文件操作
Determining If a File or Directory Existsboolean exists = (new File("filename")).exists();
if (exists) {
// File or directory exists
} else {
// File or directory does not exist
}
Creating a File
try {
File file = new File("filename");
// Create file if it does not exist
boolean success = file.createNewFile();
if (success) {
// File did not exist and was created
} else {
// File already exists
}
} catch (IOException e) {
}
Copying One File to Another
This example uses file streams to copy the contents of one file to another file.
// Copies src file to dst file.
// If the dst file does not exist, it is created
void copy(File src, File dst) throws IOException {
InputStream in = new FileInputStream(src);
OutputStream out = new FileOutputStream(dst);
// Transfer bytes from in to out
byte[] buf = new byte;
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
in.close();
out.close();
}
Getting the Size of a File
File file = new File("infilename");
// Get the number of bytes in the file
long length = file.length();
Deleting a File
boolean success = (new File("filename")).delete();
if (!success) {
// Deletion failed
}
Creating a Temporary File
try {
// Create temp file.
File temp = File.createTempFile("pattern", ".suffix");
// Delete temp file when program exits.
temp.deleteOnExit();
// Write to temp file
BufferedWriter out = new BufferedWriter(new FileWriter(temp));
out.write("aString");
out.close();
} catch (IOException e) {
}
Renaming a File or Directory
// File (or directory) with old name
File file = new File("oldname");
// File (or directory) with new name
File file2 = new File("newname");
// Rename file (or directory)
boolean success = file.renameTo(file2);
if (!success) {
// File was not successfully renamed
}
Moving a File or Directory to Another Directory
// File (or directory) to be moved
File file = new File("filename");
// Destination directory
File dir = new File("directoryname");
// Move file to new directory
boolean success = file.renameTo(new File(dir, file.getName()));
if (!success) {
// File was not successfully moved
}
Getting and Setting the Modification Time of a File or Directory
This example gets the last modified time of a file or directory and then sets it to the current time.
File file = new File("filename");
// Get the last modified time
long modifiedTime = file.lastModified();
// 0L is returned if the file does not exist
// Set the last modified time
long newModifiedTime = System.currentTimeMillis();
boolean success = file.setLastModified(newModifiedTime);
if (!success) {
// operation failed.
}
Forcing Updates to a File to the Disk
In some applications, such as transaction processing, it is necessary to ensure that an update has been made to the disk. FileDescriptor.sync() blocks until all changes to a file are written to disk.
try {
// Open or create the output file
FileOutputStream os = new FileOutputStream("outfilename");
FileDescriptor fd = os.getFD();
// Write some data to the stream
byte[] data = new byte[]{(byte)0xCA, (byte)0xFE, (byte)0xBA, (byte)0xBE};
os.write(data);
// Flush the data from the streams and writers into system buffers.
// The data may or may not be written to disk.
os.flush();
// Block until the system buffers have been written to disk.
// After this method returns, the data is guaranteed to have
// been written to disk.
fd.sync();
} catch (IOException e) {
}
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