Java 17 Recipes

8-5. Obtaining the Java Execution Path
 Problem
You want to get the path where the Java program is running.
 Solution
Invoke the System class’s getProperty method. The following is an example.
String path = System.getProperty("user.dir");
The main class is:
public class Ch_8_5_path {
public static void main(String[] args) {
String path = System.getProperty("user.dir");
System.out.println(path);
}
}
And the output in a windows OS is:
C:\eclipse-workspace\java17Recipes
 How It Works
When a Java program starts, the JRE updates the user.dir system property to record 
where the JRE was invoked. The solution example passes the "user.dir" property name 
to the getProperty method, which returns the value.
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8-6. Copying a File
 Problem
You need to copy a file from one folder to another.
 Solution
From the default 
java.nio.file
.FileSystem abstract class, you create the “to” and 
“from” paths where the files/folders exist and then use the Files.copy static method 
to copy files between the created paths.
public static void main (String[] args) {
Ch_8_6_CopyFileExample exampleCh86 = new Ch_8_6_CopyFileExample();
exampleCh86.copyFile();
}
private void copyFile() {
FileSystem fileSystem = FileSystems.getDefault();
Path sourcePath = fileSystem.getPath("file.log");
Path targetPath = fileSystem.getPath("file2.log");
System.out.println("Copy from "+sourcePath.toAbsolutePath().
toString()+
" to "+targetPath.toAbsolutePath().toString());
try {
Files.copy(sourcePath, targetPath, StandardCopyOption.REPLACE_
EXISTING);
} catch (IOException e) {
e.printStackTrace();
}
}
 How It Works
In the new NIO.2 libraries, Java works with an abstraction level that allows for more direct 
manipulation of file attributes belonging to the underlying operating system. FileSystems.
getDefaults() gets the usable abstract system on which you can do file operations.
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After getting the default FileSystem object, you can query for file objects. In the 
NIO.2 file, folders and links are all called paths. Once you get a path, you can perform 
operations with it. In this example, Files.copy is called with the source and destination 
paths. The last parameter refers to the different copy options. The different copy options 
are file system dependent, so make sure that the one you choose is compatible with the 
operating system you intend to run the application in.