多线程Java让线程返回一些东西到主线程

Question

我被什么事缠住了，似乎想不出解决办法。我有一个名为dbSelect的函数，它会创建一个线程来运行MySQL查询并获取一个ResultSet，但是我需要我的dbSelect来获取那个ResultSet并返回它。以下是我所拥有的：

public class Utils {
    public static void dbSelect(String query){
        selectQuery = query;
        Thread selectThread = new selectThreadClass();
        selectThread.start();
    }
}
class selectThreadClass extends Thread {
    public void run(){
        perform();
    }

    public ResultSet perform(){
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection("jdbc:mysql://localhost/lob/?user=root&password=");

            Statement s = conn.createStatement();
            ResultSet rs = s.executeQuery(Utils.selectQuery);
            return rs;
        }catch (SQLException | InstantiationException | IllegalAccessException | ClassNotFoundException e){
            e.printStackTrace();
            return null;
        }
    }
}

有谁能帮我得到它，以便dbSelect从线程返回ResultSet吗？谢谢

Answer 1

使用Callable

 public interface Callable<V> {
 V call() throws Exception;
}

Answer 2

从我这边开始试试

我修改了代码，得到了使用列表保存结果集值的解决方案，但我只有一个问题 也就是说，我无法在Callable中以type（ResultSet）的形式获得结果

不知怎的，当我尝试去做时，结果集是空的 使用future get（）函数检索值

结果集rs=（结果集）未来。get（）

下面是一段不起作用的代码

ExecutorService service=Executors.newFixedThreadPool(1);
Callable<ResultSet> callable = new SelectThreadResultSet();
Future<ResultSet> future = service.submit(callable);
ResultSet rs = (ResultSet)future.get();
// Here I dont get any values
while(rs.next()){
    System.out.println(rs.getString("EMPLOYEE"));
}

请在下面找到适合我的解决方案，我使用了列表 保存并返回值

类SelectThreadClass：

public class SelectThreadClass implements Callable<List<String>> {

    public List<String> call(){
        ResultSet rs = null;
        List<String> strList = new ArrayList<String>();
        try {
            rs  = perform();
            while(rs.next()){
                strList.add(rs.getString("EMPNAME"));
            }
            System.out.println("Passed");

        } catch (InstantiationException | IllegalAccessException | SQLException e) {
            e.printStackTrace();
        }
        return strList;
    }

    public ResultSet perform() throws InstantiationException, IllegalAccessException, SQLException{
        Connection conn = null;
        try {
            Class.forName("org.sqlite.JDBC");
            try {
                conn = DriverManager.getConnection("jdbc:sqlite:C:\\SqlLite\\EMPLOYEE.db");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            Statement s = null;
            try {
                s = conn.createStatement();
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            ResultSet rs = null;
            try {
                rs = s.executeQuery(Utils.selectQuery);
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return rs;
        }catch (ClassNotFoundException e){
            e.printStackTrace();
            return null;
        }
    }
}

类别UTIL：

public class Utils {

    public static String selectQuery = "SELECT EMPNAME FROM EMPLOYEEDETAILS";
    public static void dbSelect(String query) throws InterruptedException, ExecutionException, SQLException{
        ExecutorService service=Executors.newFixedThreadPool(1);
        Callable<List<String>> callable = new SelectThreadClass();

        Future<List<String>> future = service.submit(callable);

        List<String> empList = future.get();
        for(String emp : empList){
            System.out.println(emp);
        }
    }

    public static void main(String args[]) throws InterruptedException, ExecutionException, SQLException{
        dbSelect("SELECT EMPNAME FROM EMPLOYEEDETAILS");
    }

}

Answer 3

使用callable代替Runnable

public class SelectCallableClass implements Callable<ResultSet> {

    public ResultSet call() throws Exception {
        return perform();
    }

    public ResultSet perform(){
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection("jdbc:mysql://localhost/lob/?user=root&password=");

            Statement s = conn.createStatement();
            ResultSet rs = s.executeQuery(Utils.selectQuery);
            return rs;
        }catch (SQLException | InstantiationException | IllegalAccessException | ClassNotFoundException e){
            e.printStackTrace();
            return null;
        }
    }
}

要提交可调用类，请使用ExecuterService

ExecutorService service=Executors.newFixedThreadPool(1);
Future future=service.submit(new SelectCallableClass());

The above code does the following(from doc).Submits a value-returning task for execution and returns a Future> representing the pending results of the task. The Future's get method will return the task's result upon successful completion.

Answer 4

你只需要在你的线程类中有一个属性，然后获得该属性

public class Utils {
    public static void dbSelect(String query){
        selectQuery = query;
        Thread selectThread = new selectThreadClass();
        selectThread.start();

        ((SelectThreadClass) selectThread).getResult();
    }
}

class selectThreadClass extends Thread {
    ResultSet rs = null;

    public ResultSet getResult(){
        return rs;
    }

    public void run(){
        rs = perform();
    }

    public ResultSet perform(){
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection("jdbc:mysql://localhost/lob/?user=root&password=");

            Statement s = conn.createStatement();
            return s.executeQuery(Utils.selectQuery);
        } catch (SQLException | InstantiationException | IllegalAccessException | ClassNotFoundException e){
            e.printStackTrace();
            return null;
        }
    }
}

唯一的问题是，您可能最终会从dbutil中处理连接闭包和其他内容，或者，您可以将结果集转换为任何java类，然后返回该java对象列表，而不是结果集

Answer 5

run不返回结果
使用alCallable或使用共享变量并在Utils中轮询wait，直到SelectThreadClass的结果可用
但是我建议使用Callable，因为它完全适合这个任务