Question

我正面临着问题。我们正在将Java应用程序写为学校项目，我们应该使用线程。显然，应用程序并不像要求线程那么复杂，但我们必须拥有它们。

我们决定使用线程进行数据库通信，但我们不确定如何将它们用于单个方法。我们创建了数据库传输对象，其中包含一些将实体插入DB的方法请问如何使用Runnable单一方法？更具体地说，我们想在方法中创建Runnable然后将其添加到线程池中，但是，我们将能够返回返回。

public class EmployeeDTO {

    private Employee employee;
    private Connection conn;
    private int id_employee;

    /**
     * Database connection
     * @throws ClassNotFoundException
     * @throws SQLException 
     */
    public EmployeeDTO() throws ClassNotFoundException, SQLException {
        DatabaseConnection dbcon = new DatabaseConnection();
        conn = dbcon.getConnection();
    }

    public EmployeeDTO(Employee employee) throws ClassNotFoundException, SQLException {
        this.employee = employee;
        DatabaseConnection dbcon = new DatabaseConnection();
        conn = dbcon.getConnection();
    }

    /**
     * Insert new Employee into database and sets it's id
     * @param emp
     * @throws SQLException 
     */
    public void insertEmployee(Employee emp) throws SQLException {
        setEmployee(emp);
        PreparedStatement pr = conn.prepareStatement("INSERT INTO employees "
                + "(nickname,name,surname,password_emp) "
                + "VALUES (?,?,?,?)", PreparedStatement.RETURN_GENERATED_KEYS);
        pr.setString(1, employee.getNickname());
        pr.setString(2, employee.getName());
        pr.setString(3, employee.getSurname());
        pr.setString(4, employee.getPassword());
        pr.executeUpdate();
        ResultSet rs = pr.getGeneratedKeys();
        while (rs.next()) {
            employee.setId_employee(rs.getInt(1));
        }
    }

    /**
     * Delete an employee from database
     * @param id
     * @throws SQLException 
     */
    public void deleteEmployee(int id) throws SQLException {
        PreparedStatement pr = conn.prepareStatement("DELETE FROM employees WHERE id_employee=?");
        pr.setInt(1, id);
        pr.executeUpdate();
    }
}

Answer 1

更具体地说，我们想在方法中创建Runnable然后将其添加到线程池中，但是，我们将能够返回返回。

听起来您想将Callable个任务（不是Runnable）提交给线程池。当您向Callable<T>提交ExecutorService任务时，您将获得一个Future<T>对象，您可以在以后使用该对象等待任务结果。

Answer 2

您可能想要执行以下操作。您的insertEmployee方法将从call方法调用。

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.concurrent.Callable;

public class EmployeeDTO implements Callable<String> {

    private Employee employee;
    private Connection conn;
    private int id_employee;

    /**
     * Database connection
     * @throws ClassNotFoundException
     * @throws SQLException
     */
    public EmployeeDTO() throws ClassNotFoundException, SQLException {
        DatabaseConnection dbcon = new DatabaseConnection();
        conn = dbcon.getConnection();
    }

    public EmployeeDTO(Employee employee) throws ClassNotFoundException, SQLException {
        this.employee = employee;
        DatabaseConnection dbcon = new DatabaseConnection();
        conn = dbcon.getConnection();
    }

    /**
     * Insert new Employee into database and sets it's id
     * @param emp
     * @throws SQLException
     */
    public void insertEmployee(Employee emp) throws SQLException {
        setEmployee(emp);
        PreparedStatement pr = conn.prepareStatement("INSERT INTO employees "
                + "(nickname,name,surname,password_emp) "
                + "VALUES (?,?,?,?)", PreparedStatement.RETURN_GENERATED_KEYS);
        pr.setString(1, employee.getNickname());
        pr.setString(2, employee.getName());
        pr.setString(3, employee.getSurname());
        pr.setString(4, employee.getPassword());
        pr.executeUpdate();
        ResultSet rs = pr.getGeneratedKeys();
        while (rs.next()) {
            employee.setId_employee(rs.getInt(1));
        }
    }

    /**
     * Delete an employee from database
     * @param id
     * @throws SQLException
     */
    public void deleteEmployee(int id) throws SQLException {
        PreparedStatement pr = conn.prepareStatement("DELETE FROM employees WHERE id_employee=?");
        pr.setInt(1, id);
        pr.executeUpdate();
    }

    /**
     * Computes a result, or throws an exception if unable to do so.
     *
     * @return computed result
     * @throws Exception if unable to compute a result
     */
    public String call() throws Exception {
        insertEmployee(employee);
        return "SUCCESS";
    }
}

在其他课程中，您可以使用下面的ExecutorService

try{
Set<Callable<String>> callables = new HashSet<Callable<String>>();
EmployeeDTO  employee = new EmployeeDTO(emp);
  callables.add(employee); 
ExecutorService  executorService =  Executors.newFixedThreadPool(1);
List<Future<String>> futures = executorService.invokeAll(callables);
}catch (ExecutionException eEx) {
eEx.getMessage();
}finally{
executorService.shutdown();
}

如何在此代码中使用Runnable和Threads

2 个答案: