Spring OXM

Spring OXM

1. Spring OXM 概述

   Spring OXM 是Spring3.0的一个新特性，为主流O/X Mapping组件提供了统一层抽象和封装，而在Spring4.0中OXM没有增加更多新特性。O/X映射器这个概念并不新鲜，O 代表 Object，X代表XML，目的是在Java对象和XML之间进行转换操作。Spring OXM 不仅仅屏蔽了各O/XMapping组件实现的差异性，而且还提供了统一，高效的编程模型。Spring OXM的结构框架如下所示：

OXM架构图.png

Marshaller和Unmarshaller是Spring OXM的两个核心接口。实现Marshaller接口可以实现从Java对象到XML的映射转换，实现Unmarshaller接口可实现从XML到Java对象的映射转换。

Marshaller接口定义：

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n522" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace; margin-top: 0px; margin-bottom: 20px; background-color: rgb(51, 51, 51); font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; position: relative !important; padding: 10px 10px 10px 30px; width: inherit; background-position: initial initial; background-repeat: initial initial;">public interface Marshaller {
 //判断支持的编组类类型
 boolean supports(Class<?> class);
​
 //对传入对象进行编组操作
 void marshal(Object graph, Result result) throws IOException, XmlMappingException;
}</pre>

Marshaller接口中提供了两个方法，其中supports（）方法用于判断支持的编组类类型；marshal 方法用于对对象进行编组操作，其中graph参数为目标转换对象，result参数为JDK提供的XML转换接口，实现此接口的对象包含构建转换结果树所需的信息。**Spring OXM支持的Result转换实现类有 DOMResult，SAXResult，StreamResult，StaxResult**，其中 DOMResult，SAXResult，StreamResult为JDK提供的实现类，StaxResult为Spring OXM提供的扩展类。

Unmarshaller接口定义

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n532" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace; margin-top: 0px; margin-bottom: 20px; background-color: rgb(51, 51, 51); font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; position: relative !important; padding: 10px 10px 10px 30px; width: inherit; background-position: initial initial; background-repeat: initial initial;">public interface Unmarshaller {
​
 //
 boolean supports(Class<?> clazz);
//
 Object unmarshal(Source source) throws IOException, XmlMappingException;
​
}</pre>

Unmarshaller接口提供了两个方法，其中supports方法用于判断支持的反编组类类型，unmarshal方法用于将输入源对象进行反编组操作，其中source参数为目标输入源对象，Source参数为JDK提供的输入源接口，实现此接口的对象包含充当源输入（XML源或转换指令）所需的信息。Spring OXM 支持的Source输入源实现类有 DOMSource，SAXSource，StreamSource，StaxSource，其中 DOMSource，SAXSource，StreamSource为JDK提供实现类，StaxSource为Spring OXM提供的扩展类。

Spring OXM统一封装底层的O/XMapping组件异常，将各O/XMapping组件原始异常对象包装到Spring自身专为OXM建立的运行时异常 XmlMappingException中，并通过MarshallerFailureException和UnmarshallerFailureException处理编组和反编组操作之间的区别。

2. 整合OXM实现者

   Spring OXM默认提供目前几个主流O/X Mapping组件的实现，包括XStream，XMLBeans，Castor，JiBX，JAXB。这些O/XMapping组件统一实现Spring OXM 的两个核心接口 Marshaller和Unmarshaller。

   要使用Spring OXM 的 O/X功能，首先需要一个在Java对象和XML之间来回转换的组件，并将上文提到的XStream，JAXB等的相应的类库添加到工程中。各O/XMapping组件对应的实现类如下：

   O/X Mapping组件	Spring OXM实现类
   XStream	org.springframework.oxm.xstream.XStreamMarshaller
   Castor	org.springframework.oxm.castor.CastorMarshaller
   JiBX	org.springframework.oxm.jibx.JibxMarshaller
   JAXB	org.springframework.oxm.jaxb.Jaxb2Marshaller

3. 如何在Spring中进行配置

   到目前为止，我们已经介绍了各 O/X Mapping组件的使用方法以及Spring OXM整体框架，接下来介绍如何在Spring中整合这些 O/XMapping组件。

   spring.schemas 文件

   <pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="xml-dtd" cid="n588" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; background-color: rgb(51, 51, 51); font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; position: relative !important; padding: 10px 10px 10px 30px; width: inherit; background-position: initial initial; background-repeat: initial initial;">http://www.springframework.org/schema/oxm/spring-oxm-3.0.xsd=org/springframework/oxm/config/spring-oxm-3.0.xsd
   http://www.springframework.org/schema/oxm/spring-oxm-3.1.xsd=org/springframework/oxm/config/spring-oxm-3.1.xsd
   http://www.springframework.org/schema/oxm/spring-oxm-3.2.xsd=org/springframework/oxm/config/spring-oxm-3.2.xsd
   http://www.springframework.org/schema/oxm/spring-oxm-4.0.xsd=org/springframework/oxm/config/spring-oxm-4.0.xsd
   http://www.springframework.org/schema/oxm/spring-oxm-4.1.xsd=org/springframework/oxm/config/spring-oxm-4.1.xsd
   http://www.springframework.org/schema/oxm/spring-oxm-4.2.xsd=org/springframework/oxm/config/spring-oxm-4.2.xsd
   http://www.springframework.org/schema/oxm/spring-oxm.xsd=org/springframework/oxm/config/spring-oxm-4.2.xsd</pre>

