Use JDK native file operations
In JDK, we can use Java I/O API to manipulate files and folders. The Java I/O API provides many classes and interfaces to manipulate files and folders. Following are some commonly used Java I/O API classes:
- -
java.io.FileUsed to represent the path of files and folders, as well as the properties and operations of files and folders. - -
java.io.FileInputStreamUsed to read data from a file. - -
java.io.FileOutputStreamUsed to write data to a file. - -
java.io.FileReaderUsed to read characters from a file. - -
java.io.FileWriterUsed to write characters to a file. - -
java.io.BufferedReaderUsed to read text from a character stream. - -
java.io.BufferedWriterUsed to write text to a character stream.
Create a file
In Java, we can create a file using java.io.Filethe class . Here is an example:
import java.io.File;
public class FileCreateExample {
public static void main(String[] args) {
File file = new File("test.txt");
try {
if (file.createNewFile()) {
System.out.println("File created: " + file.getName());
} else {
System.out.println("File already exists.");
}
} catch (Exception e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we created an Fileobject and then used createNewFilethe method to create a file named "test.txt". If the file already exists, "File already exists." will be printed.
read file
In Java, we can use java.io.FileInputStreamthe class to read data from a file. Here is an example:
import java.io.FileInputStream;
public class FileReadExample {
public static void main(String[] args) {
try {
FileInputStream fileInputStream = new FileInputStream("test.txt");
int i;
while ((i = fileInputStream.read()) != -1) {
System.out.print((char) i);
}
fileInputStream.close();
} catch (Exception e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we use FileInputStreamthe class to read data from the "test.txt" file. Then, we use whilea loop to read the contents of the file character by character and print it out.
write to file
In Java, we can write data to a file using java.io.FileOutputStreamthe class . The following is an example
import java.io.FileOutputStream;
public class FileWriteExample {
public static void main(String[] args) {
try {
FileOutputStream fileOutputStream = new FileOutputStream("test.txt");
String text = "Hello, World!";
byte[] bytes = text.getBytes();
fileOutputStream.write(bytes);
fileOutputStream.close();
System.out.println("Successfully wrote to the file.");
} catch (Exception e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we use FileOutputStreamthe class to write the "Hello, World!" string to the "test.txt" file.
Delete Files
In Java, we can delete a file using java.io.Filethe class . Here is an example:
import java.io.File;
public class FileDeleteExample {
public static void main(String[] args) {
File file = new File("test.txt");
if (file.delete()) {
System.out.println("File deleted: " + file.getName());
} else {
System.out.println("Failed to delete the file.");
}
}
}In this example, we created an Fileobject and then used deletethe method to delete a file named "test.txt".
copy files
In Java, we can use java.io.FileInputStreamthe and java.io.FileOutputStreamclass to copy files. Here is an example:
import java.io.FileInputStream;
import java.io.FileOutputStream;
public class FileCopyExample {
public static void main(String[] args) {
try {
FileInputStream fileInputStream = new FileInputStream("test.txt");
FileOutputStream fileOutputStream = new FileOutputStream("test_copy.txt");
byte[] buffer = new byte[1024];
int length;
while ((length = fileInputStream.read(buffer)) > 0) {
fileOutputStream.write(buffer, 0, length);
}
fileInputStream.close();
fileOutputStream.close();
System.out.println("File copied successfully.");
} catch (Exception e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we use FileInputStreamthe class to read data from the "test.txt" file, and FileOutputStreamthe class to write data to the "test_copy.txt" file.
rename file
In Java, we can rename a file using java.io.Filethe class . Here is an example:
import java.io.File;
public class FileRenameExample {
public static void main(String[] args) {
File file = new File("test.txt");
File renamedFile = new File("test_renamed.txt");
if (file.renameTo(renamedFile)) {
System.out.println("File renamed successfully.");
} else {
System.out.println("Failed to rename the file.");
}
}
}In this example, we create an Fileobject and use renameTothe method to rename the "test.txt" file to "test_renamed.txt".
find files
In Java, we can use java.io.Filethe class to find files and folders. Here is an example:
import java.io.File;
public class FileSearchExample {
public static void main(String[] args) {
File dir = new File(".");
File[] files = dir.listFiles();
for (File file : files) {
if (file.isFile()) {
System.out.println("File: " + file.getName());
} else if (file.isDirectory()) {
System.out.println("Directory: " + file.getName());
}
}
}
}In this example, we create an Fileobject to represent the current directory, then listFilesuse the method to get all the files and folders in the current directory, and use a for loop to print the name of each file and folder.
Using the Apache Commons IO library
In addition to using JDK's native file operation classes, you can also use third-party class libraries for file operations. Apache Commons IO is a very popular Java file operation class library, which provides many useful classes and methods, which can make file operations easier for us. Below is some sample code showing how to use the Apache Commons IO library for file operations.
write to file
Writing to files can be even simpler with the Apache Commons IO library. Here is an example of writing to a file using FileUtilsthe class :
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
public class FileWriteExample {
public static void main(String[] args) {
try {
File file = new File("test.txt");
String text = "Hello, World!";
FileUtils.writeStringToFile(file, text, "UTF-8");
System.out.println("Successfully wrote to the file.");
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we use FileUtils.writeStringToFilethe method to write a string to a file. This method automatically creates the file, or overwrites the existing file if it already exists.
Delete Files
Deleting files is also very simple using the Apache Commons IO library. Here is an example of using FileUtilsthe class to delete a file:
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
public class FileDeleteExample {
public static void main(String[] args) {
File file = new File("test.txt");
try {
FileUtils.forceDelete(file);
System.out.println("File deleted: " + file.getName());
} catch (IOException e) {
System.out.println("Failed to delete the file.");
e.printStackTrace();
}
}
}In this example, we use FileUtils.forceDeletethe method to delete the file. FileUnlike the method of the class delete, FileUtils.forceDeletethe method can delete non-empty folders.
copy files
Copying files is also very simple using the Apache Commons IO library. Here is an example of copying files using FileUtilsthe class :
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
public class FileCopyExample {
public static void main(String[] args) {
try {
File srcFile = new File("test.txt");
File destFile = new File("test_copy.txt");
FileUtils.copyFile(srcFile, destFile);
System.out.println("File copied successfully.");
} catch (IOException e)
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}In this example, we use FileUtils.copyFilethe method to copy one file to another. This method will automatically create the target file, if the target file already exists, it will overwrite the existing file.
list files and folders
Listing files and folders is also very simple using the Apache Commons IO library. Here is an example of listing files and folders using FileUtilsthe class :
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.util.Collection;
public class FileSearchExample {
public static void main(String[] args) {
File dir = new File(".");
Collection<File> files = FileUtils.listFilesAndDirs(dir, null, true);
for (File file : files) {
if (file.isFile()) {
System.out.println("File: " + file.getName());
} else if (file.isDirectory()) {
System.out.println("Directory: " + file.getName());
}
}
}
}In this example, we use FileUtils.listFilesAndDirsthe method to get all the files and folders in the specified directory. This method returns Collectionan Fileobject that contains all files and folders.
in conclusion
File manipulation in Java is a very common task. JDK provides many useful classes and methods that allow us to easily perform file operations. In addition, there are many third-party libraries that can help us perform file operations more easily, such as Apache Commons IO and so on. Whether you choose to use the JDK or a third-party library, file manipulation is easy.