java - GWT:尝试通过 GWT AsyncCallback 检索对象列表，我得到一个仅包含最后一个值的列表

Question

我正在尝试通过 AsyncCallback 调用检索对象列表。一切看起来都很好，直到我查看 onSuccess 过程中的列表数据。事实上，我收到了一个具有正确行数的列表，但每一行都与 SQL 语句最后检索到的行相同

这是 EntryPoint 客户端模块:

package com.fantaprica.client;

import java.util.List;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.fantaprica.shared.GameDay;


/**
 * Entry point classes define <code>onModuleLoad()</code>.
 */
public class Fantaprica implements EntryPoint {

private final ODBConnectionAsync odbconnectionSvc = GWT
        .create(ODBConnection.class);

/**
 * Entry point classes define <code>onModuleLoad()</code>.
 */

public void onModuleLoad() {

    odbconnectionSvc
            .getGameDayList(new AsyncCallback<List<GameDay>>() {
                public void onFailure(Throwable caught) {
                }

                public void onSuccess(List<GameDay> result) {

                    System.out.println("#########################################");
                    System.out.println("OnModuleLoad");
                    for (int i = 0; i < result.size(); i++) {
                        System.out.println("index="+i);
                        System.out.println("result.get(i).getGameDayCompetition()="+result.get(i).getGameDayCompetition());
                        System.out.println("result.get(i).getGameDayCupFl()"+result.get(i).getGameDayCupFl());
                        System.out.println("result.get(i).getGameDayId()="+result.get(i).getGameDayId());
                        System.out.println("result.get(i).getGameDayOrder()="+result.get(i).getGameDayOrder());                                         
                        System.out.println("result.get(i).getGameDaySeason()="+result.get(i).getGameDaySeason());
                    }
                }
            });
}
}

这是服务器端的实现:

package com.fantaprica.server;

import java.text.ParseException;
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;

public class Connection2DB {

public static ResultSet resultset(String p_sql_statement) throws ParseException {

    //String db_file_name_prefix = "/home/dario/workspace/fantaprica/src/com/fantaprica/server/database/database";
    //String db_file_name_prefix = "/home/dario/workspace/fantaprica/war/database/database";
    String db_file_name_prefix = "/home/dario/Workspace/Fantaprica/war/fantaprica/database/database";
    Connection con = null;

    // connect to the database. This will load the db files and start the
    // database if it is not alread running.
    // db_file_name_prefix is used to open or create files that hold the
    // state
    // of the db.
    // It can contain directory names relative to the
    // current working directory
    try {
        Class.forName("org.hsqldb.jdbcDriver");
        con = DriverManager.getConnection("jdbc:hsqldb:file:"
                + db_file_name_prefix, // filenames prefix
                "sa", // user
                ""); // pass
        Statement statement = con.createStatement();
        ResultSet rs = statement.executeQuery(p_sql_statement);
        System.out.println("query "+p_sql_statement+" eseguita");
        statement.close();
        con.close();
        return rs;
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(TestConnection.class.getName()).log(Level.SEVERE,
                null, ex);
        System.out.println("errore "+ex.toString());
        return null;
    } catch (SQLException ex) {
        Logger.getLogger(TestConnection.class.getName()).log(Level.SEVERE,
                null, ex);
        ex.printStackTrace();
        System.out.println("errore "+ex.toString());
        return null;
    }

}

public static void  execstmt(String p_sql_statement) throws ParseException {

    String db_file_name_prefix = "/home/dario/Workspace/Fantaprica/war/fantaprica/database/database";
    Connection con = null;

    // connect to the database. This will load the db files and start the
    // database if it is not alread running.
    // db_file_name_prefix is used to open or create files that hold the
    // state
    // of the db.
    // It can contain directory names relative to the
    // current working directory
    try {
        Class.forName("org.hsqldb.jdbcDriver");
        con = DriverManager.getConnection("jdbc:hsqldb:file:"
                + db_file_name_prefix, // filenames prefix
                "sa", // user
                ""); // pass
        Statement statement = con.createStatement();
        statement.executeUpdate(p_sql_statement);

        System.out.println("statement "+p_sql_statement+" eseguito");

        statement.close();
        con.close();

    } catch (ClassNotFoundException ex) {
        Logger.getLogger(TestConnection.class.getName()).log(Level.SEVERE,
                null, ex);
        System.out.println("errore "+ex.toString());

    } catch (SQLException ex) {
        Logger.getLogger(TestConnection.class.getName()).log(Level.SEVERE,
                null, ex);
        ex.printStackTrace();
        System.out.println("errore "+ex.toString());
    }

}

}

当我运行代码时，我得到以下结果:

