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https://github.com/iambharath-ashok/java-io
Java IO
https://github.com/iambharath-ashok/java-io
Last synced: about 2 months ago
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Java IO
- Host: GitHub
- URL: https://github.com/iambharath-ashok/java-io
- Owner: iambharath-ashok
- Created: 2019-01-30T06:03:22.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2023-12-15T17:50:25.000Z (about 1 year ago)
- Last Synced: 2023-12-15T18:56:42.837Z (about 1 year ago)
- Size: 40 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Java-IO
## Java create new file
- java.io.File class can be used to create a new File in Java
- We can call createNewFile() method to create new file in Java
- File createNewFile() method returns true if new file is created and false if file already exists
- This method also throws java.io.IOException when it’s not able to create the file
- The files created is empty and of zero bytes
- When we create the File object by passing file name:
- It can be with absolute path
- Or we can only provide the file name or we can provide relative path
- For non-absolute path, File object tries to locate files in the project root directory
- If we run the program from command line, for non-absolute path, File object tries to locate files from the current directory
- While creating the file path, we should use System property "file.separator" to make our program platform independent
Code Snippet:
public static void main(String[] args) throws IOException {
String fileSeparator = System.getProperty("file.separator");
//absolute file name with path
String absoluteFilePath = fileSeparator+"Users"+fileSeparator+"Iambharath"+fileSeparator+"file.txt";
File file = new File(absoluteFilePath);
if(file.createNewFile()){
System.out.println(absoluteFilePath+" File Created");
}else System.out.println("File "+absoluteFilePath+" already exists");
//file name only
file = new File("file.txt");
if(file.createNewFile()){
System.out.println("file.txt File Created in Project root directory");
}else System.out.println("File file.txt already exists in project root directory");
//relative path
String relativePath = "tmp"+fileSeparator+"file.txt";
file = new File(relativePath);
if(file.createNewFile()){
System.out.println(relativePath+" File Created in Project root directory");
}else System.out.println("File "+relativePath+" already exists in project root directory");
}
Output:
/Users/Iambharath/file.txt File Created
file.txt File Created in Project root directory
Exception in thread "main"
java.io.IOException: No such file or directory
at java.io.UnixFileSystem.createFileExclusively(Native Method)
at java.io.File.createNewFile(File.java:947)
at com.bharath.files.CreateNewFile.main(CreateNewFile.java:32)
### FileOutputStream.write(byte[] b)
- If we want to create a new file and at the same time write some data into it,
- We can use FileOutputStream write method
Code Snippet:
String filname = "Iambharathfile1";
System.out.println(Arrays.toString(filname.getBytes()));
FileOutputStream fos = new FileOutputStream("name.txt");
fos.write(filname.getBytes());
fos.flush();
fos.close();
Output:
[98, 104, 97, 114, 97, 116, 104, 102, 105, 108, 101, 49, 46, 116, 120, 116]
### Java NIO Files.write()
- We can use Java NIO Files class to create a new file and write some data into it
Code Snippet:
String fileData = "Bahrfath";
Files.write(Paths.get("name.txt"), fileData.getBytes());
------------------------------------------------
## Java Delete File, directory
- Java File delete() method can be used to delete files or empty directory/folder in java.
- Java file delete method returns true if file gets deleted and returns false if file doesn’t exist.
- If we are trying to delete a directory, it checks java File delete() method check if it’s empty or not.
- If directory is empty, it gets deleted
- else delete() method doesn’t do anything and return false.
- So in this case, we have to recursively delete all the files and then the empty directory.
- Another way to delete a non-empty directory is by using Files.walkFileTree() method.
- In this method, we can process all the files one by one, and call delete method on single files.
Code snippet:
public class DeleteFileJava {
/**
* This class shows how to delete a File in Java
* @param args
**/
public static void main(String[] args) {
//absolute file name with path
File file = new File("/Users/Iambharath/file.txt");
if(file.delete()){
System.out.println("/Users/Iambharath/file.txt File deleted");
}else System.out.println("File /Users/Iambharath/file.txt doesn't exists");
//file name only
file = new File("file.txt");
if(file.delete()){
System.out.println("file.txt File deleted from Project root directory");
}else System.out.println("File file.txt doesn't exists in project root directory");
//relative path
file = new File("tmp/file.txt");
if(file.delete()){
System.out.println("tmp/file.txt File deleted from Project root directory");
}else System.out.println("File tmp/file.txt doesn't exists in project root directory");
//delete empty directory
file = new File("tmp");
if(file.delete()){
System.out.println("tmp directory deleted from Project root directory");
}else System.out.println("tmp directory doesn't exists or not empty in project root directory");
//try to delete directory with files
file = new File("/Users/Iambharath/project");
if(file.delete()){
System.out.println("/Users/Iambharath/project directory deleted from Project root directory");
}else System.out.println("/Users/Iambharath/project directory doesn't exists or not empty");
}
}
### Java delete directory
- Deleting Non-Empty directory in the Java 7
Code Snippet:
public class JavaDeleteDirectory {
public static void main(String[] args) {
File dir = new File("/Users/Iambharath/log");
if(dir.isDirectory() == false) {
System.out.println("Not a directory. Do nothing");
return;
}
File[] listFiles = dir.listFiles();
for(File file : listFiles){
System.out.println("Deleting "+file.getName());
file.delete();
}
//now directory is empty, so we can delete it
System.out.println("Deleting Directory. Success = "+dir.delete());
}
}
### Java delete directory recursively
- Earlier we had to write recursion based code to delete a directory with nested directories
- But with Java 7, we can do this using Files class
- Another way to delete a non-empty directory is by using Files.walkFileTree() method.
