从JAXB泛型中删除xsi：type，xmlns：xs和xmlns：xsi

Z时代
2024-01-10
分类：问答

使用JAXB时，我想在使用泛型时从XML元素中删除多余的名称空间/类型。我该怎么办或我做错了什么？我想使用泛型，这样我只需要编写一次代码块。

示例代码：

public static void main(String[] args) {
    try {
        TestRoot root = new TestRoot();
        root.name.value = "bobby";
        root.age.value = 102;
        root.color.value = "blue";
        JAXBContext context = JAXBContext.newInstance(root.getClass());
        Marshaller marsh = context.createMarshaller();
        marsh.setProperty(Marshaller.JAXB_ENCODING,"UTF-8");
        marsh.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT,Boolean.TRUE);
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter(sw);
        marsh.marshal(root,pw);
        System.out.println(sw.toString());
    }
    catch(Throwable t) {
        t.printStackTrace();
    }
}
@XmlRootElement
static class TestRoot {
    @XmlElement public TestGeneric<String> name = new TestGeneric<String>(true);
    @XmlElement public TestGeneric<Integer> age = new TestGeneric<Integer>(true);
    @XmlElement public TestWhatIWouldLike color = new TestWhatIWouldLike(true);
}
@XmlAccessorType(XmlAccessType.NONE)
static class TestGeneric<T> {
    @XmlAttribute public boolean isRequired;
    @XmlElement public T value;
    public TestGeneric() {
    }
    public TestGeneric(boolean isRequired) {
        this.isRequired = isRequired;
    }
}
@XmlAccessorType(XmlAccessType.NONE)
static class TestWhatIWouldLike {
    @XmlAttribute public boolean isRequired;
    @XmlElement public String value;
    public TestWhatIWouldLike() {
    }
    public TestWhatIWouldLike(boolean isRequired) {
        this.isRequired = isRequired;
    }
}

输出：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<testRoot>
    <name isRequired="true">
        <value xsi:type="xs:string" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">bobby</value>
    </name>
    <age isRequired="true">
        <value xsi:type="xs:int" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">102</value>
    </age>
    <color isRequired="true">
        <value>blue</value>
    </color>
</testRoot>

回答：

您的JAXB（JSR-222）实现将为每个类创建映射（即TestGeneric，不是type（即TestGeneric<Integer>）。因此，它将value字段视为type

Object。这将导致xsi:type属性，因为JAXB实现正在添加足够的信息才能解组相同的类型。

@XmlAccessorType(XmlAccessType.NONE)
static class TestGeneric<T> {
    @XmlAttribute public boolean isRequired;
    @XmlElement public T value;
    public TestGeneric() {
    }
    public TestGeneric(boolean isRequired) {
        this.isRequired = isRequired;
    }
}

下面是您可以使用的一种方法。我介绍了的子类TestGeneric来代表不同的可能类型。

package forum11192623;
import java.io.PrintWriter;
import java.io.StringWriter;
import javax.xml.bind.*;
import javax.xml.bind.annotation.*;
public class Demo {
    public static void main(String[] args) {
        try {
            TestRoot root = new TestRoot();
            root.name.value = "bobby";
            root.age.value = 102;
            root.color.value = "blue";
            JAXBContext context = JAXBContext.newInstance(root.getClass());
            Marshaller marsh = context.createMarshaller();
            marsh.setProperty(Marshaller.JAXB_ENCODING,"UTF-8");
            marsh.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT,Boolean.TRUE);
            StringWriter sw = new StringWriter();
            PrintWriter pw = new PrintWriter(sw);
            marsh.marshal(root,pw);
            System.out.println(sw.toString());
        }
        catch(Throwable t) {
            t.printStackTrace();
        }
    }
    @XmlRootElement
    static class TestRoot {
        @XmlElement public TestString name = new TestString(true);
        @XmlElement public TestInteger age = new TestInteger(true);
        @XmlElement public TestString color = new TestString(true);
    }
    @XmlAccessorType(XmlAccessType.NONE)
    @XmlTransient
    @XmlSeeAlso({TestInteger.class, TestString.class})
    static class TestGeneric<T> {
        @XmlAttribute 
        public boolean isRequired;
        public T value;
        public TestGeneric() {
        }
        public TestGeneric(boolean isRequired) {
            this.isRequired = isRequired;
        }
    }
    static class TestInteger extends TestGeneric<Integer> {
        public TestInteger() {
        }
        public TestInteger(boolean b) {
            super(b);
        }
        @XmlElement
        public Integer getValue() {
            return value;
        }
        public void setValue(Integer value) {
            this.value = value;
        }
    }
    static class TestString extends TestGeneric<String> {
        public TestString() {
        }
        public TestString(boolean b) {
            super(b);
        }
        @XmlElement
        public String getValue() {
            return value;
        }
        public void setValue(String value) {
            this.value = value;
        }
    }
}