Shulou(Shulou.com)05/31 Report--

This article mainly introduces "how Java carries on the basic operation to the file". In the daily operation, I believe that many people have doubts about how to carry on the basic operation to the file in Java. The editor has consulted all kinds of data and sorted out the simple and easy-to-use operation method. I hope it will be helpful to answer the doubt of "how to operate the file with Java". Next, please follow the editor to study!

File file class

Java.io.File is an important class of files and directories (JDK6 and previously unique)

Directories are also represented by File classes

The File class is independent of the operating system, but is limited by the permissions of the operating system

Common methods

CreateNewFile, delete, exists, getAbsolutePath, getName, getParent, getPath

IsDirectory, isFile, length, listFiles, mkdir, mkdirs

File does not involve specific file contents, only attributes

Public static void main (String [] args) {/ / create directory File directory = new File ("D:/temp"); boolean directoryDoesNotExists =! Directory.exists (); if (directoryDoesNotExists) {/ / mkdir is to create a single-level directory / / mkdirs is to create a continuous multi-level directory directory.mkdirs ();} / / create the file File file = new File ("D:/temp/test.txt"); boolean fileDoesNotExsits =! File.exists (); if (fileDoesNotExsits) {try {file.createNewFile ();} catch (IOException e) {e.printStackTrace ();}} / / traverse all file messages under directory File [] files = directory.listFiles (); for (File file1: files) {System.out.println (file1.getPath ());}}

Running result:

D:\ temp\ test.txt

Java NIO

NIO package proposed by Java 7, new file system classes Path, Files, DirectoryStream, FileVisitor, FileSystem are useful additions to java.io.File file replication and moving file relative paths recursively traversing directories recursively deleting directories

Path class

Public static void main (String [] args) {/ / Path and java.io.File are basically similar to Path path = FileSystems.getDefault (). GetPath ("D:/temp", "abc.txt"); / / D:/temp / return 1 D:/temp return 2 System.out.println (path.getNameCount ()); / / use File's toPath () method to get Path object File file = new File ("D:/temp/abc.txt") Path path2 = file.toPath (); System.out.println (path.compareTo (path2)); / / if the result is 0, the two path are equal / / get the Path method three Path path4 = Paths.get ("D:/temp", "abc.txt"); / / determine whether the file is readable System.out.println ("whether the file can be read:" + Files.isReadable (path));}

Files class

Public static void main (String [] args) {/ / move file moveFile (); / / access file properties fileAttributes (); / / create directory createDirectory ();} private static void createDirectory () {Path path = Paths.get ("D:/temp/test"); try {/ / create folder if (Files.notExists (path)) {Files.createDirectory (path) } else {System.out.println ("folder creation failed");} Path path3 = path.resolve ("a.java"); Path path4 = path.resolve ("b.java"); Path path5 = path.resolve ("c.txt"); Path path6 = path.resolve ("d.jpg"); Files.createFile (path3); Files.createFile (path4) Files.createFile (path5); Files.createFile (path6); / / unconditional traversal output DirectoryStream listDirectory = Files.newDirectoryStream (path); for (Path path2: listDirectory) {System.out.println (path2.getFileName ()) } / / create a file with filter DirectoryStream pathsFilter = Files.newDirectoryStream (path, "*. {java,txt}") ending with java txt; for (Path item: pathsFilter) {System.out.println (item.getFileName ());}} catch (Exception e) {e.printStackTrace () } @ SuppressWarnings ("all") private static void fileAttributes () {Path path = Paths.get ("D:/temp"); / / determine whether it is a directory System.out.println (Files.isDirectory (path, LinkOption.NOFOLLOW_LINKS)); try {/ / get the basic attribute of the file BasicFileAttributes attributes = Files.readAttributes (path, BasicFileAttributes.class) / / determine whether it is a directory System.out.println (attributes.isDirectory ()); / / get the last modification time of the file System.out.println (new Date (attributes.lastModifiedTime (). ToMillis ()). ToLocaleString ());} catch (Exception e) {e.printStackTrace () }} private static void moveFile () {Path from = Paths.get ("D:/temp", "text.txt"); / / move the file to D:/temp/test/text.txt and replace Path to = from.getParent (). Resolve ("test/text.txt") if the destination file exists; try {/ / file size bytes System.out.println (Files.size (from)) / / call the file movement method to replace Files.move (from, to, StandardCopyOption.REPLACE_EXISTING) if the target file already exists;} catch (Exception e) {e.printStackTrace ();}}

