ls-l/storage/FD91-1317也表示
  logs.zip
  是97993字节

结束：

/// Where is the directory that we're compressing onto the USB stick?
File dir = new File(Environment.getExternalStorageDirectory(), "logs");
if (!dir.exists() || !dir.isDirectory()) throw new IOException("Invalid directory.");

/// Where on the USB stick is the logs.zip going to go?
File zip = new File("/storage/FD91-1317/logs.zip");

/// Delete the file if it already exists then recreate it 
if (zip.exists() && !zip.delete()) throw new IOException("Failed to create zip file.");
zip.createNewFile();

/// Using try {} to manage our streams
try (FileOutputStream fileOutputStream = new FileOutputStream(zip); ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)) {
    /// Get the list of files to enumerate through
    File[] files = dir.listFiles();

    // Enumerate through each file to be compressed
    for (File file : files) {
        /// If somehow a file was deleted throw an exception
        if (!file.exists()) throw new FileNotFoundException(file.getPath());

        /// Create the new zip entry
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));

        /// Copy the file into the zip
        try (FileInputStream fileInputStream = new FileInputStream(file)) {
            IOUtils.copy(fileInputStream, zipOutputStream);
        }

        /// Close the zip entry
        zipOutputStream.closeEntry();
    }
}

/// Validate that the zip has been created successfully 
if (zip.length() == 0) throw new IOException("Zip failed to be created!!!!");
Log.v("logs", String.format("Logs collected: %s", zip.length());

---

我已经尝试了我能想到的一切，但仍然不明白为什么Java说zip包含数据，但当插入我的mac时，它说文件是0字节。Windows也在告诉我同样的事情。我所知道的唯一事实是，如果我在从Android设备上移除USB之前等待超过10秒，那么这个问题就不会发生，但我担心，根据拉链的大小，在所有情况下，这可能都不够时间。据我所知，一旦你写一个流并关闭它，它应该是100%完成

为了解决这个问题，我必须运行

fileOutputStream.getFD（）.sync（）

如果有人想知道为什么运行that会修复它，这里有一个来自Java文档的片段来解释什么是
sync（）可以


有关更多详细信息，请参阅


非常感谢@commonware的帮助
 在资源试用的底部，调用
zipOutputStream.flush（）
和
fileOutputStream.getFD（）.sync（）。看看这是否有帮助。“据我所知，一旦你写入一个流并关闭它，它应该100%完成”——而不是使用写缓冲文件系统。这就是
getFD（）.sync（）
发挥作用的地方。在封面下，它执行POSIX
fsync（）
调用，以确保所有字节都写入磁盘。@commonware我尝试了
flush（）
，但没有
getFD（）.sync（）
。我马上就去试试！谢谢你的建议☺️