如何在 Spring @Value 注释中正确指定默认值？

Question

Initially, I have the following spec:

@Value("#{props.isFPL}")
private boolean isFPL=false;

This works fine correctly getting the value from the property file:

isFPL = true

However, the following expression with default results in the error:

@Value("#{props.isFPL:false}")
private boolean isFPL=false;

Expression parsing failed; nested exception is org.springframework.expression.spel.SpelParseException: EL1041E:(pos 28): After parsing a valid expression, there is still more data in the expression: 'colon(:)'

I also tried to use $ instead of #.

@Value("${props.isFPL:true}")
private boolean isFPL=false;

Then the default value in annotation works fine but I did not get the correct value from the Properties file:

Answer 1

Try with $ as follows:

@Value("${props.isFPL:true}")
private boolean isFPL=false;

Also make sure you set the ignore-resource-no-found to true so that if the property file is missing, the default value will be taken.

Place the following in the context file if using XML based configuration:

<context:property-placeholder ignore-resource-not-found="true"/>

If using Java configurations:

 @Bean
 public static PropertySourcesPlaceholderConfigurer   propertySourcesPlaceholderConfigurer() {
     PropertySourcesPlaceholderConfigurer p =  new PropertySourcesPlaceholderConfigurer();
     p.setIgnoreResourceNotFound(true);

    return p;
 }

Answer 2

For int type variable:

@Value("${my.int.config: #{100}}")
int myIntConfig;

Note: there is no space before the colon, but an extra space after the colon.

Answer 3

Does your Spring application context file contains more than one propertyPlaceholder beans like below:

<context:property-placeholder ignore-resource-not-found="true" ignore-unresolvable="true" location="classpath*:/*.local.properties" />
<context:property-placeholder location="classpath:/config.properties" />

If so, then property lookup for: props.isFPL will only take place for the first property file ( .local.properties ), if property not found, the default value ( true ) will take effect and the second property file ( config.properties ) is effectively ignored for this property.

Answer 4

For a String you can default to null like so:

public UrlTester(@Value("${testUrl:}") String url) {
    this.url = url;
}

Answer 5

Depends on how you're loading your properties, if you use something like

<context:property-placeholder location="classpath*:META-INF/spring/*.properties" />

Then @Value should look like

@Value("${isFPL:true}")

Answer 6

The exact answer of your question depends on the type of the parameter.

for 'String' parameters, your sample code works fine:

@Value("#{props.string.fpl:test}")
private String fpl = "test";

for other types (like boolean in your question) it should be written in this way:

@Value("${props.boolean.isFPL:#{false}}")
private boolean isFPL = false;

or for 'Integers':

@Value("${props.integer.fpl:#{20}}")

Answer 7

This way of defining defaults works only if we write "value=..." in the @Value annotation. eg

Does not work : @Value("${testUrl:some-url}" // This will always set "some-url" no matter what you do in the config file.

Works : @Value(value = "${testUrl:some-url}" // This will set "some-url" only if testUrl property is missing in the config file.