Inserting tuple into database - mysql

Question

I am trying to check if a tuple is present. If it is then return the ID. If it is not present then insert it, create a new ID, and return that ID. This is what I have, however when I return the productID at the end, it is 0. I also keep getting the error:
org.postgresql.util.PSQLException: ERROR: syntax error at or near "7"Position: 360
Can anyone please help me understand where I am going wrong here? Thanks in advance
public int addProduct(String name, String manufacturer) throws SQLException{
int productId = 0;
connection.setAutoCommit(false);
Statement st = null;
st = this.connection.createStatement();
try {
int prod = 0;
Statement stmt = this.connection.createStatement();
stmt.execute("SELECT MAX(product_id) FROM Products");
ResultSet result = stmt.getResultSet();
if (result.next())
prod = result.getInt(1) + 1;
System.out.println(prod);
st.executeUpdate(
"DO " +
"$do$ " +
"BEGIN " +
"IF NOT EXISTS (SELECT 1 FROM Products WHERE " +
"Products.name = " + name + " AND " +
"Products.manufacturer = " + manufacturer + ") THEN " +
"INSERT INTO Products (product_id, name, category, manufacturer) " +
"VALUES (" + prod + ", " + name + ", " +
"" + null + ", " + manufacturer + "); " +
"END IF; " +
"END; " +
"$do$ ; "
);
ResultSet rsFind = st.executeQuery(
"SELECT Products.product_id FROM Products WHERE " +
"Products.name = '" + name + "' AND " +
"Products.manufacturer = '" + manufacturer + "; "
);
if (rsFind.next()) {
productId = rsFind.getInt("product_id");
System.out.println(productId);
}
} catch (SQLException e) {
System.err.println(e);
} finally {
if (st != null) st.close();
}
this.connection.setAutoCommit(true);
return productId;
}