Java NIO通道中的FileLock

2025 年 3 月 22 日 | 阅读需 2 分钟

FileLock锁定或尝试锁定文件的指定部分。它属于java.nio.channels包，该功能在Java 1.4及更高版本中可用。

FileLock用于以共享模式或非共享模式锁定文件。它有两个重要方法，如下所示：

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、要锁定的文件大小以及一个附加参数来决定锁是否为共享锁。

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，将创建文件锁对象。

基本的FileLock示例

让我们看看使用通道和独占锁写入（追加）文件的程序：

FileLockExample.java

package com.Tpointtech;
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 = "D:\\testout.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

package com.Tpointtech;
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.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，需要创建一个名为"testout.txt"的文本文件，文本文件内容如下：

欢迎来到Tpointtech.com

这是Java NIO通道中FileLock的示例。

输出

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.txt file is: 
    Welcome to Tpointtech.com
    This is the example of FileLock in Java NIO channel.
    * end of the file.

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