ECLIPE：间断com.mysql.jdbc.exceptions.jdbc4.CommunicationsException：通信链接失败

Question

下面是我用于所有MySQL连接的代码：

public class MySQLAccess {
    private Connection connect = null;
    private Statement statement = null;
    private ResultSet resultSet = null;
    public String query = null;
    public int lastId = 0;

    private Connection getConnection() throws Exception {
        // reads a config properties file
        AWBConfig Config = new AWBConfig();
        String host = Config.Data.getProperty("mysql.host");
        if (!Config.Data.getProperty("mysql.port").isEmpty()) host += ":" + Config.Data.getProperty("mysql.port");
        Class.forName("com.mysql.jdbc.Driver");
        return DriverManager.getConnection("jdbc:mysql://"+host+"/" + Config.Data.getProperty("mysql.name") + "?user=" + 
            Config.Data.getProperty("mysql.user") + "&password=" + Config.Data.getProperty("mysql.pass"));
    }

    public ResultSet readDataBase() throws Exception {
        if (connect == null || connect.isClosed()) connect = getConnection();
        statement = connect.createStatement();
        resultSet = statement.executeQuery(query);
        return resultSet;
    }

    public ResultSet readDataBase(String _query) throws Exception {
        this.query = _query;
        resultSet = this.readDataBase();
        return resultSet;
    }

    public void writeData() throws Exception {
        if (connect == null || connect.isClosed()) connect = getConnection();
        statement = connect.createStatement();
        if (query.substring(0, 6).equals("INSERT")) {
            statement.executeUpdate(query, Statement.RETURN_GENERATED_KEYS);
            ResultSet rs = statement.getGeneratedKeys();
            if (rs.next()){
                this.lastId=rs.getInt(1);
            }
            rs.close();
        } else {
            statement.executeUpdate(query);
            this.lastId = -1;
        }
    }

    public void close() {
        try {
            if (resultSet != null) resultSet.close();
            if (statement != null) statement.close();
            if (connect != null) connect.close();
        } catch (Exception e) {
        }
    }
}

然后与数据库交互,我使用以下格式：

    protected void getCampaignById() throws Exception {
        _dba = new MySQLAccess();
        _dba.query = "SELECT * FROM table WHERE id = '" + String.valueOf(id) + "'";
        ResultSet rs = _dba.readDataBase();
        if (rs.next()) {
            ... do stuff with rs
        }
        _dba.close();
    }

Answer 1

嗯,我不确定问题到底是什么,但我在核心应用程序的main（）方法中将_dba改为静态变量,然后在每个类构造函数中添加了以下一行：

_dba = MyMainClass._dba;

然后从各处删除这些行（MyMainClass.Main（）除外）：

_dba = new MySQLAccess();
...
_dba.close();

使数据库连接成为一个全局持久连接，这不仅解决了我的错误，而且给了我一个巨大的性能提升。