Spring Boot 找不到可接受的 XML 响应表示

Question

我找到了针对此异常和原因的多种解决方案，但都没有奏效，而且似乎不合逻辑。

我有如下 REST 服务类

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.http.MediaType;

import java.util.Map;
@RestController
public class UserRestService {

    @RequestMapping(value = "/userLogin", method = RequestMethod.POST, produces = MediaType.APPLICATION_XML_VALUE, consumes = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public @ResponseBody ResponseEntity<Map> login(@RequestBody Map<String, String> name) {
        ResponseEntity<Map> res = null;
        name.values().forEach(System.out::println);
        return new ResponseEntity<Map>(name, HttpStatus.OK);
    }
}

如您所见，我尝试创建一个 POST 请求，请求主体为 JSON，响应为 XML，在此过程中打印请求。这只是一个简单的例子，但是当请求被正确打印时，这意味着它已被接收并编组到 Map。但是响应状态是 406（不可接受）

日志中的异常是

John
30
null
2018-08-16 14:05:48.440  WARN 22820 --- [nio-8080-exec-2] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved exception caused by Handler execution: org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
2018-08-16 14:05:48.481  WARN 22820 --- [nio-8080-exec-2] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved exception caused by Handler execution: org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation

请求头只有

Accept:*/*
Content-Type:application/json

POM文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example.cms</groupId>
    <artifactId>business</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.6</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>javax.xml.bind</groupId>
            <artifactId>jaxb-api</artifactId>
            <version>2.3.0</version>
        </dependency>
        <dependency>
            <groupId>com.sun.xml.bind</groupId>
            <artifactId>jaxb-core</artifactId>
            <version>2.3.0.1</version>
        </dependency>
        <dependency>
            <groupId>com.sun.xml.bind</groupId>
            <artifactId>jaxb-impl</artifactId>
            <version>2.3.0.1</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

注意添加以下依赖解决了问题

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

请求正文 { "name":"John", "age":30, "car":null }

如果响应MediaType.APPLICATION_JSON_UTF8_VALUE被用于produces的属性@RequestMapping就是{ "name":"John", "age":30, "car":null }

响应 ifMediaType.APPLICATION_XML_VALUE用于& used 的produces属性是@RequestMappingjackson-dataformat-xml

<Map>
    <name>John</name>
    <age>30</age>
    <car/>
</Map>

为什么在此使用 JAXB 会失败？

更新 01

正如@Simon 评论一样，我创建了一个示例对象（类）以作为请求和响应。完全一样的效果。这是更新的代码

public class MockupResponse {

    private String name;
    private Integer age;
    private String car;

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    public String getCar() {
        return car;
    }

    public void setCar(String car) {
        this.car = car;
    }

@Override
public String toString() {
        StringBuffer sb = new StringBuffer();
        if (null != name)
            sb.append("Name: " + name + "\n");
        if (null != age)
            sb.append("Age: " + age + "\n");
        if (null != car)
            sb.append("Car: " + car + "\n");

        return sb.toString();
}
}

服务

@RequestMapping(value = "/userLogin", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_UTF8_VALUE, consumes = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public @ResponseBody ResponseEntity<MockupResponse> login(@RequestBody MockupResponse sample) {
        System.out.println(sample);

        return new ResponseEntity<MockupResponse>(sample, HttpStatus.OK);
    }

Answer 1

将@XmlRootElement 添加到必须由 JAXB 序列化的类中，例如

@XmlRootElement
public class MockupResponse {

    private String name;
    private Integer age;
    private String car;
...
}

然后 XML 序列化工作。

在 Spring Doc 中阅读更多相关信息：

https://docs.spring.io/spring-boot/docs/current/reference/html/howto-spring-mvc.html

如果您使用 Java 9 及更高版本，则必须将 JAXB 和 javax.activation 添加到依赖项：

    <dependency>
        <groupId>javax.xml.bind</groupId>
        <artifactId>jaxb-api</artifactId>
    </dependency>
    <dependency>
        <groupId>com.sun.xml.bind</groupId>
        <artifactId>jaxb-core</artifactId>
        <version>2.3.0.1</version>
    </dependency>
    <dependency>
        <groupId>com.sun.xml.bind</groupId>
        <artifactId>jaxb-impl</artifactId>
        <version>2.3.0.1</version>
    </dependency>
    <dependency>
        <groupId>javax.activation</groupId>
        <artifactId>activation</artifactId>
        <version>1.1.1</version>
    </dependency>