Bạn có thể kích hoạt chức năng lên lịch trình một cách đơn giản bằng việt thêm annotation @EnableScheduling vào trong main application class hay trong 1 lớp class nào đó mà bạn đătj annotation @Configuration Mình chọn cách thứ 1. Do đó, mình sẽ add anotation đó vào ngay trong DemoApplication.java

package springbootdemo.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;
@SpringBootApplication
@EnableScheduling
public class DemoApplication {
  public static void main(String[] args) {
    SpringApplication.run(DemoApplication.class, args);
  }
}

3. Lên lịch trình

Việc lên lịch trình cho các công việc trong Spring Boot cực kì đơn giản. Bạn chỉ cần thên annotation @Scheduled cho method và cung cấp 1 vài parameter được sử dụng để quyết định thời gian mà task sẽ chạy. Ta sẽ cùng xem qua xem annotation này đựoc định nghĩa như thế nào nhé

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

Như vậy, ta có thể thế, có Sprign Scheduling cho ta cài đặt 4 kiểu thuộc tính như sau

1. Khoảng cách thời gian giữa các lần chạy method ( ` /*
2. Copyright 2002-2018 the original author or authors.
4. Licensed under the Apache License, Version 2.0 (the "License");
5. you may not use this file except in compliance with the License.
6. You may obtain a copy of the License at
8. http://www.apache.org/licenses/LICENSE-2.0
10. Unless required by applicable law or agreed to in writing, software
11. distributed under the License is distributed on an "AS IS" BASIS,
12. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13. See the License for the specific language governing permissions and
14. limitations under the License. / package org.springframework.scheduling.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Repeatable; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /*
15. An annotation that marks a method to be scheduled. Exactly one of
16. the {@link

    cron()}, {@link

    fixedDelay()}, or {@link

    fixedRate()}

17. attributes must be specified.

19. The annotated method must expect no arguments. It will typically have

20. a {@code void} return type; if not, the returned value will be ignored
21. when called through the scheduler.

23. Processing of {@code @Scheduled} annotations is performed by

24. registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
25. done manually or, more conveniently, through the {@code }
26. element or @{@link EnableScheduling} annotation.

28. This annotation may be used as a meta-annotation to create custom

29. composed annotations with attribute overrides.
31. @author Mark Fisher
32. @author Dave Syer
33. @author Chris Beams
34. @since 3.0
35. @see EnableScheduling
36. @see ScheduledAnnotationBeanPostProcessor
37. @see Schedules / @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Repeatable(Schedules.class) public @interface Scheduled { /*
    • A cron-like expression, extending the usual UN*X definition to include
    • triggers on the second as well as minute, hour, day of month, month
    • and day of week. e.g. {@code "0 MON-FRI"} means once per minute on
    • weekdays (at the top of the minute - the 0th second).
    • @return an expression that can be parsed to a cron schedule
    • @see org.springframework.scheduling.support.CronSequenceGenerator / String cron() default ""; /*
    • A time zone for which the cron expression will be resolved. By default, this
    • attribute is the empty String (i.e. the server's local time zone will be used).
    • @return a zone id accepted by {@link java.util.TimeZone

      getTimeZone(String)},

    • or an empty String to indicate the server's default time zone
    • @since 4.0
    • @see org.springframework.scheduling.support.CronTrigger

      CronTrigger(String, java.util.TimeZone)

    • @see java.util.TimeZone / String zone() default ""; /*
    • Execute the annotated method with a fixed period in milliseconds between the
    • end of the last invocation and the start of the next.
    • @return the delay in milliseconds / long fixedDelay() default -1; /*
    • Execute the annotated method with a fixed period in milliseconds between the
    • end of the last invocation and the start of the next.
    • @return the delay in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2 / String fixedDelayString() default ""; /*
    • Execute the annotated method with a fixed period in milliseconds between
    • invocations.
    • @return the period in milliseconds / long fixedRate() default -1; /*
    • Execute the annotated method with a fixed period in milliseconds between
    • invocations.
    • @return the period in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2 / String fixedRateString() default ""; /*
    • Number of milliseconds to delay before the first execution of a
    • {@link

      fixedRate()} or {@link

      fixedDelay()} task.

