Scheduling is a process of executing the tasks for the specific time period. Spring Boot provides a good support to write a scheduler on the Spring applications.

Java Cron Expression

Java Cron expressions are used to configure the instances of CronTrigger, a subclass of org.quartz.Trigger. For more information about Java cron expression you can refer to this link −

https://docs.oracle.com/cd/E12058_01/doc/doc.1014/e12030/cron_expressions.htm

The @EnableScheduling annotation is used to enable the scheduler for your application. This annotation should be added into the main Spring Boot application class file.

@SpringBootApplication@EnableScheduling public class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); }}

The @Scheduled annotation is used to trigger the scheduler for a specific time period.

@Scheduled(cron = “0 * 9 * * ?”)public void cronJobSch() throws Exception {}

The following is a sample code that shows how to execute the task every minute starting at 9:00 AM and ending at 9:59 AM, every day

package com.tecklearn.demo.scheduler; import java.text.SimpleDateFormat;import java.util.Date;import org.springframework.scheduling.annotation.Scheduled;import org.springframework.stereotype.Component; @Componentpublic class Scheduler { @Scheduled(cron = “0 * 9 * * ?”) public void cronJobSch() { SimpleDateFormat sdf = new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss.SSS”); Date now = new Date(); String strDate = sdf.format(now); System.out.println(“Java cron job expression:: ” + strDate); }}

The application has started at 09:03:23 and for every one minute from that time the cron job scheduler task has executed.

Fixed Rate

Fixed Rate scheduler is used to execute the tasks at the specific time. It does not wait for the completion of previous task. The values should be in milliseconds. The sample code is shown here −

@Scheduled(fixedRate = 1000)public void fixedRateSch() { }

A sample code for executing a task on every second from the application startup is shown here −

package com.tecklearn.demo.scheduler; import java.text.SimpleDateFormat;import java.util.Date;import org.springframework.scheduling.annotation.Scheduled;import org.springframework.stereotype.Component; @Componentpublic class Scheduler { @Scheduled(fixedRate = 1000) public void fixedRateSch() { SimpleDateFormat sdf = new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss.SSS”); Date now = new Date(); String strDate = sdf.format(now); System.out.println(“Fixed Rate scheduler:: ” + strDate); }}

Observe the application that has started at 09:12:00 and after that every second fixed rate scheduler task has executed.

Fixed Delay

Fixed Delay scheduler is used to execute the tasks at a specific time. It should wait for the previous task completion. The values should be in milliseconds. A sample code is shown here −

@Scheduled(fixedDelay = 1000, initialDelay = 1000)public void fixedDelaySch() {}

Here, the initialDelay is the time after which the task will be executed the first time after the initial delay value.

An example to execute the task for every second after 3 seconds from the application startup has been completed is shown below −

package com.tecklearn.demo.scheduler; import java.text.SimpleDateFormat;import java.util.Date;import org.springframework.scheduling.annotation.Scheduled;import org.springframework.stereotype.Component; @Componentpublic class Scheduler { @Scheduled(fixedDelay = 1000, initialDelay = 3000) public void fixedDelaySch() { SimpleDateFormat sdf = new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss.SSS”); Date now = new Date(); String strDate = sdf.format(now); System.out.println(“Fixed Delay scheduler:: ” + strDate); }}

Observe the following screenshot which shows the application that has started at 09:18:39 and after every 3 seconds, the fixed delay scheduler task has executed on every second.

Spring Boot – CORS Support

Cross-Origin Resource Sharing (CORS) is a security concept that allows restricting the resources implemented in web browsers. It prevents the JavaScript code producing or consuming the requests against different origin.

For example, your web application is running on 8080 port and by using JavaScript you are trying to consuming RESTful web services from 9090 port. Under such situations, you will face the Cross-Origin Resource Sharing security issue on your web browsers.

Two requirements are needed to handle this issue −

RESTful web services should support the Cross-Origin Resource Sharing.
RESTful web service application should allow accessing the API(s) from the 8080 port.

In this chapter, we are going to learn in detail about How to Enable Cross-Origin Requests for a RESTful Web Service application.

Enable CORS in Controller Method

We need to set the origins for RESTful web service by using @CrossOrigin annotation for the controller method. This @CrossOrigin annotation supports specific REST API, and not for the entire application.

@RequestMapping(value = “/products”)@CrossOrigin(origins = “http://localhost:8080”) public ResponseEntity<Object> getProduct() { return null;}

Global CORS Configuration

We need to define the shown @Bean configuration to set the CORS configuration support globally to your Spring Boot application.

@Beanpublic WebMvcConfigurer corsConfigurer() { return new WebMvcConfigurerAdapter() { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping(“/products”).allowedOrigins(“http://localhost:9000”); } };}

To code to set the CORS configuration globally in main Spring Boot application is given below.

package com.tecklearn.demo; import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.context.annotation.Bean;import org.springframework.web.servlet.config.annotation.CorsRegistry;import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter; @SpringBootApplicationpublic class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); } @Bean public WebMvcConfigurer corsConfigurer() { return new WebMvcConfigurerAdapter() { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping(“/products”).allowedOrigins(“http://localhost:8080”); } }; }}

Now, you can create a Spring Boot web application that runs on 8080 port and your RESTful web service application that can run on the 9090 port.

So, this brings us to the end of blog. This Tecklearn ‘How to write a Scheduler on the Spring applications and CORS Support’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Spring Boot and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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