现在有一个实体类对象的集合，需要将它们转换为xml文档，xml文档就是标签集合的嵌套，例如一个学生类，有姓名、年龄等，需要转换成一下效果：

 <student>
        <age>14</age>
        <name>张三</name>
    </student>
    <student>
        <age>15</age>
        <name>李四</name>
    </student>
    <student>
        <age>16</age>
        <name>王五</name>
    </student>

首先定义student的实体类：

import lombok.Data;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@Data
@XmlRootElement
public class Student {

    private String name;
    private int age;

    // 无参构造函数（必须有）
    public Student() {}

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @XmlElement
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlElement
    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

因为是student的集合，需要再构建一个StudentListWrapper类：

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

@XmlRootElement
public class StudentListWrapper {
    private List<Student> students;

    public StudentListWrapper() {}

    public StudentListWrapper(List<Student> students) {
        this.students = students;
    }

    @XmlElement(name = "student")
    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}

两种下载方式：无返回值的：

 @GetMapping("testXmlDownload")
    public void testXmlDownload(HttpServletResponse response) throws Exception {
        try {
            // 创建一个包含 Student 对象的集合
            List<Student> studentList = new ArrayList<>();
            studentList.add(new Student("张三", 14));
            studentList.add(new Student("李四", 15));
            studentList.add(new Student("王五", 16));

            // 创建 JAXB 上下文
            JAXBContext context = JAXBContext.newInstance(StudentListWrapper.class);

            // 创建 Marshaller
            Marshaller marshaller = context.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

            // 将集合序列化为 XML
            StringWriter writer = new StringWriter();
            marshaller.marshal(new StudentListWrapper(studentList), writer);

            // 输出 XML 格式的文档
            String xmlDocument = writer.toString();


            byte[] bytes = xmlDocument.getBytes();

            // 使用 ByteArrayInputStream 将字节数组转换为 InputStream
            InputStream inputStream = new ByteArrayInputStream(bytes);

            // 使用 BufferedInputStream 包装 InputStream
            BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
            byte[] buffer = new byte[bufferedInputStream.available()];
            bufferedInputStream.read(buffer);
            bufferedInputStream.close();
            response.reset();
            response.setCharacterEncoding("UTF-8");
            response.addHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode("student".concat(".xml"), "UTF-8"));
            //response.addHeader("Content-Length", "" + file.length());
            OutputStream outputStream = new BufferedOutputStream(response.getOutputStream());
            response.setContentType("application/octet-stream");
            outputStream.write(buffer);
            outputStream.flush();

           // System.out.println(xmlDocument);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

第二种：使用 ResponseEntity 对象来封装响应内容和响应头，并返回给客户端：

@GetMapping("/download")
    public ResponseEntity<byte[]> downloadFile() throws Exception {
        // 创建一个包含 Student 对象的集合
        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student("张三", 14));
        studentList.add(new Student("李四", 15));
        studentList.add(new Student("王五", 16));

        // 创建 JAXB 上下文
        JAXBContext context = JAXBContext.newInstance(StudentListWrapper.class);

        // 创建 Marshaller
        Marshaller marshaller = context.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

        // 将集合序列化为 XML
        StringWriter writer = new StringWriter();
        marshaller.marshal(new StudentListWrapper(studentList), writer);

        // 输出 XML 格式的文档
        String xmlContent = writer.toString();


       // byte[] bytes = xmlDocument.getBytes();

        // 将 XML 内容转换为字节数组
        byte[] xmlBytes = xmlContent.getBytes(StandardCharsets.UTF_8);

        // 构造响应头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_XML);
        headers.setContentDispositionFormData("attachment", "students.xml");

        // 构造 ResponseEntity 对象，设置响应内容和响应头
        ResponseEntity<byte[]> responseEntity = new ResponseEntity<>(xmlBytes, headers, HttpStatus.OK);

        return responseEntity;
    }

使用postman测试：

复制到浏览器测试：

打开效果：