Java 4 WEB. Lesson 10 - IO, NIO

Сентябрь 4, 2022

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Java 4 WEB. Lesson 10 - IO, NIO

Содержание

2. Lesson goals Data exchange with external resources java.io – I/O: java.nio – NI/O: Non-blocking I/O 2,
3. Glossary File – a record within a file system that stores user and system data (java.exe,
4. IO
5. File class java.io.File.java - represents the pathname of a particular file or directory on the file
6. File instantiation File File file = new File("/home/video/fun.3gp"); File parent = new File("/home"); File child =
7. File class methods exists() - is the file or directory exists. getName() - the name of
8. Example File file = new File("C:\\video\\fun.3gp"); System.out.println("File Exists: " + file.exists()); if (file.exists()) { System.out.println("Absolute Path:
9. Streams A long, nearly never-ending “stream of water” with data presented one “wave” at a time.
10. Built-in streams System.in System.err System.out
11. Stream types by direction Input Output
12. Stream types by content Byte Streams (InputStream/OutputStream) Character Streams (Reader/Writer)
13. Stream types by abstraction level low-level stream high-level stream (wrapper) try (FileInputStream fis = new FileInputStream("users.dat");
14. Examples
15. Most common Stream Operations read() - InputStream read(byte[] b) – InputStream read(byte[] b, int off, int
16. File Input/Output Stream void copy(File source, File destination) throws IOException { try (InputStream in = new
17. Buffered Input/Output Stream void copy(File source, File destination) throws IOException { try (InputStream in = new
18. Object serialization\deserialization Implement the java.io.Serializable interface (not all built-in classes are serializable) Add serialVersionUID NotSerializableException public
19. Object serialization\deserialization class User implements Serializable { private static final long serialVersionUID = 1864942621136349408L; String name;
20. ObjectOutputStream (serialization) void writeUsers(List users, File dataFile) throws IOException { try (FileOutputStream fos = new FileOutputStream(dataFile);
21. ObjectInputStream (deserialization) List getUsers(File dataFile) throws IOException, ClassNotFoundException { List users = new ArrayList (); try
22. File Reader/Writer void copy(File source, File destination) throws IOException { try (Reader reader = new FileReader(source);
23. Buffered File Reader/Writer void copy(File source, File destination) throws IOException { try (BufferedReader reader = new
24. Console // Old school try ( InputStreamReader in = new InputStreamReader(System.in); BufferedReader reader = new BufferedReader(in)
25. NIO/NIO2 java.nio.file.Path – interface represents a hierarchical path on the storage system to a file or
26. Path overview
27. Backward compatibility File file = new File("video/fun.3gp"); Path path = file.toPath(); Path path = Paths.get("video/fun.3gp"); File
28. Names hierarchy Path songPath = Paths.get("c:\\home\\video\\..\\audio\\song.flac"); System.out.println(songPath); // c:\home\video\..\audio\song.flac System.out.println(songPath.getParent()); // c:\home\video\..\audio Path normalized = songPath.normalize();
29. Relativize, resolve Path path1 = Paths.get("C:\\Windows"); Path path2 = Paths.get("C:\\Program Piles\\JetBrains"); Path path3 = Paths.get("JetBrains"); println(path1.relativize(path2));
30. File existence, print and search folder content try { println(Paths.get(".").toRealPath()); Path idea = Paths.get("C:\\Program Piles\\JetBrains\\IntelliJ IDEA");
31. Interacting with Files Path idea = Paths.get("c:\\Program Files\\JetBrains\\IntelliJ IDEA 2017.1"); Path currentDir = Paths.get("."); // c:\
32. Interacting with Files. Copy, move Path fun = Paths.get("c:\\Video\\fun.3gp"); Path moreFun = Paths.get("c:\\Video\\moreFun.3gp"); Path moreMoreFun =
33. Interacting with Files. Delete Files.delete(fun); // Exception Files.deleteIfExists(fun); // silent delete Files.delete(moreFun); // deleted Files.delete(moreMoreFun); //
34. Encoding ѓ« ў-л© ‚®Їа®б †Ё§-Ё, ‚бҐ«Ґ--®© Ё ‚бҐЈ®-ўбҐЈ® java.nio.charset.Charset java.nio.charset.StandardCharsets The character encoding determines how characters
35. Read\Write files with NIO2 Path src = Paths.get("c:\\users.txt"); Path dest = Paths.get("c:\\adminUsers.txt"); try ( BufferedReader reader
36. Read\Write files with NIO2 Path src = Paths.get("c:\\users.txt"); try { List users = Files.readAllLines(src); Stream usersStream
37. File Attributes Path file = Paths.get("c:\\video\\fun.3gp"); Files.isDirectory(file); // false Files.isHidden(file); // false Files.isReadable(file); // true Files.isExecutable(file);
38. IO vs NIO2
39. Literature Basic I/O Class Charset Package java.io
40. Homework Task 1 Download ZIP by java program users.zip (direct link for download can be retrieved
41. Homework Task 1 public class User { private final int id; private final String name; private
42. Homework Task 2 Create a command line application that will create / delete / rename the
44. Скачать презентацию