    • @return the initial delay in milliseconds
    • @since 3.2 / long initialDelay() default -1; /*
    • Number of milliseconds to delay before the first execution of a
    • {@link

      fixedRate()} or {@link

      fixedDelay()} task.

    • @return the initial delay in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2

      */ String initialDelayString() default ""; }

      ` 0)
38. Khoảng cách thời gian giữa các lần chạy hoàn thành method ( ` /*
39. Copyright 2002-2018 the original author or authors.
41. Licensed under the Apache License, Version 2.0 (the "License");
42. you may not use this file except in compliance with the License.
43. You may obtain a copy of the License at
45. http://www.apache.org/licenses/LICENSE-2.0
47. Unless required by applicable law or agreed to in writing, software
48. distributed under the License is distributed on an "AS IS" BASIS,
49. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
50. See the License for the specific language governing permissions and
51. limitations under the License. / package org.springframework.scheduling.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Repeatable; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /*
52. An annotation that marks a method to be scheduled. Exactly one of
53. the {@link

    cron()}, {@link

    fixedDelay()}, or {@link

    fixedRate()}

54. attributes must be specified.

56. The annotated method must expect no arguments. It will typically have

57. a {@code void} return type; if not, the returned value will be ignored
58. when called through the scheduler.

60. Processing of {@code @Scheduled} annotations is performed by

61. registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
62. done manually or, more conveniently, through the {@code }
63. element or @{@link EnableScheduling} annotation.

65. This annotation may be used as a meta-annotation to create custom

66. composed annotations with attribute overrides.
68. @author Mark Fisher
69. @author Dave Syer
70. @author Chris Beams
71. @since 3.0
72. @see EnableScheduling
73. @see ScheduledAnnotationBeanPostProcessor
74. @see Schedules / @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Repeatable(Schedules.class) public @interface Scheduled { /*
    • A cron-like expression, extending the usual UN*X definition to include
    • triggers on the second as well as minute, hour, day of month, month
    • and day of week. e.g. {@code "0 MON-FRI"} means once per minute on
    • weekdays (at the top of the minute - the 0th second).
    • @return an expression that can be parsed to a cron schedule
    • @see org.springframework.scheduling.support.CronSequenceGenerator / String cron() default ""; /*
    • A time zone for which the cron expression will be resolved. By default, this
    • attribute is the empty String (i.e. the server's local time zone will be used).
    • @return a zone id accepted by {@link java.util.TimeZone

      getTimeZone(String)},

    • or an empty String to indicate the server's default time zone
    • @since 4.0
    • @see org.springframework.scheduling.support.CronTrigger

      CronTrigger(String, java.util.TimeZone)

    • @see java.util.TimeZone / String zone() default ""; /*
    • Execute the annotated method with a fixed period in milliseconds between the
    • end of the last invocation and the start of the next.
    • @return the delay in milliseconds / long fixedDelay() default -1; /*
    • Execute the annotated method with a fixed period in milliseconds between the
    • end of the last invocation and the start of the next.
    • @return the delay in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2 / String fixedDelayString() default ""; /*
    • Execute the annotated method with a fixed period in milliseconds between
    • invocations.
    • @return the period in milliseconds / long fixedRate() default -1; /*
    • Execute the annotated method with a fixed period in milliseconds between
    • invocations.
    • @return the period in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2 / String fixedRateString() default ""; /*
    • Number of milliseconds to delay before the first execution of a
    • {@link

      fixedRate()} or {@link

      fixedDelay()} task.

    • @return the initial delay in milliseconds
    • @since 3.2 / long initialDelay() default -1; /*
    • Number of milliseconds to delay before the first execution of a
    • {@link

      fixedRate()} or {@link

      fixedDelay()} task.

    • @return the initial delay in milliseconds as a String value, e.g. a placeholder
    • or a {@link java.time.Duration

      parse java.time.Duration} compliant value

    • @since 3.2.2

      */ String initialDelayString() default ""; }

      ` 1)
75. Thời gian delay cho lần đầu tiên chạy method ( ` /*
76. Copyright 2002-2018 the original author or authors.
78. Licensed under the Apache License, Version 2.0 (the "License");
79. you may not use this file except in compliance with the License.
80. You may obtain a copy of the License at
82. http://www.apache.org/licenses/LICENSE-2.0
84. Unless required by applicable law or agreed to in writing, software
85. distributed under the License is distributed on an "AS IS" BASIS,
86. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
87. See the License for the specific language governing permissions and
88. limitations under the License. / package org.springframework.scheduling.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Repeatable; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /*
89. An annotation that marks a method to be scheduled. Exactly one of
90. the {@link

    cron()}, {@link

    fixedDelay()}, or {@link

    fixedRate()}

91. attributes must be specified.

