JAXB中的解组器和架构

Stan Kurilin 发表于 Java

斯坦·库里林（Stan Kurilin）：

我的应用程序可以将文件保存为各种格式（所有格式均为xml）。因此，我应该确定保存哪种格式的文件来解决问题。所以，我看到了两种解决方案

不同的格式具有不同的架构，因此我可以由它们确定。我以从这里获得的方式设置模式

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

所以我想我可以用 unmarshaller.getProperty(Marshaller.JAXB_NO_NAMESPACE_SCHEMA_LOCATION)

但它抛出

javax.xml.bind.PropertyException：jaxb.noNamespaceSchemaLocation

并getSchema()返回null那么，如何获取架构位置？

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

什么方法更可取？如果是第一个，那么如何获取架构位置标签？

upd 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;}
}

以及生成模式，保存Foo实例并随后加载的代码。

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());
    }

}

生成的模式

      <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获得此文本？

bdoughan：

我将利用StAX解析器来获取此信息（请参见下面的示例）。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);
    }
}

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