Support escaping prefix and separator in property placeholders [SPR-4953]

[spring-projects-issues]

Chris Lee opened SPR-4953 and commented

There is presently no way to inject a placeholder expression (${...}) that won't be picked up by PropertyPlaceholderConfigurer. Ideally we should be able to inject a string that contains ${...} for later use in its target bean without involvement from PropertyPlaceholderConfigurer.

Perhaps a simple escape mechanism using the conventional backslash, such as "The current value is \\${...}" would suffice.

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Affects: 2.5.4, 2.5.5

11 votes, 5 watchers

[spring-projects-issues]

Timo Thomas commented

Apache Jakarta Commons-Lang has a similar technology known as "StrSubstitutor" (org.apache.commons.lang.text.StrSubstitutor). There, the default escape character is "$", but it is configurable (independently from the prefix and suffix).

I'm using StrSubstitutor on expressions in bean properties, and if there is no escaping, the only (ugly) option left for me is to change one of the prefixes.

IMHO not having an escape character nowadays should be considered as a production-critical feature (what if changing the prefix is not an option? The workarounds necessary then are even more ugly) - if not as a bug.

[spring-projects-issues]

Eric Haszlakiewicz commented

It seems that you can work around this by defining a property that has a value of '$'. e.g.
dollarsign=$

and in the xml config to get a value of e.g. '$foo', you'd write '${dollarsign}foo'

It's not pretty, but at least it works.

[spring-projects-issues]

Jim Utter commented

The workaround does not work when the replacement needs the braces passed through.
For example:

properties:
var=$

wiring:
"${var}{foo}"

or even
var=${

"${var}foo}"

or finally
var=${foo}

"${var}"

still results in an error like:

Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'id' defined in class path resource [applicationContext.xml]: Could not resolve placeholder 'foo'
at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.processProperties(PropertyPlaceholderConfigurer.java:268)

For me, I'd like to define concatenated strings like "${var1}-${var2}${var3}" etc.. where the variables would be internally replaced by velocity (requiring the braces when concatenated).

[spring-projects-issues]

Joshua Caplan commented

The following blog post details a workaround that is available starting from Spring 3.0.x (or whenever SpEL was introduced):

http://jazzjuice.blogspot.com/2011/06/escaping-property-placeholders-in.html

I still agree that native escaping would be useful, though.

[spring-projects-issues]

Aleksandr Dubinsky commented

Indeed, #{'$'}{...} seems to be a valid escape sequence for ${...}.

However, it is too long (5 characters!). It is poorly documented. It exists by sheer accident.

It is really shocking that an escape sequence does not exist. Btw, the alternative of defining a different placeholder sequence is a really, really bad idea. That feature should NOT even be there. Allowing users to arbitrarily re-define the basic syntax of a language leads to confusion.

[spring-projects-issues]

Michel Nolard commented

@Aleksandr Dubinsky: I agree to a 100% with you.

Interesting fact: there is a lot advices on the net to use your trick -- often without referencing your post properly, but this does not remove the need for this issue to be solved anyway !

[spring-projects-issues]

Jan Zidek commented

In YAML configuration files, # is the line comment sign, the rest of the line is ignored. If I escape it with backslah, so I use

\#{'$'}

then it is not ignored, but when the parameter is set by @ConfigurationProperties, the Java string simply contains the sequence as was written in YAML.