如何使用 JAXB 編組多個對象？

Question

我正在嘗試編組多個對象，例如通過setBookslst()添加到BookLists Book 。 我開始使用這個JAXBContext設置：

jaxbContext = JAXBContext.newInstance(BookLists.class);

和

 jaxbMarshaller.marshal(lists, result);

但是，我得到了以下運行時異常：

javax.xml.bind.JAXBException: com.jaxb.example.marshall.Book 或其任何超類在此上下文中都是已知的]

我的類型定義如下。

書 ：-

@XmlRootElement(name="book")
public class Book {

     private String title;
     private int year;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public int getYear() {
        return year;
    }
    public void setYear(int year) {
        this.year = year;
    }
}

書單：-

@XmlRootElement(name="lists")
public class BookLists {
List<Book> bookslst;

public List getBookslst() {
    return bookslst;
}

public void setBookslst(List bookslst) {
    this.bookslst = bookslst;
}

}

馬歇爾代碼：-

Book book;
    BookLists lists=new BookLists();
    List lst=new ArrayList();
    book = new Book();
    book.setTitle("Book title");
    book.setYear(2010);
    lst.add(book);
    book = new Book();
    book.setTitle("Book title1");
    book.setYear(2011);
    lst.add(book);
    lists.setBookslst(lst);
    JAXBContext jaxbContext;
    try {
        jaxbContext = JAXBContext.newInstance(BookLists.class);
        Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
        jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        StringWriter result = new StringWriter();

        jaxbMarshaller.marshal(lists, result);
        String xml = result.toString();
        System.out.println(xml);
    } catch (JAXBException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

我正在嘗試放置@XMLSeeAlso注釋（Ref:- JAXB Exception: Class not known to this context ）。 此注釋在我的版本中不可用。

Answer 1

默認情況下，JAXB (JSR-222) 實現會檢查公共訪問器方法。 您可以在 get/set 方法中的List上添加Book參數。

public List<Book> getBookslst() {
    return bookslst;
}

public void setBookslst(List<Book> bookslst) {
    this.bookslst = bookslst;
}

或者，您可以使用@XmlElement注釋指定屬性的類型：

@XmlElement(type=Book.class)
public List getBookslst() {
    return bookslst;
}

您還可以指定您的 JAXB 實現內省字段而不是屬性：

@XmlRootElement(name="lists")
@XmlAccessorType(XmlAccessType.FIELD)
public class BookLists {
    List<Book> bookslst;
}

---

更新

有沒有其他方法可以在 Marshallar.Marshall 中添加 List 而不是 BookList？

您可以創建一個利用@XmlAnyElement(lax=true)注釋的通用 List 包裝器對象（請參閱： http : @XmlAnyElement(lax=true) ）。 然后它冷處理一個用@XmlRootElement注釋的任何東西的List 。

列表

package forum12323397;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.*;

@XmlRootElement
public class Lists<VALUE> {

    private List<VALUE> values = new ArrayList<VALUE>();

    @XmlAnyElement(lax=true)
    public List<VALUE> getValues() {
        return values;
    }

}

演示

package forum12323397;

import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Lists.class, Book.class);

        Lists<Book> lists = new Lists<Book>();

        Book book1 = new Book();
        book1.setTitle("A Book");
        book1.setYear(2001);
        lists.getValues().add(book1);

        Book book2 = new Book();
        book2.setTitle("Another Book");
        book2.setYear(2007);
        lists.getValues().add(book2);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(lists, System.out);
    }

}

輸出

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<lists>
    <book>
        <title>A Book</title>
        <year>2001</year>
    </book>
    <book>
        <title>Another Book</title>
        <year>2007</year>
    </book>
</lists>

Answer 2

我有一個工作示例：

1）XML：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<bookstore>
    <bookList>
        <book>
            <author>Neil Strauss</author>
            <title>The Game</title>
            <publisher>Harpercollins</publisher>
            <isbn>978-0060554736</isbn>
        </book>
        <book>
            <author>Charlotte Roche</author>
            <title>Feuchtgebiete</title>
            <publisher>Dumont Buchverlag</publisher>
            <isbn>978-3832180577</isbn>
        </book>
    </bookList>
    <location>Frankfurt Airport</location>
    <name>Fraport Bookstore</name>
</bookstore>

2）Java類：

書店

package jaxbtest;

import java.util.ArrayList;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name="bookstore") // (namespace = "de.vogella.xml.jaxb.model", name="bookstore")
public class Bookstore {

