JAVA多线程读写文件如何做到线程安全？（文件锁，FileChannel）

文章目录

NIO提升性能
多线程读写同一个文件有哪些场景需要同步处理？
使用对文件加锁的方式做到线程安全
写文件线程安全
读文件线程安全
小编写的IOListener接口，用于回调
小编写的IOUtils工具类，专门用于文件读写，流的读写
写文件使用示例
读文件使用示例
欢迎联系、指正、批评

NIO提升性能

在JAVA的标准I/O中，提供了基于流的I/O实现，即InputStream和OutputStream。这种基于流的实现以字节为单位处理数据。NIO是New I/O的简称，表示一套新的JAVA I/O标准。在Jdk 1.4中开始引入，它具有以下特性：

为所有的原始类型提供（Buffer）缓存支持；

使用Java.nio.charset.Charset作为字符集编码解码解决方案；

增加通道（Cahnnel）对象，作为新的原始I/O抽象；

支持锁和内存映射文件的文件访问接口；

提供了基于Selector的异步网络I/O。

与流式的I/O不容，NIO是基于块（Block）的，它以块为基本单位处理数据。在NIO中，最为重要的2个组件是缓冲Buffer和通道Channel。缓冲是一块连续的内存块，是NIO读写数据的中转地。通道表示缓冲数据的源头或者目的地，它用于向缓冲读取或者写入数据，是访问缓冲的接口。

多线程读写同一个文件有哪些场景需要同步处理？

有线程正在读文件，另开辟线程写文件；
有线程正在写文件，另开辟线程读文件；
有线程正在写文件，另开辟线程写文件

总之，读写互斥，写读互斥，写写互斥，只有读读相容（可以异步）。

使用对文件加锁的方式做到线程安全

FileInputStream、FileOutputStream、RandomAccessFile均可得到FileChannel对象，对文件锁进行操作。
独占锁tryLock()

FileChannel的tryLock()是非阻塞的，也就是说，在发现文件被锁住的时候，直接返回null，并且抛出异常，如果没有锁住，直接返回该文件的文件锁。
它是独占锁，就是只能被一个线程持有，它能禁止其他线程获取共享锁，可用于写文件。

  while (true) {try {fileLock = fileChannel.tryLock();//独占锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}

共享锁tryLock(0, Long.MAX_VALUE, true)

FileChannel的tryLock(0, Long.MAX_VALUE, true)是非阻塞的，在发现文件被锁住的时候，直接返回null，并且抛出异常，如果没有锁住，直接返回该文件的文件锁。
它是共享锁，能被多个线程同时持有，它能禁止其他线程获取独占锁，可用于读文件。

while (true) {try {fileLock = fileChannel.tryLock(0, Long.MAX_VALUE, true);//共享锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}

独占锁lock()

而FileChannel的lock()是阻塞的，在文件被锁定的情况下，会保持阻塞，直到获得该锁为止。

fileLock = fileChannel.lock();

写文件线程安全

 /*** 将str写入文件,同步操作,独占锁*/public void writeStr2ReplaceFileSync(String str, String pathFile, IOListener ioListener) {File file;try {file = FileUtils.createFile(pathFile);} catch (IOException e) {e.printStackTrace();ioListener.onFail("文件创建失败，请检查路径是否合法以及读写权限");return;}FileOutputStream fileOutputStream = null;FileChannel fileChannel = null;FileLock fileLock = null;//文件锁try {/*** 写文件*/fileOutputStream = new FileOutputStream(file);fileChannel = fileOutputStream.getChannel();while (true) {try {fileLock = fileChannel.tryLock();//独占锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}if (fileLock != null) {int len = 0;long current = file.length();if (isRunning ) {fileChannel.write(ByteBuffer.wrap(str.getBytes()));current += len;LogUtils.log("当前线程" + Thread.currentThread().getName());ioListener.onLoading(str.getBytes(), current, str.length());}else {//中断ioListener.onInterrupted();}if (fileLock != null && fileLock.isValid()) {LogUtils.log("release-write-lock");fileLock.release();}close(fileChannel);close(fileOutputStream);if (file.length() == str.getBytes().length) {ioListener.onCompleted(file);}}} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {}}

