Tagged: java

2017-01-26

Injecting Property Values into EJBs from Database

references

Inject Java Properties in Java EE Using CDI

Property.java

@Entity
@NamedQueries({
@NamedQuery(name = "Property.find",
            query = "SELECT p FROM Property AS p WHERE p.name = :name")
})
public class Property {

    @Basic(optional = false)
    @Column(name = "NAME", nullable = false, unique = true)
    @NotNull
    private String name;

    @Basic(Optional = false)
    @Column(name = "VALUE_", nullable = false)
    @NotNull
    private String value = "";
}

find

public static Property findNamed(final EntityManager entityManager,
                                 final String name) {
    final TypedQuery typedQuery
        = entityManager.createNamedQuery("Property.find", Property.class);
    typedQuery.setParameter("name", name);
    try {
        return typedQuery.getSingleResult();
    } catch (final NoResultException nre) {
        return null;
    }
}

public static Property findCriteria(final EntityManager entityManager,
                                    final String name) {
    final CriteriaBuilder criteriaBuilder
        = entityManager.getCriteriaBuilder();
    final CriteriaQuery criteriaQuery
        = criteriaBuilder.createQuery(Property.class);
    final Root<Property> property = criteriaQuery.from(Property.class);
    criteriaQuery.select(property);
    criteriaQuery.where(
        criteriaBuilder.equal(property.get(Property_.name), name));
    final TypedQuery typedQuery
        = entityManager.createQuery(criteriaQuery);
    try {
        return typedQuery.getSingleResult();
    } catch (final NoResultException nre) {
        return null;
    }
}

public static Property find(final EntityManager entityManager,
                            final String name) {
    if (current().nextBoolean()) {
        return findNamed(entityManager, name);
    }
    return findCriteria(entityManager, name);
}

PropertyValue.java

@Qualifier
@Retention(RUNTIME)
@Target({FIELD, METHOD, PARAMETER, TYPE})
public @interface PropertyValue {

    @Nonbinding
    String name() default "";

    @Nonbinding
    boolean optional() default true;
}

PropertyFactory.java

@Dependent
public class PropertyValueFactory {

@Produces
@PropertyValue
public String producePropertyValue(final InjectionPoint injectionPoint) {
    final PropertyValue annotation
        = injectionPoint.getAnnotated().getAnnotation(PropertyValue.class);
    final String name = annotation.name();
    final boolean optional = annotation.optional();
    final Property property = Property.find(entityManger, name);
    if (property == null && !optional) {
        throw new InjectionException("property not found; name= " + name);
    }
    return ofNullable(property).map(Property::getValue).orElse(null);
}

public void diposePropertyValue(
    @Disposes @PropertyValue final String value) {
    // empty


@PersistenceContext
private EntityManager entityManger;
}

StorageObjectServiceFtp.java

 @Stateless
 public class StorageObjectServiceFtp extends StorageObjectService {

    @Inject
    @PropertyValue(name = "ftp.hostname", optional = false)
    private String hostname;

    @Inject
    @PropertyValue(name = "ftp.username", optional = false)
    private String username;

    @Inject
    @PropertyValue(name = "ftp.password", optional = false)
    private String password;

    @Inject
    @PropertyValue(name = "ftp.rootpath", optional = true)
    private String rootpath;
}

2016-10-21

orElse, or orElseGet, that is the question:

static String B() {
    System.out.println("B()...");
    return "B";
}

public static void main(final String... args) {
    System.out.println(Optional.of("A").orElse(B()));
    System.out.println(Optional.of("A").orElseGet(() -> B()));
}

2016-09-09

format/parse ISO 8601 ignoring the fraction

    static Instant parseIsoInstant(final String formatted) {
        return Instant.from(DateTimeFormatter.ISO_INSTANT.parse(formatted))
                .with(ChronoField.NANO_OF_SECOND, 0L);
    }

    static String formatIsoInstant(final TemporalAccessor parsed) {
        return DateTimeFormatter.ISO_INSTANT.format(
                Instant.from(parsed).with(ChronoField.NANO_OF_SECOND, 0L));
    }

    static Date parseIsoDate(final String formatted) {
        return Date.from(parseIsoInstant(formatted));
    }

    static String formatIsoDate(final Date parsed) {
        return formatIsoInstant(parsed.toInstant());
    }

2016-08-24

how to exclude generated jpa metamodels from being javadoc-ed

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-javadoc-plugin</artifactId>
    <configuration>
      <sourceFileExcludes>
        <exclude>**/**_.java</exclude>
      </sourceFileExcludes>
    </configuration>
  </plugin>
</plugins>

2016-08-18

how to set final variable in catch block?

references

as final as possible, but not final-er.

꽤나 오랫동안 궁금했었다.

final SecureRandom random;
try {
    random = SecureRandom.getInstanceStrong();
} catch (final NoSuchAlgorithmException nsae) {
    random = new SecureRandom(); // won't compile
    // variable random might already have been assigned
}

let it go, let it go~~~

그냥 이렇게 하면 되지 뭐…

SecureRandom random;
try {
    random = SecureRandom.getInstanceStrong();
} catch (final NoSuchAlgorithmException nsae) {
    random = new SecureRandom();
}

// ----------------------------------
// 권팀장 죽어버려!!! -퇴사자-
random = null;
// ----------------------------------

final int i = random.nextInt(128); // NPE

we will find a way. we always have.

