如何使用Java从MySQL数据库中获取图像

Question

I am trying to fetch every picture from a database and put it in a ArrayList, then printing it out. But I get a result that I dont understand.

The result:

Q1: Why does I get this result?

Q2: If I then want to show the picture with a ImageIcon, is ArrayList they way to go?

Here is my code:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.*;


public class ImageData {

    public static void main(String[] args){

        Connection con = null;
        Statement st = null;
        ResultSet rs = null;

        //databasens lokalisation, namn, användare & lösenord
        String url      = "jdbc:mysql://localhost:3306/";
        String dbname   = "101207-facemash";
        String user     = "root";
        String pwd      = "root";
        List<String> img = new ArrayList<String>();

        try{
            // Vi upprätta en anslutning till databasen med hjälp av anslutningen URL, dbnamnet, användarnamn och lösenord.
            con = DriverManager.getConnection(url + dbname, user, pwd);
            st = con.createStatement();
            rs = st.executeQuery("SELECT filename FROM images");

            while(rs.next()){
                img.add(rs.getString("filename"));
                System.out.println(img);
            }

         } catch (SQLException ex) {
                Logger lgr = Logger.getLogger(ImageData.class.getName());
                lgr.log(Level.SEVERE, ex.getMessage(), ex);

            } finally {
                try {
                    if (rs != null) {
                        rs.close();
                    }
                    if (st != null) {
                        st.close();
                    }
                    if (con != null) {
                        con.close();
                    }

                } catch (SQLException ex) {
                    Logger lgr = Logger.getLogger(ImageData.class.getName());
                    lgr.log(Level.WARNING, ex.getMessage(), ex);
                }
            }

        }

    }

Answer 1

You're retrieving the names of the image files, not the images themselves. If the images are stored in the data base, you'll have to retrieve them, either with a second query using the image name retrieved from the db with the first query or by retrieving a different column of the table (depending on how your db is organized). If they are stored in separate files (with the db containing only the file names), then you'll need to read each image in after retrieving the name. The ImageIO class will be useful for that. (Also, the ImageIcon class can retrieve images itself if you put the name in the form of a URL.)

As to using an ArrayList — that's generally a good way of dealing with an array of indeterminate size. I don't think that the fact that you're using an ImageIcon (which deals with one image at a time) is relevant to whether an ArrayList is a good idea.