「java任务式解决问题」java中遇到的问题和解决方案
本篇文章给大家谈谈java任务式解决问题，以及java中遇到的问题和解决方案对应的知识点，希望对各位有所帮助，不要忘了收藏本站喔。
本文目录一览：
java如何解决同时执行多项任务的问题
启用3个线程，每个线程做一件事
如
public Thread1 implements Runnable
{
public void run()
{
//自己的代码，如listTxt1();
}
}
启动线程new Thread(new Thread1()).start()
Java 定时任务的几种实现方式
1 创建一个thread，然后让它在while循环里一直运行着，通过sleep方法来达到定时任务的效果；
2 用Timer和TimerTask与第一种方法相比有如下好处：
当启动和去取消任务时可以控制
第一次执行任务时可以指定你想要的delay时间
3 用ScheduledExecutorService是从的java.util.concurrent里，做为并发工具类被引进的，这是最理想的定时任务实现方式，相比于上两个方法，它有以下好处：
相比于Timer的单线程，它是通过线程池的方式来执行任务的
可以很灵活的去设定第一次执行任务delay时间
提供了良好的约定，以便设定执行的时间间隔
java多实例下任务调度问题
有个比较简单的方法，
那就是首先在数据库中加入一个表，用来专门保存任务的。
在应用启动任务时，根据任务ID，去select * from taskID=*** for update
利用 for update的特性实现一个锁机制（如果获取数据成功就执行任务，如果失败就退出）。
在任务完成后再释放。
在JAVA中如何实现长时间任务
一、问题背景 在应用程序中我们经常需要一个类去完成像数据处理、监听事件或检查另一个类的活动等任务。为了达到这个目标，我们可能使用带有一套锁和消息通知的线程。JAVA 线程API已经很好的文档化，但为了使线程能够正确而高效地运行，程序员仍然需要丰富的编程经验并编写大量的代码。通过应用本篇文章中讨论的框架，程序员能够避免忍受煎熬写大量的代码，快速创建健壮的应用程序。 二、长时间运行任务的程序框架 Framework for long-running tasksThe primary thing about a long-lived task is that it should somehow be kept running during the application lifetime. The right way to accomplish this is to provide a thread of execution for a particular task. You create a task as a thread or as an implementation of the java.lang.Runnable interface. If you implement Runnable, you can gain better object-oriented design and avoid the single-inheritance problems. You can also more efficiently manipulate with Runnable instances, for example, using a thread pool that usually needs a Runnable instance, not a thread, to run. 关于长时间运行的任务的主要事情是如何在应用程序的生命期使它一直保持运行。实现的恰当方法是提供一个线程来执行这个特定的任务。我们可以通过继承Thread类或实现java.lang.Runnable接口来达到该目标。如果采用实现Runnable接口的方式，就可以能够获得更好的面向对象的设计，同时可以避免JAVA中的单继承问题。另外，我们也能更有效的处理Runnable实例（例如使用线程池通常需要一个Runnable实例而不是线程来运行）。 The essence of the framework is the abstract class Worker ( Listing A), which implements the Runnable interface and provides the helper methods for efficient task handling. Some of the methods are fully implemented, like the run() method, but some are abstract and have to be filled by you. If you want to create a long-running class, you need only to extend the Worker class and implement several abstract methods. Let’s look at these methods in more detail. 框架的基础是一个叫Worker的抽象类，它实现了Runnable接口，并提供了有效处理任务的好方法。这些方法有些已经被实现，如run()方法，但有些是抽象方法，开发人员必须自己来实现。如果要创建一个长时间运行的类，你只需要继承Worker类并实现几个抽象方法。让我们看看这些方法的细节。 The run() method of the Worker class is designed to continuously execute the work() method until it is stopped. The work() method can be responsible for data processing, reaction to some event, file reading or writing, SQL execution, etc. It can throw an exception, so it is a good practice to propagate it and let the run() method handle it. Worker 类的run()方法被设计成只要不停止运行就持续的执行work()方法。work()方法可以负责数据处理、事件响应、文件读写、，执行SQL命令等操作。这样work()方法能够抛出异常，并将异常传给run()，然后由run()方法来处理这些异常。 