在Spring的配置里，最好不要配置xsd文件的版本号

叁歲伎倆 2022-05-21 05:26 170阅读 0赞

### 为什么dubbo启动没有问题？ ###

这篇blog源于一个疑问：

我们公司使了阿里的dubbo，但是阿里的开源网站http://code.alibabatech.com，挂掉有好几个月了，为什么我们的应用启动没有问题？

我们的应用的Spring配置文件里有类似的配置：

1.  <?xml version="1.0" encoding="UTF-8"?>
2.  <beans xmlns="http://www.springframework.org/schema/beans"
3.  xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo= "http://code.alibabatech.com/schema/dubbo"
4.  xsi:schemaLocation= "http://www.springframework.org/schema/beans
5.   http://www.springframework.org/schema/beans/spring-beans.xsd
6.   http://code.alibabatech.com/schema/dubbo
7.   http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

我们都知道Spring在启动时是要检验XML文件的。或者为什么在Eclipse里xml没有错误提示？

比如这样的一个Spring配置：

1.  <?xml version="1.0" encoding="UTF-8"?>
2.  <beans xmlns="http://www.springframework.org/schema/beans"
3.  xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance"
4.  xsi:schemaLocation= "http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5.  </beans>

我们也可以在后面加上版本号：

xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

有这个版本号和没有有什么区别呢？

### XML的一些概念 ###

首先来看下xml的一些概念：

xml的schema里有namespace，可以给它起个别名。比如常见的spring的namespace：

1.  xmlns:mvc="http://www.springframework.org/schema/mvc"
2.  xmlns:context="http://www.springframework.org/schema/context"

通常情况下，namespace对应的URI是一个存放XSD的地址，尽管规范没有这么要求。如果没有提供schemaLocation，那么Spring的XML解析器会从namespace的URI里加载XSD文件。我们可以把配置文件改成这个样子，也是可以正常工作的：

1.  <?xml version="1.0" encoding="UTF-8"?>
2.  <beans xmlns="http://www.springframework.org/schema/beans/spring-beans.xsd"
3.  xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance">

schemaLocation提供了一个xml namespace到对应的XSD文件的一个映射，所以我们可以看到，在xsi:schemaLocation后面配置的字符串都是成对的，前面的是namespace的URI，后面是xsd文件的URI。比如：

1.  xsi:schemaLocation="http://www.springframework.org/schema/beans
2.  http://www.springframework.org/schema/beans/spring-beans.xsd
3.  http://www.springframework.org/schema/security
4.  http://www.springframework.org/schema/security/spring-security.xsd"

### Spring是如何校验XML的 ###

Spring默认在启动时是要加载XSD文件来验证xml文件的，所以如果有的时候断网了，或者一些开源软件切换域名，那么就很容易碰到应用启动不了。我记得当时Oracle收购Sun公司时，遇到过这个情况。

为了防止这种情况，Spring提供了一种机制，默认从本地加载XSD文件。打开spring-context-3.2.0.RELEASE.jar，可以看到里面有两个特别的文件：

spring.handlers

http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
    http\://www.springframework.org/schema/jee=org.springframework.ejb.config.JeeNamespaceHandler
    http\://www.springframework.org/schema/lang=org.springframework.scripting.config.LangNamespaceHandler
    http\://www.springframework.org/schema/task=org.springframework.scheduling.config.TaskNamespaceHandler
    http\://www.springframework.org/schema/cache=org.springframework.cache.config.CacheNamespaceHandler

spring.schemas

http\://www.springframework.org/schema/context/spring-context-2.5.xsd=org/springframework/context/config/spring-context-2.5.xsd
    http\://www.springframework.org/schema/context/spring-context-3.0.xsd=org/springframework/context/config/spring-context-3.0.xsd
    http\://www.springframework.org/schema/context/spring-context-3.1.xsd=org/springframework/context/config/spring-context-3.1.xsd
    http\://www.springframework.org/schema/context/spring-context-3.2.xsd=org/springframework/context/config/spring-context-3.2.xsd
    http\://www.springframework.org/schema/context/spring-context.xsd=org/springframework/context/config/spring-context-3.2.xsd
    ...

