Question

我是春豆的新手。我指的是书籍和博客。在某些情况下，上下文配置为<beans:bean>，有些仅为<beans>。有什么不同？我们应该在上下文文件中提供XML命名空间吗？它是否会在应用程序部署时引用该实际站点？

Answer 1

就Spring而言无关紧要 - XML必须是有效的，以便Spring可以理解它，就是这样。您可以选择哪种格式。通常，您使用默认命名空间来避免键入太多（所有示例都基于Appendix C. XML Schema-based configuration）：

<?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="..."属性定义默认命名空间（如果您根本没有指定任何命名空间，则使用该命名空间，例如<beans/>。只要您只使用单个beans命名空间，这就没用了偶尔也很少来自其他命名空间的声明：

<?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beans命名空间相比，您使用的是来自不同命名空间的更多节点。一个很好的例子是Spring Security configuration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>

你看到它有多笨拙，因为beans默认命名空间的使用很少，但整个文件必须用security:前缀混乱？那怎么样（注意xmlns名称空间声明如何变化）：

<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>

这两个配置文件在语义上是等效的（它只是对相同信息进行编码的不同方式）。但后者更具可读性。只需使用默认命名空间，无论使用哪个命名空间。

Answer 2

它取决于XML命名空间配置而不是Spring功能，对代码没有任何区别，对编码器有所不同，实际上是在根xml元素上定义xmlns属性的效果。 Read more about <beans:bean> in this chapter of Spring Security（实际上它与Spring Framework不同，但非常常见，并且在XML文件中使用自己的命名空间）。你可以写：

<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>

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>

我个人总是使用bean作为主命名空间，但这是习惯问题。

spring beans Context配置

2 个答案: