[JAVA] A trip to decipher Spring's "GUIDES" Scheduling Tasks edition.

Scheduling Tasks

I will decipher this page.

environment sts 3.8.4 Launch sts and search for the target project from "File"-> "New"-> "Import Spring Getting started content". I have imported it and confirmed its operation.

Background I was learning Spring boot, but I decided to read the original document without relying on commercial books. It's all in English, so I'm struggling to read it.

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I am writing it as a memorandum for learning. If you have any advice, such as points to be corrected or supplements, please do not hesitate to contact us.

Creating a component

ScheduledTasks.java

package hello;

import java.text.SimpleDateFormat;
import java.util.Date;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class ScheduledTasks {

    private static final Logger log = LoggerFactory.getLogger(ScheduledTasks.class);

    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

    @Scheduled(fixedRate = 5000)
    public void reportCurrentTime() {
        log.info("The time is now {}", dateFormat.format(new Date()));
    }
}

First of all, from this code. By setting @Component, it can be used in the Main class of Application.java to be created next. The Main class must be annotated with @ SpringBootApplication (including @ComponentScan). This will allow you to automatically find the components in the same package. You will also be able to use the components you create here.

Read the ScheduledTasks method

This class creates a mechanism to display the log on the console every 5 seconds. private static final Logger log = LoggerFactory.getLogger(ScheduledTasks.class); Get the logger at.

LoggerFactory is a logging library created by the developers of Log4j. Set a Class object of a class that uses a logger, such as ScheduledTasks.class, as an argument.

This allows log.info () to be displayed on the console by default.

If you annotate @Scheduled (fixedRate = 5000), the method will be executed periodically. By the way, if you annotate a method with arguments, an exception will occur. By specifying @EnableScheduling in the file to be created next, the method with @Scheduled will be executed.

SimpleDateFormat and Date are omitted.

Creating Application.java

Next, let's look at the code of application.java that has the main method.

Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@SpringBootApplication
@EnableScheduling
public class Application {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class);
    }
}

Explanation of annotations

This code is annotated with @ SpringBootApplication. This reads @Configuration`` @EnableAutoConfiguration @EnableWebMvc`` @ComponentScan as a set.

@ComponentScan will find the ScheduledTasks class you just created. With @EnableScheduling, the reportCurrentTime () method annotated with@Scheduled (fixedRate = 5000)will be executed periodically. Annotations seem to allow for more complex scheduling by using @Scheduled (cron =" ").

Run

In sts, if you click the project name and press the play button, it will automatically compile and execute.

Logs will be added to the console every 5 seconds.