读文件线程安全

  /*** 同步读取，共享锁，但无法同时进行写操作** @param ioListener*/public void read2StrSync(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;FileChannel fileChannel = null;FileLock fileLock = null;//文件锁ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();try {/*** 读文件*/fileInputStream = new FileInputStream(pathFile);fileChannel = fileInputStream.getChannel();while (true) {try {fileLock = fileChannel.tryLock(0, Long.MAX_VALUE, true);//共享锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}if (fileLock != null) {ByteBuffer byteBuffer = ByteBuffer.allocate(1024);int len = 0;long current = 0;while (isRunning && (len = fileChannel.read(byteBuffer)) != -1) {//0,byteBuffer.position()，必须写这个，否则GG，读取文件错乱byteArrayOutputStream.write(byteBuffer.array(),0,byteBuffer.position());current += len;ioListener.onLoading("", current, fileChannel.size());byteBuffer.clear();}if (fileLock != null && fileLock.isValid()) {LogUtils.log("release-read-lock");fileLock.release();}close(fileChannel);close(fileInputStream);//中断if (len != -1) {ioListener.onInterrupted();} else {ioListener.onCompleted(byteArrayOutputStream.toString("utf-8"));}}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {}}

小编写的IOListener接口，用于回调

public interface IOListener<T> {public void onCompleted(T result);public void onLoading(T readedPart, long current, long length);public void onInterrupted();public void onFail(String errorMsg);
}

