Java: Insert batched data in MySQL database with Prepared Statements

Question

I have created a custom function to insert data in my MySQL database. The functions first creates a query based on the input given. The query wil look like INSERT INTO tableName (columnName1, ..., columnNamei) VALUES (?, ..., ?), ..., (?, ...,?) . After that, the PreparedStatement needs to made, which contains the real values. These need to be added to a batch, because I want to add multiple rows at once (as showed here: Java: Insert multiple rows into MySQL with PreparedStatement ). Here is the code:

insertData() Function

public static void insertData(String table, List<HashMap<String, Object>> list) throws SQLException {

    //Create query: make sure all of the rows in the table get the same amount of values passed
    //Prepare colnames string
    String colNamesParsed = "";
    int counter = 1;

    //Iterate over only the first hashmap of the list (THATS WHY ALL THE ROWS NEED TO HAVE THE SAME AMOUNT OF VALUES PASSED)
    for (String colName : list.get(0).keySet()) {

        //Check if it is the last col name
        if (counter != list.get(0).keySet().size()) {
            colNamesParsed = colNamesParsed + colName+", ";
        }
        else {
            colNamesParsed = colNamesParsed + colName;
        }

        counter++;
    }

    //Now create the place holder for the query variables
    String queryVariablesPlaceholder = "";
    int rowSize = 0;
    for (HashMap<String, Object> row : list) {

        //This part is to check if all row sizes are equal
        if (rowSize == 0) {
            rowSize = row.values().size();
        }
        else {
            //Check if the rowsize is equal for all rows
            if (row.values().size() != rowSize) {
                System.out.println("The rows of the arrays are from a different size");
                return;
            }
        }

        String queryVariablesRow = "(?, ";
        for (int j = 1; j < (row.values().size()-1); j++) {
            queryVariablesRow = queryVariablesRow+"?, ";
        }
        queryVariablesRow = queryVariablesRow+"?)";

        //Make sure the query does not start with a comma
        if (queryVariablesPlaceholder.equals("")) {
            queryVariablesPlaceholder = queryVariablesRow;
        }
        else {
            queryVariablesPlaceholder = queryVariablesPlaceholder+", "+queryVariablesRow;
        }
    }

    //The MySQL query needs to be built now
    String query = "INSERT INTO "+table+" ("+colNamesParsed+") VALUES "+queryVariablesPlaceholder+";";
    System.out.println(query);

    //Init prepared statement
    PreparedStatement statement = con.prepareStatement(query);

    for (HashMap<String, Object> map : list) {

        int varCounter = 1;
        //Iterate over all values that need to be inserted
        for (Object object : map.values()) {

            if (object instanceof Integer) {
                statement.setInt(varCounter, Integer.parseInt(object.toString()));
            }
            else if (object instanceof String) {
                statement.setString(varCounter, object.toString());
            }
            else if (object instanceof Timestamp) {
                statement.setTimestamp(varCounter, parseStringToTimestamp(object.toString()));
            }
            else if (object instanceof Double) {
                statement.setDouble(varCounter, Double.parseDouble(object.toString()));
            }
            System.out.println(varCounter);
            varCounter++;
        }

        //Add row to the batch
        try {
            statement.addBatch();
        }
        catch (SQLException e) {
            e.printStackTrace();
        }

    }
    //Execute the query, which is in fact the batch
    statement.executeBatch();
}

When I want to insert some data in the database, I execute the following code:

Functional part

List<HashMap<String, Object>> list = new ArrayList<>();
    for (Object object : listOfObjects) {
        HashMap<String, Object> map = new HashMap<>();
        map.put("columnName1", object.getSomeValue());
        /....../
        map.put("columnName2", object.getSomeOtherValue());

        list.add(map);
    }

    Functions.insertData("tableName", list);

Creating the dynamic query seems to work perfectly. However, I can't get the statement.addBatch() to work. It keeps giving me the following error:

java.sql.SQLException: No value specified for parameter 9

I don't get it, because I only have 8 parameters to pass in every unit of the batch. My target table has 9 columns, so I tried to add a value for that column, but then it says: No value specified for parameter 10 , so it seems like it isn't closing the 'batch unit' or something.

What am I missing here?

Any help is greatly appreciated!

Answer 1

This

INSERT INTO tableName (columnName1, ..., columnNamei) VALUES (?, ..., ?), ..., (?, ...,?) 

is not standard SQL syntax. If you use this JDBC will a parameter for each "?" in your query.

Use:

INSERT INTO tableName (columnName1, ..., columnNamei) VALUES (?, ..., ?)

and add every statement to a batch.