java实现文件拷贝的七种方式

1. 通过字节流实现文件的拷贝

 /**
   * 通过字节流实现文件的拷贝
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByStream(String sourcePath,String targetPath){
    //源文件路径
    File source = new File(sourcePath);
    //目标文件路径
    File target = new File(targetPath);

    //如果源文件不存在则不能拷贝
    if(!source.exists()){
      return;
    }
    //如果目标文件目录不存在则创建
    if(!target.getParentFile().exists()){
      target.getParentFile().mkdirs();
    }

    try {
      //实现文件的拷贝
      InputStream inputStream = new FileInputStream(source);
      OutputStream outputStream = new FileOutputStream(target);
      int temp = 0;
      //每次读取1024个字节
      byte[] data = new byte[1024];
      //将每次读取的数据保存到字节数组里面，并且返回读取的个数
      while ((temp = inputStream.read(data)) != -1){
        //输出数组
        outputStream.write(data,0,temp);
      }

      inputStream.close();
      outputStream.close();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

2. 通过字符流实现文件拷贝

使用字符流只能拷贝文本文件

  /**
   * 通过字符流实现文件的拷贝
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByReaderAndWriter(String sourcePath, String targetPath) {
    //源文件路径
    File source = new File(sourcePath);
    //目标文件路径
    File target = new File(targetPath);

    //如果源文件不存在则不能拷贝
    if (!source.exists()) {
      return;
    }
    //如果目标文件目录不存在则创建
    if (!target.getParentFile().exists()) {
      target.getParentFile().mkdirs();
    }

    FileReader in = null;
    FileWriter out = null;
    try {
      //字符输入流和字符输出流
      in = new FileReader(source);
      out = new FileWriter(target);

      char[] c = new char[1024];
      int temp = 0;
      //每次读取1024个字符
      while ((temp = in.read(c)) != -1) {
        //输出到文件
        out.write(c, 0, temp);
      }
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      //关闭流
      try {
        if (in != null) {
          in.close();
        }
        if (out != null) {
          out.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

3. 通过字节缓冲流实现文件拷贝

/**
   * 通过字节缓冲流实现文件的拷贝
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByBuffered(String sourcePath, String targetPath){
    //源文件路径
    File source = new File(sourcePath);
    //目标文件路径
    File target = new File(targetPath);

    //如果源文件不存在则不能拷贝
    if (!source.exists()) {
      return;
    }
    //如果目标文件目录不存在则创建
    if (!target.getParentFile().exists()) {
      target.getParentFile().mkdirs();
    }

    InputStream in = null;
    OutputStream out = null;
    try {
      //字节缓冲输入流和字节缓冲输出流
      in = new BufferedInputStream(new FileInputStream(source));
      out = new BufferedOutputStream(new FileOutputStream(target));

      byte[] b = new byte[1024];
      int temp = 0;
      //每次读取一个1024的字节数组
      while((temp = in.read(b)) != -1){
        //输出到文件
        out.write(b,0,temp);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }finally {
      //关闭流
      try {
        if (in != null) {
          in.close();
        }
        if (out != null) {
          out.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

4. 通过字符缓冲流拷贝文件

字符缓冲流只能读取文本文件

 /**
   * 通过字符缓冲流实现文件的拷贝
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByBufferedChar(String sourcePath, String targetPath){
    //源文件路径
    File source = new File(sourcePath);
    //目标文件路径
    File target = new File(targetPath);

    //如果源文件不存在则不能拷贝
    if (!source.exists()) {
      return;
    }
    //如果目标文件目录不存在则创建
    if (!target.getParentFile().exists()) {
      target.getParentFile().mkdirs();
    }

    BufferedReader in = null;
    BufferedWriter out = null;

    try {
      //字符缓冲输入流和字符缓冲输出流
      in = new BufferedReader(new FileReader(source));
      out = new BufferedWriter(new FileWriter(target));

      //读取文件（每次读取一行）
      String temp = null;
      while((temp = in.readLine()) != null){
        //输出到文件
        out.write(temp);
      }

    } catch (Exception e) {
      e.printStackTrace();
    }finally {
      //关闭流
      try {
        if (in != null) {
          in.close();
        }
        if (out != null) {
          out.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

5. 通过JAVA NIO 非直接缓冲区拷贝文件

  /**
   * 通过JAVA NIO 非直接缓冲区拷贝文件
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByChannel(String sourcePath, String targetPath) {
    FileChannel outChannel = null;
    FileChannel inChannel = null;

    FileInputStream fis = null;
    FileOutputStream fos = null;

    try {
      fis = new FileInputStream(sourcePath);
      fos = new FileOutputStream(targetPath);

      //获取通道
      inChannel = fis.getChannel();
      outChannel = fos.getChannel();

      //分配指定大小的缓冲区
      ByteBuffer buf = ByteBuffer.allocate(1024);

      while (inChannel.read(buf) != -1) {
        //转换为读取数据模式
        buf.flip();
        //写入到磁盘
        outChannel.write(buf);
        //清空缓冲区
        buf.clear();
      }

