Spring 4 @Value where property default is a java system property

Question

In Spring 4, using the @Value annotation, what is the right way to specify a system property as a default if a specified property does not exists?

Whereas this works for the no-default case:

@Value("${myapp.temp}")
private String tempDirectory;

This doesn't work when I need a default:

@Value("#{myapp.temp ?: systemProperties.java.io.tmpdir}")
private String tempDirectory;

Nor does this:

@Value("#{myapp.temp ?: systemProperties(java.io.tmpdir)}")
private String tempDirectory;

Both of these give me an exception at the time Spring is trying to create the bean:

org.springframework.beans.factory.BeanCreationException: Error creating bean  
     with name 'configurationService': Invocation of init method failed;
     nested exception is java.lang.NullPointerException

Can this be done?

@chrylis -- Spring throws an exception when trying to create the bean. I've edited the question to be more explicit. — David H, Jun 29 '15 at 16:26
You have a "nested exception", which presumably has useful information. Post the *whole* stack trace. — chrylis -cautiouslyoptimistic-, Jun 29 '15 at 17:04

score 13 · Accepted Answer · edited Jun 20 '20 at 09:12

I tried the following and it worked for me:

@Value("${myapp.temp:#{systemProperties['java.io.tmpdir']}}")
private String tempDirectory;

The missing parts for you I believe was not using ?: and needing the #{}. According to this answer:

${...} is the property placeholder syntax. It can only be used to dereference properties.

#{...} is SpEL syntax, which is far more capable and complex. It can also handle property placeholders, and a lot more besides.

So basically what is happening is we are telling Spring to first interpret myapp.temp as property placeholder syntax by using the ${} syntax. We then use : instead of ?: (which is called the Elvis operator) since the elvis operator only applies to Spring Expression Language expressions, not property placeholder syntax. The third part of our statement is #{systemProperties['java.io.tmpdir']} which is telling Spring to interpret the next expression as a Spring Expression and allows us to get system properties.

You don't need SpEL for that. `@Value("${myapp.temp:${java.io.tmpdir}}") works evenly wel.. — M. Deinum, Jun 29 '15 at 19:03

score 1 · Answer 2 · answered Jun 29 '15 at 16:34

1

Try systemProperties['java.io.tmpdir'].

It's a map, so if the key has a dot in the name, you should use [..]

answered Jun 29 '15 at 16:34

Bozho

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score 0 · Answer 3 · answered Oct 21 '15 at 12:53

For me it only works with different property-names (being property.name.a a key with a value in my application.properties and property.name.b a Environment-Variable) like:

@Value("${property.name.a:${property.name.b}}")

The same names didn´t work for me like expected (loading the default, when the first property isn´t present), e.g.:

@Value("${property.name.a:${property.name.a}}")

Spring 4 @Value where property default is a java system property

3 Answers3