#########################################
ODBConnectionImpl
Start creating the list
scanning resultset
v_game_day_tmp.getGameDayCompetition()=campionato
v_game_day_tmp.getGameDayCupFl()=false
v_game_day_tmp.getGameDayId()=0
v_game_day_tmp.getGameDayOrder()15
v_game_day_tmp.getGameDaySeason()2012/2013
0
index=0
v_game_day_list.get(i).getGameDayCompetition()=campionato
v_game_day_list.get(i).getGameDayCupFl()=false
v_game_day_list.get(i).getGameDayId()=0
v_game_day_list.get(i).getGameDayOrder()=15
v_game_day_list.get(i).getGameDaySeason()=2012/2013
scanning resultset
v_game_day_tmp.getGameDayCompetition()=campionato
v_game_day_tmp.getGameDayCupFl()=false
v_game_day_tmp.getGameDayId()=1
v_game_day_tmp.getGameDayOrder()14
v_game_day_tmp.getGameDaySeason()2012/2013
1
index=1
v_game_day_list.get(i).getGameDayCompetition()=campionato
v_game_day_list.get(i).getGameDayCupFl()=false
v_game_day_list.get(i).getGameDayId()=1
v_game_day_list.get(i).getGameDayOrder()=14
v_game_day_list.get(i).getGameDaySeason()=2012/2013
scanning resultset
v_game_day_tmp.getGameDayCompetition()=campionato
v_game_day_tmp.getGameDayCupFl()=false
v_game_day_tmp.getGameDayId()=2
v_game_day_tmp.getGameDayOrder()13
v_game_day_tmp.getGameDaySeason()2012/2013
2
index=2
v_game_day_list.get(i).getGameDayCompetition()=campionato
v_game_day_list.get(i).getGameDayCupFl()=false
v_game_day_list.get(i).getGameDayId()=2
v_game_day_list.get(i).getGameDayOrder()=13
v_game_day_list.get(i).getGameDaySeason()=2012/2013
scanning resultset
v_game_day_tmp.getGameDayCompetition()=mundialito
v_game_day_tmp.getGameDayCupFl()=false
v_game_day_tmp.getGameDayId()=3
v_game_day_tmp.getGameDayOrder()12
v_game_day_tmp.getGameDaySeason()2012/2013
3
index=3
v_game_day_list.get(i).getGameDayCompetition()=mundialito
v_game_day_list.get(i).getGameDayCupFl()=false
v_game_day_list.get(i).getGameDayId()=3
v_game_day_list.get(i).getGameDayOrder()=12
v_game_day_list.get(i).getGameDaySeason()=2012/2013
list created
#########################################
OnModuleLoad
index=0
result.get(i).getGameDayCompetition()=mundialito
result.get(i).getGameDayCupFl()false
result.get(i).getGameDayId()=3
result.get(i).getGameDayOrder()=12
result.get(i).getGameDaySeason()=2012/2013
index=1
result.get(i).getGameDayCompetition()=mundialito
result.get(i).getGameDayCupFl()false
result.get(i).getGameDayId()=3
result.get(i).getGameDayOrder()=12
result.get(i).getGameDaySeason()=2012/2013
index=2
result.get(i).getGameDayCompetition()=mundialito
result.get(i).getGameDayCupFl()false
result.get(i).getGameDayId()=3
result.get(i).getGameDayOrder()=12
result.get(i).getGameDaySeason()=2012/2013
index=3
result.get(i).getGameDayCompetition()=mundialito
result.get(i).getGameDayCupFl()false
result.get(i).getGameDayId()=3
result.get(i).getGameDayOrder()=12
result.get(i).getGameDaySeason()=2012/2013

如您所见，列表在 ODBConnectionImpl 中正确创建，并且由 4 个不同的行组成。但是，当我扫描返回到 AsyncCallback 调用的列表时，我有四个相等的行，全部等于 ResultSet 中的最后一行。

感谢您的帮助和建议，达里奥

Answer 1

我相信问题出在 getGameDayList 中的代码:

List<GameDay> v_game_day_list = new ArrayList<GameDay>();
GameDay v_game_day_tmp = new GameDay();
String v_sql_statement;

从此代码块中删除 GameDay v_game_day_tmp = new GameDay()。

您正在做的是在列表中使用同一个对象 (v_game_day_tmp) 4 次。当 while 循环重新填充 v_game_day_tmp 并添加到列表中时，列表中的先前条目仍然引用同一对象 (v_game_day_tmp)，因此必然具有相同的值。

不要使用 1 个临时对象。

该对象必须使用 new() 重新创建、填充，然后添加到列表中。

简单移动GameDay v_game_day_tmp = new GameDay();成为 while(rs.next()) 的第一行应该可以解决您的问题。

问候。