java - JAXB 中的解码器和模式

Question

我的应用程序可以保存各种格式的文件(所有格式都是 xml)。所以我应该通过确定保存的格式文件来解决问题。所以，我看到了 2 个解决方案

• 不同的格式有不同的模式，所以我可以根据它们来确定。我以从 here 获得的方式设置模式

marshaller.setProperty(Marshaller.JAXB_NO_NAMESPACE_SCHEMA_LOCATION, "bla-bla.xsd");

所以我想我可以使用 unmarshaller.getProperty(Marshaller.JAXB_NO_NAMESPACE_SCHEMA_LOCATION) 得到它

但是它扔了

javax.xml.bind.PropertyException: jaxb.noNamespaceSchemaLocation

和getSchema()返回空那么，我怎样才能获得架构位置？

• 使用 setAdapter(Class<A> type, A adapter) 为不同的 beans 指定不同的适配器方法

哪种方式比较好？如果是第一个，那么如何获取架构位置标签？

更新代码示例假设我们有 bean

@XmlRootElement
public class Foo{
    String bar;
    public String getBar() {return bar; }
    public void setBar(String bar) {this.bar = bar;}
}

和生成模式的代码，保存 Foo 的实例然后加载。

public class Test {
    final static String schemaLoc = "fooschema.xsd";


    public static void write(File file, Foo foo, Schema schema) throws Throwable {
        XMLEventWriter xsw = null;
        try{
            JAXBContext context = JAXBContext.newInstance(Foo.class);
            XMLOutputFactory xof = XMLOutputFactory.newInstance();
            OutputStream out = new FileOutputStream(file);
            xsw = xof.createXMLEventWriter(out);
            Marshaller m = context.createMarshaller();
            m.setSchema(schema);    //schema setted
            System.out.println(">>>marchal : " + m.getSchema());    //check it
            m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
            m.setProperty(Marshaller.JAXB_NO_NAMESPACE_SCHEMA_LOCATION, schemaLoc);
            m.marshal(foo, xsw);
        } finally{
             xsw.close();
        }
    }

    public static Foo load(File file) throws Throwable {
        JAXBContext context = JAXBContext.newInstance(Foo.class);
        Unmarshaller unmarshaller = context.createUnmarshaller();


        System.out.println("unmarshaller schema:" + unmarshaller.getSchema());  //I need get it here
    //  System.out.println("schema_prop:" + unmarshaller.getProperty(Marshaller.JAXB_NO_NAMESPACE_SCHEMA_LOCATION));

        InputStreamReader in = new InputStreamReader(new FileInputStream(file));
        XMLEventReader xer = XMLInputFactory.newInstance()
                .createXMLEventReader(in);
        return Foo.class.cast(unmarshaller.unmarshal(xer));
    }

    private static File createSchema(String schemaLocation) throws Throwable{
        final File target = new File(schemaLocation);
        if(!target.exists()){
            JAXBContext jaxbContext = JAXBContext.newInstance(Foo.class);
            SchemaOutputResolver sor = new SchemaOutputResolver() {
                public Result createOutput(String namespaceURI, String suggestedFileName)
                throws IOException {
                    StreamResult result = new StreamResult(target);
                    result.setSystemId(target.toURI().toURL().toString());
                    return result;
                }
            };
            jaxbContext.generateSchema(sor);
        }
        return target;
    }

    public static void main(String[] args) throws Throwable {
        createSchema(schemaLoc);
        File file = new File("temp.xml");
        Foo foo = new Foo();
        foo.setBar("test bar");
        SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        Schema schema = factory.newSchema(createSchema(schemaLoc));
        write(file, foo, schema);
        System.out.println("result " + load(file).getBar());
    }

}

生成的架构

      <xs:element name="foo" type="foo"/>

      <xs:complexType name="foo">
        <xs:sequence>
          <xs:element name="bar" type="xs:string" minOccurs="0"/>
        </xs:sequence>
      </xs:complexType>
    </xs:schema>

我们的临时文件

<?xml version="1.0"?>
<foo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="fooschema.xsd">
<bar>test bar</bar></foo>

如我们所见，有

xsi:noNamespaceSchemaLocation="fooschema.xsd"

如何使用 JAXB 获取此文本？

Answer 1

我会利用 StAX 解析器来获取此信息(参见下面的示例)。在输入上创建一个 XMLStreamReader。使用 nextTag() 方法将 XMLStreamReader 推进到根元素。然后获取根元素的 noNamespaceSchemaLocation 属性。然后将 XMLStreamReader 传递给 Unmarshaller 上的unmarshal(XMLStreamReader) 方法。

import java.io.FileInputStream;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
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 context = JAXBContext.newInstance(Categories.class);

        XMLInputFactory xif = XMLInputFactory.newInstance();
        FileInputStream fis = new FileInputStream("input.xml");
        XMLStreamReader xsr = xif.createXMLStreamReader(fis);
        xsr.nextTag();
        String noNamespaceSchemaLocation = xsr.getAttributeValue(XMLConstants.W3C_XML_SCHEMA_INSTANCE_NS_URI, "noNamespaceSchemaLocation");
        System.out.println(noNamespaceSchemaLocation);

        Unmarshaller um = context.createUnmarshaller();
        Categories response = (Categories) um.unmarshal(xsr);
    }
}