- In this method, we can process all the files one by one, and call delete method on single files.
Code Snippet:
public class JavaDeleteDirectoryRecursively {
public static void main(String[] args) throws IOException {
Path directory = Paths.get("/Users/Iambharath/log");
Files.walkFileTree(directory, new SimpleFileVisitor() {
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) throws IOException {
Files.delete(file); // this will work because it's always a File
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
Files.delete(dir); //this will work because Files in the directory are already deleted
return FileVisitResult.CONTINUE;
}
});
}
}
---------------------------------------------
## Java File separator, separatorChar, pathSeparator, pathSeparatorChar
- java.io.File class contains four static separator variables
- File.separator: Platform dependent default name-separator character as String.
- For windows, it’s ‘\’ and for unix it’s ‘/’.
- File.separatorChar: Same as separator but it’s char.
- File.pathSeparator: Platform dependent variable for path-separator.
- For example PATH or CLASSPATH variable list of paths separated by ‘:’ in Unix systems and ‘;’ in Windows system.
- File.pathSeparatorChar: Same as pathSeparator but it’s char.
Code snippet:
public static void main(String[] args) {
System.out.println("File.separator = "+File.separator);
System.out.println("File.separatorChar = "+File.separatorChar);
System.out.println("File.pathSeparator = "+File.pathSeparator);
System.out.println("File.pathSeparatorChar = "+File.pathSeparatorChar);
}
Output linux:
File.separator = /
File.separatorChar = /
File.pathSeparator = :
File.pathSeparatorChar = :
Output widows:
File.separator = \
File.separatorChar = \
File.pathSeparator = ;
File.pathSeparatorChar = ;
-----------------------------------------------------------------
## How to Delete a Directory/Folder in Java using Recursion
Code Snippet:
public class DeleteFolderRecursively {
public static void main(String[] args) {
String folder = "/Users/Iambharath/tmp";
//delete folder recursively
recursiveDelete(new File(folder));
}
public static void recursiveDelete(File file) {
//to end the recursive loop
if (!file.exists())
return;
//if directory, go inside and call recursively
if (file.isDirectory()) {
for (File f : file.listFiles()) {
//call recursively
recursiveDelete(f);
}
}
//call delete to delete files and empty directory
file.delete();
System.out.println("Deleted file/folder: "+file.getAbsolutePath());
}
}
-----------------------------------------------------------------
## Java Rename File – Jave Move File
- We can use File.renameTo(File dest) method for java rename file and java move file operations.
- File renameTo method returns true if file rename is successful, else it returns false.
- Some of the rename operation are platform dependent.
- For example it might fail if we move a file from one filesystem to another or if a file already exists with the same name at destination directory
- In Mac OS, if destination file already exists renameTo override the existing file with source file
- We should always check the renameTo return value to make sure rename file is successful
- Because it’s platform dependent and it doesn’t throw IO exception if rename fails
public static void main(String[] args) {
//absolute path rename file
File file = new File("/Users/Iambharath/java.txt");
File newFile = new File("/Users/Iambharath/java1.txt");
if(file.renameTo(newFile)){
System.out.println("File rename success");;
}else{
System.out.println("File rename failed");
}
//java move file from one directory to another
file = new File("/Users/Iambharath/DB.properties");
newFile = new File("DB_Move.properties");
if(file.renameTo(newFile)){
System.out.println("File move success");;
}else{
System.out.println("File move failed");
}
}
-----------------------------------------------------------------
## Java get file size
### Java get file size using File class
- Java File length() method returns the file size in bytes.
- Will only work for file and not for directory.
- So before calling this method to get file size in java
- Make sure file exists and it’s not a directory.