  // XmLElementWrapper generates a wrapper element around XML representation
  @XmlElementWrapper(name = "bookList")
  // XmlElement sets the name of the entities
  @XmlElement(name = "book")
  private ArrayList<Book> bookList;
  private String name;
  private String location;

  public void setBookList(ArrayList<Book> bookList) {
    this.bookList = bookList;
  }

  public ArrayList<Book> getBooksList() {
    return bookList;
  }

  public String getName() {
    return name;
  }

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

  public String getLocation() {
    return location;
  }

  public void setLocation(String location) {
    this.location = location;
  }
} 

3) 預訂

package jaxbtest;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement(name = "book")
// If you want you can define the order in which the fields are written
// Optional
@XmlType(propOrder = { "author", "name", "publisher", "isbn" })
public class Book {

  private String name;
  private String author;
  private String publisher;
  private String isbn;

  // If you like the variable name, e.g. "name", you can easily change this
  // name for your XML-Output:
  @XmlElement(name = "title")
  public String getName() {
    return name;
  }

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

  public String getAuthor() {
    return author;
  }

  public void setAuthor(String author) {
    this.author = author;
  }

  public String getPublisher() {
    return publisher;
  }

  public void setPublisher(String publisher) {
    this.publisher = publisher;
  }

  public String getIsbn() {
    return isbn;
  }

  public void setIsbn(String isbn) {
    this.isbn = isbn;
  }

} 

4) 主要

package jaxbtest;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class BookMain {

  private static final String BOOKSTORE_XML = "./bookstore-jaxb.xml";

  public static void main(String[] args) throws JAXBException, IOException {

    ArrayList<Book> bookList = new ArrayList<Book>();

    // create books
    Book book1 = new Book();
    book1.setIsbn("978-0060554736");
    book1.setName("The Game");
    book1.setAuthor("Neil Strauss");
    book1.setPublisher("Harpercollins");
    bookList.add(book1);

    Book book2 = new Book();
    book2.setIsbn("978-3832180577");
    book2.setName("Feuchtgebiete");
    book2.setAuthor("Charlotte Roche");
    book2.setPublisher("Dumont Buchverlag");
    bookList.add(book2);

    // create bookstore, assigning book
    Bookstore bookstore = new Bookstore();
    bookstore.setName("Fraport Bookstore");
    bookstore.setLocation("Frankfurt Airport");
    bookstore.setBookList(bookList);

    // create JAXB context and instantiate marshaller
    JAXBContext context = JAXBContext.newInstance(Bookstore.class);
    Marshaller m = context.createMarshaller();
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);

    // Write to System.out
    m.marshal(bookstore, System.out);

    // Write to File
    m.marshal(bookstore, new File(BOOKSTORE_XML));

    // get variables from our xml file, created before
    System.out.println();
    System.out.println("Output from our XML File: ");
    Unmarshaller um = context.createUnmarshaller();
    Bookstore bookstore2 = (Bookstore) um.unmarshal(new FileReader(BOOKSTORE_XML));
    ArrayList<Book> list = bookstore2.getBooksList();
    for (Book book : list) {
      System.out.println("Book: " + book.getName() + " from "
          + book.getAuthor());
    }

      /*
      String xmlStr = readFileToString(BOOKSTORE_XML);
      Bookstore bookstore = getPartial3(Bookstore.class ,xmlStr);
      for (Book b : bookstore.getBooksList())
          System.out.println(b.getName()+ " ---- " + b.getAuthor() );
       xmlStr = readFileToString("./listApplianceOfferings.xml");
      ApplianceList bookstore1 = getPartial3(ApplianceList.class ,xmlStr);
      for (Appliance b : bookstore1.getBooksList())
          System.out.println(b.getName() + " ---- " + b.getDescription() );
    */
      //88888
      // String xmlStr = readFileToString("./listStorageOfferings.xml");
//    StorageOfferings storageOfferingsList = jaxbXmlString2Class(StorageOfferings.class ,xmlStr);
      StorageOfferings storageOfferingsList = jaxbXmlFile2Class(StorageOfferings.class ,"./listStorageOfferings.xml");
      for (StorageOffering s : storageOfferingsList.getStorageOfferingList() )
          System.out.println("8888--> "+ s.getName() + " ---- " + s.getId() );
      //99999
  }//main



private static void getPartial() {
    // get variables from our xml file, created before
    System.out.println();
    System.out.println("Output from our XML File: ");
    Unmarshaller um;
    try {
        JAXBContext context = JAXBContext.newInstance(Bookstore.class);;
        um = context.createUnmarshaller();
//      um.setEventHandler(new DefaultValidationEventHandler());
        FileReader fileReader = new FileReader(BOOKSTORE_XML);
    Bookstore bookstore = (Bookstore) um.unmarshal(fileReader );
    ArrayList<Book> list = bookstore.getBooksList();
    for (Book book : list) {
      System.out.println("Book: " + book.getName() + " from "
          + book.getAuthor());
    }
    } catch (Exception e) {
        e.printStackTrace();
    }