93. The annotated method must expect no arguments. It will typically have

94. a {@code void} return type; if not, the returned value will be ignored
95. when called through the scheduler.

97. Processing of {@code @Scheduled} annotations is performed by

98. registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
99. done manually or, more conveniently, through the {@code }
100. element or @{@link EnableScheduling} annotation.

102. This annotation may be used as a meta-annotation to create custom

103. composed annotations with attribute overrides.
105. @author Mark Fisher
106. @author Dave Syer
107. @author Chris Beams
108. @since 3.0
109. @see EnableScheduling
110. @see ScheduledAnnotationBeanPostProcessor
111. @see Schedules / @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Repeatable(Schedules.class) public @interface Scheduled { /*
     • A cron-like expression, extending the usual UN*X definition to include
     • triggers on the second as well as minute, hour, day of month, month
     • and day of week. e.g. {@code "0 MON-FRI"} means once per minute on
     • weekdays (at the top of the minute - the 0th second).
     • @return an expression that can be parsed to a cron schedule
     • @see org.springframework.scheduling.support.CronSequenceGenerator / String cron() default ""; /*
     • A time zone for which the cron expression will be resolved. By default, this
     • attribute is the empty String (i.e. the server's local time zone will be used).
     • @return a zone id accepted by {@link java.util.TimeZone

       getTimeZone(String)},

     • or an empty String to indicate the server's default time zone
     • @since 4.0
     • @see org.springframework.scheduling.support.CronTrigger

       CronTrigger(String, java.util.TimeZone)

     • @see java.util.TimeZone / String zone() default ""; /*
     • Execute the annotated method with a fixed period in milliseconds between the
     • end of the last invocation and the start of the next.
     • @return the delay in milliseconds / long fixedDelay() default -1; /*
     • Execute the annotated method with a fixed period in milliseconds between the
     • end of the last invocation and the start of the next.
     • @return the delay in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2 / String fixedDelayString() default ""; /*
     • Execute the annotated method with a fixed period in milliseconds between
     • invocations.
     • @return the period in milliseconds / long fixedRate() default -1; /*
     • Execute the annotated method with a fixed period in milliseconds between
     • invocations.
     • @return the period in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2 / String fixedRateString() default ""; /*
     • Number of milliseconds to delay before the first execution of a
     • {@link

       fixedRate()} or {@link

       fixedDelay()} task.

     • @return the initial delay in milliseconds
     • @since 3.2 / long initialDelay() default -1; /*
     • Number of milliseconds to delay before the first execution of a
     • {@link

       fixedRate()} or {@link

       fixedDelay()} task.

     • @return the initial delay in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2

       */ String initialDelayString() default ""; }

       ` 2)
112. Cron chạy method ( ` /*
113. Copyright 2002-2018 the original author or authors.
115. Licensed under the Apache License, Version 2.0 (the "License");
116. you may not use this file except in compliance with the License.
117. You may obtain a copy of the License at
119. http://www.apache.org/licenses/LICENSE-2.0
121. Unless required by applicable law or agreed to in writing, software
122. distributed under the License is distributed on an "AS IS" BASIS,
123. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
124. See the License for the specific language governing permissions and
125. limitations under the License. / package org.springframework.scheduling.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Repeatable; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /*
126. An annotation that marks a method to be scheduled. Exactly one of
127. the {@link

     cron()}, {@link

     fixedDelay()}, or {@link

     fixedRate()}

128. attributes must be specified.

130. The annotated method must expect no arguments. It will typically have

131. a {@code void} return type; if not, the returned value will be ignored
132. when called through the scheduler.

134. Processing of {@code @Scheduled} annotations is performed by

135. registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
136. done manually or, more conveniently, through the {@code }
137. element or @{@link EnableScheduling} annotation.

