Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,

Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

see Spiral Matrix I

public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        if (n<1) {
            return matrix;
        }

        generateMatrix(matrix, n, n, 0, 1);

        return matrix;        
    }

     private void generateMatrix(int[][] matrix, int rows, int columns, int level, int number) {
         if (rows<=0||columns<=0) {
             return;
         }

        // single row for not square matrix
        if (rows == 1) {
            for (int j = 0; j < columns; j++) {
                matrix[level][level+j] = number;
                number++;
            }
            return;
         }
         // single row for not square matrix
         if (columns == 1) {
            for (int i = 0; i < rows; i++) {
                matrix[level+i][level] = number;
                number++;
            }
            return;
         }

         // print from top left
         for (int j = 0; j < columns - 1; j++) {
             matrix[level][level+j] = number;
             number++;
         }
         // print from top right
         for (int i=0; i<rows-1; i++) {
             matrix[level+i][level+columns-1] = number;
             number++;
         }
         // print from bottom right
         for (int j=0; j<columns-1; j++) {
             matrix[level+rows-1][level+columns-1-j] = number;
             number++;
         }
         // print from bottom left
         for (int i=0; i<rows-1; i++) {
             matrix[level+rows-1-i][level] = number;
             number++;
         }
         generateMatrix(matrix, rows-2, columns-2, level+1, number);
     }