}
private static void getPartial1() {
    // get variables from our xml file, created before
    System.out.println();
    System.out.println("Output from our XML File: ");
    Unmarshaller um;
    try {
        JAXBContext context = JAXBContext.newInstance(ApplianceList.class);;
        um = context.createUnmarshaller();
//      um.setEventHandler(new DefaultValidationEventHandler());
        FileReader fileReader = new FileReader("./listApplianceOfferings.xml");
        ApplianceList alist = (ApplianceList) um.unmarshal(fileReader );
    ArrayList<Appliance> list = alist.getBooksList();
    for (Appliance book : list) {
      System.out.println("appliance: " + book.getName() + " from "
          + book.getDescription());
    }
    } catch (Exception e) {
        e.printStackTrace();
    }

}
//-------------------
private static <T> T getPartial2(Class<T> cls, String fname) {
    // get variables from our xml file, created before
    System.out.println();
    System.out.println("Output from our XML File: ");
    Unmarshaller um;
    T alist = null;
    try {
        JAXBContext context = JAXBContext.newInstance(cls);;
        um = context.createUnmarshaller();
//      um.setEventHandler(new DefaultValidationEventHandler());
        FileReader fileReader = new FileReader(fname);
        alist = (T) um.unmarshal(fileReader );
        //ArrayList<?> list = alist.getBooksList();
//    for (Appliance book : list) {
//      System.out.println("appliance: " + book.getName() + " from "
//          + book.getDescription());
//    }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return alist;

}
//-------------------
private static <T> T jaxbXmlFile2Class(Class<T> cls, String fileName) {
        FileReader fr = null;
        char [] cbuf = null;
        try {
            fr = new FileReader(fileName);

        cbuf = new char[3000];
        Arrays.fill(cbuf, ' ');
        fr.read(cbuf);
        }catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally{
            try { fr.close(); } 
            catch (IOException e) {
                e.printStackTrace();
            }
        }
        String s = new String(cbuf);
        return jaxbXmlString2Class(cls, s);
    }
@SuppressWarnings("unchecked")
private static <T> T jaxbXmlString2Class(Class<T> cls, String xmlStr) {
  // get variables from our xml file, created before
  System.out.println();
  System.out.println("Output from our XML File: ");
  Unmarshaller um;
  T alist = null;
    try {
        JAXBContext context = JAXBContext.newInstance(cls);;
        um = context.createUnmarshaller();
        System.out.println(xmlStr);
        InputStream is = new ByteArrayInputStream(xmlStr.getBytes());
        alist = (T) um.unmarshal( is );
    } catch (Exception e) {
        e.printStackTrace();
    }
    return alist;

}
} 

Answer 3

嘗試將這兩個類添加到您的 JAXBContext.newInstance 調用中。

JAXBContext.newInstance(BookLists.class, Book.class);

使用你的類這有效：

public static void main(String [] args) throws JAXBException {
    BookLists books = new BookLists();

    String [] titles = {"To Kill a Mockingbird", "Twelve Angry Men", "Are You My Mother", "Green Eggs And Ham"};

    List<Book> list = new ArrayList<Book>();
    for (String title : titles) {
        Book book = new Book();
        book.setTitle(title);
        list.add(book);
    }
    books.setBookslst(list);

    JAXBContext jc = JAXBContext.newInstance(BookLists.class, Book.class);
    Marshaller nm = jc.createMarshaller();
    nm.setProperty("jaxb.formatted.output", true);
    nm.marshal(books, System.out);

}

輸出：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<lists>
<book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="book">
    <title>To Kill a Mockingbird</title>
    <year>0</year>
</book>
<book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="book">
    <title>Twelve Angry Men</title>
    <year>0</year>
</book>
<book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="book">
    <title>Are You My Mother</title>
    <year>0</year>
</book>
<book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="book">
    <title>Green Eggs And Ham</title>
    <year>0</year>
</book>
</lists>

Answer 4

采用

List<Book> lst=new ArrayList<Book>();

代替 ：

List lst=new ArrayList();

還定義 BoolList 如下：

@XmlRootElement(name="lists")
public class BookLists {
List<Book> bookslst;

public List<Book> getBookslst() {
    return bookslst;
}

public void setBookslst(List<Book> bookslst) {
    this.bookslst = bookslst;
}

}

Answer 5

將注釋 @XmlSeeAlso(value = {Book.class }) 添加到 BookList 類。 現在應該工作。

Answer 6

實際輸出：

<lists>
    <book>
        <title>A Book</title>
        <year>2001</year>
    </book>
    <book>
        <title>Another Book</title>
        <year>2007</year>
    </book>
</lists>

預期輸出：

<lists>
    <book>
        <title>A Book</title>
        <year>2001</year>
        <title>Another Book</title>
        <year>2007</year>
    </book>
</lists>

積極尋求建議。