我在基于 GWT 的应用程序中使用 JAXB 解析 XML 文件。 XML 看起来像这样(一个简化的示例):

<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>

我定义了如下所示的类:

@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;
    }

    ...
    ...
}

这是代码:

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();
}

我需要根据公司名称获取联系人列表。例如，获取公司“abc”的所有联系人。我可以解析整个 XML 文件，然后手动过滤记录。但是如果输入文件很大，只解析我需要的可能会更有效。那么是否可以预先指定一个标准并仅解析特定记录？

谢谢。

最佳答案

您可以在 EclipseLink JAXB (MOXy 中使用 @XmlPath 扩展名) 来处理这种情况(我是 MOXy 技术主管):

@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

下面的示例演示了如何将 StreamFilter 用于此用例:

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);
    }
}

StreamFilter的实现如下:

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;
    }

}

关于java - JAXB 过滤解析，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5949265/