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" .