Code Snippet:
public class JavaGetFileSize {
static final String FILE_NAME = "/Users/Iambharath/Downloads/file.pdf";
public static void main(String[] args) {
File file = new File(FILE_NAME);
if (!file.exists() || !file.isFile()) return;
System.out.println(getFileSizeBytes(file));
System.out.println(getFileSizeKiloBytes(file));
System.out.println(getFileSizeMegaBytes(file));
}
private static String getFileSizeMegaBytes(File file) {
return (double) file.length() / (1024 (Mul) 1024) + " mb";
}
private static String getFileSizeKiloBytes(File file) {
return (double) file.length() / 1024 + " kb";
}
private static String getFileSizeBytes(File file) {
return file.length() + " bytes";
}
}
Output;
34353544343 bytes
343.345323 kb
3.35343 mb
---------------------------------------------
## How to Get File Extension in Java
Code Snippet:
private static String getFileExtension(File file) {
String fileName = file.getName();
if(fileName.lastIndexOf(".") != -1 && fileName.lastIndexOf(".") != 0)
return fileName.substring(fileName.lastIndexOf(".")+1);
else return "";
}
---------------------------------------------
## How to check if File exists in Java
Code Snippet:
public class FileExists {
public static void main(String[] args) {
File file = new File("/Users/Iambharath/source.txt");
File notExist = new File("xyz.txt");
try {
System.out.println(file.getCanonicalPath() + " exists? "+file.exists());
System.out.println(notExist.getCanonicalPath() + " exists? "+notExist.exists());
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
/Users/Iambharath/source.txt exists? true
/Users/Iambharath/JavaPrograms/xyz.txt exists? false
---------------------------------------------
## How to check File is Directory or File in java
- java.io.File class contains two methods using which we can find out if the file is a directory or a regular file in java.
- isFile(): This method returns true if file exists and is a regular file
- Note that if file doesn’t exist then it returns false.
- isDirectory(): This method returns true if file is actually a directory
- If path doesn’t exist then it returns false.
- While checking if a file is directory or regular file, we should first check if file exists or not.
- If it exists then only we should check if it’s a directory or file.
Code Snippet:
public class CheckDirectoryOrFile {
public static void main(String[] args) {
File file = new File("/Users/Iambharath/source.txt");
File dir = new File("/Users/Iambharath");
File notExists = new File("/Users/Iambharath/notafile");
System.out.println("/Users/Iambharath/source.txt is file?"+file.isFile());
System.out.println("/Users/Iambharath/source.txt is directory?"+file.isDirectory());
System.out.println("/Users/Iambharath is file?"+dir.isFile());
System.out.println("/Users/Iambharath is directory?"+dir.isDirectory());
System.out.println("/Users/Iambharath/notafile is file?"+notExists.isFile());
System.out.println("/Users/Iambharath/notafile is directory?"+notExists.isDirectory());
}
}
Output:
/Users/Iambharath/source.txt is file?true
/Users/Iambharath/source.txt is directory?false
/Users/Iambharath is file?false
/Users/Iambharath is directory?true
/Users/Iambharath/notafile is file?false
/Users/Iambharath/notafile is directory?false
---------------------------------------------
## How to get File last modified date in Java
- java.io.File class lastModified() returns last modified date in long
- we can construct date object in human readable format with this time.
- If file doesn’t exists, lastModified() returns 0L,
Code Snippet:
public class FileDate {
public static void main(String[] args) {
File file = new File("employee.xml");
long timestamp = file.lastModified();
System.out.println("employee.xml last modified date = "+new Date(timestamp));
}
}
Output:
employee.xml last modified date = Fri Dec 07 14:19:10 PST 2012
- After deleting employee.xml then the output is:
Output:
employee.xml last modified date = Wed Dec 31 16:00:00 PST 1969
---------------------------------------------
## Java File Path, Absolute Path and Canonical Path
### Getting file paths in java
- getPath()
- getAbsolutePath()
- getCanonicalPath()
- These methods returns String value of file Path based on how its created
- They just work on the pathname of the file used while creating the File object
Code Snippet:
public static void main(String[] args) throws IOException, URISyntaxException {
File file = new File("/Users/Iambharath/test.txt");
printPaths(file);
// relative path
file = new File("test.xsd");
printPaths(file);
// complex relative paths
file = new File("/Users/Iambharath/../Iambharath/test.txt");
printPaths(file);
// URI paths
file = new File(new URI("file:///Users/Iambharath/test.txt"));
printPaths(file);
}
private static void printPaths(File file) throws IOException {
System.out.println("Absolute Path: " + file.getAbsolutePath());
System.out.println("Canonical Path: " + file.getCanonicalPath());
System.out.println("Path: " + file.getPath());
}
- Using canonical path is best suitable to avoid any issues because of relative paths
- Java file path methods doesn’t check if file exists or not.
