Question

使用JAXB时，我想在使用Generics时从XML元素中删除多余的命名空间/类型。我怎么能这样做或我做错了什么？我想使用泛型，所以我只需要编写一段代码。

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>

Answer 1

测试通用

您的JAXB（JSR-222）实现将为每个类创建映射（即TestGeneric，而不是类型（即TestGeneric<Integer>）。因此它将处理value字段为Object类型。这将导致xsi:type属性，因为您的JAXB实现正在添加足够的信息以便能够解组相同的类型。

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

    public TestGeneric() {
    }

    public TestGeneric(boolean isRequired) {
        this.isRequired = isRequired;
    }
}

<强>演示

以下是您可以使用的方法。我已经引入了TestGeneric的子类来表示不同的可能类型。

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;
        }
    }

}

Answer 2

我遇到同样的问题，并通过建议解决了 Programmatically determine if a JAXB annotation will result in a xsi:type annotation?

仅使用@XmlAnyElement(lax=true)而不是在通用类对象上使用@XmlElement（此示例的值）。

Answer 3

我能够在由于泛型参数导致我出现问题的属性上使用@XmlAnyElement（lax = true），然后必须在正在编组的实际类上添加@XmlRootElement，并且声明消失了！奇妙！

从JAXB Generics中删除xsi：type，xmlns：xs和xmlns：xsi

3 个答案: