JavaPersistenceWithHibernate第二版笔记-第五章-Mapping value types-006类型转换器( @Converter(autoApply = true) 、type="converter:qualified.ConverterName" )

一、结构

二、代码

1.

 package org.jpwh.model.advanced;

 import java.io.Serializable;
 import java.math.BigDecimal;
 import java.util.Currency;

 /*
    This value-typed class should be <code>java.io.Serializable</code>: When Hibernate stores entity
    instance data in the shared second-level cache (see <a href="#Caching"/>), it <em>disassembles</em>
    the entity's state. If an entity has a <code>MonetaryAmount</code> property, the serialized
    representation of the property value will be stored in the second-level cache region. When entity
    data is retrieved from the cache region, the property value will be deserialized and reassembled.
  */
 public class MonetaryAmount implements Serializable {

     /*
  The class does not need a special constructor, you can make it immutable, even with
         <code>final</code> fields, as your code will be the only place an instance is created.
      */
     protected final BigDecimal value;
     protected final Currency currency;

     public MonetaryAmount(BigDecimal value, Currency currency) {
         this.value = value;
         this.currency = currency;
     }

     public BigDecimal getValue() {
         return value;
     }

     public Currency getCurrency() {
         return currency;
     }

     /*
  You should implement the <code>equals()</code> and <code>hashCode()</code>
         methods, and compare monetary amounts "by value".
      */
     public boolean equals(Object o) {
         if (this == o) return true;
         if (!(o instanceof MonetaryAmount)) return false;

         final MonetaryAmount monetaryAmount = (MonetaryAmount) o;

         if (!value.equals(monetaryAmount.value)) return false;
         if (!currency.equals(monetaryAmount.currency)) return false;

         return true;
     }

     public int hashCode() {
         int result;
         result = value.hashCode();
         result = 29 * result + currency.hashCode();
         return result;
     }

     /*
  You will need a <code>String</code> representation of a monetary
         amount. Implement the <code>toString()</code> method and a static method to
         create an instance from a <code>String</code>.
      */
     public String toString() {
         return getValue() + " " + getCurrency();
     }

     public static MonetaryAmount fromString(String s) {
         String[] split = s.split(" ");
         return new MonetaryAmount(
             new BigDecimal(split[0]),
             Currency.getInstance(split[1])
         );
     }
 }

2.

 package org.jpwh.converter;

 import org.jpwh.model.advanced.MonetaryAmount;

 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;

 @Converter(autoApply = true) // Default for MonetaryAmount properties
 public class MonetaryAmountConverter
     implements AttributeConverter<MonetaryAmount, String> {

     @Override
     public String convertToDatabaseColumn(MonetaryAmount monetaryAmount) {
         return monetaryAmount.toString();
     }

     @Override
     public MonetaryAmount convertToEntityAttribute(String s) {
         return MonetaryAmount.fromString(s);
     }
 }

3.

 package org.jpwh.model.advanced.converter;

 import org.jpwh.converter.MonetaryAmountConverter;
 import org.jpwh.model.advanced.MonetaryAmount;

 import javax.persistence.Column;
 import javax.persistence.Convert;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.validation.constraints.NotNull;
 import java.util.Date;

 @Entity
 public class Item {

     @Id
     @GeneratedValue(generator = "ID_GENERATOR")
     protected Long id;

     @NotNull
     protected String name;

     @NotNull
     @Convert( // Optional, autoApply is enabled
         converter = MonetaryAmountConverter.class,
         disableConversion = false)
     @Column(name = "PRICE", length = 63)
     protected MonetaryAmount buyNowPrice;

     @NotNull
     protected Date createdOn = new Date();

     public Long getId() {
         return id;
     }

     public String getName() {
         return name;
     }

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

     public MonetaryAmount getBuyNowPrice() {
         return buyNowPrice;
     }

     public void setBuyNowPrice(MonetaryAmount buyNowPrice) {
         this.buyNowPrice = buyNowPrice;
     }

     // ...
 }

4.

 package org.jpwh.model.advanced.converter;

 abstract public class Zipcode {

     protected String value;

     public Zipcode(String value) {
         this.value = value;
     }

     public String getValue() {
         return value;
     }

     @Override
     public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
         Zipcode zipcode = (Zipcode) o;
         return value.equals(zipcode.value);
     }

     @Override
     public int hashCode() {
         return value.hashCode();
     }
 }

5.

 package org.jpwh.converter;

 import org.jpwh.model.advanced.converter.GermanZipcode;
 import org.jpwh.model.advanced.converter.SwissZipcode;
 import org.jpwh.model.advanced.converter.Zipcode;

