Question

I am trying to update a column in already exists MySQL table. The values must be read from a text file, and then they must be inserted into the specified column.

I have tried the following:

int counter=0;
        while((fileLine=in.readLine())!=null) 
        { 
            System.out.println("Line read is: "+fileLine);

                //execute db insertion
                try {
                    //insert in the database
                    Query= "update db.table set col4=?";    //database
                    preparedStmt3 = DBConnection.con.prepareStatement(Query); 
                    preparedStmt3.setString (1, fileLine);
                    preparedStmt3.executeUpdate();
                    System.out.println("Complete update statement for row: "+counter);
                    counter++;
                } catch (Exception e) {
                    System.out.println("DB_Error:_"+ e.toString());
                }

        } //end while loop 

I have tried to output fileLine value and it seems correct and change correctly with every loop round. But, after I run the program and check the database, I find that the value inserted is the last line only (and this repeated in all records, it is not what I am supposed to do, which is insert every line in records consequently). what is the cause for this problem ?

EDIT:
The text file contains the following lines:
aaa
bbb
ccc
ddd
eee
fff

The run output after I added some printline statements to see debug is as the following:

while the DB contains the last line inserted only

Answer 1

try this,

Connection conn = ConnectionBean.getInstance().getDBConnection();
int counter=0;
String fileLine;
BufferedReader in;
String query1 = "select id from test"; // get all the id's from the table you wanna do  the update
ArrayList<Integer> al = new ArrayList<Integer>(); // store them in an arraylist
try {
PreparedStatement stmnt = conn.prepareStatement(query1);
ResultSet rs = stmnt.executeQuery();
while(rs.next()) {
    al.add(rs.getInt("id"));
}
}
catch(Exception ex) {
    ex.printStackTrace();
}

try {
    in = new BufferedReader(new FileReader("file1.txt"));
    int h=1;
    while((fileLine=in.readLine())!=null && al.size()>0)  
    {   

        String query="UPDATE chaitu.test SET col=? WHERE id="+h ;
        PreparedStatement statement = conn.prepareStatement(query);

        statement.setString(1, fileLine);
        statement.executeUpdate();
        h++;
    } //end while loo


} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (SQLException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
    }