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spring

spring

   @NotNull
    @Min(18)
    private Integer age;

@NotNull won't allow an empty value
@Min(18) won't allow if the age is less than 18

!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head> 
    <title>Getting Started: Handing Form Submission</title> 
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
    <h1>Form</h1>
    <form action="#" th:action="@{/greeting}" th:object="${greeting}" method="post">
        <p>Id: <input type="text" th:field="*{id}" /></p>
        <p>Message: <input type="text" th:field="*{content}" /></p>
        <p><input type="submit" value="Submit" /> <input type="reset" value="Reset" /></p>
    </form>
</body>
</html>
The th:action="@{/greeting}" expression directs the form to POST to the /greetingendpoint, while the th:object="${greeting}" expression declares the model object to use for collecting the form data. The two form fields, expressed with th:field="*{id}" andth:field="*{content}", correspond to the fields in the Greeting object above@EnableScheduling

public class ScheduledTasks {

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

    @Scheduled(fixedRate = 5000)
    public void reportCurrentTime() {
        System.out.println("The time is now " + dateFormat.format(new Date()));
    }
}

The key components that make this code perform scheduled tasks are the@EnableScheduling and @Scheduled annotations.

@EnableScheduling ensures that a background task executor is created. Without it, nothing gets scheduled.

You use @Scheduled to configure when a particular method is run.
Note: This example uses fixedRate, which specifies the interval between method invocations measured from the start time of each invocation. There are other options, likefixedDelay, which specifies the interval between invocations measured from the completion of the task. You can also use @Scheduled(cron=". . .") expressions for more sophisticated task scheduling.
```
http://localhost:8080/greeting?name=World"   @RequestParam(value="name",required=false,defaultValue="World")
```
```
@Entity
public class Customer {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;
    private String firstName;
    private String lastName;

    private Customer() {}

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return String.format(
                "Customer[id=%d, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }

}
```
Here you have a Customer class with three attributes, the id, the firstName, and thelastName. You also have two constructors. The default constructor only exists for the sake of JPA. You won't use it directly, so it is designated as private.

The Customer class is annotated with @Entity, indicating that it is a JPA entity. For lack of a@Table annotation, it is assumed that this entity will be mapped to a table named Customer.

The Customer's id property is annotated with @Id so that JPA will recognize it as the object's ID. The id property is also annotated with @GeneratedValue to indicate that the ID should be generated automatically
```
@EnableJpaRepositories
public class Application {

    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder().setType(H2).build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) {
        LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean();
        lef.setDataSource(dataSource);
        lef.setJpaVendorAdapter(jpaVendorAdapter);
        lef.setPackagesToScan("hello");
        return lef;
    }

    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter();
        hibernateJpaVendorAdapter.setShowSql(false);
        hibernateJpaVendorAdapter.setGenerateDdl(true);
        hibernateJpaVendorAdapter.setDatabase(Database.H2);
        return hibernateJpaVendorAdapter;
    }

    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory entityManagerFactory) {
        return new JpaTransactionManager(entityManagerFactory);
    }
```
In the configuration, you need to add the @EnableJpaRepositories annotation. This annotation tells Spring Data JPA that it should seek out any interface that extendsorg.springframework.data.repository.Repository and automatically generate an implementation. By extending JpaRepository, your CustomerRepository interface transitively extends Repository. Therefore, Spring Data JPA will find it and create an implementation for you.

Most of the content in Application sets up several beans to support Spring Data JPA and the sample:
- The dataSource() method defines a DataSource bean, as an embedded database to which the objects are persisted.
- The entityManagerFactory() method defines aLocalContainerEntityManagerFactoryBean that is ultimately used to createLocalContainerEntityManagerFactory a bean that implements theEntityManagerFactory interface. It is the bean through which JPA operations will be performed. Note that this factory bean's packagesToScan property is set to look for entities in the package named "hello". This makes it possible to work with JPA without defining a "persistence.xml" file.
- The jpaVendorAdapter() method defines a Hibernate-based JPA vendor adapter bean for use by the EntityManagerFactory bean.
- The transactionManager() method defines a JpaTransactionManager bean for transactional persistence.
@Service
```
public class FacebookLookupService {

    RestTemplate restTemplate = new RestTemplate();

    @Async
    public Future<Page> findPage(String page) throws InterruptedException {
        System.out.println("Looking up " + page);
        Page results = restTemplate.getForObject("http://graph.facebook.com/" + page, Page.class);
        Thread.sleep(1000L);
        return new AsyncResult<Page>(results);
    }

}
```
The class is marked with the @Service annotation, making it a candidate for Spring's component scanning to detect it and add it to the application context.

The findPage method is flagged with Spring's @Async annotation, indicating it will run on a separate thread. The method's return type is Future<Page> instead of Page, a requirement for any asynchronous service. This code uses the concrete implementation of AsyncResultto wrap the results of the Facebook query.
```
@Configuration
@EnableAsync
@EnableAutoConfiguration
@ComponentScan
public class Application implements CommandLineRunner {

    @Autowired
    FacebookLookupService facebookLookupService;

    @Override
    public void run(String... args) throws Exception {
        // Start the clock
        long start = System.currentTimeMillis();

        // Kick of multiple, asynchronous lookups
        Future<Page> page1 = facebookLookupService.findPage("GoPivotal");
        Future<Page> page2 = facebookLookupService.findPage("CloudFoundry");
        Future<Page> page3 = facebookLookupService.findPage("SpringFramework");

        // Wait until they are all done
        while (!(page1.isDone() && page2.isDone() && page3.isDone())) {
            Thread.sleep(10); //millisecond pause between each check
        }

        // Print results, including elapsed time
        System.out.println("Elapsed time: " + (System.currentTimeMillis() - start));
        System.out.println(page1.get());
        System.out.println(page2.get());
        System.out.println(page3.get());
    }

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

}
```
The @EnableAsync annotation switches on Spring's ability to run @Async methods in a background thread pool.

The @EnableAutoConfiguration annotation switches on reasonable default behaviors based on the content of your classpath. For example, it looks for any class that implements theCommandLineRunner interface and invokes its run() method. In this case, it runs the demo code for this guide.
```
public class HelloController {

    @RequestMapping("/")
    public String index() {
        return "Greetings from Spring Boot!";
    }

}
```
@RestController combines @Controller and @ResponseBody, two annotations that results in web requests returning data rather than a view
```
public class FacebookLookupService {

    RestTemplate restTemplate = new RestTemplate();

    @Cacheable("hello")
    public Page findPage(String page) {
        return restTemplate.getForObject("http://graph.facebook.com/" + page, Page.class);
    }

}
```
@Cacheable("hello"). Spring's caching abstraction intercepts the call to findPageto check whether it's already been called. If so, Spring's caching abstraction returns the cached copy. Otherwise, it proceeds to invoke the method, store the response in the cache, and then return the results to the caller.

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2013-10-02 10:17
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