 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;

 @Converter
 public class ZipcodeConverter
     implements AttributeConverter<Zipcode, String> {

     @Override
     public String convertToDatabaseColumn(Zipcode attribute) {
         return attribute.getValue();
     }

     @Override
     public Zipcode convertToEntityAttribute(String s) {
         if (s.length() == 5)
             return new GermanZipcode(s);
         else if (s.length() == 4)
             return new SwissZipcode(s);

         // If you get to this point, you should consider
         // cleaning up your database... or you can create
         // an InvalidZipCode subclass and return it here.

         throw new IllegalArgumentException(
             "Unsupported zipcode in database: " + s
         );
     }
 }

6.

 package org.jpwh.model.advanced.converter;

 public class GermanZipcode extends Zipcode {

     public GermanZipcode(String value) {
         super(value);
     }
 }

7.

 package org.jpwh.model.advanced.converter;

 public class SwissZipcode extends Zipcode {

     public SwissZipcode(String value) {
         super(value);
     }
 }

8.

 package org.jpwh.model.advanced.converter;

 import org.jpwh.converter.ZipcodeConverter;
 import org.jpwh.model.Constants;

 import javax.persistence.Convert;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.persistence.Table;
 import javax.validation.constraints.NotNull;
 import java.io.Serializable;

 @Entity
 @Table(name = "USERS")
 public class User implements Serializable {

     @Id
     @GeneratedValue(generator = Constants.ID_GENERATOR)
     protected Long id;

     @NotNull
     protected String username;

     // Group multiple attribute conversions with @Converts
     @Convert(
         converter = ZipcodeConverter.class,
         attributeName = "zipcode" // Or "city.zipcode" for nested embeddables
     )
     protected Address homeAddress;

     public Long getId() {
         return id;
     }
     public String getUsername() {
         return username;
     }

     public void setUsername(String username) {
         this.username = username;
     }

     public Address getHomeAddress() {
         return homeAddress;
     }

     public void setHomeAddress(Address homeAddress) {
         this.homeAddress = homeAddress;
     }

     // ...
 }

9.

 package org.jpwh.model.advanced.converter;

 import javax.persistence.Column;
 import javax.persistence.Embeddable;
 import javax.validation.constraints.NotNull;

 @Embeddable
 public class Address {

     @NotNull
     @Column(nullable = false)
     protected String street;

     @NotNull
     @Column(nullable = false, length = 5)
     protected Zipcode zipcode;

     @NotNull
     @Column(nullable = false)
     protected String city;

     protected Address() {
     }

     public Address(String street, Zipcode zipcode, String city) {
         this.street = street;
         this.zipcode = zipcode;
         this.city = city;
     }

     public String getStreet() {
         return street;
     }

     public void setStreet(String street) {
         this.street = street;
     }

     public Zipcode getZipcode() {
         return zipcode;
     }

     public void setZipcode(Zipcode zipcode) {
         this.zipcode = zipcode;
     }

     public String getCity() {
         return city;
     }

     public void setCity(String city) {
         this.city = city;
     }
 }

也可以转换集合，If several @Convert annotations are required on a single embedded property, to convert several attributes of the Address , for example, you can group them within an @Converts annotation. You can also apply converters to values of collections and maps, if their values and/or keys are of basic or embeddable type. For example, you can add the @Convert annotation on a persistent Set<Zipcode> . We’ll show you how

to map persistent collections later, with @ElementCollection , in chapter 7.
For persistent maps, the attributeName option of the @Convert annotation has some special syntax:

 On a persistent Map<Address, String> , you can apply a converter for the zipcode property of each map key with the attribute name key.zipcode .
 On a persistent Map<String, Address> , you can apply a converter for the zipcode property of each map value with the attribute name value.zipcode .
 On a persistent Map<Zipcode, String> , you can apply a converter for the key of each map entry with the attribute name key .
 On a persistent Map<String, Zipcode> , you can apply a converter for the value of each map entry by not setting any attributeName .
As before, the attribute name can be a dot-separated path if your embeddable classes are nested; you can write key.city.zipcode to reference the zipcode property of the City class, in a composition with the Address class.
Some limitations of the JPA converters are as follows:
 You can’t apply them to identifier or version properties of an entity.
 You shouldn’t apply a converter on a property mapped with @Enumerated or @Temporal , because these annotations already declare what kind of conversion has to occur. If you want to apply a custom converter for enums or date/time properties, don’t annotate them with @Enumerated or @Temporal .
 You can apply a converter to a property mapping in an hbm.xml file, but you have to prefix the name: type="converter:qualified.ConverterName" .