SimpleTrigger vs CronTrigger in Quartz Scheduler

SimpleTrigger
SimpleTrigger is used for scenarios in which we need to execute a job at a specific moment in time.

SimpleTrigger trigger = (SimpleTrigger) TriggerBuilder.newTrigger()
  .withIdentity("trigger1", "group1")
  .startAt(myStartTime)
  .forJob("job1", "group1")
  .build();

CronTrigger
The CronTrigger is used when we need schedules based on calendar-like statements.

CronTrigger trigger = TriggerBuilder.newTrigger()
  .withIdentity("trigger3", "group1")
  .withSchedule(CronScheduleBuilder.cronSchedule("0 0/2 8-17 * * ?"))
  .forJob("myJob", "group1")
  .build();

References
https://www.baeldung.com/quartz
https://stackoverflow.com/questions/26403391/difference-between-cron-trigger-and-simple-trigger-in-quartz-scheduler
http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/crontrigger.html
https://www.freeformatter.com/cron-expression-generator-quartz.html

Volatile memory in Java

To ensure that updates to variables propagate predictably to other threads, we should apply the volatile modifier to those variables:

public class TaskRunner {

    private volatile static int number;
    private volatile static boolean ready;

    // same as before
}

This way, we communicate with runtime and processor to not reorder any instruction involving the volatile variable. Also, processors understand that they should flush any updates to these variables right away.

References
https://www.baeldung.com/java-volatile
https://www.baeldung.com/java-stack-heap

Using Fetch API in JavaScript

Get Method using JavaScript Promise

fetch('http://example.com/movies.json')
  .then(response => response.json())
  .then(data => console.log(data));

Supplying request options

// Example POST method implementation:
async function postData(url = '', data = {}) {
  // Default options are marked with *
  const response = await fetch(url, {
    method: 'POST', // *GET, POST, PUT, DELETE, etc.
    mode: 'cors', // no-cors, *cors, same-origin
    cache: 'no-cache', // *default, no-cache, reload, force-cache, only-if-cached
    credentials: 'same-origin', // include, *same-origin, omit
    headers: {
      'Content-Type': 'application/json'
      // 'Content-Type': 'application/x-www-form-urlencoded',
    },
    redirect: 'follow', // manual, *follow, error
    referrerPolicy: 'no-referrer', // no-referrer, *no-referrer-when-downgrade, origin, origin-when-cross-origin, same-origin, strict-origin, strict-origin-when-cross-origin, unsafe-url
    body: JSON.stringify(data) // body data type must match "Content-Type" header
  });
  return response.json(); // parses JSON response into native JavaScript objects
}

postData('https://example.com/answer', { answer: 42 })
  .then(data => {
    console.log(data); // JSON data parsed by `data.json()` call
  });

Checking that the fetch was successful

fetch('flowers.jpg')
  .then(response => {
    if (!response.ok) {
      throw new Error('Network response was not OK');
    }
    return response.blob();
  })
  .then(myBlob => {
    myImage.src = URL.createObjectURL(myBlob);
  })
  .catch(error => {
    console.error('There has been a problem with your fetch operation:', error);
  });

Supplying your own request object

const myHeaders = new Headers();

const myRequest = new Request('flowers.jpg', {
  method: 'GET',
  headers: myHeaders,
  mode: 'cors',
  cache: 'default',
});

fetch(myRequest)
  .then(response => response.blob())
  .then(myBlob => {
    myImage.src = URL.createObjectURL(myBlob);
  });

Headers

const content = 'Hello World';
const myHeaders = new Headers();
myHeaders.append('Content-Type', 'text/plain');
myHeaders.append('Content-Length', content.length.toString());
myHeaders.append('X-Custom-Header', 'ProcessThisImmediately');
const myHeaders = new Headers({
  'Content-Type': 'text/plain',
  'Content-Length': content.length.toString(),
  'X-Custom-Header': 'ProcessThisImmediately'
});
console.log(myHeaders.has('Content-Type')); // true
console.log(myHeaders.has('Set-Cookie')); // false
myHeaders.set('Content-Type', 'text/html');
myHeaders.append('X-Custom-Header', 'AnotherValue');

console.log(myHeaders.get('Content-Length')); // 11
console.log(myHeaders.get('X-Custom-Header')); // ['ProcessThisImmediately', 'AnotherValue']

myHeaders.delete('X-Custom-Header');
console.log(myHeaders.get('X-Custom-Header')); // null
fetch(myRequest)
  .then(response => {
     const contentType = response.headers.get('content-type');
     if (!contentType || !contentType.includes('application/json')) {
       throw new TypeError("Oops, we haven't got JSON!");
     }
     return response.json();
  })
  .then(data => {
      /* process your data further */
  })
  .catch(error => console.error(error));

References
https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch

Force Spring Boot to use Gson instead of Jackson

Well, WebMvcConfigurerAdapter is deprecated. As of Spring 5.0 do this:

@SpringBootApplication(exclude = {JacksonAutoConfiguration.class})
public class Spring01Application {

    public static void main(String[] args) {
        SpringApplication.run(Spring01Application.class, args);
    }

