How to serialize and de-serialize objects using JA

问题:

I have an issue. I want to convert an object into another object using JAXB. As in, I have a class com.home.Student, and another class com.school.Student, both have same arguments, in fact both are same (copy paste), but different package. I want to perform the conversion between them using JAXB.

How to do that, please help me.

回答1:

You could do the following.

Note:

• It does not require that you ever materialize the data as XML, by leveraging JAXBSource.
• It does not require any annotations on your object model.

com.home.Student

package com.home;

public class Student {

    private String name;
    private Status status;

    public String getName() {
        return name;
    }

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

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }

}

com.home.Status

package com.home;

public enum Status {

    FULL_TIME("F"),
    PART_TIME("P");

    private final String code;

    Status(String code) {
        this.code = code;
    }

    public String getCode() {
        return code;
    }

}

com.school.Student

package com.school;

public class Student {

    private String name;
    private Status status;

    public String getName() {
        return name;
    }

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

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }

}

com.school.Status

package com.school;

public enum Status {

    FULL_TIME("F"),
    PART_TIME("P");

    private final String code;

    Status(String code) {
        this.code = code;
    }

    public String getCode() {
        return code;
    }

}

com.example.Demo;

package com.example;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.util.JAXBSource;
import javax.xml.namespace.QName;

public class Demo {

    public static void main(String[] args) throws Exception {
        com.home.Student studentA = new com.home.Student();
        studentA.setName("Jane Doe");
        studentA.setStatus(com.home.Status.FULL_TIME);

        JAXBContext contextA = JAXBContext.newInstance(com.home.Student.class);
        JAXBElement<com.home.Student> jaxbElementA = new JAXBElement(new QName("student"), com.home.Student.class, studentA);
        JAXBSource sourceA = new JAXBSource(contextA, jaxbElementA);

        JAXBContext contextB = JAXBContext.newInstance(com.school.Student.class);
        Unmarshaller unmarshallerB = contextB.createUnmarshaller();
        JAXBElement<com.school.Student> jaxbElementB = unmarshallerB.unmarshal(sourceA, com.school.Student.class);

        com.school.Student studentB = jaxbElementB.getValue();
        System.out.println(studentB.getName());
        System.out.println(studentB.getStatus().getCode());
    }

}

回答2:

It would be nice if you included some code that explains your problem.

JAXB 101 says you should place the right annotations, then you can serialize and deserialize correctly. You should properly annotate your classes with @XmlRootElement, @XmlElement, @XmlAttribute, etc

For example:

@XmlRootElement(name="student")
@XmlAccessorType(XmlAccessType.NONE)
class Student {
  @XmlElement(name="name")
  private String name;

  @XmlElement(name="age")
  private int age;

  public Student() {
  }

  public String getName() { return name; }

  public int getAge() { return age; }
}

Then you can use serialize it using JAXB Marshaller:

StringWriter writer = new StringWriter();
JAXBContext context = JAXBContext.newInstance(Student.class);
Marshaller m = context.createMarshaller();
m.marshal(student, writer);

And deserialize it as well by Unmarshelling the input ..

JAXBContext context = JAXBContext.newInstance(Student.class);
Unmarshaller m = context.createUnmarshaller();
return (Student)m.unmarshal(new StringReader(input));

Make sure you look at the JavaDoc I mentioned above since there are many ways to do so.

If you cannot modify your classes, you can still use JAXB (or you can use XStream) Assuming your class is the following:

class Student {
  private String name;
  private int age;

  public Student() {
  }

  public void setName(String name) { this.name = name; }
  public String getName() { return name; }
  public void setAge(int age) { this.age = age; }
  public int getAge() { return age; }
}

You can serialize it by doing:

Student student = new Student();
student.setAge(25);
student.setName('FooBar');
StringWriter writer = new StringWriter();
JAXBContext context = JAXBContext.newInstance(Student.class);
Marshaller m = context.createMarshaller();
m.marshal(new JAXBElement(new QName(Student.class.getSimpleName()), Student.class, student), writer);
System.out.println(writer.toString());

If you are using XStream, you can do the serialization without Annotations too (and it is more controllable). http://x-stream.github.io/tutorial.html

回答3:

If your goal is simply to convert (assign actually) between the two, and they're identical except package name, I would think you could use simple reflection. Just iterate over the fields of source object, and assign to the field of the same name in the target object. Vaguely, like this:

import java.lang.reflect.Field;

public class Converter {
    public void convert (com.home.Student src, com.school.Student dst) throws Exception {
        for (Field f : src.getFields()) {

            // src field name
            String name = f.getName();

            // get corresponding field in dst
            Field dstField = dst.getDeclaredField(name);

            dstField.set(dst, f.get());
        }
    }
}

Note: I didn't compile this, which is why I say "vaguely". You'll need to use the Field.isAccessible()/Field.setAccessible(true) if the fields are private, so that you can temporarily change accessibility while you're assigning values. Or, you an write slightly more complex code that uses public setters/getters rather than directly using field access.