# XML Serialization

[TOC]

###### tags: `java` `xml`

---

Jackson Project<SUP>[🔗](https://github.com/FasterXML/jackson)</SUP>

> …supports XML; provides both streaming and databind implementations. Similar to JAXB' "code-first" mode (no support for "XML Schema first", but can use JAXB beans)…

## Maven Repositories<SUP>[🔗](https://mvnrepository.com/artifact/com.fasterxml.jackson.core)</SUP>

<dependency>
	<groupId>com.fasterxml.jackson.dataformat</groupId>
	<artifactId>jackson-dataformat-xml</artifactId>
	<version>2.12.5</version>
</dependency>

:::info
其它 Jackson-related repositories [ㄉㄧˇㄐㄧㄚˉㄌㄚ˙](https://mvnrepository.com/artifact/com.fasterxml.jackson)。
:::

## Configuring the Jackson XML Module<SUP>[🔗](https://stackify.com/java-xml-jackson/)</SUP>

> The absolute simplest way of working with this is to just use the default configuration:
>
>```java
>ObjectMapper xmlMapper = new XmlMapper();
>```
>
> To construct the Jackson Module manually:
>
>```java
>JacksonXmlModule jacksonXmlModule = new JacksonXmlModule();
>jacksonXmlModule.setDefaultUseWrapper(false);
>ObjectMapper xmlMapper = new XmlMapper(jacksonXmlModule);
>```
>
> As of version **2.9.0**, the only configuration options for the XML Module are:
>
>- `setDefaultUseWrapper` – defines whether or not to use a wrapper for non-annotated List properties by default
>- `setXMLTextElementName` – defines the virtual name to use when processing character data sections – when not binding to Java beans
>
> To configure it to produce indented output:
>
>```java
>xmlMapper.enable(SerializationFeature.INDENT_OUTPUT);
>```

## Jackson Annotations for Serialization

> Given the following bean:
>
>```java
>@JsonPropertyOrder({"age", "id", "name"})
>public class Person {
>
> @JsonProperty("_id")
> private String id;
>
> private String name;
>
> private int age;
>
> @JsonIgnore
> private String note;
>}
>```
>
> will produce this XML:
>
>
>```xml
><Person>
> <age>4</age>
> <_id>12345</_id>
> <name>George</name>
></Person>
>```

## Additional Jackson XML-specific annotations<SUP>[🔗](https://github.com/FasterXML/jackson-dataformat-xml/wiki/Jackson-XML-annotations)</SUP>

### `@JacksonXmlRootElement`

> Allows specifying XML element to use for wrapping the root element (default uses *simple name* of the value class). This only needs to be used for objects serialized as root values: for other values property name is used; for root values there is no referring property and separate annotation is needed on class itself.
>
> Properties:
>
> `namespace` (default: `""`): Which XML namespace to use for root element
> `localName`: Local name of root element
>
> Let’s look at this POJO:
>
>```java
>@JacksonXmlRootElement(
> namespace = "urn:somenamespace",
> localName = "PersonData"
>)
>public class Person {
>
> private String id;
>
> private String name;
>
> private String note;
>}
>```
>
> When serialized, this will result in the following XML:
>```java
><PersonData xmlns="urn:somenamespace">
> <id xmlns="">12345</id>
> <name xmlns="">Graham</name>
> <note xmlns="">Hello</note>
></PersonData>
>```

### `@JacksonXmlProperty`

> Allows specifying XML namespace and local name for a property; as well as whether property is to be written as an XML element or attribute.
>
> Properties:
>
> - `namespace` (default: `""`): Which XML namespace to use for property element or attribute
> - `localName`: Local name of property element or attribute
> - `isAttribute` (default: `false`): Whether property should be serialized as an attribute (`true`) or element (`false`)
>
> The following bean:
>
>```java
>public class Person {
>
> @JacksonXmlProperty(
> isAttribute = true,
> namespace = "urn:somenamespace",
> localName = "_id"
> )
> private String id;
>
> @JacksonXmlProperty(namespace = "urn:anothernamespace")
> private String name;
>
> private String note;
>}
>```
>
> generates the following XML output:
>
>```xml
><Person xmlns:wstxns1="urn:somenamespace" wstxns1:_id="12345">
> <wstxns2:name xmlns:wstxns2="urn:anothernamespace">Graham</wstxns2:name>
> <note>Hello</note>
></Person>
>```

### `@JacksonXmlElementWrapper`

> Allows specifying XML element to use for wrapping List and Map properties; or disabling use (with `useWrapping` set to `false`).
>
> Properties:
>
> - `namespace` (default: `""`): Which XML namespace to use for wrapper element (defaults to: `""`)
> - `localName`: Local name for wrapper element
> - `useWrapping` (default: `true`) Whether to use wrapper element or not: by specifying `false` one can disable use

### `@JacksonXmlText`

> Allows specifying that value of one property is to be serialized as **unwrapped** text, and not in an element.
>
> Properties:
>
> `value` (default: `true`): Whether annotated property value is to be serialized as basic XML text (without surrounding XML element) or not.

## References

- [Solving the XML Problem with Jackson](https://stackify.com/java-xml-jackson/)