🗊Презентация Java 4 WEB. Lesson 10 - IO, NIO

Java 4 WEB Lesson 10 - IO, NIO

Lesson goals Data exchange with external resources java.io – I/O: java.nio – NI/O: Non-blocking I/O 2,

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, …)

IO

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

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);

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.

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()); } } }

Streams A long, nearly never-ending “stream of water” with data presented one “wave” at a time.

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

Stream types by direction Input Output

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

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()); }

Examples

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

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); } } }

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(); } } }

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)); }

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 + '}'; } }

ObjectOutputStream (serialization) void writeUsers(List<User> 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); } } }

ObjectInputStream (deserialization) List<User> getUsers(File dataFile) throws IOException, ClassNotFoundException { List<User> users = new ArrayList<User>(); 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; }

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); } } }

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(); } } }

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); }

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");

Path overview

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

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

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

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()); }

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

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

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

Encoding ѓ« ў-л© ‚®Їа®б †Ё§-Ё, ‚ᥫҐ--®© Ё ‚ᥣ®-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 …

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... }

Read\Write files with NIO2 Path src = Paths.get("c:\\users.txt"); try { List<String> users = Files.readAllLines(src); Stream<String> usersStream = Files.lines(src); } catch (IOException e) { // Handle file I/O exception... }

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)

IO vs NIO2

Literature Basic I/O Class Charset Package java.io

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

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 */ }

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.

Homework Task 3 Implement Copying files. Create an application that will copy the file to the specified folder. In this case, the user should be able to select the type of stream: with and without buffering. Also, the application must display the time for which the operation was performed. Testing the application by taking a large file (2-4GB for example) and copy it using buffering and without. Compare the execution time.