java中的ArrayList打印最后插入的值？

Question

I have following java class

package com.picvik.model;

import java.util.Date;

public class ViewAlbum {

private Integer albumid;
private String albumname;
private String description;
private String location;
private Date date;
private Integer uid;

public Integer getAlbumid() {
    return albumid;
}
public void setAlbumid(Integer albumid) {
    this.albumid = albumid;
}
public String getAlbumname() {
    return albumname;
}
public void setAlbumname(String albumname) {
    this.albumname = albumname;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}
public String getLocation() {
    return location;
}
public void setLocation(String location) {
    this.location = location;
}
public Date getDate() {
    return date;
}
public void setDate(Date date) {
    this.date = date;
}
public Integer getUid() {
    return uid;
}
public void setUid(Integer uid) {
    this.uid = uid;
}

}

I am retrieving data from db and adding it to my array list like this

public ArrayList getAllAlbums(Integer uid) {
    ViewAlbum album = new  ViewAlbum();
    ArrayList<ViewAlbum>allAlbums = new ArrayList<ViewAlbum>();
    try {
        String qstring = "SELECT albumid, albumname, description, location," +
                " date, uid FROM picvik_picture_album WHERE " +
                "uid = '" + uid + "';";

        System.out.println(qstring);
        connection = com.picvik.util.MySqlConnection.getInstance().getConnection();
        ptmt = connection.prepareStatement(qstring);
        resultSet = ptmt.executeQuery();
        while(resultSet.next()) {
            //System.out.println(resultSet.getString("albumname"));
            album.setAlbumid(resultSet.getInt("albumid"));
            album.setAlbumname(resultSet.getString("albumname"));
            album.setDescription(resultSet.getString("description"));
            album.setLocation(resultSet.getString("location"));
            album.setDate(resultSet.getDate("date"));
            album.setUid(resultSet.getInt("uid"));
            allAlbums.add(album);
        }

        resultSet.close();
        ptmt.close();
        connection.close();


    } catch (Exception e) {
        e.printStackTrace();
    }   
    return allAlbums;
}

But when I am trying to print the values stored in array list. Its always giving me the last inserted record.

<div class="row">
                <div class="span10">
                    <s:iterator value="allAlbums">
                        <s:property value="albumname"/>
                    </s:iterator>   
                </div>
            </div>

Answer 1

Here,

ViewAlbum album = new ViewAlbum();
// ...

while (resultSet.next()) {
    album.setAlbumid(resultSet.getInt("albumid"));
    // ...
    allAlbums.add(album);
}

you're reusing the very same album instance for all records. The instance's data get overridden everytime in the loop. The list does not contain copies of the instance, but it contains copies of the reference to the single instance. You know, Java is Object Oriented.

You should be creating a new album instance per record. Move the instantiation to inside the loop.

// ...

while (resultSet.next()) {
    ViewAlbum album = new ViewAlbum();
    album.setAlbumid(resultSet.getInt("albumid"));
    // ...
    allAlbums.add(album);
}

See also:

• How can I pass an Integer class correctly by reference?

---

Unrelated to the concrete problem, you should be closing JDBC resources in the finally block, or be opening them in the try() try-with-resources statement, otherwise they will still leak away in case of an exception during executing the query or processing the result set. You should also move the declarations of JDBC resources to inside the method block, otherwise you'll run into threadsafety issues as well. Last but not least, you should use the setter methods of PreparedStatement to set user-controlled variables in a SQL string. If they were strings, you'd have a SQL injection attack hole.

See also:

• Java Iterator backed by a ResultSet
• JDBC MySql connection pooling practices to avoid exhausted connection pool

Answer 2

You have only one instance of ViewAlbum and you are playing(setting the values) only with that single instance throughout the loop. So after completition of loop you have only one object inserted into ArrayList for N(Size of Resultset) no of times.