Examples of java.nio.channels.FileChannel.truncate()

java.nio.channels.FileChannel.truncate()
Truncates the file underlying this channel to a given size.
Any bytes beyond the given size are removed from the file. If there are no bytes beyond the given size then the file contents are unmodified.

If the file position is currently greater than the given size, then it is set to be the given size.
@param size the maximum size of the underlying file @throws IllegalArgumentException the requested size is negative. @throws ClosedChannelException the channel is closed. @throws NonWritableChannelException the channel cannot be written. @throws IOException some other IO problem occured. @return this channel

            FileChannel channel = file.getChannel();
            int newsize = random.nextInt((int)channel.size()/2);
            System.out.println("Deliberately truncating file " + 
                               blocks[idx].getName() + 
                               " to size " + newsize + " bytes.");
            channel.truncate(newsize);
            file.close();
          } else {
            //
            // corrupt a few bytes of the metafile
            //

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        File mf = b.getMetaFile();
        // Truncate a block file that has a corresponding metadata file
        if (f.exists() && f.length() != 0 && mf.exists()) {
          FileOutputStream s = new FileOutputStream(f);
          FileChannel channel = s.getChannel();
          channel.truncate(0);
          LOG.info("Truncated block file " + f.getAbsolutePath());
          return b.getBlockId();
        }
      }
    }

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        File mf = b.getMetaFile();
        // Truncate a block file that has a corresponding metadata file
        if (f.exists() && f.length() != 0 && mf.exists()) {
          FileOutputStream s = new FileOutputStream(f);
          FileChannel channel = s.getChannel();
          channel.truncate(0);
          LOG.info("Truncated block file " + f.getAbsolutePath());
          return b.getBlockId();
        }
      }
    }

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      public void purge(File f) throws IOException {
         // Avoid a delete per-se because it hampers any fsync-like functionality
         // cos any cached file channel write won't change the file's exists
         // status. So, clear the file rather than delete it.
         FileChannel channel = streams.get(f.getPath());
         channel.truncate(0);
         // Apart from truncating, it's necessary to reset the position!
         channel.position(0);
      }


      @Override

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  @Test
  public void testTruncate() throws IOException {
    RegularFile file = regularFile(10);
    FileChannel channel = channel(file, WRITE);


    channel.truncate(10); // no resize, >= size
    assertEquals(10, file.size());
    channel.truncate(11); // no resize, > size
    assertEquals(10, file.size());
    channel.truncate(5); // resize down to 5
    assertEquals(5, file.size());

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    RegularFile file = regularFile(10);
    FileChannel channel = channel(file, WRITE);


    channel.truncate(10); // no resize, >= size
    assertEquals(10, file.size());
    channel.truncate(11); // no resize, > size
    assertEquals(10, file.size());
    channel.truncate(5); // resize down to 5
    assertEquals(5, file.size());


    channel.position(20);

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    channel.truncate(10); // no resize, >= size
    assertEquals(10, file.size());
    channel.truncate(11); // no resize, > size
    assertEquals(10, file.size());
    channel.truncate(5); // resize down to 5
    assertEquals(5, file.size());


    channel.position(20);
    channel.truncate(10);
    assertEquals(10, channel.position());

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    assertEquals(10, file.size());
    channel.truncate(5); // resize down to 5
    assertEquals(5, file.size());


    channel.position(20);
    channel.truncate(10);
    assertEquals(10, channel.position());
    channel.truncate(2);
    assertEquals(2, channel.position());
  }

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    assertEquals(5, file.size());


    channel.position(20);
    channel.truncate(10);
    assertEquals(10, channel.position());
    channel.truncate(2);
    assertEquals(2, channel.position());
  }


  @Test
  public void testFileTimeUpdates() throws IOException {

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    assertNotEquals(modifiedTime, file.getLastModifiedTime());


    modifiedTime = file.getLastModifiedTime();
    Uninterruptibles.sleepUninterruptibly(2, MILLISECONDS);


    channel.truncate(0);
    assertNotEquals(modifiedTime, file.getLastModifiedTime());


    modifiedTime = file.getLastModifiedTime();
    Uninterruptibles.sleepUninterruptibly(2, MILLISECONDS);

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