Interview knowledge-NiO

Most of the content is taken from thinking in Java .. Baodian-grade books

1. Package NiO;
3. Import java. Io. fileinputstream;
4. Import java. Io. fileoutputstream;
5. Import java. Io. randomaccessfile;
6. Import java. NiO. bytebuffer;
7. Import java. NiO. channels. filechannel;
9. /**
10. * The NiO speed is improved because the structure closer to the operating system I/O processing mode is used: channels and buffers.
11. * If the channel is compared to a corner, the buffer is a hoe.
12. * We will not directly move the corners. However, you only need to throw your hair ......
13. *
14. * There is only one minimum implementation type for dealing directly with channels: bytebuffer
15. * During creation, you even need to specify the amount of memory space allocated. It only implements the byte format and the basic data format (primitive data)
16. * The input and output functions cannot even directly input an object or string.
17. *
18. * The channel function is very simple: it processes bytebuffer read/write and locks the file block content.
19. * The channel constructor is used to modify three byte-based objects in the original I/O system:
20. * Fileinputstream, fileoutputstream, randomaccessfile
21. *
22. * @ Author Wei. songw
23. * Oct 16,200 8 3:54:16
24. */
25. Public class basic {
27. Private Static final int bsize = 1024;
29. Public static void main (string [] ARGs) throws exception {
31. // Write File
32. Filechannel fc = new fileoutputstream ("abc.txt"). getchannel ();
33. FC. Write (bytebuffer. Wrap ("some string". getbytes ()));
34. FC. Close ();
36. Fc = new randomaccessfile ("abc.txt", "RW"). getchannel ();
37. FC. Position (FC. Size (); // go the end
38. FC. Write (bytebuffer. Wrap ("more string". getbytes ()));
39. FC. Close ();
41. Fc = new fileinputstream ("abc.txt"). getchannel ();
42. Bytebuffer BF = bytebuffer. Allocate (bsize );
43. FC. Read (BF );
44. BF. Flip (); // notice here. Flip Filter !!
45. While (BF. hasremaining ()){
46. System. Out. Print (char) BF. Get ());
47. }
48. }
49. }

1. Package NiO;
3. Import java. NiO. bytebuffer;
4. Import java. NiO. intbuffer;
6. /**
7. * Although bytebuffer only holds byte arrays, Apis provide some methods to handle primitives.
8. * (Providing corresponding operations for objects is often a good OO design concept.
9. * For example, if collection is provided, you must provide an iterator traversal instead of letting the user
10. * To implement iteration or determine whether the dependency is out of bounds due to exceptions)
11. *
12. * (It is also a good habit to provide APIs with consistent structures and function naming rules .. Ascharbuffer,
13. * Asintbuffer, asdoublebuffer, getint, getlong ....)
14. * @ Author Wei. songw
15. * Oct 16,200 8 8:19:49
16. */
17. Public class getdata {
19. Private Static final int bsize = 1024;
21. Public static void main (string [] ARGs) throws exception {
22. Bytebuffer BB = bytebuffer. Allocate (bsize); // filled by 0
24. // Char
25. BB. ascharbuffer (). Put ("Heihei ");
26. Char C;
27. While (C = BB. getchar ())! = 0 ){
28. System. Out. Print (C + "");
29. }
31. BB. Rewind ();
32. // Int
33. BB. asintbuffer (). Put (12345 );
34. System. Out. Print (BB. getint ());
36. // Batches
37. BB. Clear ();
38. Intbuffer IB = BB. asintbuffer ();
39. Ib. Put (New int [] {11,22, 33,44, 55 });
40. System. Out. println (IB. Get (3 ));
41. }
42. }

1. Package NiO;
3. Import java. Io. randomaccessfile;
4. Import java. NiO. mappedbytebuffer;
5. Import java. NiO. channels. filechannel;
7. /**
8. * In the online copy example, the memory ing file is mainly used to operate large files. The maximum size is 2 GB.
9. * @ Author Wei. songw
10. * Oct 16,200 8 10:34:52
11. */
12. Public class memorymappedfile {
14. Static int length = 0x8ffffff; // 128 MB
15. Public static void main (string [] ARGs) throws exception {
16. Mappedbytebuffer out =
17. New randomaccessfile ("test. dat", "RW"). getchannel ()
18. . Map (filechannel. mapmode. read_write, 0, length );
19. For (INT I = 0; I <length; I ++)
20. Out. Put (byte) 'X ');
21. System. Out. println ("finished writing ");
22. For (INT I = length/2; I <length/2 + 6; I ++)
23. System. Out. Print (char) Out. Get (I); // Read File
24. }
25. }

1. Package NiO;
3. Import java. Io. fileoutputstream;
4. Import java. NiO. channels. filelock;
5. Import java. util. Concurrent. timeunit;
7. /**
8. * It mainly studies the APIs of trylock () and lock.
9. * Full-text locking without parameters supports changing the file size,
10. * Partial locking with a fixed size will not automatically adapt to file growth (
11. * If a locked region initially contains the end Of the file
12. * And the file grows beyond the region then the new portion of the file
13. * Will not be covered by the lock .)
14. *
15. *
16. * File locks also support memorymappedfile.
17. *
18. * @ Author Wei. songw
19. * Oct 16,200 8 11:16:14
20. */
21. Public class filelocking {
23. Public static void main (string [] ARGs) throws exception {
24. Fileoutputstream Fos = new fileoutputstream ("abc.txt ");
25. // Locking the hole File
26. Filelock FL = FOS. getchannel (). trylock ();
27. If (FL! = NULL ){
28. System. Out. println ("file locked ");
29. // Do your work
30. Timeunit. milliseconds. Sleep (2000 );
31. Fl. Release ();
32. System. Out. println ("released lock ");
33. }
35. // For locking a part of the file, use:
36. // Filelock trylock (long position, long size, Boolean shared)
37. // Filelock lock (long position, long size, Boolean shared)
40. FOS. Close ();
41. }
42. }