如何在Spring Boot應用程序中自動配置默認的XmlMapper

Question

我在我的一個Spring Boot項目中自動裝配了默認的Jackson XmlMapper。我創建了一個簡單的示例項目來說明這一點。

我在做什麼在這裏大致在此基礎上：

http://docs.spring.io/spring-boot/docs/1.2.2.RELEASE/reference/htmlsingle/#howto-write-an-xml-rest-service

http://docs.spring.io/spring-boot/docs/1.2.2.RELEASE/reference/htmlsingle/#howto-customize-the-jackson-objectmapper

從pom.xml的

<!-- ... --> 

<parent> 
    <groupId>org.springframework.boot</groupId> 
    <artifactId>spring-boot-starter-parent</artifactId> 
    <version>1.2.2.RELEASE</version> 
</parent> 

<!-- ... --> 

<dependencies> 
    <dependency> 
     <groupId>org.springframework.boot</groupId> 
     <artifactId>spring-boot-starter</artifactId> 
    </dependency> 
    <dependency> 
     <groupId>org.springframework.boot</groupId> 
     <artifactId>spring-boot-starter-web</artifactId> 
    </dependency> 
    <dependency> 
     <groupId>com.fasterxml.jackson.dataformat</groupId> 
     <artifactId>jackson-dataformat-xml</artifactId> 
    </dependency> 
</dependencies> 

<!-- ... --> 

主類：

@SpringBootApplication 
public class DemoApplication { 

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

演示POJO，不指定@XmlRootElement，所以它不會使用JAXB：

@JsonInclude(Include.NON_NULL) 
public class Demo { 
    private String stringProperty; 
    private int intProperty; 
    public String getStringProperty() { 
     return stringProperty; 
    } 
    public void setStringProperty(String stringProperty) { 
     this.stringProperty = stringProperty; 
    } 
    public int getIntProperty() { 
     return intProperty; 
    } 
    public void setIntProperty(int intProperty) { 
     this.intProperty = intProperty; 
    } 
} 

演示控制器：

@RestController 
public class DemoController { 
    @Autowired 
    private ObjectMapper objectMapper; 
    // @Autowired 
    // private XmlMapper xmlMapper; 

    @RequestMapping(value = "/demo", method = RequestMethod.GET) 
    public Demo getDemo() { 
     Demo demo = new Demo(); 
     demo.setStringProperty("Hello world!"); 
     demo.setIntProperty(42); 
     return demo; 
    } 
} 

一切正常，事情是這樣的，這取決於Accept頭，無論是JSON或XML將被返回。

我可以輕鬆自動裝入由Spring Boot配置的默認ObjectMapper。到現在爲止還挺好。

如果我在XmlMapper我得到的自動裝配評論：

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.fasterxml.jackson.dataformat.xml.XmlMapper] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301) 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047) 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942) 
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533) 
... 18 more 

任何想法，這是爲什麼？我會假定它的工作方式與ObjectMapper相同。只是澄清，我不要想要自定義映射器，我只是想引用由Spring Boot創建的默認值。

Answer 1

春天啓動不公開XmlMapper的，因爲它會與同時使用JSON映射ObjectMapper豆（傑克遜的XmlMapper是傑克遜的ObjectMapper的子類）衝突的豆。

Answer 2

基於@Andy Wilkinson的回答，我做了一些更多的挖掘並找到了一種方法來獲得我想要的東西。 Spring Boot不會將XmlMapper作爲Bean公開，但它確實公開了它用於的消息轉換器，即MappingJackson2XmlHttpMessageConverter。所以我可以自動連接這個bean並從中獲得ObjectMapper（現在是XmlMapper）。

演示控制器從我現在的問題是這樣的：

@RestController 
public class DemoController { 
    @Autowired 
    private ObjectMapper objectMapper; 
    @Autowired 
    private MappingJackson2XmlHttpMessageConverter xmlConverter; 

    @RequestMapping(value = "/demo", method = RequestMethod.GET) 
    public Demo getDemo() { 
     Demo demo = new Demo(); 
     demo.setStringProperty("Hello world!"); 
     demo.setIntProperty(42); 
     ObjectMapper xmlMapper = xmlConverter.getObjectMapper(); 
     return demo; 
    } 
}