I could not find a library that allows you to fill the matrix in a spiral, like this:

1 2 3
8 9 4
7 6 5

or vice versa – from the center outward.

Who knows how to do it yourself?

Answer 1, authority 100%

Use the getSpiralMatrix () method implemented below:

package com.example;
import java.util.stream.IntStream;
public class SpiralMatrix {
  public int [] [] getSpiralMatrix (int n, boolean reverse) {
    int [] [] matrix = new int [n] [];
    IntStream.range (0, n) .forEach (i - & gt; matrix [i] = new int [n]);
    int x = 0;
    int y = 0;
    int z = n;
    for (int i = 0, j = n * n; i & lt; j;) {
      matrix [x] [y] = reverse? j - i ++: ++ i;
      if (x & lt; z + (n - z) / 2 - 1 & amp; & amp; y == (n - z) / 2) {
        x ++;
      } else if (x == z + (n - z) / 2 - 1 & amp; & amp; y & lt; z + (n - z) / 2 - 1) {
        y ++;
      } else if (x & gt; (n - z) / 2 & amp; & amp; y == z + (n - z) / 2 - 1) {
        x--;
      } else if (x == (n - z) / 2 & amp; & amp; y & gt; (n - z) / 2 + 1) {
        y--;
      } else {
        x ++;
        z - = 2;
      }
    }
    return matrix;
  }
  public static void main (String [] args) {
    SpiralMatrix sp = new SpiralMatrix ();
    int n = 9;
    int [] [] matrix = sp.getSpiralMatrix (n, true);
    printMatrix (matrix);
    System.out.println ("==========================");
    matrix = sp.getSpiralMatrix (n, false);
    printMatrix (matrix);
  }
  private static void printMatrix (int [] [] matrix) {
    IntStream.range (0, matrix.length) .forEach (i - & gt; {
      IntStream.range (0, matrix.length) .forEach (j - & gt; System.out.printf ("% 02d", matrix [j] [i]));
      System.out.println ();
    });
  }
}

This demo code will print:

81 80 79 78 77 76 75 74 73
50 49 48 47 46 45 44 43 72
51 26 25 24 23 22 21 42 71
52 27 10 09 08 07 20 41 70
53 28 11 02 01 06 19 40 69
54 29 12 03 04 05 18 39 68
55 30 13 14 15 16 17 38 67
56 31 32 33 34 35 36 37 66
57 58 59 60 61 62 63 64 65
============================
01 02 03 04 05 06 07 08 09
32 33 34 35 36 37 38 39 10
31 56 57 58 59 60 61 40 11
30 55 72 73 74 75 62 41 12
29 54 71 80 81 76 63 42 13
28 53 70 79 78 77 64 43 14
27 52 69 68 67 66 65 44 15
26 51 50 49 48 47 46 45 16
25 24 23 22 21 20 19 18 17

Answer 2

// at PascalABC.net
// Matrix in a spiral from any corner or from the center, clockwise or counterclockwise
begin
 var n: = 3;
 var FromCenter: = 0; // 0 - from corner 1 - from Center
 Var Center: = Ceil (n / 2) - 1; // The coordinate of the center of the matrix
 var (i, j, Direction, nEven): = (0, 0, 1, n.IsEven? 1: 0); // from the top left
 if FromCenter = 1 then (i, j, Direction, nEven): = (Center, Center, 1, 0); // from the center
 var Matrix: = new integer [n, n];
 for var Element: = 1 to n * n do
  begin
   Matrix [i, j]: = Element; {
[i, j] - from the top left clockwise; from the Center to the right clockwise
[j, i] - from the top left counterclockwise; from Center down counterclockwise
[n-1-i, j] - from the bottom left counterclockwise; from Center to the right counterclockwise
[n-1-j, i] - from the bottom left clockwise; from the center up clockwise
[j, n-1-i] - from the top right clockwise; from Center down clockwise
[i, n-1-j] - top right counterclockwise; from Center to the left counterclockwise
[n-1-i, n-1-j] - from the bottom right clockwise; from Center to the left clockwise
[n-1-j, n-1-i] - from the bottom right counterclockwise; from the center up clockwise
}
    case Direction of
     1: begin {right}
      inc (j);
      if (Center - i + FromCenter) = (j - Center - nEven) then Direction: = 2;
      end;
     2: begin {down}
      inc (i); 
IF i = j pin direction: = 3;
      end;
     3: Begin {Left}
      DEC (J);
      if (I - center) = (center - J + NEVEN) Then direction: = 4;
      end;
     4: Begin {up}
      DEC (I);
      if (i - 1) = (J - to the center) of the direction: = 1;
      End.
    end;
   end;
  Matrix.printLN;
end.