}
@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Bean
    public Gson gson() {
        GsonBuilder b = new GsonBuilder();
        b.registerTypeAdapterFactory(HibernateProxyTypeAdapter.FACTORY);
        b.registerTypeAdapterFactory(DateTypeAdapter.FACTORY);
        b.registerTypeAdapterFactory(TimestampTypeAdapter.FACTORY);
        b.registerTypeAdapterFactory(LocalDateTypeAdapter.FACTORY);
        b.registerTypeAdapterFactory(LocalDateTimeTypeAdapter.FACTORY);
        return b.create();
    }

    @Override
    public void configureMessageConverters(
        List<HttpMessageConverter<?>> converters) {
        StringHttpMessageConverter stringConverter = new StringHttpMessageConverter();
        stringConverter.setWriteAcceptCharset(false);
        stringConverter.setSupportedMediaTypes(Collections
            .singletonList(MediaType.TEXT_PLAIN));
        converters.add(stringConverter);
        converters.add(new ByteArrayHttpMessageConverter());
        converters.add(new SourceHttpMessageConverter<>());
        GsonHttpMessageConverter gsonHttpMessageConverter = new GsonHttpMessageConverter();
        gsonHttpMessageConverter.setGson(gson());
        gsonHttpMessageConverter.setSupportedMediaTypes(Arrays
            .asList(MediaType.APPLICATION_JSON));
        converters.add(gsonHttpMessageConverter);
    }
}

References
https://stackoverflow.com/questions/40786366/force-spring-boot-to-use-gson-instead-of-jackson

Parallel foreach in Java

List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4);
listOfNumbers.parallelStream().forEach(number ->
    System.out.println(number + " " + Thread.currentThread().getName())
);

Custom Thread Pool

List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4);
ForkJoinPool customThreadPool = new ForkJoinPool(4);
int sum = customThreadPool.submit(
    () -> listOfNumbers.parallelStream().reduce(0, Integer::sum)).get();
customThreadPool.shutdown();
assertThat(sum).isEqualTo(10);

References
https://www.baeldung.com/java-when-to-use-parallel-stream

Configuring Quartz Scheduler in Spring Boot

QuartzConfig.java

@Configuration
public class QuartzConfig {

    @Bean
    public JobDetailFactoryBean jobDetail() {
        JobDetailFactoryBean jobDetailFactory = new JobDetailFactoryBean();
        jobDetailFactory.setJobClass(GarbageCollectorJob.class);
        jobDetailFactory.setDescription("Invoke Sample Job service...");
        jobDetailFactory.setDurability(true);
        return jobDetailFactory;
    }

    @Bean
    public SimpleTriggerFactoryBean trigger(JobDetail job) {
        SimpleTriggerFactoryBean trigger = new SimpleTriggerFactoryBean();
        trigger.setJobDetail(job);
        // every one hour
        trigger.setRepeatInterval(60 * 60 * 1000);
        trigger.setRepeatCount(SimpleTrigger.REPEAT_INDEFINITELY);
        return trigger;
    }

    @Bean
    public SchedulerFactoryBean scheduler(Trigger trigger, JobDetail job, JobFactory springBeanJobFactory) {
        SchedulerFactoryBean schedulerFactory = new SchedulerFactoryBean();
        schedulerFactory.setConfigLocation(new ClassPathResource("quartz.properties"));

        schedulerFactory.setJobFactory(springBeanJobFactory);
        schedulerFactory.setJobDetails(job);
        schedulerFactory.setTriggers(trigger);
        return schedulerFactory;
    }

    @Bean
    public SpringBeanJobFactory springBeanJobFactory(ApplicationContext applicationContext) {
        AutoWiringSpringBeanJobFactory jobFactory = new AutoWiringSpringBeanJobFactory();
        jobFactory.setApplicationContext(applicationContext);
        return jobFactory;
    }
}

AutoWiringSpringBeanJobFactory.java

public final class AutoWiringSpringBeanJobFactory
        extends SpringBeanJobFactory
        implements ApplicationContextAware {

    private transient AutowireCapableBeanFactory beanFactory;

    public void setApplicationContext(
            final ApplicationContext context) {
        beanFactory = context.getAutowireCapableBeanFactory();
    }

    @Override
    protected Object createJobInstance(
            final TriggerFiredBundle bundle)
            throws Exception {
        final Object job = super.createJobInstance(bundle);
        beanFactory.autowireBean(job);
        return job;
    }
}

quartz.properties

org.quartz.threadPool.class=org.quartz.simpl.SimpleThreadPool
org.quartz.threadPool.threadCount=10
org.quartz.threadPool.threadsInheritContextClassLoaderOfInitializingThread=true

org.quartz.jobStore.class=org.quartz.simpl.RAMJobStore

References
https://www.baeldung.com/spring-quartz-schedule
http://www.btmatthews.com/blog/2011/inject-application-context+dependencies-in-quartz-job-beans.html
https://www.candidjava.com/spring-boot/quartz-example/