   spring-oxm-4.2.xsd文件：

   <pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="xml" cid="n594" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; background-color: rgb(51, 51, 51); font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; position: relative !important; padding: 10px 10px 10px 30px; width: inherit; background-position: initial initial; background-repeat: initial initial;"><?xml version="1.0" encoding="UTF-8" standalone="no"?>
   <xsd:schema xmlns="http://www.springframework.org/schema/oxm" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:beans="http://www.springframework.org/schema/beans"
   xmlns:tool="http://www.springframework.org/schema/tool"
   targetNamespace="http://www.springframework.org/schema/oxm"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified">
   ​
   <xsd:import namespace="http://www.springframework.org/schema/beans" schemaLocation="http://www.springframework.org/schema/beans/spring-beans-4.2.xsd"/>
   <xsd:import namespace="http://www.springframework.org/schema/tool" schemaLocation="http://www.springframework.org/schema/tool/spring-tool-4.2.xsd"/>
   ​
   <xsd:annotation>
   <xsd:documentation>
   Defines the elements used in Spring's Object/XML Mapping integration.
   </xsd:documentation>
   </xsd:annotation>
   ​
   <xsd:element name="jaxb2-marshaller">
   <xsd:complexType>
   <xsd:annotation>
   <xsd:documentation source="java:org.springframework.oxm.jaxb.Jaxb2Marshaller">
   Defines a JAXB2 Marshaller.
   </xsd:documentation>
   <xsd:appinfo>
   <tool:annotation>
   <tool:exports type="org.springframework.oxm.jaxb.Jaxb2Marshaller"/>
   </tool:annotation>
   </xsd:appinfo>
   </xsd:annotation>
   <xsd:complexContent>
   <xsd:extension base="beans:identifiedType">
   <xsd:sequence>
   <xsd:element name="class-to-be-bound" minOccurs="0" maxOccurs="unbounded">
   <xsd:complexType>
   <xsd:attribute name="name" type="classType" use="required"/>
   </xsd:complexType>
   </xsd:element>
   </xsd:sequence>
   <xsd:attribute name="context-path" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The JAXB context path.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   </xsd:extension>
   </xsd:complexContent>
   </xsd:complexType>
   </xsd:element>
   ​
   <xsd:element name="jibx-marshaller">
   <xsd:complexType>
   <xsd:annotation>
   <xsd:documentation source="java:org.springframework.oxm.jibx.JibxMarshaller">
   Defines a JiBX Marshaller.
   </xsd:documentation>
   <xsd:appinfo>
   <tool:annotation>
   <tool:exports type="org.springframework.oxm.jibx.JibxMarshaller"/>
   </tool:annotation>
   </xsd:appinfo>
   </xsd:annotation>
   <xsd:complexContent>
   <xsd:extension base="beans:identifiedType">
   <xsd:attribute name="target-class" type="classType">
   <xsd:annotation>
   <xsd:documentation>The target class to be bound with JiBX.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   <xsd:attribute name="target-package" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The target package for the JiBX binding.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   <xsd:attribute name="binding-name" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The binding name used by this marshaller.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   </xsd:extension>
   </xsd:complexContent>
   </xsd:complexType>
   </xsd:element>
   ​
   <xsd:element name="castor-marshaller">
   <xsd:complexType>
   <xsd:annotation>
   <xsd:documentation
   source="java:org.springframework.oxm.castor.CastorMarshaller">
   Defines a Castor Marshaller.
   </xsd:documentation>
   <xsd:appinfo>
   <tool:annotation>
   <tool:exports type="org.springframework.oxm.castor.CastorMarshaller" />
   </tool:annotation>
   </xsd:appinfo>
   </xsd:annotation>
   <xsd:complexContent>
   <xsd:extension base="beans:identifiedType">
   <xsd:attribute name="encoding" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The encoding to use for stream reading.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   <xsd:attribute name="target-class" type="classType">
   <xsd:annotation>
   <xsd:documentation>The target class to be bound with the Castor marshaller.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   <xsd:attribute name="target-package" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The target package that contains Castor descriptor classes.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   <xsd:attribute name="mapping-location" type="xsd:string">
   <xsd:annotation>
   <xsd:documentation>The path to the Castor mapping file.</xsd:documentation>
   </xsd:annotation>
   </xsd:attribute>
   </xsd:extension>
   </xsd:complexContent>
   </xsd:complexType>
   </xsd:element>
   ​
   <xsd:simpleType name="classType">
   <xsd:annotation>
   <xsd:documentation source="java:java.lang.Class">A class supported by a marshaller.</xsd:documentation>
   <xsd:appinfo>
   <tool:annotation kind="direct">
   <tool:expected-type type="java.lang.Class"/>
   <tool:assignable-to restriction="class-only"/>
   </tool:annotation>
   </xsd:appinfo>
   </xsd:annotation>
   <xsd:union memberTypes="xsd:string"/>
   </xsd:simpleType>
   ​
   </xsd:schema></pre>