Recursively traverse to find the specified file

Public class Demo2 {public static void main (String [] args) {/ / find String ext = "* .jpg" ending with .jpg; Path fileTree = Paths.get ("D:/temp/"); Search search = new Search (ext); EnumSet options = EnumSet.of (FileVisitOption.FOLLOW_LINKS); try {Files.walkFileTree (fileTree, options, Integer.MAX_VALUE, search) } catch (IOException e) {e.printStackTrace ();} class Search implements FileVisitor {private PathMatcher matcher; public Search (String ext) {this.matcher = FileSystems.getDefault (). GetPathMatcher ("glob:" + ext);} public void judgeFile (Path file) throws IOException {Path name = file.getFileName () If (name! = null & & matcher.matches (name)) {/ / the file name matches System.out.println ("matching file name:" + name);}} / / call @ Override public FileVisitResult preVisitDirectory (Object dir, BasicFileAttributes attrs) throws IOException {return FileVisitResult.CONTINUE before accessing the directory } / / call @ Override public FileVisitResult visitFile (Object file, BasicFileAttributes attrs) throws IOException {judgeFile ((Path) file) when accessing the file; return FileVisitResult.CONTINUE;} / / call @ Override public FileVisitResult visitFileFailed (Object file, IOException exc) throws IOException {return FileVisitResult.CONTINUE after failure to access the file } / / call @ Override public FileVisitResult postVisitDirectory (Object dir, IOException exc) throws IOException {System.out.println ("postVisit:" + (Path) dir); return FileVisitResult.CONTINUE;}} after visiting a directory

Running result:

Matching file name: d.jpg

PostVisit: d:\ temp\ test

PostVisit: d:\ temp

Java's IO package

Java read and write files, only in the form of data flow to read and write java.io package node classes: directly read and write files wrapper class: 1, conversion class: byte / character / data type conversion class. 2. Decoration class: decoration node class.

Node class

Direct manipulation of file classes InputStream,OutStream (byte) FileInputStream, FileOutputStream Reader, Writer (character) FileReader, FileWriter

Conversion class

Conversion from character to byte InputStreamReader: when a file is read, bytes are converted into characters that Java can understand OutputStreamWriter: Java converts characters into bytes and inputs them into the file

Decorative category

DataInputStream, DataOutputStream: encapsulated data flow BufferedInputStream, BufferOutputStream: cache byte stream BufferedReader, BufferedWriter: cache character stream

Reading and writing of text files

Write operation

Public static void main (String [] args) {writeFile ();} public static void writeFile () {try (BufferedWriter bw = new BufferedWriter (new OutputStreamWriter (new FileOutputStream ("D:/temp/demo3.txt") {bw.write ("hello world"); bw.newLine (); bw.write ("Java Home"); bw.newLine ();} catch (Exception e) {e.printStackTrace ();}}

Demo3.txt file content

Hello world

Java Home

Read operation

Public static void main (String [] args) {readerFile ();} private static void readerFile () {String line = ""; try (BufferedReader br = new BufferedReader (new InputStreamReader (new FileInputStream ("D:/temp/demo3.txt") {while ((line = br.readLine ())! = null) {System.out.println (line);} catch (Exception e) {e.printStackTrace () }}

Running result:

