JAXB处理XML与对象互转

梦里梦外; 2023-07-14 08:04 32阅读 0赞

# 一、简介 #

*  本文主要讲解JAXB来处理对象与XML进行互转。
 *  其中关于CDATA数据的处理参考： [Jaxb如何优雅的处理CData][Jaxb_CData] 这篇文章的实现，并略作改动。

# 二、常用注解（TODO） #

# 三、封装 #

## 3.1 pom依赖（TODO） ##

## 3.2 CDataAdapter ##

package com.zhenai.sweet.qywx.provider.util;
    
    import javax.xml.bind.annotation.adapters.XmlAdapter;
    
    /**
     * JAXB的CDATA转换处理类
     */
    public class CDataAdapter extends XmlAdapter<String, String> {
    
        @Override
        public String unmarshal(String v) throws Exception {
            return v;
        }
    
        @Override
        public String marshal(String v) throws Exception {
            return new StringBuilder("<![CDATA[").append(v).append("]]>").toString();
        }
    
    }

## 3.3 CDataHandler ##

package com.zhenai.sweet.qywx.provider.util;
    
    import javax.xml.stream.XMLStreamWriter;
    import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    
    /**
     * 动态代理处理
     */
    public class CDataHandler implements InvocationHandler {
    
        private XMLStreamWriter writer;
    
        public CDataHandler(XMLStreamWriter writer) {
            this.writer = writer;
        }
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            Method gWriteCharactersMethod = null;
            try {
                gWriteCharactersMethod = XMLStreamWriter.class.getDeclaredMethod("writeCharacters", String.class);
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            }
            if (gWriteCharactersMethod.equals(method)) {
                String text = (String) args[0];
                if (text != null && text.startsWith("<![CDATA[") && text.endsWith("]]>")) {
                    writer.writeCData(text.substring(9, text.length() - 3));
                    return null;
                }
            }
            return method.invoke(writer, args);
        }
    
    }

## 3.4 JaxbXmlUtil ##

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.extern.slf4j.Slf4j;
    
    import javax.xml.bind.JAXBContext;
    import javax.xml.bind.Marshaller;
    import javax.xml.bind.Unmarshaller;
    import javax.xml.stream.XMLOutputFactory;
    import javax.xml.stream.XMLStreamWriter;
    import javax.xml.transform.OutputKeys;
    import javax.xml.transform.Transformer;
    import javax.xml.transform.TransformerException;
    import javax.xml.transform.TransformerFactory;
    import javax.xml.transform.stream.StreamResult;
    import javax.xml.transform.stream.StreamSource;
    import java.io.StringReader;
    import java.io.StringWriter;
    import java.lang.reflect.Proxy;
    import java.util.ArrayList;
    import java.util.List;
    
    
    /**
     * @Description Jaxb工具类 xml和java类相互转换
     * @Author: qjwyss
     * @Date: 2020/3/13 16:59
     * @Version V1.0
     */
    @Slf4j
    public class JaxbXmlUtil {
    
        private static final String DEFAULT_ENCODING = "UTF-8";
    
        /**
         * pojo转换成xml 默认编码UTF-8
         *
         * @param obj 待转化的对象
         * @return xml格式字符串
         * @throws Exception JAXBException
         */
        public static String pojo2xml(Object obj) throws Exception {
            return pojo2xml(obj, DEFAULT_ENCODING);
        }
    
    
        /**
         * pojo转换成xml
         *
         * @param obj      待转化的对象
         * @param encoding 编码
         * @return xml格式字符串
         * @throws Exception JAXBException
         */
        public static String pojo2xml(Object obj, String encoding) throws Exception {
            String result = null;
    
            JAXBContext context = JAXBContext.newInstance(obj.getClass());
            Marshaller marshaller = context.createMarshaller();
            // 指定是否使用换行和缩排对已编组 XML 数据进行格式化的属性名称。
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
            marshaller.setProperty(Marshaller.JAXB_ENCODING, encoding);
    
            try (StringWriter writer = new StringWriter();) {
                XMLStreamWriter streamWriter = XMLOutputFactory.newInstance().createXMLStreamWriter(writer);
                XMLStreamWriter cdataStreamWriter = (XMLStreamWriter) Proxy.newProxyInstance(
                        streamWriter.getClass().getClassLoader(),
                        streamWriter.getClass().getInterfaces(),
                        new CDataHandler(streamWriter)
                );
                marshaller.marshal(obj, cdataStreamWriter);
                result = formatXml(writer.toString());
            } catch (Exception e) {
                log.error("读取数据失败", e);
            }
    
