guanxf

元注解：

　　元注解的作用就是負責注解其他注解。Java5.0定義了4個標準的meta-annotation類型，它們被用來提供對其它 annotation類型作說明。Java5.0定義的元注解：
　　　　1.@Target,
　　　　2.@Retention,
　　　　3.@Documented,
　　　　4.@Inherited

@Target(TYPE)
@Retention(RUNTIME)
public @interface Table {
    /**
     * (Optional) The name of the table.
     * <p/>
 * Defaults to the entity name.
     */
 String name() default "";
}

@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface Column {

    /**
     * (Optional) The name of the column. Defaults to
     * the property or field name.
     */
 String name() default "";
}

@Table(name = "t_s_user")
public class User {
    @Column(name="name")
    private String name;

 @Column(name="pwd")
    private String pwd;

    public String getName() {
        return name;
 }

    public void setName(String name) {
        this.name = name;
 }

    public String getPwd() {
        return pwd;
 }

    public void setPwd(String pwd) {
        this.pwd = pwd;
 }
}

public static void print() {
  System.out.println("table's name：" + User.class.getAnnotation(Table.class).name());
 Field[] fields = User.class.getDeclaredFields();
    for (int i = 0; i < fields.length; i++) {
        Field field = fields[i];
 System.out.println("field's type:" + field.getType().getName());
 System.out.println("field's columnName:" + field.getAnnotation(Column.class).name());
 }
}