- They just work on the pathname of the file used while creating the File object
---------------------------------------------
## Java File Permissions
- Java File class contains methods to check file permissions for application user
- They also have some methods to set file permissions for the user and everybody else
- These File set permission methods return false if they are not able to set the file permissions
- This can happen due to user privilege
- For example, if I change the owner of my sample file to root
- Then all the set file permission method calls return false
Code Snippet:
public class JavaFilePermissions {
public static void main(String[] args) {
File file = new File("/Users/Iambharath/run.sh");
//check file permissions for application user
System.out.println("File is readable? "+file.canRead());
System.out.println("File is writable? "+file.canWrite());
System.out.println("File is executable? "+file.canExecute());
//change file permissions for application user only
file.setReadable(false);
file.setWritable(false);
file.setExecutable(false);
//change file permissions for other users
file.setReadable(true, false);
file.setWritable(true, false);
file.setExecutable(true, true);
}
}
--------------------------------------------------
## How to set File Permissions in Java Easily using Java 7 PosixFilePermission
- Java File class has the ability to set the file permissions but it’s not versatile
- The biggest drawback is that:
- we can divide file permissions into two set of users – owner and everybody else only
- We can’t set different file permissions for group and other users
- Java 7 has introduced PosixFilePermission Enum and java.nio.file.Files
- java.nio.file.Files includes a method setPosixFilePermissions(Path path, Set perms) that can be used to set file permissions easily
Code Snippet:
public class FilePermissions {
/**
* File Permissions Java Example using File and PosixFilePermission
* @param args
* @throws IOException
***/
public static void main(String[] args) throws IOException {
File file = new File("/Users/Iambharath/temp.txt");
//set application user permissions to 455
file.setExecutable(false);
file.setReadable(false);
file.setWritable(true);
//change permission to 777 for all the users
//no option for group and others
file.setExecutable(true, false);
file.setReadable(true, false);
file.setWritable(true, false);
//using PosixFilePermission to set file permissions 777
Set perms = new HashSet();
//add owners permission
perms.add(PosixFilePermission.OWNER_READ);
perms.add(PosixFilePermission.OWNER_WRITE);
perms.add(PosixFilePermission.OWNER_EXECUTE);
//add group permissions
perms.add(PosixFilePermission.GROUP_READ);
perms.add(PosixFilePermission.GROUP_WRITE);
perms.add(PosixFilePermission.GROUP_EXECUTE);
//add others permissions
perms.add(PosixFilePermission.OTHERS_READ);
perms.add(PosixFilePermission.OTHERS_WRITE);
perms.add(PosixFilePermission.OTHERS_EXECUTE);
Files.setPosixFilePermissions(Paths.get("/Users/Iambharath/run.sh"), perms);
}
}
--------------------------------------------------
## Java File Copy
- No Direct Methods on java.io.File class
- 4 Other ways are
- Using Input Stream and Output Stream
- Java 4 NIO FileChannels
- Apache Common FileUtils
- Java 7 Files.copy
### Using Input and Output Stream
Code Snippet:
private static void copyFileUsingStream(File source, File dest) throws IOException {
InputStream is = null;
OutputStream os = null;
try {
is = new FileInputStream(source);
os = new FileOutputStream(dest);
byte[] buffer = new byte[1024];
int length;
while ((length = is.read(buffer)) > 0) {
os.write(buffer, 0, length);
}
} finally {
is.close();
os.close();
}
}
### Using NIO FileChannels
- Java NIO classes were introduced in Java 1.4 and FileChannel can be used to copy file in java
- According to transferFrom() method javadoc, FileChannel is supposed to be faster than using Streams for java copy files
Code snippet:
private static void copyFileUsingChannel(File source, File dest) throws IOException {
FileChannel sourceChannel = null;
FileChannel destChannel = null;
try {
sourceChannel = new FileInputStream(source).getChannel();
destChannel = new FileOutputStream(dest).getChannel();
destChannel.transferFrom(sourceChannel, 0, sourceChannel.size());
}finally{
sourceChannel.close();
destChannel.close();
}
}
### Apache Common FileUtils
Code Snippet:
private static void copyFileUsingApacheCommonsIO(File source, File dest) throws IOException {
FileUtils.copyFile(source, dest);
}
### Java 7 Files.copy()
Code Snippet:
private static void copyFileUsingJava7Files(File source, File dest) throws IOException {
Files.copy(source.toPath(), dest.toPath());
}
-------------------------------------
createNewFile()
delete()
isDirectory()
lists()
exists()
renameTo() - move and rename both
isFile()
length()
mkdirs()
getCanonicalPath()
getPath()
getAbsolutePath()
// Permission
canRead()
canExecute()
canWrite()
setReadable(true)
setWriteable(false)
setExecutable(false)
Files.setPosixFilePermissions(Path.get(), Set)
inputStream to OutStream
destChannel.transferFrom(srcChannel,0, srcChannel.size())
FileUtils.copyFile(File, File)
Files.copy(File, File)
readAllByets(Path)
readAllLines(Path)
lines(Path, StCharSets.UTF_16)
FileReader