我刚接触Spring Bean。我正在参考一些书籍和博客。有些书中上下文配置是给定为<beans:bean>
,而在其他一些书中只是<beans>
。这有什么区别?我们是否应该在上下文文件中给出XML名称空间?它会在应用部署时引用实际站点吗?
我刚接触Spring Bean。我正在参考一些书籍和博客。有些书中上下文配置是给定为<beans:bean>
,而在其他一些书中只是<beans>
。这有什么区别?我们是否应该在上下文文件中给出XML名称空间?它会在应用部署时引用实际站点吗?
就 Spring 来说,XML 必须是有效的,以便 Spring 能够理解它,这是唯一需要考虑的。您可以选择任何格式。通常使用默认命名空间可以避免过多的输入(所有示例基于 附录 C. 基于 XML Schema 的配置):
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="..."/>
</beans>
xmlns="..."
属性定义了默认命名空间(如果您未指定任何命名空间,则使用该命名空间,例如<beans/>
)。只要您仅使用单个beans
命名空间并偶尔使用其他命名空间的少数声明,这是可以接受的:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd">
<bean id="..." class="...">
<property name="isolation">
<util:constant static-field="java.sql.Connection.TRANSACTION_SERIALIZABLE"/>
</property>
</bean>
</beans>
但有时您会注意到,与默认的beans
命名空间相比,您使用了来自不同命名空间的节点更多。一个很好的例子是Spring Security配置文件:
<beans xmlns:security="http://www.springframework.org/schema/security"
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/security
http://www.springframework.org/schema/security/spring-security-3.0.3.xsd">
<security:http auto-config='true'>
<security:intercept-url pattern="/login.jsp*" access="IS_AUTHENTICATED_ANONYMOUSLY"/>
<security:intercept-url pattern="/**" access="ROLE_USER" />
<security:form-login login-page='/login.jsp'/>
<security:session-management>
<security:concurrency-control max-sessions="1" />
</security:session-management>
<security:openid-login>
<security:attribute-exchange>
<security:openid-attribute name="email" type="http://axschema.org/contact/email" required="true" />
<security:openid-attribute name="name" type="http://axschema.org/namePerson" />
</security:attribute-exchange>
</security:openid-login>
</security:http>
<security:authentication-manager>
<security:authentication-provider user-service-ref='myUserDetailsService'/>
</security:authentication-manager>
<bean id="myUserDetailsService" class="org.springframework.security.core.userdetails.jdbc.JdbcDaoImpl">
<property name="dataSource" ref="dataSource"/>
</bean>
</beans>
您看到了吗,因为beans
默认命名空间很少使用,所以整个文件都必须充斥着security:
前缀,这是多么笨拙的做法呀?那么换成这种方式(注意xmlns
命名空间声明已经更改):
<beans:beans xmlns="http://www.springframework.org/schema/security"
xmlns:beans="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/security
http://www.springframework.org/schema/security/spring-security-3.0.3.xsd">
<http auto-config='true'>
<intercept-url pattern="/login.jsp*" access="IS_AUTHENTICATED_ANONYMOUSLY"/>
<intercept-url pattern="/**" access="ROLE_USER" />
<form-login login-page='/login.jsp'/>
<session-management>
<concurrency-control max-sessions="1" />
</session-management>
<openid-login>
<attribute-exchange>
<openid-attribute name="email" type="http://axschema.org/contact/email" required="true" />
<openid-attribute name="name" type="http://axschema.org/namePerson" />
</attribute-exchange>
</openid-login>
</http>
<authentication-manager>
<authentication-provider user-service-ref='myUserDetailsService'/>
</authentication-manager>
<beans:bean id="myUserDetailsService" class="org.springframework.security.core.userdetails.jdbc.JdbcDaoImpl">
<beans:property name="dataSource" ref="dataSource"/>
</beans:bean>
</beans:beans>
这取决于XML命名空间配置,而不是Spring功能,对代码没有影响,但对编码人员有一定影响,实际上定义xmlns
属性对根XML元素的影响不同。 在Spring Security的本章中阅读更多关于<beans:bean>
的内容(它实际上与Spring Framework不同,但非常常见,并在XML文件中使用自己的命名空间)。您可以编写:
<beans:beans xmlns="http://www.springframework.org/schema/security"
xmlns:beans="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/security
http://www.springframework.org/schema/security/spring-security-3.1.xsd">
<global-method-security pre-post-annotations="enabled">
<expression-handler ref="expressionHandler"/>
</global-method-security>
<beans:bean id="expressionHandler" class=
"org.springframework.security.access.expression.method.DefaultMethodSecurityExpressionHandler">
<beans:property name="permissionEvaluator" ref="myPermissionEvaluator"/>
</beans:bean>
</beans:beans>
这相当于:
<beans xmlns="http://www.springframework.org/schema/beans" <!-- see the difference here? -->
xmlns:security="http://www.springframework.org/schema/security"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/security
http://www.springframework.org/schema/security/spring-security-3.1.xsd">
<security:global-method-security pre-post-annotations="enabled">
<security:expression-handler ref="expressionHandler"/>
</security:global-method-security>
<bean id="expressionHandler" class=
"org.springframework.security.access.expression.method.DefaultMethodSecurityExpressionHandler">
<property name="permissionEvaluator" ref="myPermissionEvaluator"/>
</bean>
</beans>
个人而言,我总是使用beans作为主要命名空间,但这只是习惯问题。