如何在 JDBC 中使用 PreparedStatement

Question

I'm new to JDBC and Java.

I'm coming from Javascript and Typescript background. I decided to learn JDBC with Oracle by creating a small basic project.

I'm using JDK 8 . I'm following this study material: TutorialsPoint-PreparedStatement . I figured out that problem is with my DataService .

Here's my DataService class:

import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DataService {
    Connection con;
    PreparedStatement pstmt;

    static String branch_name="";
    static LocalDate branch_created_on;
    static String branch_pulled_from="";

    DataService() {
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","system","scott");
        }
        catch(Exception e){ 
            System.out.println(e);
        }
    }

    public void getValue() {
        branch_name=AddNewBranchRecord.branchNameTextField.getText();
        branch_created_on=AddNewBranchRecord.datePicker1.getValue();
        branch_pulled_from=(String) AddNewBranchRecord.combo_box_1.getValue();
    }

    public void putValue() {
        System.out.println("Branch name: "+branch_name);
        System.out.println("Branch created on: "+branch_created_on);
        System.out.println("Branch pulled from: "+branch_pulled_from);
    }

    public void insertRecord() {
        System.out.println("Adding a record...");
        getValue();
        try {
            String sql;
            sql = "insert into mybranches values (branch_name, branch_created_on, branch_pulled_from);";
            pstmt = con.prepareStatement(sql);
        } catch (SQLException ex) {
            Logger.getLogger(DataService.class.getName()).log(Level.SEVERE, null, ex);
        }
        pstmt .close();
    }
}

I'm sure there's something that I missed out.

I'm not getting any error or exception but no row is inserted in the database.

I cross checked with select * from mybranches .

However, the same code works perfectly if I use the normal Statement .

Answer 1

You create the PreparedStatement but you don't use it.

A prepared statement is there to eg insert different values into a table multiple times.

You create the PreparedStatement once like you would execute a normal Statement and include ? instead of the values that differ.

If you want to execute it, you have to set the values (the ? s will be replaced with them) by using the setXXX(int,Type) methods and then execute it with .execute() .

As pointed out in the comments of the question, the SQL code is not valid. The sql code prepared statement is just like the sql code of a regular statement but the values that change all the time are replaced by ? .

The SQL code of the prepared statement would be something like that:

INSERT INTO mybranches VALUES (?,?,?)

If you want to use the PreparedStatement , you could set the values like that:

pstmt.setString(1,branch_name);
pstmt.setObject(2,branch_created_from);
pstmt.setString(3,branch_pulled_from);

Finally, execute it with

pstmt.execute();

Note that (as I already said) you should create the PreparedStatement once and not every time you execute the insertRecord() method and in that method, you should just call the setXXX methods and the execute() method.

The PreparedStatement (and the Connection object) should be closed when you don't need it anymore.

Also, as @ TT. suggests in the comments, you should specify the columns in an INSERT statement. It would be something like

INSERT INTO mybranches (name,createdFrom,pulledFrom) VALUES (?,?,?)