139. This annotation may be used as a meta-annotation to create custom

140. composed annotations with attribute overrides.
142. @author Mark Fisher
143. @author Dave Syer
144. @author Chris Beams
145. @since 3.0
146. @see EnableScheduling
147. @see ScheduledAnnotationBeanPostProcessor
148. @see Schedules / @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Repeatable(Schedules.class) public @interface Scheduled { /*
     • A cron-like expression, extending the usual UN*X definition to include
     • triggers on the second as well as minute, hour, day of month, month
     • and day of week. e.g. {@code "0 MON-FRI"} means once per minute on
     • weekdays (at the top of the minute - the 0th second).
     • @return an expression that can be parsed to a cron schedule
     • @see org.springframework.scheduling.support.CronSequenceGenerator / String cron() default ""; /*
     • A time zone for which the cron expression will be resolved. By default, this
     • attribute is the empty String (i.e. the server's local time zone will be used).
     • @return a zone id accepted by {@link java.util.TimeZone

       getTimeZone(String)},

     • or an empty String to indicate the server's default time zone
     • @since 4.0
     • @see org.springframework.scheduling.support.CronTrigger

       CronTrigger(String, java.util.TimeZone)

     • @see java.util.TimeZone / String zone() default ""; /*
     • Execute the annotated method with a fixed period in milliseconds between the
     • end of the last invocation and the start of the next.
     • @return the delay in milliseconds / long fixedDelay() default -1; /*
     • Execute the annotated method with a fixed period in milliseconds between the
     • end of the last invocation and the start of the next.
     • @return the delay in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2 / String fixedDelayString() default ""; /*
     • Execute the annotated method with a fixed period in milliseconds between
     • invocations.
     • @return the period in milliseconds / long fixedRate() default -1; /*
     • Execute the annotated method with a fixed period in milliseconds between
     • invocations.
     • @return the period in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2 / String fixedRateString() default ""; /*
     • Number of milliseconds to delay before the first execution of a
     • {@link

       fixedRate()} or {@link

       fixedDelay()} task.

     • @return the initial delay in milliseconds
     • @since 3.2 / long initialDelay() default -1; /*
     • Number of milliseconds to delay before the first execution of a
     • {@link

       fixedRate()} or {@link

       fixedDelay()} task.

     • @return the initial delay in milliseconds as a String value, e.g. a placeholder
     • or a {@link java.time.Duration

       parse java.time.Duration} compliant value

     • @since 3.2.2

       */ String initialDelayString() default ""; }

       ` 3)

Trước tiên, ta hãy tạo 1 class là container để chứa đựng các công việc cần lên lịch trình. Tạo 1 class có tên là

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

4 như mình nhé

package springbootdemo.demo.scheduledtasks;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
@Component
public class ScheduledTasks {
    private static final Logger logger = LoggerFactory.getLogger(ScheduledTasks.class);
    public void scheduleTaskWithFixedRate() {
    }
    public void scheduleTaskWithFixedDelay() {
    }
    public void scheduleTaskWithInitialDelay() {
    }
    public void scheduleTaskWithCronExpression() {
    }
}

3.1. Chạy lặp (Sử dụng fixedRate)

Thử hình dung ra, hệ thống của bạn có 1 yêu cầu, đó là sau khi deploy, cứ mỗi ngày cần phải gửi báo cáo về số lượng người mua hàng tới email của nhà bán hàng. Như vậy, ta có thể sử dụng schedule với

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

0 là

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

6 (Trong đoạn code dưới đây, mình để là 2000ms để ta có thể nhìn dễ hơn nhé)

    @Scheduled(fixedRate = 2000)
    public void scheduleTaskWithFixedRate() {
        // call send email method here
        LOGGER.info("Send email to producers to inform quantity sold items");
    }

Bạn chạy application và nhìn vào log.

Nhìn vào log, bạn có thể thấy cứ 2s thì message

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

7 hiện ra 1 lần và ngay sau khi web app được deploy thành công

3.2. Chạy lặp (Sử dụng fixedDelay)

Cùng với bài toán ở phía trên, nhưng thay đổi 1 chút. Đó là thay vì mỗi giờ bạn gửi email, thì giờ bạn muốn thay đổi là, khi tác vụ gửi email đó hoàn thành, 1 tiếng sau đó, lại thực hiện lại tác vụ gửi email. Cứ như thế... Nó khác gì với yêu cầu thứ phía trên? Khác là ở chỗ