지저분해 보일지도 모르겠다.

final SecureRandom random;
{
    Random random_;
    try {
        random_ = SecureRandom.getInstanceStrong();
    } catch (final NoSuchAlgorithmException nsae) {
        random_ = new SecureRandom();
    }
    random = random_;
}

메서드로 따로 빼 놓고 써도 되고, 뭐…

static SecureRandom secureRandomPossiblyStrong() {
    try {
        return SecureRandom.getInstanceStrong();
    } catch (final NoSuchAlgorithmException nsae) {
        return new SecureRandom();
    }
}

Supplier 를 사용해도 될 듯…

final static SecureRandom RANDOM =
    ((Supplier<SecureRandom>)() ->{
        try {
            return SecureRandom.getInstanceStrong();
        } catch (final NoSuchAlgorithmException nsae) {
            return new SecureRandom();
        } 
    }).get();

2016-08-16

exclusive or with java

references

15.22. Bitwise and Logical Operators

`^`

XOR 을 사용할 일은 많이 없을 듯 하지만, 의외로 사용할 일이 있을 때 모르고 지나치는 일이 있다. 아래 코드는 condition1과 condition2중 하나만 true 일 때 특정 작업을 수행하는 코드이다.

void some() {
    if (condition1) {
        if (!condition2) {
            // do some!                     // T F
            return;
        }
    } else { // !condition1
        if (condition2) {
            // do some!                     // F T
            return;
        }
    }
    assert (condition1 && condition2)       // T T
           || (!condition1 && !condition2); // F F
}

Exclusive OR 를 다음과 같이 사용할 수 있다.

void some() {
    if (condition1 ^ condition2) {            // T F | F T
        // do some!
    }
}

2016-08-12

do we need to call flush()? can’t we just call close()?

You can find your own answer from following links.

flush() will never hurt anyone and it has its own purposes.
DON’T YOU EVER SAY THAT close() WILL DO flush() FOR YOU!

2016-08-09

When are generated primary key values available?

JSR 338: Java^TM Persistence 2.1 says, in 3.5.3, that

Generated primary key values are available in the PostPersist method.

It’s a pity that even those ids with GenerationType.TABLE are not available in the PrePersist method and it’s a bigger pity that I didn’t rely on the spec.

public class MyEntity {

    @PrePersist
    private void onPrePersist() {
        derived = Stirng.format("%1$016x", id);
    }

    @GeneratedValue(generator = "some",
                    strategy = GenerationType.TABLE)
    @TableGenerator(
            ...
            name = "some",
            ...
    )
    @NotNull
    private Long id;

    @Basic(optional = false)
    @Column(name = "DERIVED", nullable = false, updatable = false)
    @NotNull
    private String derived;
}

I just found that above code doesn’t work with WildFly while works with Payara.

I have to change my database and the code.

public class MyEntity {

    @PrePersist
    private void onPrePersist() {
        //derived = Stirng.format("%1$016x", id);
    }

    @PostPersist
    private void onPostPersist() {
        derived = Stirng.format("%1$016x", id);
    }

    @GeneratedValue(generator = "some",
                    strategy = GenerationType.TABLE)
    @TableGenerator(
            ...
            name = "some",
            ...
    )
    @NotNull
    private Long id;

    @Basic // optional
    @Column(name = "DERIVED") // nullable, updatable
    //@NotNull
    private String derived;
}

2016-07-26

diagnosing system with jax-rs

@Path("/system/diagnoses")
public class DiagnosesResource {

    private static final Logger logger
            = getLogger(DiagnosesResource.class.getName());

    private Response response() {
        handler.flush();
        return Response.ok(baos.toByteArray(), MediaType.TEXT_PLAIN).build();
    }

    @PostConstruct
    private void onPostConstruct() {
        baos = new ByteArrayOutputStream();
        formatter = new SimpleFormatter();
        handler = new StreamHandler(baos, formatter);
        logger.addHandler(handler);
    }

    @PreDestroy
    private void onPreDestroy() {
        logger.removeHandler(handler);
        handler = null;
        formatter = null;
        baos = null;
    }

    private ByteArrayOutputStream baos;

    private Formatter formatter;

    private Handler handler;
}

Now we can add some methods for diagnosing.

@POST
@Path("/some")
@Produces({MediaType.TEXT_PLAIN})
public Response some() {
    // diagnose here with some logs
    return response();
}

2016-07-22

finding an entity by its unique attribute value.

    public static <T extends BaseEntity, Y> Optional<T> findByUniqueAttribute(
            final EntityManager entityManager,
            final Class<T> entityClass,
            final Supplier<SingularAttribute<? super T, Y>> attributeSupplier,
            final Supplier<? extends Y> valueSupplier) {
        final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
        final CriteriaQuery<T> criteria = builder.createQuery(entityClass);
        final Root<T> root = criteria.from(entityClass);
        criteria.select(root);
        criteria.where(builder.equal(root.get(
                attributeSupplier.get()), valueSupplier.get()));
        try {
            return Optional.of(
                    entityManager.createQuery(criteria).getSingleResult());
        } catch (final NoResultException nre) {
            return Optional.empty();
        }
    }

    public static <T extends BaseEntity, Y> Optional<T> findByUniqueAttribute2(
            @NotNull final EntityManager entityManager,
            @NotNull final Class<T> entityClass,
            @NotNull final Function<ManagedType<T>, SingularAttribute<? super T, Y>> attributeSupplier,
            @NotNull final Supplier<? extends Y> valueSupplier) {
        final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
        final CriteriaQuery<T> criteria = builder.createQuery(entityClass);
        final Root<T> root = criteria.from(entityClass);
        criteria.select(root);
        criteria.where(builder.equal(
                root.get(attributeSupplier.apply(
                        entityManager.getMetamodel().entity(entityClass))),
                valueSupplier.get()));
        try {
            return Optional.of(
                    entityManager.createQuery(criteria).getSingleResult());
        } catch (final NoResultException nre) {
            return Optional.empty();
        }
    }