The run() method has two levels of try-catch clause: outside and inside the while-loop. The first try-catch clause is meant to catch all nonprogrammed exceptions and guarantee that the run() method never exits. The second clause will catch any kind of exceptions belonging to business logic and behave accordingly. If some waiting operation takes place in the work() method (e.g., waiting on an InputStream or a Socket), it is advisable to propagate an InterruptedException. The thing to keep in mind is that the work() method does not need to have any while-loop to keep it going as long as an application runs. The Worker does this for you. run()方法有内外两层try-catch语句：一层处于while-loop循环外，一层在while-loop循环内。前一个try-catch用于捕获非编程异常以确保run()方法不退出。后一个try-catch语句捕获关于业务逻辑和相应行为的各种异常。如果在work()方法中发生了一些等待操作（例如等待一个输入流或一个Socket），抛出一个InterruptedException的方法是可取的。要记住的是只要应用程序在运行，work()方法不需要任何while-loop循环去维持它运行，这一切由Worker代办了。 When the run() method starts, it calls the prepareWorker() which is designed to prepare all resources needed for a long-running task (Listing A). In this method call, you can, for example, establish a database connection or open a file that will be used further. It is especially good to place here some blocking operations like opening a socket, because they will be done in a separate thread and thus will not block the main thread of execution. run()开始时，调用prepareWorker()方法来准备长时间运行任务需要的所有资源（参考程序清单A）。例如 ，在这个方法中可以打开一个将要用到的数据库连接或文件。尤其对于那些像建立一个socket这样的阻塞操作放在这儿是很好的。因为若让它们在一个独立的线程中运行，则不会阻塞主线程的执行。 The opposite of the previous method is the releaseWorker() which is called when the run() method is about to exit (Listing A). Here, you can put the code to dispose of system resources used by this task or to perform other cleanup. This method is similar to java.lang.Object.finalize(), but it is explicitly called before a thread terminates. 与前面方法相反的是releaseWorker()，它在run()方法准备退出时被调用（参考程序清单A）。在该方法中你可以编写那些释放系统资源或执行其它清除动作的代码。该方法类似于java.lang.Object.finalize()，但它在线程中止时被显式的调用。 三、框架中的错误处理机制 Handling errors in the frameworkAnother important method is the handleError(), which takes a java.lang.Throwable as a parameter. This method is called each time an error situation occurs within the run() method. It is up to you how to implement error handling. One way is to log errors and control task termination by calling halt() method (Listing A). The isCondition() method is used to tell whether execution of the work() method can be started, thus allowing granular control over a task. It is useful in event-triggered frameworks when execution of the work() method is pending until some condition?for example, a buffer is not empty?is fulfilled. In Worker’s implementation, the condition is checked upon a lock notification and periodically with a time interval you specify in the setTimeout() method (Listing A). If you don’t need any waiting blocks in a task, just make the isCondition() method always return true. isCondition()方法用于判断work()方法是否能够被执行。因此允许细粒度地控制任务。这在事件触发的框架中非常有用。当work()方法的执行条件未满足时，work方法将被挂起，直到条件完全满足（例如，缓存区非空）。在Worker的实现中这个条件将按在方法setTimeout()中指定的时间周期地检查一个锁通知。如果在任务中不需要任何等待阻塞，仅仅只要使isCondition()方法总是返回真值。四、任务终止时机
java任务式解决问题的介绍就聊到这里吧，感谢你花时间阅读本站内容，更多关于java中遇到的问题和解决方案、java任务式解决问题的信息别忘了在本站进行查找喔。
发布于：2022-12-19，除非注明，否则均为原创文章，转载请注明出处。