Trim string field in JPA

Question

I have a db table with column of datatype char(20). I'm not allowed to change it to a varchar.

I'm writing a JPA entity mapped to this table. I would like the string field representing this column in my entity class to always contain the trimmed value, not the 20-character value padded with spaces that exists in the db.

I can't see any easy way to do this. (an annotation would rock!). At the moment I'm just returning a trimmed value from my getter(), but this feels like a kludge.

A google search is offering no help on this. Any ideas?

Answer 1

Or you can use lifecycle annotations:

@Entity public class MyEntity {      @PostLoad     protected void repair(){         if(myStringProperty!=null)myStringProperty=myStringProperty.trim();     }      private String myStringProperty;     public String getMyStringProperty() {         return myStringProperty;     }     public void setMyStringProperty(String myStringProperty) {         this.myStringProperty = myStringProperty;     }  } 

If this occurs on multiple entities you can create a custom annotation and write a dedicated EntityListener.

Annotation

@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface Trim {} 

Listener

public class TrimListener {      private final Map<Class<?>, Set<Field>> trimProperties =          new HashMap<Class<?>, Set<Field>>();      @PostLoad     public void repairAfterLoad(final Object entity) throws Exception {         for (final Field fieldToTrim : getTrimProperties(entity.getClass())) {             final String propertyValue = (String) fieldToTrim.get(entity);             if (propertyValue != null)                 fieldToTrim.set(entity, propertyValue.trim());         }     }      private Set<Field> getTrimProperties(Class<?> entityClass) throws Exception {         if (Object.class.equals(entityClass))             return Collections.emptySet();         Set<Field> propertiesToTrim = trimProperties.get(entityClass);         if (propertiesToTrim == null) {             propertiesToTrim = new HashSet<Field>();             for (final Field field : entityClass.getDeclaredFields()) {                 if (field.getType().equals(String.class)                     && field.getAnnotation(Trim.class) != null) {                     field.setAccessible(true);                     propertiesToTrim.add(field);                 }             }             trimProperties.put(entityClass, propertiesToTrim);         }         return propertiesToTrim;     }  } 

Now annotate all relevant String fields with @Trim and register the Listener as default entity listener in your persistence.xml:

<persistence-unit ..>     <!-- ... -->     <default-entity-listeners>       com.somepackage.TrimListener       and.maybe.SomeOtherListener     </default-entity-listeners> </persistence-unit>