javasqldb2-zos

Does setString() of SQL PreparedStatement will change null characters of string with space while inserting data to db2zos table?


Lets say I have one column with datatype of VARCHAR(500) in db2 zOS table and I wanted to insert data into that column using prepared statement. But that data/string has null character in between. e.g: "hello\0test\0example!". My question is does setString(index, str) will change those null characters with space or any other character ? or will get it inserted as it is ?

I tried inserting data but not sure. I found change in hex values of original string and inserted string.


Solution

  • '\0' in Java is considered null. Answering your question, your string will be inserted as-is. It will have null inside. It will then be dependent on your DBMS in your case 'db2' that how it will handle null inside string.

    I have tested it using MySQL . I am getting the same data which is inserted. Additionally I have verified it using char instead of String and by printing their ascii values which is just an additional check.

    I have used this code for printing every character value:

    private static void printStringAndAscii(String str)
        {
            System.out.println("Incoming String:" + str);
    
            System.out.println("Char with ASCII Values:");
    
            for (char c : str.toCharArray())
            {
                System.out.println(((int) c) + "-" + c);
            }
        }
    

    To test it with database I have first printed your given string and save in database, then extracted it and got it printed (deletion is for my own testing). I have tested following code with MySQL utf8 default colation :

        Class.forName("com.mysql.jdbc.Driver").newInstance();
    
        String originalString = "hello\0test\0example!";
    
        try (Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/corporate", "user", "pwd"))
        {
            printStringAndAscii(originalString);
    
            //Removing previously inserted entry
            PreparedStatement prepareStatement = connection.prepareStatement("DELETE FROM tip WHERE tip_id=?");
            prepareStatement.setInt(1, 1);
    
            int result = prepareStatement.executeUpdate();
            prepareStatement.close();
    
            System.out.println("Delete Result:" + result);
    
            //Inserting new entry
            prepareStatement = connection.prepareStatement("INSERT INTO tip(tip_id,tip_text) VALUES(?,?)");
            prepareStatement.setString(1, "1");
            prepareStatement.setString(2, originalString);
    
            result = prepareStatement.executeUpdate();
    
            System.out.println("Insert Result:" + result);
            prepareStatement.close();
    
            Statement statement = connection.createStatement();
    
            //Loading inserted entry from database
            ResultSet resultSet = statement.executeQuery("SELECT * FROM tip WHERE tip_id=1");
    
            if (resultSet.next())
            {
                //printing the fetched string from database
                String string = resultSet.getString(2);
                printStringAndAscii(string);
            }
    
            resultSet.close();
            statement.close();
            connection.close();
        }
        catch (Throwable e)
        {
            e.printStackTrace();
        }
    

    Interestingly, I have found out that System.out.println() prints until it finds '\0' (like c), however prepared statement inserts complete string with length.