java-半多线程JDBC连接

内容导读

互联网集市收集整理的这篇技术教程文章主要介绍了java-半多线程JDBC连接，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含3909字，纯文字阅读大概需要6分钟。

内容图文

我有下面的Callable实例,在这里将SQLException抛出：

public long[] call() throws Exception {
    long[] stats = new long[6];
    try {
        executer.acquire();
        PreparedStatement statement =
            connection
                .prepareStatement("SELECT `War`.`EndTime` FROM `WarSim`.`War` WHERE `War`.`WarName` = ?");
        statement.setString(1, warName);
        ResultSet res = statement.executeQuery(); //<--------------SQLEXCEPTION HERE
        if (res.first()) {
        Timestamp ts = res.getTimestamp("EndTime");
        if (ts != null)
            stats[0] = 1;
        statement =
            connection
                .prepareStatement("SELECT COUNT(`ID`) FROM `Missile` WHERE `WarName` = ?");
        statement.setString(1, warName);
        res = statement.executeQuery();
        stats[1] = res.getInt(1);
        statement =
            connection
                .prepareStatement("SELECT COUNT(`ID`) FROM `Missile` WHERE `WarName` =  ?  AND `Intercepted` = '1'");
        statement.setString(1, warName);
        res = statement.executeQuery();
        stats[2] = res.getInt(1);
        stats[3] = stats[1] - stats[2];
        statement =
            connection
                .prepareStatement("SELECT COUNT(`ID`) FROM `EnemyLauncher` WHERE `WarName` = ? AND `Intercepted` = '1'");
        statement.setString(1, warName);
        res = statement.executeQuery();
        stats[4] = res.getInt(1);
        statement =
            connection
                .prepareStatement("SELECT SUM(`Damage`) FROM `Missile` WHERE `WarName` =  ? AND `Intercepted` = '0'");
        statement.setString(1, warName);
        res = statement.executeQuery();
        stats[5] = res.getInt(1);
        }
    } catch (SQLException e) {
        System.out.println(warName + " is problematic");
        while (e != null) {
        System.out.println("\tmsg: " + e.getMessage()+
                       "\n\tstate: " + e.getSQLState());
        e = e.getNextException();
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        executer.release();
    }
    return stats;
    }

执行者是我使用的单许可,公平信号量.

当我调试代码时,一切正常(没有异常),但是当我“正常”运行程序时,我得到了“结果集开始” SQLException和SQLState S1000.

即使我使用信号量来获取要查询的互斥锁,我也如何获得异常？

请帮助 ：)

编辑：这是堆栈跟踪.

java.sql.SQLException: Before start of result set

    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1075)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:984)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:929)
    at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:841)
    at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2672)
    at db.jdbc.GetWarStatsTask.call(GetWarStatsTask.java:37)
    at db.jdbc.GetWarStatsTask.call(GetWarStatsTask.java:1)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

处理与数据库的连接的类：

public class JDBCConnection implements DBConnection {

    private Connection connection;
    private String dbUrl;
    private Semaphore executer;
    private ExecutorService es;
    private static JDBCConnection instance;

    public static JDBCConnection getInstance() {
    if (instance == null) {
        instance = new JDBCConnection();
    }
    return instance;
    }

    private JDBCConnection() {
    dbUrl = "jdbc:mysql://---------/WarSim";
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        connection =
            DriverManager.getConnection(dbUrl, "------", "-------");
    } catch (InstantiationException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        while (e != null) {
        System.out.println(e.getMessage());
        e = e.getNextException();
        }
    }
    es = Executors.newCachedThreadPool();
    executer = new Semaphore(1, true);
    }

    public Future<long[]> getWarStats(String warName) {
    return es.submit(new GetWarStatsTask(executer, connection, warName));
    }

    public void closeDB() {
    try {
     if (connection != null) {
        connection.close();
     }
    } catch (Exception e) {
        System.out.println("Could not close the current connection.");
        e.printStackTrace();
    }
}

解决方法:

基本上,您将光标放在第一行之前,然后请求数据.您需要将光标移动到第一行.

因此,首先调用result.next();

内容总结

以上是互联网集市为您收集整理的java-半多线程JDBC连接全部内容，希望文章能够帮你解决java-半多线程JDBC连接所遇到的程序开发问题。 如果觉得互联网集市技术教程内容还不错，欢迎将互联网集市网站推荐给程序员好友。

内容备注

版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 gblab@vip.qq.com 举报，一经查实，本站将立刻删除。

内容手机端