使用MySQL连接器Java改善查询

Question

When I have to deal with MySQL DB in Java, I use the driver developed by MySQL itself. It is very easy to work with this library but I have a question about performance. What "closing" method should I use each time I make a query to a DB?

If for example I have a for loop, which makes more inserts in DB, what should I use ?

private void invioInsert(String query){
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();
    } catch (Exception E) {
        System.err.println("Non trovo il driver da caricare.");
        E.printStackTrace();
    }
    try {
        PreparedStatement statement = conn.prepareStatement(query);
        statement.execute();
        statement.close();

    } catch (SQLException E) {
        System.out.println("SQLException: " + E.getMessage());
        System.out.println("SQLState:     " + E.getSQLState());
        System.out.println("VendorError:  " + E.getErrorCode());
    }
}

For example the for loop can be:

for(int i=0; i<=10, i++){
    String query = "INSERT TABLE VALUES ("+i+")";
    sendQuery(query);
}

So this is the complete code of for loop:

for (int i = 0; i < file.getList().size(); i++) {
        StringTokenizer tokenizer = new StringTokenizer(file.getList().get(i).replace("\"", ""));
        String ID = tokenizer.nextToken("|");
        int j = 0;
        while(j<5){
            tokenizer.nextToken("|");
            j++;
        }
        String voto = tokenizer.nextToken("|");
        String query = "Insert RisultatiGiocatori values ('"+giornata+"','"+ID+"','"+voto+"')";
        invioInsert(query);
    }

Answer 1

This is a classic usecase for a PreparedStatement with batch execution:

String query = "INSERT TABLE VALUES (?)";
try {
    PreparedStatement statement = conn.prepareStatement(query);
    for(int i=0; i<=10, i++){
        statement.setInt(1, i);
        statement.addBatch();
    }
    statement.executeBatch();
    statement.close();

} catch (SQLException E) {
    System.out.println("SQLException: " + E.getMessage());
    System.out.println("SQLState:     " + E.getSQLState());
    System.out.println("VendorError:  " + E.getErrorCode());
}

Answer 2

Never create a PreparedStatement inside loops. Try to create the statement outside and you'll have a great improvement.