如何使用具有完整文件路径的java Scanner类？

Question

How do I use it with the complete path? For example: "/home/user/file.txt"?

public class ScannerSample {

  public static void main(String[] args) throws FileNotFoundException {
  //Z means: "The end of the input but for the final terminator, if any"
     String output = new Scanner(new File("file.txt")).useDelimiter("\\Z").next();
     System.out.println("" + output);
 }
}

if I do this:

public class ScannerSample {

  public static void main(String[] args) throws FileNotFoundException {
  //Z means: "The end of the input but for the final terminator, if any"
     String output = new Scanner(new File("/home/user/file.txt")).useDelimiter("\\Z").next();
     System.out.println("" + output);
 }
}

it generates the error:

java.io.FileNotFoundException: \home\user\file.txt (The system cannot find the path specified)
java.io.FileInputStream.open(Native Method)
java.io.FileInputStream.<init>(Unknown Source)
java.util.Scanner.<init>(Unknown Source)
util.CompareDevices.doPost(CompareDevices.java:54)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

Answer 1

If I understand your question then you could use File(String, String) constructor and the "user.home" property to construct that path like

new File(System.getProperty("user.home"), "file.txt")

or (on a DOS based system) if you really prefer

new File("c:/home/user/file.txt")

Edit

A more complete example, and using a try-with-resources statement

File f = new File(System.getProperty("user.home"), "file.txt");
try (Scanner scanner = new Scanner(f)) {
    scanner.useDelimiter("\\Z");
    String output = scanner.next();
    System.out.println(output);
} catch (Exception e) {
    e.printStackTrace();
}