小编写的IOUtils工具类，专门用于文件读写，流的读写

public class IOUtils {private boolean isRunning = true;private long contentLength = 0;private String encodeType = "utf-8";public IOUtils() {isRunning = true;}public IOUtils setContentLength(long contentLength) {this.contentLength = contentLength;return this;}public IOUtils setEncodeType(String encodeType) {this.encodeType = encodeType;return this;}public static void close(Closeable closeable) {if (closeable != null) {try {closeable.close();} catch (IOException e) {e.printStackTrace();}}}public void stop() {this.isRunning = false;}public void read(boolean isLine, InputStream inputStream, IOListener ioListener) {if (isLine) {readLine2String(inputStream, ioListener);} else {read2String(inputStream, ioListener);}}/*** @param ioListener*/public void read2String(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;try {fileInputStream = new FileInputStream(pathFile);} catch (FileNotFoundException e) {e.printStackTrace();ioListener.onFail(e.getMessage());return;}read2String(fileInputStream, ioListener);}public void read2String(InputStream inputStream, IOListener ioListener) {if (!(inputStream instanceof BufferedInputStream)) {inputStream = new BufferedInputStream(inputStream);}BufferedReader bufferedReader = null;InputStreamReader inputStreamReader = null;try {inputStreamReader = new InputStreamReader(inputStream, encodeType);bufferedReader = new BufferedReader(inputStreamReader);StringBuilder sb = new StringBuilder();char[] buf = new char[1024];int len = 0;long current = 0;while (isRunning && (len = bufferedReader.read(buf)) != -1) {sb.append(buf, 0, len);current += len;ioListener.onLoading("", current, contentLength);}//中断if (len != -1) {ioListener.onInterrupted();} else {ioListener.onCompleted(sb.toString());}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {close(bufferedReader);close(inputStreamReader);close(inputStream);}}/*** 同步读取，共享锁，但无法同时进行写操作** @param ioListener*/public void read2StrSync(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;FileChannel fileChannel = null;FileLock fileLock = null;//文件锁ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();try {/*** 读文件*/fileInputStream = new FileInputStream(pathFile);fileChannel = fileInputStream.getChannel();while (true) {try {fileLock = fileChannel.tryLock(0, Long.MAX_VALUE, true);//共享锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}if (fileLock != null) {ByteBuffer byteBuffer = ByteBuffer.allocate(1024);int len = 0;long current = 0;while (isRunning && (len = fileChannel.read(byteBuffer)) != -1) {//0,byteBuffer.position()，必须写这个，否则GG，读取文件错乱byteArrayOutputStream.write(byteBuffer.array(),0,byteBuffer.position());current += len;ioListener.onLoading("", current, fileChannel.size());byteBuffer.clear();}if (fileLock != null && fileLock.isValid()) {LogUtils.log("release-read-lock");fileLock.release();}close(fileChannel);close(fileInputStream);//中断if (len != -1) {ioListener.onInterrupted();} else {ioListener.onCompleted(byteArrayOutputStream.toString("utf-8"));}}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {}}/*** @param ioListener*/public void readLine2String(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;try {fileInputStream = new FileInputStream(pathFile);} catch (FileNotFoundException e) {e.printStackTrace();ioListener.onFail(e.getMessage());return;}readLine2String(fileInputStream, ioListener);}/*** 一行一行地读** @param inputStream* @param ioListener*/public void readLine2String(InputStream inputStream, IOListener ioListener) {BufferedReader bufferedReader = null;InputStreamReader inputStreamReader = null;try {inputStreamReader = new InputStreamReader(inputStream, encodeType);bufferedReader = new BufferedReader(inputStreamReader);StringBuilder sb = new StringBuilder();long current = 0;String str;while (isRunning && (str = bufferedReader.readLine()) != null) {sb.append(str);current += str.length();ioListener.onLoading(str, current, contentLength);}//中断if ((str = bufferedReader.readLine()) != null) {ioListener.onInterrupted();} else {ioListener.onCompleted(sb.toString());}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {close(bufferedReader);close(inputStreamReader);close(inputStream);}}public void readL2StrNoBuffer(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;try {fileInputStream = new FileInputStream(pathFile);} catch (FileNotFoundException e) {e.printStackTrace();ioListener.onFail(e.getMessage());return;}readL2StrNoBuffer(fileInputStream, ioListener);}/*** 一行一行地读，不拼接** @param inputStream* @param ioListener*/public void readL2StrNoBuffer(InputStream inputStream, IOListener ioListener) {BufferedReader bufferedReader = null;InputStreamReader inputStreamReader = null;try {inputStreamReader = new InputStreamReader(inputStream, encodeType);bufferedReader = new BufferedReader(inputStreamReader);long current = 0;String str;while (isRunning && (str = bufferedReader.readLine()) != null) {current += str.length();ioListener.onLoading(str, current, contentLength);}//中断if ((str = bufferedReader.readLine()) != null) {ioListener.onInterrupted();} else {ioListener.onCompleted("");}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {close(bufferedReader);close(inputStreamReader);close(inputStream);}}public void readL_N2String(String pathFile, IOListener ioListener) {FileInputStream fileInputStream = null;try {fileInputStream = new FileInputStream(pathFile);} catch (FileNotFoundException e) {e.printStackTrace();ioListener.onFail(e.getMessage());return;}readL_N2String(fileInputStream, ioListener);}/*** 一行一行地读，\n拼接** @param inputStream* @param ioListener*/public void readL_N2String(InputStream inputStream, IOListener ioListener) {BufferedReader bufferedReader = null;InputStreamReader inputStreamReader = null;try {inputStreamReader = new InputStreamReader(inputStream, encodeType);bufferedReader = new BufferedReader(inputStreamReader);StringBuilder sb = new StringBuilder();long current = 0;String str;while (isRunning && (str = bufferedReader.readLine()) != null) {sb.append(str);sb.append("\n");current += str.length();ioListener.onLoading(str, current, contentLength);}//中断if ((str = bufferedReader.readLine()) != null) {ioListener.onInterrupted();} else {ioListener.onCompleted(sb.toString());}} catch (UnsupportedEncodingException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {close(bufferedReader);close(inputStreamReader);close(inputStream);}}/*** 读取到文件** @param inputStream* @param outputStream* @param ioListener*/public void read2File(InputStream inputStream, OutputStream outputStream, IOListener ioListener) {try {byte[] buffer = new byte[1024];int len = 0;long current = 0;while (isRunning && (len = inputStream.read(buffer)) != -1) {outputStream.write(buffer, 0, len);current += len;ioListener.onLoading(new String(buffer), current, contentLength);}outputStream.flush();//中断if (len != -1) {ioListener.onInterrupted();} else {ioListener.onCompleted(null);}} catch (IOException e) {e.printStackTrace();} finally {close(outputStream);close(inputStream);}}/*** 将str写入文件*/public void writeStr2File(String str, String pathFile, IOListener ioListener) {BufferedWriter bufferedWriter = null;OutputStreamWriter outputStreamWriter = null;OutputStream outputStream = null;try {outputStream = new FileOutputStream(pathFile);outputStreamWriter = new OutputStreamWriter(outputStream);bufferedWriter = new BufferedWriter(outputStreamWriter);bufferedWriter.write(str);ioListener.onCompleted("");} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {close(bufferedWriter);close(outputStreamWriter);close(outputStream);}}/*** 将str写入文件,同步操作,独占锁*/public void writeStr2ReplaceFileSync(String str, String pathFile, IOListener ioListener) {File file;try {file = FileUtils.createFile(pathFile);} catch (IOException e) {e.printStackTrace();ioListener.onFail("文件创建失败，请检查路径是否合法以及读写权限");return;}FileOutputStream fileOutputStream = null;FileChannel fileChannel = null;FileLock fileLock = null;//文件锁try {/*** 写文件*/fileOutputStream = new FileOutputStream(file);fileChannel = fileOutputStream.getChannel();while (true) {try {fileLock = fileChannel.tryLock();//独占锁break;} catch (Exception e) {System.out.println("有其他线程正在操作该文件，当前线程" + Thread.currentThread().getName());}}if (fileLock != null) {int len = 0;long current = file.length();if (isRunning ) {fileChannel.write(ByteBuffer.wrap(str.getBytes()));current += len;LogUtils.log("当前线程" + Thread.currentThread().getName());ioListener.onLoading(str.getBytes(), current, str.length());}else {//中断ioListener.onInterrupted();}if (fileLock != null && fileLock.isValid()) {LogUtils.log("release-write-lock");fileLock.release();}close(fileChannel);close(fileOutputStream);if (file.length() == str.getBytes().length) {ioListener.onCompleted(file);}}} catch (IOException e) {e.printStackTrace();ioListener.onFail(e.getMessage());} finally {}}}

写文件使用示例

 new IOUtils().writeStr2ReplaceFileSync(jsonObjectOld.toJSONString(), Constants.PATH_GAME_JSON, new IOListener() {@Overridepublic void onCompleted(Object result) {}@Overridepublic void onLoading(Object readedPart, long current, long length) {}@Overridepublic void onInterrupted() {}@Overridepublic void onFail(String errorMsg) {}});

读文件使用示例

new IOUtils().read2StrSync(Constants.PATH_CONFIG_APPLICATION_JSON, new IOListener<String>() {@Overridepublic void onCompleted(String result) {}@Overridepublic void onLoading(String readedPart, long current, long length) {}@Overridepublic void onInterrupted() {}@Overridepublic void onFail(String errorMsg) {}});

欢迎联系、指正、批评

Github:https://github.com/AnJiaoDe

CSDN：https://blog.csdn.net/confusing_awakening

OpenCV入门教程：https://blog.csdn.net/confusing_awakening/article/details/113372425

ffmpeg入门教程:https://blog.csdn.net/confusing_awakening/article/details/102007792

微信公众号

QQ群