Annotations came to JDK with JDK5 (2004) since then they evaluated and are accepted so widely and even became more powerful and useful than XML in just 4 years.

While you are developing a project with java at any scale you’ll need a very large number of XML files defined in very different API’s and DTD/XSDs. Which makes configuration very complex.

eg:struts.xml,tiles.xml,validation.xml,hibernate.cfg.xml,spring-context.xml,web.xml,and so on

Although it is easy to read and modify there are lots files

Now with annotations:

Yes you still have lots of things/APIs to configure and you should still use XML, but you can now get rid of some of them and decrease the number of files in your repository.And bind multiple configuration files in just one file

Look at the sample:

Here, in a single file, it is possible to configure both JPA, hibernate and JAXB easily and in a human readable way.

import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlID;
import javax.xml.bind.annotation.XmlType;
import javax.xml.bind.annotation.adapters.CollapsedStringAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Column;

@Entity
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "IdentifiedType")
public abstract class IdentifiedType {
@Id
@Column(name="id")
@XmlAttribute
@XmlJavaTypeAdapter(CollapsedStringAdapter.class)
@XmlID
protected String id;

Of source do not forget other points:

• since annotations are embedded configuration they are really fast
• on the other hand they are one time configuration cannot be change at any time (beware)
• annotations are not replacement of XML but complementary of them

Related posts:

1. too much annotation is also bad
2. Clean database schema with inheritance
3. hibernate native Id generator tip
4. hibernate cache injection: missing…
5. hibernate tip: smart id generator