Spring - 仅当值不为null时才设置属性 [英] Spring - set a property only if the value is not null
问题描述
使用Spring时,是否可以仅在传递的值不为null时设置属性?
When using Spring, is it possible to set a property only if the value passed is not null?
示例:
<bean name="myBean" class="some.Type">
<property name="abc" value="${some.param}"/>
</bean>
我正在寻找的行为是:
some.Type myBean = new some.Type();
if (${some.param} != null) myBean.setAbc(${some.param});
我需要这个的原因是因为 abc
有一个默认值,我不想用 null
覆盖。
我正在创建的Bean不在我的源代码控制之下 - 所以我无法改变它的行为。 (另外, abc
为此目的可能是原始的,所以无论如何我都不能用null设置它。
The reason I need this is since abc
has a default value which I don't want to override with a null
.
And the Bean I am creating is not under my source control - so I cannot change its behavior. (Also, abc
for this purpose might be a primitive, so I can't set it with a null anyway.
编辑:
根据答案,我认为我的问题需要澄清。
According to the answers I think my question requires clarification.
我有需要的bean实例化并传递给我使用的第三方。这个bean有许多不同类型的属性(当前12个)( int
, boolean
,字符串
等)
每个属性都有一个默认值 - 我不知道它是什么,除非需要知道,否则这是一个问题。
我正在寻找的是一个来自Spring的能力的通用解决方案 - 目前我唯一的解决方案是基于反射。
I have bean I need to instantiate and pass to 3rd party I use. This bean has many properties (12 currently) of various types (int
, boolean
, String
, etc.)
Each property has a default value - I don't know what it is and would prefer not needing to know unless it becomes an issue.
What I'm looking for is a generic solution that comes from Spring's abilities - currently the only solution I have is a reflection based.
配置
<bean id="myBean" class="some.TypeWrapper">
<property name="properties">
<map>
<entry key="abc" value="${some.value}"/>
<entry key="xyz" value="${some.other.value}"/>
...
</map>
</property>
</bean>
代码
public class TypeWrapper
{
private Type innerBean;
public TypeWrapper()
{
this.innerBean = new Type();
}
public void setProperties(Map<String,String> properties)
{
if (properties != null)
{
for (Entry<String, Object> entry : properties.entrySet())
{
String propertyName = entry.getKey();
Object propertyValue = entry.getValue();
setValue(propertyName, propertyValue);
}
}
}
private void setValue(String propertyName, Object propertyValue)
{
if (propertyValue != null)
{
Method method = getSetter(propertyName);
Object value = convertToValue(propertyValue, method.getParameterTypes()[0]);
method.invoke(innerBean, value);
}
}
private Method getSetter(String propertyName)
{
// Assume a valid bean, add a "set" at the beginning and toUpper the 1st character.
// Scan the list of methods for a method with the same name, assume it is a "valid setter" (i.e. single argument)
...
}
private Object convertToValue(String valueAsString, Class type)
{
// Check the type for all supported types and convert accordingly
if (type.equals(Integer.TYPE))
{
...
}
else if (type.equals(Integer.TYPE))
{
...
}
...
}
}
真正的困难是为所有可能的值类型实现 convertToValue
。
我一生中不止一次这样做 - 所以对于我需要的所有可能的类型(主要是原语和一些枚举)实现它并不是一个主要问题 - 但我希望存在更智能的解决方案。
The real "difficulty" is in implementing convertToValue
for all possible value types.
I have done this more than once in my life - so it is not a major issue to implement it for all possible types that I need (mostly primitives and a few enums) - but I hoped a more intelligent solution existed.
推荐答案
您可以使用 SpEL
以及占位符机制的占位符和默认值如下所示:
You can use SpEL
and placeholder and default value for placeholder mechanisms together as following:
<bean name="myBean" class="some.Type">
<property name="abc" value="${some.param:#{null}}"/>
</bean>
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