• Ở 3.1, nếu bạn deploy app thành công lúc 12h, thì tác vụ gửi mail sẽ được gọi đầu tiên lúc 12h trưa, sau đó 1h, 2h, 3h .v.v. là những mốc thời gian mà tác vụ gửi mail đc thực hiện
• Ở 3.2, khác 1 chút, vẫn là 12h deploy thành công, 12h thực hiện tác vụ gửi mail đầu tiên. Nhưng nếu việc gửi mail mất 5p, thì 1 tiếng sau đó (tức là 1h5p) thì tác vụ gửi mail mới dc gọi lần thứ 2, lần này gửi mail lại mất 10p (tức là 1h15p ms hoàn thành) thì phải chờ tới 2h15p mới được gọi lại

Ta cùng thử ở code sau nhé

    @Scheduled(fixedDelay = 10000)
    public void scheduleTaskWithFixedDelay() {
        // Call send email method here
        // Pretend it takes 1000ms
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        LOGGER.info("Send email to producers to inform quantity sold items");
    }

Kết quả log nhận được

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)
2018-04-10 09:15:16.061  INFO 22208 --- [           main] springbootdemo.demo.DemoApplication      : Starting DemoApplication on nhs3108-ms-7817 with PID 22208 (/home/nhs3108/Codes/SpringBootDemo/target/classes started by nhs3108 in /home/nhs3108/Codes/SpringBootDemo)
2018-04-10 09:15:16.064  INFO 22208 --- [           main] springbootdemo.demo.DemoApplication      : No active profile set, falling back to default profiles: default
2018-04-10 09:15:16.105  INFO 22208 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@4d14b6c2: startup date [Tue Apr 10 09:15:16 ICT 2018]; root of context hierarchy
2018-04-10 09:15:16.618  INFO 22208 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-04-10 09:15:16.628  INFO 22208 --- [           main] s.a.ScheduledAnnotationBeanPostProcessor : No TaskScheduler/ScheduledExecutorService bean found for scheduled processing
2018-04-10 09:15:16.635  INFO 22208 --- [           main] springbootdemo.demo.DemoApplication      : Started DemoApplication in 0.875 seconds (JVM running for 1.401)
2018-04-10 09:15:17.633  INFO 22208 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:15:28.633  INFO 22208 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:15:39.634  INFO 22208 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:15:50.635  INFO 22208 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:16:01.636  INFO 22208 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items

Bạn thấy rằng, ta đang để

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

8, nhưng khoảng cách giữa các lần log là khoảng 11s. Lý do việc thực thi hàm này hết 1s và phải chờ 10s sau nó mới lại dc gọi lại. Nếu như phần 3.1, các lần log cách nhau chính xác tới từng miliseconds, thì 3.2 lại khác. Bởi phần trên nó k cần care tới việc method này chạy hết bao lâu và xong hay chưa

3.3. Chạy lặp với khoảng thời gian fixedRate sau khi đi deploy initialDelay (Sử dụng kết hợp fixedRate và initialDelay)

Gần giống như 3.1, Ở đây chỉ khác là, nếu như 3.1 bạn chạy tác vụ gửi mail ngay khi deploy xong, thì

