JAXB過濾解析

Question

我正在使用JAXB在我的基於GWT的應用程序中解析XML文件。的XML看起來像這樣（簡化的例子）：

<addressbook> 

    <company name="abc"> 
     <contact> 
      <name>...</name> 
      <address>...</address> 
     </contact> 

     <contact> 
      <name>...</name> 
      <address>...</address> 
     </contact> 

     <contact> 
      <name>...</name> 
      <address>...</address> 
     </contact> 
     ... 
     ... 
    </company> 

    <company name="def"> 
     <contact> 
      <name>...</name> 
      <address>...</address> 
     </contact> 
     ... 
     ... 
    </company> 

    ... 
    ... 

</addressbook> 

我已經定義的類，如下所示：

@XmlRootElement(name="addressbook") 
public class Addressbook implements Serializable { 

    private ArrayList<Company> companyList = new ArrayList<Company>(); 

    public Addressbook() {    
    } 

    @XmlElement(name = "company") 
    public ArrayList<Company> getCompanyList() { 
     return companyList; 
    } 


} 

============================= 

@XmlRootElement(name="company") 
public class Company implements Serializable { 

    private String name; 

    private ArrayList<Contact> contactList = new ArrayList<Contact>(); 

    public Company() {  
    } 

    @XmlAttribute 
    public String getName() { 
     return name; 
    } 

    @XmlElement(name = "contact") 
    public ArrayList<Contact> getContactList() { 
     return contactList; 
    } 

    ... 
    ... 
} 

============================= 

@XmlRootElement(name="contact") 
public class Contact implements Serializable 
{ 
    private String name; 
    private String address; 

    public Contact() { 
    } 

    @XmlElement 
    public String getName() 
    { 
     return name; 
    } 

    @XmlElement 
    public String getAddress() 
    { 
     return address; 
    } 

    ... 
    ... 
} 

這是代碼：

try { 
    JAXBContext jc = JAXBContext.newInstance(Addressbook.class); 
    Unmarshaller um = jc.createUnmarshaller(); 
    addressbook = (Addressbook) um.unmarshal(new FileReader("ds/addressbook.xml"));   
} catch (JAXBException e) { 
    e.printStackTrace(); 
} 

我需要根據公司名稱獲取聯繫人列表。例如，獲取公司「abc」的所有聯繫人。我可以解析整個XML文件，然後手動過濾記錄。但是如果輸入文件很大，解析我所需要的可能會更有效率。那麼是否可以預先指定標準並僅解析特定記錄？

謝謝。

Answer 1

你既可以

• 應用XSLT轉換XML文件，或
• 解組文件到DOM，並使用XPath選擇通過之前，你要

節點所產生的對象到解組方法

儘管如此，創建一個內存爲Map的公司名稱爲：

public class SearchableAddressBook { 

    public final Map<String, Company> companyMap = new HashMap<String,Company>(); 

    public SearchableAddressBook(List<Company> companyList) { 
     for (Company company: companyList) { 
      companyMap.add(company.getName(), company)); 
     } 

} 

或者如果您真的想過度設計內存數據庫，請創建內存數據庫。

Answer 2

你可以使用EclipseLink JAXB (MOXy的@XmlPath擴展）來處理這種情況（我是莫西技術主管）：

@XmlRootElement(name="addressbook") 
public class Addressbook implements Serializable { 

    private ArrayList<Company> companyList = new ArrayList<Company>(); 

    public Addressbook() {    
    } 

    @XmlPath("company[@name='abc']") 
    public ArrayList<Company> getCompanyList() { 
     return companyList; 
    } 


} 

更多信息：

• http://bdoughan.blogspot.com/2011/03/map-to-element-based-on-attribute-value.html

---

更新 - 使用StreamFilter

下面的例子演示了一個StreamFilter可以如何利用這個用例：

import java.io.FileInputStream; 

import javax.xml.bind.JAXBContext; 
import javax.xml.bind.Marshaller; 
import javax.xml.bind.Unmarshaller; 
import javax.xml.stream.XMLInputFactory; 
import javax.xml.stream.XMLStreamReader; 

public class Demo { 

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

     XMLInputFactory xif = XMLInputFactory.newFactory(); 
     FileInputStream xmlStream = new FileInputStream("input.xml"); 
     XMLStreamReader xsr = xif.createXMLStreamReader(xmlStream); 
     xsr = xif.createFilteredReader(xsr, new CompanyFilter()); 

     Unmarshaller unmarshaller = jc.createUnmarshaller(); 
     Addressbook addressbook = (Addressbook) unmarshaller.unmarshal(xsr); 

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

的StreamFilter的實現如下：

import javax.xml.stream.StreamFilter; 
import javax.xml.stream.XMLStreamReader; 

public class CompanyFilter implements StreamFilter { 

    private boolean accept = true; 

    public boolean accept(XMLStreamReader reader) { 
     if(reader.isStartElement() && "company".equals(reader.getLocalName())) { 
      accept = "abc".equals(reader.getAttributeValue(null, "name")); 
     } else if(reader.isEndElement()) { 
      boolean returnValue = accept; 
      accept = true; 
      return returnValue; 
     } 
     return accept; 
    } 

}