Jackson 除了可以处理 JSON，还可以用来处理 XML(jackson-dataformat-xml 模块)，可以轻松完成 Java 对象和 XML 文档的互转；本文主要介绍使用 Jackson 来处理 XML，文中所使用到的软件版本：Java 1
Jackson 除了可以处理 JSON，还可以用来处理 XML(jackson-dataformat-xml 模块)，可以轻松完成 Java 对象和 XML 文档的互转；本文主要介绍使用 Jackson 来处理 XML，文中所使用到的软件版本：Java 1.8.0_321、Jackson 2.13.3。
1、简介
jackson-dataformat-xml 模拟 JAXB "代码优先" 的数据绑定方式，提供低级以及高级的方法来完成数据绑定工作。值得注意的是，jackson-dataformat-xml 的目标不是完整的 JAXB 克隆，或者成为一个通用的 XML 工具包。具体来说：
- While XML serialization should ideally be similar to JAXB output, deviations are not automatically considered flaws (there are reasons for some differences)
- What should be guaranteed is that any XML written using this module must be readable using module as well ("read what I wrote"): that is, we do aim for full round-trip support
- From above: there are XML constructs that module will not be able to handle; including some cases JAXB (and other Java XML libraries) supports
- This module also support constructs and use cases JAXB does not handle: specifically, rich type and object id support of Jackson are supported.
详情可参考官网文档：https://github.com/FasterXML/jackson-dataformat-xml.
2、Jackson 配置
处理 XML 的 XMLMapper 对象继承自处理 JSON 的 ObjectMapper 对象，因此他们的配置是类似的，具体可参考：Java 操作 JSON 数据(4)--Jackson 操作 JSON 数据。这里列出仅针对 XML 处理的注解：
注解
作用域
说明
实现时机
@JacksonXmlRootElement
类上
指定 XML 根标签的名字
序列化时
@JacksonXmlProperty
属性或getter/setter方法上
指定属性对应 XML 映射的名称
序列化和反序列化时
@JacksonXmlText
属性或getter/setter方法上
将属性直接作为未被标签包裹的普通文本
序列化和反序列化时
@JacksonXmlCData
属性或getter/setter方法上
将属性值包裹在 CDATA 标签中
序列化时
@JacksonXmlElementWrapper
属性或getter/setter方法上
类中有集合的属性时，是否生成包裹的标签
序列化时
3、具体使用
3.1、引入依赖
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
<version>2.13.3</version>
</dependency>
3.2、定义实体类
3.2.1、Grade
package com.abc.demo.xml;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;
import lombok.Data;
import lombok.ToString;
import java.util.List;
@Data
@ToString
@JacksonXmlRootElement(namespace = "http://www.w3.org/TR/html4/school/", localName = "school:grade")
public class Grade {
@JacksonXmlElementWrapper(useWrapping = false)
@JacksonXmlProperty(localName = "student", namespace = "http://www.w3.org/TR/html4/school/")
List<Student> students;
}
3.2.2、Student
package com.abc.demo.xml;
import com.fasterxml.jackson.dataformat.xml.annotation.*;
import lombok.Data;
import lombok.ToString;
@Data
@ToString
public class Student {
@JacksonXmlProperty(isAttribute = true)
private int rollno;
@JacksonXmlProperty(isAttribute = true)
private int age;
@JacksonXmlProperty(namespace = "http://www.w3.org/TR/html4/school/")
private String firstname;
private String lastname;
private String nickname;
private String marks;
public Student() {}
public Student(int rollno, int age, String firstname, String lastname, String nickname, String marks) {
this.rollno = rollno;
this.age = age;
this.firstname = firstname;
this.lastname = lastname;
this.nickname = nickname;
this.marks = marks;
}
}
3.3、定义待解析 XML(student.xml)
<?xml version="1.0" encoding="utf-8" ?>
<school:grade xmlns:school="http://www.w3.org/TR/html4/school/">
<school:student rollno="1" school:age="10">
<school:firstname>cxx1</school:firstname>
<lastname>Bob1</lastname>
<nickname>stars1</nickname>
<marks>85</marks>
</school:student>
<student rollno="2">
<firstname>cxx2</firstname>
<lastname>Bob2</lastname>
<nickname>stars2</nickname>
<marks>85</marks>
</student>
<student rollno="3">
<firstname>cxx3</firstname>
<lastname>Bob3</lastname>
<nickname>stars3</nickname>
<marks>85</marks>
</student>
</school:grade>
3.4、序列化及反序列化
package com.abc.demo.xml;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
public class JacksonCase {
private static final Logger logger = LoggerFactory.getLogger(JacksonCase.class);
/**
* 序列化
*/
@Test
public void serialize() throws IOException {
List<Student> students = new ArrayList<>();
Student student1 = new Student(1, 11,"cxx1", "Bob1", "stars1", "85");
Student student2 = new Student(2, 12, "cxx2", "Bob2", "stars2", "85");
Student student3 = new Student(3, 13, "cxx3", "Bob3", "stars3", "85");
students.add(student1);
students.add(student2);
students.add(student3);
Grade grade = new Grade();
grade.setStudents(students);
XmlMapper xmlMapper = new XmlMapper();
//美化输出
xmlMapper.enable(SerializationFeature.INDENT_OUTPUT);
logger.info(xmlMapper.writeValueAsString(grade));
}
/**
* 反序列化
*/
@Test
public void deserialize() throws IOException {
XmlMapper xmlMapper = new XmlMapper();
InputStream inputStream = JacksonCase.class.getResourceAsStream("student.xml");
//反序列化为实体对象
Grade grade = xmlMapper.readValue(inputStream, Grade.class);
logger.info(grade.toString());
inputStream = JacksonCase.class.getResourceAsStream("student.xml");
TypeReference<List<Student>> typeReference = new TypeReference<List<Student>>(){};
//反序列化为集合
List<Student> students = xmlMapper.readValue(inputStream, typeReference);
logger.info(students.toString());
inputStream = JacksonCase.class.getResourceAsStream("student.xml");
//使用树模型 API 解析 XML
JsonNode root = xmlMapper.readTree(inputStream);
JsonNode jsonNode = root.get("student").get(1);
logger.info("第一条数据,{}",jsonNode.toString());
logger.info("第一条数据,firstname={}", jsonNode.get("firstname").asText());
logger.info("第一条数据,marks={}", jsonNode.get("marks").asInt());
}
}