/*
Copyright 2002-2018 the original author or authors.
 *
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 *
http://www.apache.org/licenses/LICENSE-2.0
 *
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 /
package org.springframework.scheduling.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
An annotation that marks a method to be scheduled. Exactly one of
the {@link 
# cron()}, {@link 
# fixedDelay()}, or {@link 
# fixedRate()}
attributes must be specified.
 *
The annotated method must expect no arguments. It will typically have
a {@code void} return type; if not, the returned value will be ignored
when called through the scheduler.
 *
Processing of {@code @Scheduled} annotations is performed by
registering a {@link ScheduledAnnotationBeanPostProcessor}. This can be
done manually or, more conveniently, through the {@code }
element or @{@link EnableScheduling} annotation.
 *
This annotation may be used as a meta-annotation to create custom
composed annotations with attribute overrides.
 *
@author Mark Fisher
@author Dave Syer
@author Chris Beams
@since 3.0
@see EnableScheduling
@see ScheduledAnnotationBeanPostProcessor
@see Schedules
 /
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
  /*
A cron-like expression, extending the usual UN*X definition to include
triggers on the second as well as minute, hour, day of month, month
and day of week.  e.g. {@code "0     MON-FRI"} means once per minute on
weekdays (at the top of the minute - the 0th second).
@return an expression that can be parsed to a cron schedule
@see org.springframework.scheduling.support.CronSequenceGenerator
   /
  String cron() default "";
  /*
A time zone for which the cron expression will be resolved. By default, this
attribute is the empty String (i.e. the server's local time zone will be used).
@return a zone id accepted by {@link java.util.TimeZone
# getTimeZone(String)},
or an empty String to indicate the server's default time zone
@since 4.0
@see org.springframework.scheduling.support.CronTrigger
# CronTrigger(String, java.util.TimeZone)
@see java.util.TimeZone
   /
  String zone() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds
   /
  long fixedDelay() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between the
end of the last invocation and the start of the next.
@return the delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedDelayString() default "";
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds
   /
  long fixedRate() default -1;
  /*
Execute the annotated method with a fixed period in milliseconds between
invocations.
@return the period in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   /
  String fixedRateString() default "";
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds
@since 3.2
   /
  long initialDelay() default -1;
  /*
Number of milliseconds to delay before the first execution of a
{@link 
# fixedRate()} or {@link 
# fixedDelay()} task.
@return the initial delay in milliseconds as a String value, e.g. a placeholder
or a {@link java.time.Duration
# parse java.time.Duration} compliant value
@since 3.2.2
   */
  String initialDelayString() default "";
}

2 cho phép bạn thực hiện việc này sau 1 khoảng thời gian là initialDelay(miliseconds)

    @Scheduled(fixedRate = 2000, initialDelay = 10000)
    public void scheduleTaskWithInitialDelay() {
        LOGGER.info("Send email to producers to inform quantity sold items");
    }

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)
2018-04-10 09:23:06.296  INFO 22556 --- [           main] springbootdemo.demo.DemoApplication      : Starting DemoApplication on nhs3108-ms-7817 with PID 22556 (/home/nhs3108/Codes/SpringBootDemo/target/classes started by nhs3108 in /home/nhs3108/Codes/SpringBootDemo)
2018-04-10 09:23:06.298  INFO 22556 --- [           main] springbootdemo.demo.DemoApplication      : No active profile set, falling back to default profiles: default
2018-04-10 09:23:06.331  INFO 22556 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2145433b: startup date [Tue Apr 10 09:23:06 ICT 2018]; root of context hierarchy
2018-04-10 09:23:06.797  INFO 22556 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-04-10 09:23:06.806  INFO 22556 --- [           main] s.a.ScheduledAnnotationBeanPostProcessor : No TaskScheduler/ScheduledExecutorService bean found for scheduled processing
2018-04-10 09:23:06.811  INFO 22556 --- [           main] springbootdemo.demo.DemoApplication      : Started DemoApplication in 0.732 seconds (JVM running for 1.197)
2018-04-10 09:23:16.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:23:18.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:23:20.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:23:22.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:23:24.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items
2018-04-10 09:23:26.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items

Bạn để ý

2018-04-10 09:23:06.811  INFO 22556 --- [           main] springbootdemo.demo.DemoApplication      : Started DemoApplication in 0.732 seconds (JVM running for 1.197)
2018-04-10 09:23:16.809  INFO 22556 --- [pool-1-thread-1] s.demo.scheduledtasks.ScheduledTasks     : Send email to producers to inform quantity sold items

3.4. Hẹn giờ với cron (Sử dụng cron)

Cũng vẫn yêu cầu gửi mail, nhưng bạn muốn gửi vào 12h thứ 6 hàng tuần, hoặc 23h59 ngày cuối tháng .v.v.v. Những thứ bên trên kia là ko đủ. Vậy bạn hãy nghĩ tới cron. Mình ví dụ, log ra màn hình vào giây 15 của mỗi phút. Ta làm như sau

@Scheduled(cron = "15 * * * * ?")
public void scheduleTaskWithCronExpression() {
    LOGGER.info("Send email to producers to inform quantity sold items");
}

Bạn có thể thay đổi cron expression để phù hợp với yêu cầu của hệ thống. Bạn có thể tham khảo trên https://www.freeformatter.com/cron-expression-generator-quartz.html, 1 công cụ generate cron expression cũng như explain cron expression rất hay.