IllegalAnnotationExceptions ...没有无参默认构造函数。
是的，我的类没有默认的无参构造函数。这太容易出错了。我的类有package可见的构造函数/最终方法和参数，我该怎么办 - 创建一些特定的momemto/builder类或将我的构造函数指定给JAXB（以什么方式？）？谢谢。
JAXB可以通过使用XML适配器来支持这种情况。 假设您有以下没有零参数构造函数的对象：
package blog.immutable;
public class Customer {
private final String name;
private final Address address;
public Customer(String name, Address address) {
this.name = name;
this.address = address;
}
public String getName() {
return name;
}
public Address getAddress() {
return address;
}
}
你只需要创建一个可以被映射的这个类的版本：
package blog.immutable.adpater;
import javax.xml.bind.annotation.XmlAttribute;
import blog.immutable.Address;
public class AdaptedCustomer {
private String name;
private Address address;
@XmlAttribute
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
还需要一个XML适配器来在它们之间进行转换：
package blog.immutable.adpater;
import javax.xml.bind.annotation.adapters.XmlAdapter;
import blog.immutable.Customer;
public class CustomerAdapter extends XmlAdapter<AdaptedCustomer, Customer> {
@Override
public Customer unmarshal(AdaptedCustomer adaptedCustomer) throws Exception {
return new Customer(adaptedCustomer.getName(), adaptedCustomer.getAddress());
}
@Override
public AdaptedCustomer marshal(Customer customer) throws Exception {
AdaptedCustomer adaptedCustomer = new AdaptedCustomer();
adaptedCustomer.setName(customer.getName());
adaptedCustomer.setAddress(customer.getAddress());
return adaptedCustomer;
}
}
对于涉及到Customer类的属性，只需使用@XmlJavaTypeAdapter注释：
package blog.immutable;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import blog.immutable.adpater.CustomerAdapter;
@XmlRootElement(name="purchase-order")
public class PurchaseOrder {
private Customer customer;
@XmlJavaTypeAdapter(CustomerAdapter.class)
public Customer getCustomer() {
return customer;
}
public void setCustomer(Customer customer) {
this.customer = customer;
}
}
更详细的示例请参见：
您可以使用注解@XmlType，并以不同的组合使用factoryMethod / factoryClass属性，例如：
@XmlType(factoryMethod="newInstance")
@XmlRootElement
public class PurchaseOrder {
@XmlElement
private final String address;
@XmlElement
private final Customer customer;
public PurchaseOrder(String address, Customer customer){
this.address = address;
this.customer = customer;
}
private PurchaseOrder(){
this.address = null;
this.customer = null;
}
/** Creates a new instance, will only be used by Jaxb. */
private static PurchaseOrder newInstance() {
return new PurchaseOrder();
}
public String getAddress() {
return address;
}
public Customer getCustomer() {
return customer;
}
}
令人惊讶的是，这个方法可以工作并在非编组时返回一个初始化实例。您应该记住不要在代码中调用newInstance方法，因为它会返回一个无效的实例。
为了让JAXB能够实例化您的类，您应该拥有一个默认构造函数。也许有一种我不知道的解决方法。
JAXB特别适用于类似bean的类，允许通过在对象上调用setter来配置对象。