            return result;
        }
    
    
        /**
         * xml转换成pojo
         *
         * @param xml xml格式字符串
         * @param t   待转化的对象
         * @return 转化后的对象
         * @throws Exception JAXBException
         */
        @SuppressWarnings("unchecked")
        public static <T> T xml2pojo(String xml, Class<T> t) throws Exception {
            T obj;
            JAXBContext context = JAXBContext.newInstance(t);
            Unmarshaller unmarshaller = context.createUnmarshaller();
    
            try (StringReader stringReader = new StringReader(xml)) {
                obj = (T) unmarshaller.unmarshal(stringReader);
            }
            return obj;
        }
    
    
        /**
         * xml文本对齐
         */
        private static String formatXml(String xml) {
            try {
                TransformerFactory factory = TransformerFactory.newInstance();
                Transformer transformer = factory.newTransformer();
                // 打开对齐开关
                transformer.setOutputProperty(OutputKeys.INDENT, "yes");
                // 忽略掉xml声明头信息
                transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
                transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
                transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
    
                StringWriter formattedStringWriter = new StringWriter();
                transformer.transform(new StreamSource(new StringReader(xml)),
                        new StreamResult(formattedStringWriter));
    
                return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
                        + formattedStringWriter.toString();
            } catch (TransformerException e) {
            }
            return null;
        }
    
    
    }

# 四、使用 #

## 4.1 简单对象互转 ##

### 4.1.0 说明 ###

*  此处仅使用一个简单User对象来进行转换；

### 4.1.1 User对象 ###

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.Data;
    
    import javax.xml.bind.annotation.*;
    import java.io.Serializable;
    
    @Data
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlRootElement(name = "user")
    @XmlType(propOrder = {
            "uid",
            "username",
            "password"
    })
    public class User implements Serializable {
    
        private static final long serialVersionUID = -4476533660865890728L;
    
        private Long uid;
    
        private String username;
    
        private String password;
    
        @XmlAttribute
        private String gender;
    
        public User() {
        }
    
        public User(Long uid, String username, String password, String gender) {
            this.uid = uid;
            this.username = username;
            this.password = password;
            this.gender = gender;
        }
    }

### 4.1.2 使用 ###

// 简单对象互转
    User user = new User(1L, "小明", "123456", "男");
    String userXml = JaxbXmlUtil.pojo2xml(user);
    log.info("简单对象转换XML结果: {}", userXml);
    user = JaxbXmlUtil.xml2pojo(userXml, User.class);
    log.info("简单XML转换对象结果: {}", user.toString());

### 4.1.3 结果 ###

19:31:57.023 [main] INFO com.zhenai.sweet.qywx.provider.util.JaxbXmlUtil - 简单对象转换XML结果: <?xml version="1.0" encoding="UTF-8"?>
    <user gender="男">
        <uid>1</uid>
        <username>小明</username>
        <password>123456</password>
    </user>
    
    19:31:57.035 [main] INFO com.zhenai.sweet.qywx.provider.util.JaxbXmlUtil - 简单XML转换对象结果: User(uid=1, username=小明, password=123456, gender=男)

## 4.2 复杂对象互转 ##

### 4.2.0 说明 ###

*  此处通过设置嵌套对象来转换复杂的xml
 *  有三个对象，班级对象，老师对象，学生对象； 一个班级对应一个老师，一个班级对应一群学生；

### 4.2.1 对象 ###

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.Data;
    
    import javax.xml.bind.annotation.*;
    import java.io.Serializable;
    import java.util.List;
    
    @Data
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlRootElement(name = "banji")
    @XmlType(propOrder = {
            "classId",
            "className",
            "teacher",
            "studentList"
    })
    public class Banji implements Serializable {
    
        private static final long serialVersionUID = -7645165684680423691L;
    
        private Long classId;
    
        private String className;
    
        private Teacher teacher;
    
        @XmlElementWrapper
        @XmlElement(name = "student")
        private List<Student> studentList;
    
        public Banji() {
        }
    
        public Banji(Long classId, String className, Teacher teacher, List<Student> studentList) {
            this.classId = classId;
            this.className = className;
            this.teacher = teacher;
            this.studentList = studentList;
        }
    }

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.Data;
    
    import javax.xml.bind.annotation.XmlAccessType;
    import javax.xml.bind.annotation.XmlAccessorType;
    import javax.xml.bind.annotation.XmlRootElement;
    import javax.xml.bind.annotation.XmlType;
    import java.io.Serializable;
    