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Lesson goals
Data exchange with external resources
java.io – I/O:
java.nio – NI/O:

Non-blocking I/O 2,

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Glossary
File – a record within a file system that stores user

and system data (java.exe, movie.mp4…)
Directory - a record within a file system that contains files as well as other directories (Program Files, home, …)
Root directory - the topmost directory in the file system (c:\, /, …)
File system - in charge of reading and writing data within a computer (NTFS, FAT32, …)
Path - String representation of a file or directory within a file system (/user/home/zoo.txt, video/fun.3gp, …)

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IO

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File class
java.io.File.java - represents the pathname of a particular file or

directory on the file system
File class can be used to represent directories as well as files
Does not require file existence for creation of File object
Types
Relative (video/fun.mkv) - concerning current directory
Absolute (/home/video/fun.3gp) - concerning root directory

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File instantiation
File
File file = new File("/home/video/fun.3gp"); File parent = new File("/home"); File child

= new File(parent,"video/fun.3gp");
File separator
System.out.println(System.getProperty("file.separator")); System.out.println(java.io.File.separator);

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File class methods
exists() - is the file or directory exists.
getName() -

the name of the file or directory denoted by this path.
getAbsolutePath() - the absolute pathname string of this path.
isDirectory() - is the file denoted by this path is a directory.
isFile() - is the file denoted by this path is a file.
length() - the number of bytes in the file.
lastModified() - the number of milliseconds since the epoch when the file was last modified.
delete() - delete the file or directory. (if directory, then the directory must be empty).
renameTo(File) - rename the file denoted by this path.
mkdir() - create the directory named by this path.
mkdirs() - create the directory named by this path including any nonexistent parent directories.
getParent() - return the abstract pathname of this abstract pathname’s parent or null
listFiles() - return the files in the directory.

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$Example File file = new File("C:\\video\\fun.3gp"); System.out.println("File Exists: " + file.exists());$

Example
File file = new File("C:\\video\\fun.3gp"); System.out.println("File Exists: " + file.exists()); if (file.exists()) {

System.out.println("Absolute Path: " + file.getAbsolutePath()); System.out.println("Is Directory: " + file.isDirectory()); System.out.println("Parent Path: " + file.getParent()); if (file.isFile()) { System.out.println("File size: " + file.length()); System.out.println("File LastModified: " + file.lastModified()); } else { for (File subfile : file.listFiles()) { System.out.println("\t" + subfile.getName()); } } }

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Streams
A long, nearly never-ending “stream of water” with data presented one

“wave” at a time.

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Built-in streams
System.in
System.err
System.out

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Stream types by direction
Input
Output

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Stream types by content
Byte Streams (InputStream/OutputStream)
Character Streams (Reader/Writer)

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Stream types by abstraction level
low-level stream
high-level stream (wrapper)
try (FileInputStream fis =

new FileInputStream("users.dat"); BufferedInputStream bfis = new BufferedInputStream(fis); ObjectInputStream objectStream = new ObjectInputStream(bfis) ) { System.out.println(objectStream.readObject()); }

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Examples

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Most common Stream Operations
read() - InputStream
read(byte[] b) – InputStream
read(byte[] b, int

off, int len) - InputStream
write(…) - OutputStream
close() - InputStream, OutputStream (use automatic resource management, I/O stream)
flush() - OutputStream
boolean markSupported() - InputStream
mark(readlimit)/reset() - InputStream (use markSupported() - before)
skip(n) - InputStream
int available() - InputStream

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File Input/Output Stream
void copy(File source, File destination) throws IOException { try

(InputStream in = new FileInputStream(source); OutputStream out = new FileOutputStream(destination) ) { int b; while((b = in.read()) != -1) { out.write(b); } } }

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Buffered Input/Output Stream
void copy(File source, File destination) throws IOException { try

(InputStream in = new BufferedInputStream(new FileInputStream(source)); OutputStream out = new BufferedOutputStream(new FileOutputStream(destination)) ) { byte[] buffer = new byte[1024]; int lengthRead; while ((lengthRead = in.read(buffer)) > 0) { out.write(buffer, 0, lengthRead); out.flush(); } } }

