Question

我有点不确定，必须得到建议我有：

public class MyApp extends JFrame{

从那里我做;

MyServer = new MyServer (this);
MyServer.execute();

MyServer是：

public class MyServer extends SwingWorker<String, Object> {

MyServer正在listen_socket.accept()

中进行doInBackground()

并在连接时创建一个新的

class Connection implements Runnable {

我有一个单身的belove DbHelper。

它拥有Sqlite连接。我在上面的MyApp中发起了它并将引用一直传递给我的runnable：

class Connection implements Runnable {

我的问题是，如果有两个同时read或“写”，会发生什么？我的想法是，单身人士的所有方法都是同步的将所有调用放入队列等待锁定同步方法。

这会起作用还是我可以改变什么？

public final class DbHelper {

    private boolean initalized = false;
    private String HomePath = "";
    private File DBFile;

    private static final String SYSTEM_TABLE = "systemtable";   
    Connection con = null;
    private Statement stmt;
    private static final DbHelper instance = new DbHelper ();

    public static DbHelper getInstance() {

        return instance;

    }

    private DbHelper () {

        if (!initalized)
        {
            initDB();

            initalized = true;
        }
    }

    private void initDB()
    {
        DBFile = locateDBFile();
        try {

            Class.forName("org.sqlite.JDBC");

            // create a database connection
            con = DriverManager.getConnection("jdbc:sqlite:J:/workspace/workComputer/user_ptpp");

        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    private File locateDBFile()
    {
        File f = null;
        try{
            HomePath = System.getProperty("user.dir");
            System.out.println("HomePath: " + HomePath);
            f = new File(HomePath + "/user_ptpp");
            if (f.canRead())
                return f;
            else
            {
                boolean success = f.createNewFile();
                if (success) {
                    System.out.println("File did not exist and was created " + HomePath);
                    // File did not exist and was created
                } else {
                    System.out.println("File already exists " + HomePath);

                    // File already exists

                }
            }
        } catch (IOException e) {
             System.out.println("Maybe try a new directory. " + HomePath);
            //Maybe try a new directory.
        }
        return f;
    }

    public String getHomePath()
    {
        return HomePath;
    }



    public synchronized String getSelectedSystemTableColumn( String column) {

        String query = "select "+ column + " from " + SYSTEM_TABLE ;
        try {
            stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
            ResultSet rs = stmt.executeQuery(query);
            while (rs.next()) {

                String value = rs.getString(column);

                if(value == null || value == "")
                    return "";
                else
                    return value;
            }

        } catch (SQLException e ) {
            e.printStackTrace();
            return "";
        } finally {

        }
        return "";

    }

}

Answer 1

根据规范

，java.sql中的类必须是线程安全的

http://docs.oracle.com/javase/1.3/docs/guide/jdbc/spec/jdbc-spec.frame9.html

我们要求对所有java.sql对象进行所有操作多线程安全，能够正确处理几个线程同时调用同一个对象。一些司机可能允许比其他人更多的并发执行。开发人员可以充分考虑并发执行;如果司机需要某种形式的同步，它将提供它。可见的唯一区别开发人员将会减少运行应用程序并发性。

这不太可能是一个好主意。你应该重新考虑这个设计。我认为汇集连接并在最窄范围内关闭它们将是一个更好的主意。

java将这个线程设置工作或我可以做错什么

1 个答案: