Java 如何使用@XmlElement 注释列表？

How to annotate a list using @XmlElement?

提问by user3429010

I have the following annotation using javax.xml.bind.annotation.XmlElement:

我使用以下注释javax.xml.bind.annotation.XmlElement：

@XmlElement         
public List<String> getKeywords() {
    return keywords;
}

Which produces the following XML when I marshall some example content:

当我编组一些示例内容时，它会生成以下 XML：

<keywords>keyword1</keywords>
<keywords>keyword2</keywords>

I would like to get the following XML:

我想获得以下 XML：

<keywords>
    <keyword>keyword1</keyword>
    <keyword>keyword2</keyword>
</keywords>

What kind of an annotation should I use?

我应该使用什么样的注释？

I've tried

我试过了

@XmlElementWrapper
@XmlElement(name="keyword")

But then the whole content disappears and the result is:

但随后整个内容消失了，结果是：

<keywords/>

The same happens also if I only try to rename the element:

如果我只尝试重命名元素，也会发生同样的情况：

@XmlElement(name="keyword")

What am I doing wrong?

我究竟做错了什么？

UPDATE:

更新：

Here is the updated full code for the class according to the first answers, but it is still not working (the result is an empty list <keywords/>when marshalled to XML):

这是根据第一个答案更新的类的完整代码，但它仍然无法正常工作（<keywords/>当编组为 XML 时，结果是一个空列表）：

import java.util.List;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Content {

    private List<String> keywords;

    public Content() {}

    @XmlElementWrapper(name="keywords")
    @XmlElement(name="keyword")
    public List<String> getKeywords() {
        return keywords;
    }

    public void setKeywords(List<String> keywords) {
        this.keywords = keywords;
    }  

}

I also tried the following with the same result:

我还尝试了以下相同的结果：

import java.util.List;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Content {

    @XmlElementWrapper(name="keywords")
    @XmlElement(name="keyword")
    private List<String> keywords;

    public Content() {}

    public List<String> getKeywords() {
        return keywords;
    }

    public void setKeywords(List<String> keywords) {
        this.keywords = keywords;
    }  

}

However, the keywords are not empty as the following produces <keywords>keyword1</keywords><keywords>keyword2</keywords>instead of an empty list:

但是，关键字不是空的，因为以下生成<keywords>keyword1</keywords><keywords>keyword2</keywords>而不是空列表：

import java.util.List;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Content {

    private List<String> keywords;

    public Content() {}

    @XmlElement
    public List<String> getKeywords() {
        return keywords;
    }

    public void setKeywords(List<String> keywords) {
        this.keywords = keywords;
    }  

}

The code for marshalling is (JAX-RS):

编组的代码是（JAX-RS）：

import java.io.StringWriter;
import javax.ws.rs.Consumes;
import javax.ws.rs.Path;
import javax.ws.rs.POST;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;

@Path("process")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_XML)
public class ContentHandler {

    @POST
    public Response process(Content content) {

        StringWriter stringWriter = new StringWriter();
        try {
            JAXBContext jaxbContext = JAXBContext.newInstance(Content.class);
            Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
            jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
            jaxbMarshaller.marshal(content, stringWriter);
        } catch (JAXBException e) {
            return Response.serverError().entity(e.getMessage()).build();
        }
        return Response.ok(stringWriter.toString(), MediaType.APPLICATION_XML).build();       
    }

}

采纳答案by bdoughan

You need to leverage @XmlElementWrapperand @XmlElement.

您需要利用@XmlElementWrapper和@XmlElement。

Java Model

Java模型

Content

内容

import java.util.List;
import javax.xml.bind.annotation.*;

@XmlRootElement
public class Content {

    private List<String> keywords;

    public Content() {}

    @XmlElementWrapper
    @XmlElement(name="keyword")
    public List<String> getKeywords() {
        return keywords;
    }

    public void setKeywords(List<String> keywords) {
        this.keywords = keywords;
    }  

}

Demo Code

演示代码

Demo

演示

import java.util.*;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Content.class);

        List<String> strings = new ArrayList<String>(2);
        strings.add("foo");
        strings.add("bar");

        Content content = new Content();
        content.setKeywords(strings);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(content, System.out);
    }

}

Output

输出

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<content>
    <keywords>
        <keyword>foo</keyword>
        <keyword>bar</keyword>
    </keywords>
</content>

For More Information

想要查询更多的信息

Below are links to a couple articles from my blog that provide additional information:

以下是我博客中提供更多信息的几篇文章的链接：

• http://blog.bdoughan.com/2010/09/jaxb-collection-properties.html
• http://blog.bdoughan.com/2012/12/jaxb-representing-null-and-empty.html

• http://blog.bdoughan.com/2010/09/jaxb-collection-properties.html
• http://blog.bdoughan.com/2012/12/jaxb-representing-null-and-empty.html

回答by Adam Arold

Use this form:

使用这个表格：

@XmlElementWrapper(name="keywords")
@XmlElement(name="keyword")

Please note that if keywordsis emptythen you will get <keywords />.

请注意，如果keywords为空，那么您将获得<keywords />.

Sometimes you will need to add @XmlRootElementto your class (depends on the context) and the @XmlAccessorType(XmlAccessType.?)annotation. I usually use @XmlAccessorType(XmlAccessType.FIELD)and annotate my fieldswith @XmlElement.

有时您需要添加@XmlRootElement到您的类（取决于上下文）和@XmlAccessorType(XmlAccessType.?)注释。我通常使用@XmlAccessorType(XmlAccessType.FIELD)和标注我的领域有@XmlElement。

回答by Ashish Shetkar

Above answer by - Blaise Doughan is completely correct

以上答案 - Blaise Doughan 是完全正确的

Another simple way is , even if you don't write the - @XmlElementWrapper

另一个简单的方法是，即使你不写 - @XmlElementWrapper

 private List<String> keywords;

 @XmlElementWrapper
    @XmlElement(name="keyword")
    public List<String> getKeywords() {
        return keywords;
    }

You can use it this way - write the XmlAccessorType on Class level , then XML element name will be same as the class member name - keywords

您可以这样使用它 - 在 Class 级别编写 XmlAccessorType ，然后 XML 元素名称将与类成员名称相同 - 关键字

import java.util.List;
import javax.xml.bind.annotation.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Content {

    private List<String> keywords;

    public Content() {}


    public List<String> getKeywords() {
        return keywords;
    }

    public void setKeywords(List<String> keywords) {
        this.keywords = keywords;
    }  

}