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$Object serialization\deserialization Implement the java.io.Serializable interface (not all built-in classes are$

Object serialization\deserialization
Implement the java.io.Serializable interface (not all built-in classes are serializable)
Add

serialVersionUID
NotSerializableException
public static void main(String[] args) throws Exception { File usersStore = new File("users.dat"); writeUsers(Arrays.asList(new User("Simon", 12, 3)), usersStore); System.out.println(getUsers(usersStore)); }

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$Object serialization\deserialization class User implements Serializable { private static final long$

Object serialization\deserialization
class User implements Serializable { private static final long serialVersionUID

= 1864942621136349408L; String name; int age; transient int badHabbits; public User(String name, int age, int badHabbits) { this.name = name; this.age = age; this.badHabbits = badHabbits; } @Override public String toString() { return "User{" + "name='" + name + '}'; } }

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ObjectOutputStream (serialization)
void writeUsers(List users, File dataFile) throws IOException { try (FileOutputStream

fos = new FileOutputStream(dataFile); BufferedOutputStream bos = new BufferedOutputStream(fos); ObjectOutputStream out = new ObjectOutputStream(bos) ) { for (User user : users) { out.writeObject(user);
} } }

Слайд 21

ObjectInputStream (deserialization)
List getUsers(File dataFile) throws IOException, ClassNotFoundException { List users =

new ArrayList(); try (FileInputStream fis = new FileInputStream(dataFile); BufferedInputStream bis = new BufferedInputStream(fis); ObjectInputStream in = new ObjectInputStream(bis) ) { while (true) { Object object = in.readObject(); if (object instanceof User){ users.add((User) object);
} } } catch (EOFException e) { // File end reached } return users; }

Слайд 22

File Reader/Writer
void copy(File source, File destination) throws IOException { try (Reader

reader = new FileReader(source); Writer writer = new FileWriter(destination) ) { int c; while ((c = reader.read()) > -1) { writer.write(c); } } }

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Buffered File Reader/Writer
void copy(File source, File destination) throws IOException { try

(BufferedReader reader = new BufferedReader(new FileReader(source)); BufferedWriter writer = new BufferedWriter(new FileWriter(destination)) ) { String s; while ((s = reader.readLine()) != null) { writer.write(s); writer.newLine(); } } }

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Console
// Old school
try ( InputStreamReader in = new InputStreamReader(System.in); BufferedReader reader

= new BufferedReader(in) ) { String userInput = reader.readLine(); System.out.println("You entered the following: " + userInput); }
// New school Console console = System.console(); if(console != null) { String userInput = console.readLine(); console.writer().println ("You entered the following: "+userInput); }

Слайд 25

NIO/NIO2
java.nio.file.Path – interface represents a hierarchical path on the storage system

to a file or directory.
direct replacement for the legacy java.io.File class.
Immutable (thread safe)
Unlike the File class, the Path interface contains full support for symbolic links
java.nio.files.Paths – factory for path instantiation
Unlike the File class, the Path interface contains support for symbolic links
Does not require file existence for creation of Path object
‘.’ - A reference to the current directory
‘..’ - A reference to the parent of the current directory
Path path1 = Paths.get("video/fun.3gp"); Path path2 = Paths.get("c:\\video\\fun.3gp"); Path path3 = Paths.get("/”,“home”,“video”,“fun.3gp");
Path path4 = Paths.get(new URI("http://www.google.com")); Path path5 = Paths.get(new URI("ftp://username:password@ftp.the-ftp-server.com"));
Path path1 = FileSystems.getDefault().getPath("video/3gp.png");

Слайд 26

Path overview

Слайд 27

Backward compatibility
File file = new File("video/fun.3gp"); Path path = file.toPath(); Path path =

Paths.get("video/fun.3gp"); File file = path.toFile();

Слайд 28

$Names hierarchy Path songPath = Paths.get("c:\\home\\video\\..\\audio\\song.flac"); System.out.println(songPath); // c:\home\video\..\audio\song.flac System.out.println(songPath.getParent()); //$

Names hierarchy
Path songPath = Paths.get("c:\\home\\video\\..\\audio\\song.flac"); System.out.println(songPath); // c:\home\video\..\audio\song.flac System.out.println(songPath.getParent()); // c:\home\video\..\audio Path normalized =

songPath.normalize(); System.out.println(normalized); // c:\home\audio\song.flac System.out.println(normalized.getParent()); // c:\home\audio Path absolute = normalized.toAbsolutePath(); System.out.println(absolute); // c:\home\audio\song.flac System.out.println(absolute.getRoot()); // c:\ System.out.println(absolute.getNameCount()); // 3 System.out.println(absolute.getFileName()); // song.flac System.out.println(absolute.getName(0)); // home System.out.println(absolute.subpath(1, 3)); // audio\song.flac

Слайд 29

$Relativize, resolve Path path1 = Paths.get("C:\\Windows"); Path path2 = Paths.get("C:\\Program Piles\\JetBrains");$

Relativize, resolve
Path path1 = Paths.get("C:\\Windows"); Path path2 = Paths.get("C:\\Program Piles\\JetBrains"); Path path3 =

Paths.get("JetBrains"); println(path1.relativize(path2)); // ..\Program Piles\JetBrains println(path2.relativize(path1)); // ..\..\Windows println(path2.relativize(path3)); // Exception! Path path4 = Paths.get("IntelliJ IDEA"); println(path2.resolve(path4)); // C:\Program Piles\JetBrains\IntelliJ IDEA println(path1.resolve(path2)); // C:\Program Piles\JetBrains

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File existence, print and search folder content
try { println(Paths.get(".").toRealPath()); Path idea

= Paths.get("C:\\Program Piles\\JetBrains\\IntelliJ IDEA"); println(idea.toRealPath()); println(idea.toRealPath(LinkOption.NOFOLLOW_LINKS));
Files.list(idea).forEach(c::println); Files.walk(idea, 1).forEach(c::println); // DFS
Files.find(idea, 1, (p,a) -> p.startsWith("bin")).forEach(c::println); } catch (IOException e) { println("Can not read path: " + e.getMessage()); }

Слайд 31

$Interacting with Files Path idea = Paths.get("c:\\Program Files\\JetBrains\\IntelliJ IDEA 2017.1"); Path$

Interacting with Files
Path idea = Paths.get("c:\\Program Files\\JetBrains\\IntelliJ IDEA 2017.1"); Path currentDir

= Paths.get("."); // c:\ Files.exists(idea); // true Files.isDirectory(idea); // true Files.isSameFile(idea, idea.resolve("bin\\..")); // true Files.isSameFile(idea, currentDir); // false Path newIdea = idea.resolveSibling(Paths.get("IntelliJ IDEA 2018.1")); Files.exists(newIdea); // false Files.createDirectory(newIdea); // c:\Program Files\JetBrains\IntelliJ IDEA 2018.1 Files.createDirectories(newIdea); // c:\Program Files\JetBrains\IntelliJ IDEA 2018.1 Files.exists(newIdea); // true

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$Interacting with Files. Copy, move Path fun = Paths.get("c:\\Video\\fun.3gp"); Path moreFun$

Interacting with Files. Copy, move
Path fun = Paths.get("c:\\Video\\fun.3gp"); Path moreFun =

Paths.get("c:\\Video\\moreFun.3gp"); Path moreMoreFun = Paths.get("c:\\Video\\moreMoreFun.3gp"); Files.exists(fun); // true Files.exists(moreFun); // false Files.exists(moreMoreFun); // false Files.copy(fun, moreFun); // shallow copy Files.exists(moreFun); // true Files.exists(moreMoreFun); // false Files.move(fun, moreMoreFun, REPLACE_EXISTING); // shallow move Files.exists(moreMoreFun); // true

Слайд 33

Interacting with Files. Delete
Files.delete(fun); // Exception Files.deleteIfExists(fun); // silent delete Files.delete(moreFun); //

deleted Files.delete(moreMoreFun); // deleted
Files.exists(fun); // false Files.exists(moreFun); // false Files.exists(moreMoreFun); // false

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Encoding
ѓ« ў-л© ‚®Їа®б †Ё§-Ё, ‚бҐ«Ґ--®© Ё ‚бҐЈ®-ўбҐЈ®
java.nio.charset.Charset
java.nio.charset.StandardCharsets
The character encoding

determines how characters are encoded and stored in bytes and later read back or decoded as characters
Win-1251
UTF-8
ISO-8859-5
…

Слайд 35

$Read\Write files with NIO2 Path src = Paths.get("c:\\users.txt"); Path dest =$

Read\Write files with NIO2
Path src = Paths.get("c:\\users.txt"); Path dest = Paths.get("c:\\adminUsers.txt"); try (

BufferedReader reader = Files.newBufferedReader(src, Charset.forName("US-ASCII")); BufferedWriter writer = Files.newBufferedWriter(dest, Charset.forName("UTF-16")) ) { String currentLine; while ((currentLine = reader.readLine()) != null) { writer.write(currentLine); } } catch (IOException e) { // Handle file I/O exception... }

