Spring Boot SpEL ConditionalOnExpression check multiple properties

问题

Question:

How can I use Spring Expression Language to check that 2 Boolean properties are true?

For example, checking that a single property is true would use the syntax:

Example

@ConditionalOnExpression("${property.from.properties.file}")

What would be the syntax for checking property1 == true && property2 == false? Where the properties can potentially have different values.

The answer from a similar question: How to check two condition while using @ConditionalOnProperty or @ConditionalOnExpression concatenates two strings together and performs a check like so:

Concatenation Solution

@ConditionalOnExpression("'${com.property1}${com.property2}'=='value1value2'")

That syntax seems confusing to someone reading that code and it seems like a hacky solution. There are some edge cases where the solution fails as well. I want to find the proper way to check two separate properties without concatenating the values.

Note: Also just to be clear, the answer isn't something you can easily search for from what I've seen. It seems like it would be a really simple answer but it's proving to be fairly elusive.

回答1:

The annotations @ConditionalOnProperty and @ConditionalOnExpression both do NOT have the java.lang.annotation.Repeatable annotation so you would not be able to just add multiple annotations for checking multiple properties.

The following syntax has been tested and works:

Solution for Two Properties

@ConditionalOnExpression("${properties.first.property.enable:true} && ${properties.second.property.startServer:false}")

Note the following:

• You need to using colon notation to indicate the default value of the property in the expression language statement
• Each property is in a separate expression language block ${}
• The && operator is used outside of the SpEL blocks

It allows for multiple properties that have differing values and can extend to multiple properties.

If you want to check more then 2 values and still maintain readability, you can use the concatenation operator between different conditions you are evaluating:

Solution for more then 2 properties

@ConditionalOnExpression("${properties.first.property.enable:true} " +
        "&& ${properties.second.property.enable:true} " +
        "&& ${properties.third.property.enable:true}")

The drawback is that you cannot use a matchIfMissing argument as you would be able to when using the @ConditionalOnProperty annotation so you will have to ensure that the properties are present in the .properties or YAML files for all your profiles/environments or just rely on the default value

回答2:

As far as i remember, You could use this kind of expression:

@ConditionalOnExpression("'${com.property1}'.equals('${com.property2}')")

for further reading here is the link

if it was helpful, please do comment so that my confusion may also get cleared.

来源：https://stackoverflow.com/questions/40477251/spring-boot-spel-conditionalonexpression-check-multiple-properties