Hello world

Java Home

Java for reading and writing binary files

Public static void main (String [] args) {writeFile ();} private static void writeFile () {try (DataOutputStream dos = new DataOutputStream (new BufferedOutputStream (new FileOutputStream ("D:/temp/test.dat") {dos.writeUTF ("hello"); dos.writeUTF ("hello world is test bytes"); dos.writeInt (20); dos.writeUTF ("world") } catch (Exception e) {e.printStackTrace ();}}

File content

Hellohello world is test bytes world

Read operation

Public static void main (String [] args) {readFile ();} private static void readFile () {try (DataInputStream in = new DataInputStream (new BufferedInputStream (new FileInputStream ("D:/temp/test.dat") {System.out.println (in.readUTF () + in.readUTF () + in.readInt () + in.readUTF ());} catch (Exception e) {e.printStackTrace ();}}

Running result:

Hellohello world is test bytes20world

Reading and writing of ZIP files

Zip file operation class: in the java.util.zip package

Java.io.InputStream, a subclass of java.io.OutputStream

ZipInputStream, ZipOutputStream compressed file input / output stream

ZipEntry compression term

Multiple file compression

/ / multiple file compression public static void main (String [] args) {zipFile ();} public static void zipFile () {File file = new File ("D:/temp"); File zipFile = new File ("D:/temp.zip"); FileInputStream input = null Try (ZipOutputStream zos = new ZipOutputStream (new FileOutputStream (zipFile) {/ / add comments zos.setComment (new String ("multiple file compression" .getBytes (), "UTF-8")); / / compression process int temp = 0; / / determine whether it is a folder if (file.isDirectory ()) {File [] listFile = file.listFiles () For (int I = 0; I < listFile.length; iTunes +) {/ / the output stream of the definition file input = new FileInputStream (listFile [I]) / / set Entry object zos.putNextEntry (new ZipEntry (file.getName () + File.separator + listFile [I] .getName ()); System.out.println ("compressing:" + listFile [I] .getName ()) / / read content while ((temp = input.read ())! =-1) {/ / compress output zos.write (temp);} / close input stream input.close () Catch (Exception e) {e.printStackTrace ();}}

Note: compressed folders cannot have subdirectories, otherwise FileNotFoundException: d:\ temp\ test (access denied.) , this is because input = new FileInputStream (listFile [I]); the file type read is caused by the folder

Decompress multiple files

/ / multiple files unzip public static void main (String [] args) throws Exception {/ / zip files to be extracted. You need to build an input stream on the zip file and read the data into Java File file = new File ("C:\ Users\\ Wong\\ Desktop\\ test.zip"); / / output files with folder operation File outFile = null / / instantiate the ZipEntry object ZipFile zipFile = new ZipFile (file); / / define the unzipped file name OutputStream out = null; / / define the input stream, read each Entry InputStream input = null; / / each compressed Entry ZipEntry entry = null / / define the compressed input stream, instantiate ZipInputStream try (ZipInputStream zipInput = new ZipInputStream (new FileInputStream (file) {/ / traverse the file while ((entry = zipInput.getNextEntry ())! = null) {System.out.println ("decompress" + entry.getName (). ReplaceAll ("/", ") +" File ") / / define the file path of the output outFile = new File ("outFile.getParentFile /" + entry.getName ()); boolean outputDirectoryNotExsits =! outFile.getParentFile () .file () / / when the output folder does not exist, if (outputDirectoryNotExsits) {/ / create the output folder outFile.getParentFile () .mkdirs ();} boolean outFileNotExists =! outFile.exists () / / if (outFileNotExists) {if (entry.isDirectory ()) {outFile.mkdirs ();} else {outFile.createNewFile ();}} boolean entryNotDirctory =! entry.isDirectory () when the output file does not exist If (entryNotDirctory) {input = zipFile.getInputStream (entry); out = new FileOutputStream (outFile); int temp = 0; while ((temp = input.read ())! =-1) {out.write (temp);} input.close () Out.close (); System.out.println ("unzipped successfully");} catch (Exception e) {e.printStackTrace ();}} at this point, the study on "how to perform basic operations on files by Java" is over, hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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