Spring - 使用静态最终字段（常量）进行 bean 初始化
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Spring - using static final fields (constants) for bean initialization
提问by lisak
is it possible to define a bean with the use of static final fields of CoreProtocolPNames class like this:
是否可以使用 CoreProtocolPNames 类的静态最终字段来定义一个 bean，如下所示：
<bean id="httpParamBean" class="org.apache.http.params.HttpProtocolParamBean">
<constructor-arg ref="httpParams"/>
<property name="httpElementCharset" value="CoreProtocolPNames.HTTP_ELEMENT_CHARSET" />
<property name="version" value="CoreProtocolPNames.PROTOCOL_VERSION">
</bean>
public interface CoreProtocolPNames {
public static final String PROTOCOL_VERSION = "http.protocol.version";
public static final String HTTP_ELEMENT_CHARSET = "http.protocol.element-charset";
}
If it is possible, what is the best way of doing this ?
如果可能，最好的方法是什么？
回答by Paul McKenzie
Something like this (Spring 2.5)
像这样的东西（Spring 2.5）
<bean id="foo" class="Bar">
<property name="myValue">
<util:constant static-field="java.lang.Integer.MAX_VALUE"/>
</property>
</bean>
Where utilnamespace is from xmlns:util="http://www.springframework.org/schema/util"
util命名空间来自哪里xmlns:util="http://www.springframework.org/schema/util"
But for Spring 3, it would be cleaner to use the @Valueannotation and the expression language. Which looks like this:
但是对于 Spring 3，使用@Value注解和表达式语言会更干净。看起来像这样：
public class Bar {
@Value("T(java.lang.Integer).MAX_VALUE")
private Integer myValue;
}
回答by cr7pt0gr4ph7
Or, as an alternative, using Spring EL directly in XML:
或者，作为替代方案，直接在 XML 中使用 Spring EL：
<bean id="foo1" class="Foo" p:someOrgValue="#{T(org.example.Bar).myValue}"/>
This has the additional advantage of working with namespace configuration:
这具有使用命名空间配置的额外优势：
<tx:annotation-driven order="#{T(org.example.Bar).myValue}"/>
回答by sampath
don't forget to specify the schema location..
不要忘记指定架构位置..
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd">
</beans>
回答by Balaji Boggaram Ramanarayan
One more example to add for the instance above. This is how you can use a static constant in a bean using Spring.
为上述实例添加的另一个示例。这就是使用 Spring 在 bean 中使用静态常量的方式。
<bean id="foo1" class="Foo">
<property name="someOrgValue">
<util:constant static-field="org.example.Bar.myValue"/>
</property>
</bean>
package org.example;
public class Bar {
public static String myValue = "SOME_CONSTANT";
}
package someorg.example;
public class Foo {
String someOrgValue;
foo(String value){
this.someOrgValue = value;
}
}
回答by chetan singhal
<util:constant id="MANAGER"
static-field="EmployeeDTO.MANAGER" />
<util:constant id="DIRECTOR"
static-field="EmployeeDTO.DIRECTOR" />
<!-- Use the static final bean constants here -->
<bean name="employeeTypeWrapper" class="ClassName">
<property name="manager" ref="MANAGER" />
<property name="director" ref="DIRECTOR" />
</bean>