Слайд 36

$Read\Write files with NIO2 Path src = Paths.get("c:\\users.txt"); try { List$

Read\Write files with NIO2
Path src = Paths.get("c:\\users.txt"); try { List users =

Files.readAllLines(src); Stream usersStream = Files.lines(src); } catch (IOException e) { // Handle file I/O exception... }

Слайд 37

$File Attributes Path file = Paths.get("c:\\video\\fun.3gp"); Files.isDirectory(file); // false Files.isHidden(file); //$

File Attributes
Path file = Paths.get("c:\\video\\fun.3gp"); Files.isDirectory(file); // false Files.isHidden(file); // false Files.isReadable(file); // true Files.isExecutable(file);

// true Files.isSymbolicLink(file); // false Files.getLastModifiedTime(file); // 2017-12-03T13:46:24.818731Z Files.size(file); // 13 Files.getOwner(file); // BUILTIN\Admin (Alias)

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IO vs NIO2

Слайд 39

Literature
Basic I/O
Class Charset
Package java.io

Слайд 40

Homework Task 1
Download ZIP by java program users.zip (direct link for download

can be retrieved in browser)
Unzip it by program and find file named 'users.dat' (it can be in a child folder)
Try to deserialize 'users.dat' file into list of user objects (modify User class if needed)
Fix serialization problems in User class
Deserialize 'users.dat' file into list of user objects
int allUsersCount = Count all deserialized users
String mostFavoriteEncodingAmongAllUsers = Find the most favorite encoding among users
Between users who has higher access level than average, find 'int targetUserId' = user id with biggest name length
Write ALL deserialized users names into file1. Every name in separate line (use next encoding '{mostFavoriteEncodingAmongAllUsers}-{targetUserId}' ). Use system temp folder (files should be removed after usage)
Write ALL deserialized users names into file2. Every name in separate line (use next encoding '{mostFavoriteEncodingAmongAllUsers}-{allUsersCount}' ). Use system temp folder (files should be removed after usage)
Answer – found files encodings and the difference of two files sizes in bytes
Cover by unit tests

Слайд 41

Homework Task 1
public class User { private final int id; private

final String name; private final int accessLevel; private final String favoriteEncoding; public User(int id, String name, int accessLevel, String favoriteEncoding) { this.id = id; this.name = name; this.accessLevel = accessLevel; this.favoriteEncoding = favoriteEncoding; } /* getters/setter and other are omitted */ }

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Homework Task 2
Create a command line application that will create /

delete / rename the folder with the specified name. The folder name and the number (or code) of the operation must be passed as incoming parameters in runtime. If folder with such name already exists – prompt user for confirmation of replacement.

Java 4 WEB. Lesson 10 - IO, NIO

Содержание

Lesson goalsData exchange with external resourcesjava.io – I/O: java.nio – NI/O:

GlossaryFile – a record within a file system that stores user

IO

File classjava.io.File.java - represents the pathname of a particular file or

File instantiationFileFile file = new File("/home/video/fun.3gp"); File parent = new File("/home"); File child

File class methodsexists() - is the file or directory exists.getName() -

ExampleFile file = new File("C:\\video\\fun.3gp"); System.out.println("File Exists: " + file.exists()); if (file.exists()) {

StreamsA long, nearly never-ending “stream of water” with data presented one

Built-in streamsSystem.inSystem.errSystem.out

Stream types by directionInputOutput

Stream types by contentByte Streams (InputStream/OutputStream)Character Streams (Reader/Writer)

Stream types by abstraction levellow-level streamhigh-level stream (wrapper)try (FileInputStream fis =

Examples

Most common Stream Operationsread() - InputStreamread(byte[] b) – InputStreamread(byte[] b, int

File Input/Output Streamvoid copy(File source, File destination) throws IOException { try

Buffered Input/Output Streamvoid copy(File source, File destination) throws IOException { try

Object serialization\deserializationImplement the java.io.Serializable interface (not all built-in classes are serializable)Add

Object serialization\deserializationclass User implements Serializable { private static final long serialVersionUID

ObjectOutputStream (serialization)void writeUsers(List users, File dataFile) throws IOException { try (FileOutputStream

ObjectInputStream (deserialization)List getUsers(File dataFile) throws IOException, ClassNotFoundException { List users =

File Reader/Writervoid copy(File source, File destination) throws IOException { try (Reader

Buffered File Reader/Writervoid copy(File source, File destination) throws IOException { try

Console// Old schooltry ( InputStreamReader in = new InputStreamReader(System.in); BufferedReader reader

NIO/NIO2java.nio.file.Path – interface represents a hierarchical path on the storage system