再打开jar包里的org/springframework/context/config/ 目录，可以看到下面有

spring-context-2.5.xsd  
spring-context-3.0.xsd  
spring-context-3.1.xsd  
spring-context-3.2.xsd

很明显，可以想到Spring是把XSD文件放到本地了，再在spring.schemas里做了一个映射，优先从本地里加载XSD文件。

并且Spring很贴心，把旧版本的XSD文件也全放了。这样可以防止升级了Spring版本，而配置文件里用的还是旧版本的XSD文件，然后断网了，应用启动不了。

我们还可以看到，在没有配置版本号时，用的就是当前版本的XSD文件：

http\://www.springframework.org/schema/context/spring-context.xsd=org/springframework/context/config/spring-context-3.2.xsd

同样，我们打开dubbo的jar包，可以在它的spring.schemas文件里看到有这样的配置：

http\://code.alibabatech.com/schema/dubbo/dubbo.xsd=META-INF/dubbo.xsd

所以，Spring在加载dubbo时，会从dubbo的jar里加载dubbo.xsd。

### 如何跳过Spring的XML校验？ ###

可以用这样的方式来跳过校验：

1.  GenericXmlApplicationContext context = new GenericXmlApplicationContext();
2.  context.setValidating(false);

### 如何写一个自己的spring xml namespace扩展 ###

可以参考Spring的文档，实际上是相当简单的。只要实现自己的NamespaceHandler，再配置一下spring.handlers和spring.schemas就可以了。

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/extensible-xml.html

### 其它的一些东东 ###

#### 防止XSD加载不成功的一个思路 ####

http://hellojava.info/?p=135

#### 齐全的Spring的namespace的列表 ####

http://stackoverflow.com/questions/11174286/spring-xml-namespaces-how-do-i-find-what-are-the-implementing-classes-behind-t

# Spring core #

*  `aop` - [`AopNamespaceHandler`][AopNamespaceHandler]
 *  `c` - [`SimpleConstructorNamespaceHandler`][SimpleConstructorNamespaceHandler]
 *  `cache` - [`CacheNamespaceHandler`][CacheNamespaceHandler]
 *  `context` - [`ContextNamespaceHandler`][ContextNamespaceHandler]
 *  `jdbc` - [`JdbcNamespaceHandler`][JdbcNamespaceHandler]
 *  `jee` - [`JeeNamespaceHandler`][JeeNamespaceHandler]
 *  `jms` - [`JmsNamespaceHandler`][JmsNamespaceHandler]
 *  `lang` - [`LangNamespaceHandler`][LangNamespaceHandler]
 *  `mvc` - [`MvcNamespaceHandler`][MvcNamespaceHandler]
 *  `oxm` - [`OxmNamespaceHandler`][OxmNamespaceHandler]
 *  `p` - [`SimplePropertyNamespaceHandler`][SimplePropertyNamespaceHandler]
 *  `task` - [`TaskNamespaceHandler`][TaskNamespaceHandler]
 *  `tx` - [`TxNamespaceHandler`][TxNamespaceHandler]
 *  `util` - [`UtilNamespaceHandler`][UtilNamespaceHandler]

# Spring Security #

*  `security` - [`SecurityNamespaceHandler`][SecurityNamespaceHandler]
 *  `oauth` - [`OAuthSecurityNamespaceHandler`][OAuthSecurityNamespaceHandler]

# Spring integration #

*  `int` - [`IntegrationNamespaceHandler`][IntegrationNamespaceHandler]
 *  `amqp` - [`AmqpNamespaceHandler`][AmqpNamespaceHandler]
 *  `event` - [`EventNamespaceHandler`][EventNamespaceHandler]
 *  `feed` - [`FeedNamespaceHandler`][FeedNamespaceHandler]
 *  `file` - [`FileNamespaceHandler`][FileNamespaceHandler]
 *  `ftp` - [`FtpNamespaceHandler`][FtpNamespaceHandler]
 *  `gemfire` - [`GemfireIntegrationNamespaceHandler`][GemfireIntegrationNamespaceHandler]
 *  `groovy` - [`GroovyNamespaceHandler`][GroovyNamespaceHandler]
 *  `http` - [`HttpNamespaceHandler`][HttpNamespaceHandler]
 *  `ip` - [`IpNamespaceHandler`][IpNamespaceHandler]
 *  `jdbc` - [`JdbcNamespaceHandler`][JdbcNamespaceHandler 1]
 *  `jms` - [`JmsNamespaceHandler`][JmsNamespaceHandler 1]
 *  `jmx` - [`JmxNamespaceHandler`][JmxNamespaceHandler]
 *  `mail` - [`MailNamespaceHandler`][MailNamespaceHandler]
 *  `redis` - [`RedisNamespaceHandler`][RedisNamespaceHandler]
 *  `rmi` - [`RmiNamespaceHandler`][RmiNamespaceHandler]
 *  `script` - [`ScriptNamespaceHandler`][ScriptNamespaceHandler]
 *  `security` - [`IntegrationSecurityNamespaceHandler`][IntegrationSecurityNamespaceHandler]
 *  `sftp` - [`SftpNamespaceHandler`][SftpNamespaceHandler]
 *  `stream` - [`StreamNamespaceHandler`][StreamNamespaceHandler]
 *  `twitter` - [`TwitterNamespaceHandler`][TwitterNamespaceHandler]
 *  `ws` - [`WsNamespaceHandler`][WsNamespaceHandler]
 *  `xml` - [`IntegrationXmlNamespaceHandler`][IntegrationXmlNamespaceHandler]
 *  `xmpp` - `XmppNamespaceHandler`

