In actual development, we will more or less use some scheduled task scenarios. This article will talk about commonly used scheduled tasks.
Commonly used timing task implementation solutions include the following:
Timer: This is the java.util.Timer class that comes with java. This class allows you to schedule a java.util.TimerTask task. Using this method allows your program to be executed at a certain frequency, but not at a specified time. Generally used less.
ScheduledExecutorService: It is also a class that comes with jdk; it is a scheduled task class based on the thread pool design. Each scheduled task will be assigned to a thread pool Threads are executed, that is to say, tasks are executed concurrently and do not affect each other.
Spring Task：Spring3.0For future tasks, you can regard it as a lightweight Quartz and use It's much simpler than Quartz.
Quartz: This is a relatively powerful scheduler that allows your program to be executed at a specified time or at a certain frequency. The configuration is a bit complicated.
In the database, create a table and store cron expressions in the table.
nacos, using distributed configuration to implement dynamic configuration cron expression.
XXL-JOB, distributed task
Use Timer
This is currently rarely used in projects, and the demo code is posted directly.
For a detailed introduction, please view the API:
public class TestTimer {
public static void main(String[] args) {
TimerTask timerTask = new TimerTask() {
@Override
public void run() {
System.out.println("task run:"+ new Date());
}
};
Timer timer = new Timer();
//安排指定的任务在指定的时间开始进行重复的固定延迟执行。这里是每3秒执行一次
timer.schedule(timerTask,10,3000);
}
}
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Use ScheduledExecutorService
This method is similar to Timer, just look at the demo:
public class TestScheduledExecutorService {
public static void main(String[] args) {
ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
// 参数：1、任务体 2、首次执行的延时时间
// 3、任务执行间隔 4、间隔时间单位
service.scheduleAtFixedRate(()->System.out.println("task ScheduledExecutorService "+new Date()), 0, 3, TimeUnit.SECONDS);
}
}
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Use Spring Task
Simple scheduled tasks
In the Spring Boot project, we can use annotations to implement scheduled tasks very elegantly. First, create the project and import the dependencies:
@Slf4j
@Component
public class ScheduledService {
@Scheduled(cron = "0/5 * * * * *")
public void scheduled(){
log.info("=====>>>>>使用cron {}",System.currentTimeMillis());
}
@Scheduled(fixedRate = 5000)
public void scheduled1() {
log.info("=====>>>>>使用fixedRate{}", System.currentTimeMillis());
}
@Scheduled(fixedDelay = 5000)
public void scheduled2() {
log.info("=====>>>>>fixedDelay{}",System.currentTimeMillis());
}
}
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Use the @EnableScheduling annotation on the main class to enable support for scheduled tasks, and then start the project
You can see When all three scheduled tasks have been executed, and they are executed serially in the same thread, if there is only one scheduled task, this will definitely be fine. When the number of scheduled tasks increases, if one task is stuck, other tasks will not be able to execute.
Multi-threaded execution
In traditional Spring projects, we can add task configuration in the xml configuration file, while in Spring Boot projects we generally use the config configuration class to add configuration, so Create a new AsyncConfig class
@Configuration
@EnableAsync
public class AsyncConfig {
/*
此处成员变量应该使用@Value从配置中读取
*/
private int corePoolSize = 10;
private int maxPoolSize = 200;
private int queueCapacity = 10;
@Bean
public Executor taskExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(corePoolSize);
executor.setMaxPoolSize(maxPoolSize);
executor.setQueueCapacity(queueCapacity);
executor.initialize();
return executor;
}
}
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@Configuration: Indicates that this class is a configuration class@EnableAsync: Enables support for asynchronous events
Then add @Async to the class or method of the scheduled task. Finally restart the project, each task is in a different thread.
