在使用Spring Boot返回XML作为HTTP响应时，需要添加类似下面的XML声明。

<?xml version='1.0' encoding='UTF-8'?>

源代码

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>

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

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.http.MediaType;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator;

@SpringBootApplication
@RestController
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @GetMapping(value = "/xml", produces = { MediaType.TEXT_XML_VALUE })
    public XmlResponse xml() {
        return new XmlResponse();
    }

    @Bean
    public MappingJackson2XmlHttpMessageConverter mappingJackson2XmlHttpMessageConverter(Jackson2ObjectMapperBuilder builder) {
        XmlMapper xmlMapper = builder.createXmlMapper(true).build();
        xmlMapper.configure(ToXmlGenerator.Feature.WRITE_XML_DECLARATION, true);
        return new MappingJackson2XmlHttpMessageConverter(xmlMapper);
    }
}

<?xml version='1.0' encoding='UTF-8'?>
<XmlResponse>
    <id>aa</id>
</XmlResponse>

如何在从端点返回的XML中添加XML声明