### 总结： ###

为什么不要在Spring的配置里，配置上XSD的版本号？  
因为如果没有配置版本号，取的就是当前jar里的XSD文件，减少了各种风险。

而且这样约定大于配置的方式很优雅。

### 参考： ###

http://stackoverflow.com/questions/10768873/spring-di-applicationcontext-xml-how-exactly-is-xsischemalocation-used

http://stackoverflow.com/questions/11174286/spring-xml-namespaces-how-do-i-find-what-are-the-implementing-classes-behind-t

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/extensible-xml.html

本文转自： [https://blog.csdn.net/hengyunabc/article/details/22295749][https_blog.csdn.net_hengyunabc_article_details_22295749]

[AopNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/aop/config/AopNamespaceHandler.html
[SimpleConstructorNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/beans/factory/xml/SimpleConstructorNamespaceHandler.html
[CacheNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/cache/config/CacheNamespaceHandler.html
[ContextNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/context/config/ContextNamespaceHandler.html
[JdbcNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/jdbc/config/JdbcNamespaceHandler.html
[JeeNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/ejb/config/JeeNamespaceHandler.html
[JmsNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/jms/config/JmsNamespaceHandler.html
[LangNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/scripting/config/LangNamespaceHandler.html
[MvcNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/web/servlet/config/MvcNamespaceHandler.html
[OxmNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/oxm/config/OxmNamespaceHandler.html
[SimplePropertyNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/beans/factory/xml/SimplePropertyNamespaceHandler.html
[TaskNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/scheduling/config/TaskNamespaceHandler.html
[TxNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/transaction/config/TxNamespaceHandler.html
[UtilNamespaceHandler]: http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/beans/factory/xml/UtilNamespaceHandler.html
[SecurityNamespaceHandler]: http://static.springsource.org/spring-security/site/docs/2.0.x/apidocs/org/springframework/security/config/SecurityNamespaceHandler.html
[OAuthSecurityNamespaceHandler]: http://static.springsource.org/spring-security/oauth/apidocs/org/springframework/security/oauth/config/OAuthSecurityNamespaceHandler.html
[IntegrationNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/config/xml/IntegrationNamespaceHandler.html
[AmqpNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/amqp/config/AmqpNamespaceHandler.html
[EventNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/event/config/EventNamespaceHandler.html
[FeedNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/feed/config/FeedNamespaceHandler.html
[FileNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/file/config/FileNamespaceHandler.html
[FtpNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/ftp/config/FtpNamespaceHandler.html
[GemfireIntegrationNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/gemfire/config/xml/GemfireIntegrationNamespaceHandler.html
[GroovyNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/groovy/config/GroovyNamespaceHandler.html
[HttpNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/http/config/HttpNamespaceHandler.html
[IpNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/ip/config/IpNamespaceHandler.html
[JdbcNamespaceHandler 1]: http://static.springsource.org/spring-integration/api/org/springframework/integration/jdbc/config/JdbcNamespaceHandler.html
[JmsNamespaceHandler 1]: http://static.springsource.org/spring-integration/api/org/springframework/integration/jms/config/JmsNamespaceHandler.html
[JmxNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/jmx/config/JmxNamespaceHandler.html
[MailNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/mail/config/MailNamespaceHandler.html
[RedisNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/redis/config/RedisNamespaceHandler.html
[RmiNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/rmi/config/RmiNamespaceHandler.html
[ScriptNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/scripting/config/jsr223/ScriptNamespaceHandler.html
[IntegrationSecurityNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/security/config/IntegrationSecurityNamespaceHandler.html
[SftpNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/sftp/config/SftpNamespaceHandler.html
[StreamNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/stream/config/StreamNamespaceHandler.html
[TwitterNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/twitter/config/TwitterNamespaceHandler.html
[WsNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/ws/config/WsNamespaceHandler.html
[IntegrationXmlNamespaceHandler]: http://static.springsource.org/spring-integration/api/org/springframework/integration/xml/config/IntegrationXmlNamespaceHandler.html
[https_blog.csdn.net_hengyunabc_article_details_22295749]: https://blog.csdn.net/hengyunabc/article/details/22295749