Configuration of execution time
In the above scheduled task, we use the @Scheduled annotation on the method to set the execution time of the task, and use three A property configuration method:
fixedRate: Define a scheduled task that is executed at a certain frequency
fixedDelay: Define a scheduled task that is executed at a certain frequency. The difference from the above is that, The attribute can be changed in conjunction with initialDelay to define the delayed execution time of the task.
cron: Configure task execution time through expressions
Detailed explanation of cron expression
A cron expression has at least 6 (possibly 7) space-separated time elements. In order:
Each element can be a value (such as 6), a continuous interval (9-12), an interval (8-18/4) (/ means each 4 hours apart), a list (1,3,5), wildcard. Since the two elements "day of month" and "day of week" are mutually exclusive, one of them must be set. Configuration example:
Execute every 5 seconds: */5* * ?
Execute every 1 minute: 0 /1 ?
0 0 10,14,16 ? Every day 10 am, 2 pm, 4 pm
0 0/30 9- 17 ? Every half hour during 9 to 5 working hours
0 0 12 ? *WED means every Wednesday at 12 noon
" 0 0 12 ?" Triggered every day at 12 noon
"0 15 10 ? "Triggered every day at 10:15 am
"0 15 10 ?" Triggers every day at 10:15 AM
##"0 15 10 ? *" Triggers every day at 10:15 AM
"0 15 10 ? 2005" Triggered every day at 10:15 AM in 2005
"0 14 * ?" every 1 minute from 2 PM to 2:59 PM every day Trigger
##"0 0/5 14 ?" Trigger every 5 minutes from 2pm to 2:55pm every day
" 0 0/5 14,18 ?" Trigger every 5 minutes from 2pm to 2:55pm and every 5 minutes from 6pm to 6:55pm
"0 0-5 14 ?" Fires every 1 minute between 2pm and 2:05pm every day
"0 10,44 14 ? 3 WED" Every Wednesday in March at 2pm: Triggers at 10 and 2:44
"0 15 10 ? * MON-FRI" Triggers at 10:15 am from Monday to Friday
"0 15 10 15 * ?" Triggers at 10:15 am on the 15th of each month
"0 15 10 L * ?" Triggers at 10:15 am on the last day of each month
"0 15 10 ? * 6L" Triggered at 10:15 am on the last Friday of every month
"0 15 10 ? * 6L 2002- 2005" Triggered on the last Friday of each month at 10:15 AM from 2002 to 2005
"0 15 10 ? * 6#3" On the third Friday of each month at 10 AM :15 trigger
Some subexpressions can contain some ranges or lists
For example: the subexpression (day (week)) can be "MON- FRI", "MON, WED, FRI", "MON-WED,SAT"
The "*" characters represent all possible values
The "/" character is used to specify the increment of the value
For example: "0/15" in the subexpression (minutes) means starting from minute 0, every 15 minutes
"3/20" in the subexpression (minutes) means that starting from the 3rd minute, every 20 minutes (it has the same meaning as "3, 23, 43")
"?" The character is only used in the two sub-expressions of day (month) and day (week), indicating that no value is specified.
When one of the two subexpressions is assigned a value, in order to avoid conflicts, the value of the other subexpression needs to be set to "?"
The "L" character is only used for days (months) and day (week) are two subexpressions, which are the abbreviation of the word "last"
If there is something specific before the "L", it has other meanings.
For example: "6L" means the sixth to last day of this month
Note: When using the "L" parameter, do not specify a list or range, as this will cause problems
The W character represents weekdays (Mon-Fri) and can only be used in the day domain. It is used to specify the closest weekday to the specified date. Most business processing is based on the work week, so the W character can be very important.
For example, 15W in the day field means "the closest weekday to the 15th of the month." If the 15th is a Saturday, then the trigger will be triggered on the 14th (Friday), because Thursday is smaller than Monday is closer to the 15th.
C: stands for "Calendar". It means the date associated with the schedule, or all dates in the calendar if the date is not associated.
For example, 5C in the date field is equivalent to the first day after the 5th in the calendar. 1C in the day of the week field corresponds to the first day after Sunday.
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