    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      //关闭流
      try {
        if (outChannel != null) {
          outChannel.close();
        }
        if (inChannel != null) {
          inChannel.close();
        }
        if (fis != null) {
          fis.close();
        }
        if (fos != null) {
          fos.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

6. 通过JAVA NIO 直接缓冲区拷贝文件

/**
   * 通过JAVA NIO 直接缓冲区拷贝文件（内存映射文件）
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByChannelBufferd(String sourcePath, String targetPath) {
    FileChannel inChannel = null;
    FileChannel outChannel = null;
    try {
      //获取通道,StandardOpenOption.READ表示可读，StandardOpenOption.WRITE表示可写，StandardOpenOption.CREATE表示可以创建
      inChannel = FileChannel.open(Paths.get(sourcePath), StandardOpenOption.READ);
      outChannel = FileChannel.open(Paths.get(targetPath), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);

      //创建内存映射文件
      MappedByteBuffer inMapped = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
      MappedByteBuffer outMapped = outChannel.map(FileChannel.MapMode.READ_WRITE, 0, inChannel.size());

      //直接操作内存映射文件
      byte[] buf = new byte[inMapped.limit()];
      inMapped.get(buf);
      outMapped.put(buf);

    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      //关闭流
      try {
        if (outChannel != null) {
          outChannel.close();
        }
        if (inChannel != null) {
          inChannel.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

7. 通过JAVA NIO 通道传输拷贝文件

方式一

 /**
   * 通过JAVA NIO 通道传输拷贝文件
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByChannelTransfer(String sourcePath, String targetPath) {
    FileChannel inChannel = null;
    FileChannel outChannel = null;
    try {
      //获取通道
      inChannel = FileChannel.open(Paths.get(sourcePath), StandardOpenOption.READ);
      outChannel = FileChannel.open(Paths.get(targetPath),StandardOpenOption.WRITE,StandardOpenOption.READ,StandardOpenOption.CREATE);

      inChannel.transferTo(0,inChannel.size(),outChannel);
    } catch (IOException e) {
      e.printStackTrace();
    }finally {
      //关闭流
      try {
        if (outChannel != null) {
          outChannel.close();
        }
        if (inChannel != null) {
          inChannel.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

方式二

 /**
   * 通过JAVA NIO 通道传输拷贝文件
   *
   * @param sourcePath 源文件路径
   * @param targetPath 目标文件路径
   */
  public static void copyFileByChannelTransfer2(String sourcePath, String targetPath) {
    FileInputStream fis = null;
    FileOutputStream fos = null;
    FileChannel inChannel = null;
    FileChannel outChannel = null;
    try {
      fis = new FileInputStream(sourcePath);
      fos = new FileOutputStream(targetPath);

      //获取通道
      inChannel = fis.getChannel();
      outChannel = fos.getChannel();

      inChannel.transferTo(0,inChannel.size(),outChannel);
    } catch (IOException e) {
      e.printStackTrace();
    }finally {
      //关闭流
      try {
        if (outChannel != null) {
          outChannel.close();
        }
        if (inChannel != null) {
          inChannel.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }

使用示例

    String source = "e:\\demo\\纵天神帝.txt";
    String target = "e:\\demo\\";
    long time1 = System.currentTimeMillis();
    copyFileByStream(source, target + "1.txt");
    System.out.println("通过字节流实现文件的拷贝耗时：" + (System.currentTimeMillis() - time1));

    long time2 = System.currentTimeMillis();
    copyFileByReaderAndWriter(source, target + "2.txt");
    System.out.println("通过字符流实现文件的拷贝耗时：" + (System.currentTimeMillis() - time2));

    long time3 = System.currentTimeMillis();
    copyFileByBuffered(source, target + "3.txt");
    System.out.println("通过字节缓冲流实现文件的拷贝耗时：" + (System.currentTimeMillis() - time3));

    long time4 = System.currentTimeMillis();
    copyFileByBufferedChar(source, target + "4.txt");
    System.out.println("通过字符缓冲流实现文件的拷贝耗时：" + (System.currentTimeMillis() - time4));

    long time5 = System.currentTimeMillis();
    copyFileByChannel(source, target + "5.txt");
    System.out.println("通过JAVA NIO通道（非直接缓冲区）实现文件的拷贝耗时：" + (System.currentTimeMillis() - time5));

    long time6 = System.currentTimeMillis();
    copyFileByChannelBufferd(source, target + "6.txt");
    System.out.println("通过JAVA NIO通道（直接缓冲区）实现文件的拷贝耗时：" + (System.currentTimeMillis() - time6));

    long time7 = System.currentTimeMillis();
    copyFileByChannelTransfer(source, target + "7.txt");
    System.out.println("通过JAVA NIO通道传输实现文件的拷贝耗时：" + (System.currentTimeMillis() - time7));

    long time8 = System.currentTimeMillis();
    copyFileByChannelTransfer(source, target + "8.txt");
    System.out.println("通过JAVA NIO通道传输2实现文件的拷贝耗时：" + (System.currentTimeMillis() - time8));

通过测试发现，使用JAVA NIO通道传输、JAVA NIO通道直接缓冲区以及字节缓冲流拷贝文件效率最高

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