FileLock锁定或尝试锁定文件的给定部分。它属于java.nio.channels包，该功能在JDK 1.4以上版本可用。
FileLock用于在共享模式或非共享模式下锁定文件。它有两个重要的方法如下：
FileLock.lock(long position, long size, boolean shared)FileLock.tryLock(long position, long size, boolean shared)
上述方法使用参数作为初始位置，文件大小锁定和一个参数来决定是否共享锁定。
创建文件锁
当使用FileChannel或AsynchronousFileChannel的lock()或tryLock()方法之一获取文件锁时，将创建文件锁定对象。
基本FileLock示例
下面来看看使用专用锁定的通道在文件中写入(附加)的程序(FileLockExample.java)：
package com.yiibai;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.ByteBuffer;
import java.nio.file.Paths;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
public class FileLockExample {
public static void main (String [] args)
throws IOException {
String input = "* end of the file.";
System.out.println("Input string to the test file is: " + input);
ByteBuffer buf = ByteBuffer.wrap(input.getBytes());
String fp = "testout-file.txt";
Path pt = Paths.get(fp);
FileChannel fc = FileChannel.open(pt, StandardOpenOption.WRITE,
StandardOpenOption.APPEND);
System.out.println("File channel is open for write and Acquiring lock...");
fc.position(fc.size() - 1); // position of a cursor at the end of file
FileLock lock = fc.lock();
System.out.println("The Lock is shared: " + lock.isShared());
fc.write(buf);
fc.close(); // Releases the Lock
System.out.println("Content Writing is complete. Therefore close the channel and release the lock.");
PrintFile.print(fp);
}
}
PrintFile.java文件的内容如下 -
package com.yiibai;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
public class PrintFile {
public static void print(String path) throws IOException {
FileReader filereader = new FileReader(path);
BufferedReader bufferedreader = new BufferedReader(filereader);
String tr = bufferedreader.readLine();
System.out.println("The Content of testout-file.txt file is: ");
while (tr != null) {
System.out.println(" " + tr);
tr = bufferedreader.readLine();
}
filereader.close();
bufferedreader.close();
}
}
注意：在运行代码之前，需要创建一个名称为“testout-file.txt”的文本文件，文本文件的内容如下：
Welcome to yiibai.com
This is the example of FileLock in Java NIO channel.
执行上面示例代码，得到以下结果 -
Input string to the test file is: * end of the file.
File channel is open for write and Acquiring lock...
The Lock is shared: false
Content Writing is complete. Therefore close the channel and release the lock.
The Content of testout-file.txt file is:
Welcome to yiibai.com
This is the example of FileLock in Java NIO channel.* end of the file.
