带有JDBC的MySQL，没有while循环，select不起作用，with不需要下一个查询

Question

FileReader fr = new FileReader(new File("D:\\folder\\mySQLFile1.txt"));
BufferedReader br = new BufferedReader(fr);

while((s = br.readLine()) != null) {
    sb.append(s);
}
br.close();

String sbq=sb.toString();
String S1 = sbq.replaceAll("(?:/\\*(?:[^*]|(?:\\*+[^*/]))*\\*+/)|(?://.*)","");
String[] inst = S1.split(";|/");

for (int i = 0; i<inst.length; i++) {           
    if (!inst[i].trim().equals("")) { 
        ResultSet resultSet = stmt.executeQuery(inst[i]);
        ResultSetMetaData rsmd = resultSet.getMetaData();
        int columnsNumber = rsmd.getColumnCount();
        // while (resultSet.next()) {
            for (int x = 1; x <= columnsNumber; x++) {
                String columnValue = resultSet.getString(x);
                System.out.print(columnValue + " " );
            }
            System.out.println("");
        // }
    }
    System.out.println();
}

Without while loop, select doesn't work, with while it doesn't take next query.

Answer 1

The ResultSet is very general propose interface and it is cursor based .

Here is quote from official documentation:

A ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The next method moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set.

This is means you have to perform next to move cursor. Here is the graphical illustration.

So why ResultSet is cursor based?

To allow underlying implementation not load the potentially huge number of rows into memory. The cursor is the very common pattern to kind of scroll over the potentially big data. For example the PgResultSet uses ResultCursor to do so.

PS Also please always perform ResultSet.close() to free up resources.

Answer 2

First, in using replaceAll you must escape all character, one time for Java, and second time for regex.

So if you use a \\ in a replaceAll you must write like that \\\\\\\\ .

Second, print with sysout the content of inst[i] before send it.