    @Data
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlRootElement(name = "teacher")
    @XmlType(propOrder = {
            "teacherName",
            "teacherGender",
    })
    public class Teacher implements Serializable {
    
        private static final long serialVersionUID = 9190597564351664551L;
    
        private String teacherName;
        private String teacherGender;
    
        public Teacher() {
        }
    
        public Teacher(String teacherName, String teacherGender) {
            this.teacherName = teacherName;
            this.teacherGender = teacherGender;
        }
    }

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.Data;
    
    import javax.xml.bind.annotation.XmlAccessType;
    import javax.xml.bind.annotation.XmlAccessorType;
    import javax.xml.bind.annotation.XmlRootElement;
    import javax.xml.bind.annotation.XmlType;
    import java.io.Serializable;
    
    @Data
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlRootElement(name = "student")
    @XmlType(propOrder = {
            "studentName",
            "age",
    })
    public class Student implements Serializable {
    
        private static final long serialVersionUID = -7099299365239347614L;
    
        private String studentName;
        private Integer age;
    
        public Student() {
        }
    
        public Student(String studentName, Integer age) {
            this.studentName = studentName;
            this.age = age;
        }
    }

### 4.2.2 使用 ###

// 复合对象互转
    Teacher teacher = new Teacher("语文老师", "女");
    List<Student> studentList = new ArrayList<>();
    Student student1 = new Student("小雪", 15);
    Student student2 = new Student("小花", 13);
    Student student3 = new Student("小李", 14);
    studentList.add(student1);
    studentList.add(student2);
    studentList.add(student3);
    Banji banji = new Banji(2L, "三年一班", teacher, studentList);
    String banjiXml = JaxbXmlUtil.pojo2xml(banji);
    log.info("复合对象转XML：{}", banjiXml);
    banji = JaxbXmlUtil.xml2pojo(banjiXml, Banji.class);
    log.info("复合XML转对象结果：{}", banji.toString());

### 4.2.3 结果 ###

19:35:42.168 [main] INFO com.zhenai.sweet.qywx.provider.util.JaxbXmlUtil - 复合对象转XML：<?xml version="1.0" encoding="UTF-8"?>
    <banji>
        <classId>2</classId>
        <className>三年一班</className>
        <teacher>
            <teacherName>语文老师</teacherName>
            <teacherGender>女</teacherGender>
        </teacher>
        <studentList>
            <student>
                <studentName>小雪</studentName>
                <age>15</age>
            </student>
            <student>
                <studentName>小花</studentName>
                <age>13</age>
            </student>
            <student>
                <studentName>小李</studentName>
                <age>14</age>
            </student>
        </studentList>
    </banji>
    
    19:35:42.171 [main] INFO com.zhenai.sweet.qywx.provider.util.JaxbXmlUtil - 复合XML转对象结果：Banji(classId=2, className=三年一班, teacher=Teacher(teacherName=语文老师, teacherGender=女), studentList=[Student(studentName=小雪, age=15), Student(studentName=小花, age=13), Student(studentName=小李, age=14)])

### 4.3 CDATA使用 ###

### 4.3.0 说明 ###

*  仅需要在需要CDATA的字段上加上注解@XmlJavaTypeAdapter(CDataAdapter.class)即可；

### 4.3.1 User对象 ###

package com.zhenai.sweet.qywx.provider.util;
    
    import lombok.Data;
    
    import javax.xml.bind.annotation.*;
    import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
    import java.io.Serializable;
    
    @Data
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlRootElement(name = "user")
    @XmlType(propOrder = {
            "uid",
            "username",
            "password"
    })
    public class User implements Serializable {
    
        private static final long serialVersionUID = -4476533660865890728L;
    
        private Long uid;
    
        @XmlJavaTypeAdapter(CDataAdapter.class)
        private String username;
    
        private String password;
    
        @XmlAttribute
        private String gender;
    
        public User() {
        }
    
        public User(Long uid, String username, String password, String gender) {
            this.uid = uid;
            this.username = username;
            this.password = password;
            this.gender = gender;
        }
    }

### 4.3.2 结果 ###

19:40:34.177 [main] INFO com.zhenai.sweet.qywx.provider.util.JaxbXmlUtil - 简单对象转换XML结果: <?xml version="1.0" encoding="UTF-8"?>
    <user gender="男">
        <uid>1</uid>
        <username><![CDATA[小明]]></username>
        <password>123456</password>
    </user>

[Jaxb_CData]: https://blog.csdn.net/weixin_33757911/article/details/86261394