How to fill HashMap from java property file with Spring @Value
Is it possible to use Spring @Value, to map values from properties file to the HashMap.
Currently I have something like this, and mapping one value is not a problem. But I need to map custom values in HashMap expirations. Is something like this possible?
@Service
@PropertySource(value = "classpath:my_service.properties")
public class SomeServiceImpl implements SomeService {
@Value("#{conf['service.cache']}")
private final boolean useCache = false;
@Value("#{conf['service.expiration.[<custom name>]']}")
private final HashMap<String, String> expirations = new HashMap<String, String>();
Property file: 'my_service.properties'
service.cache=true
service.expiration.name1=100
service.expiration.name2=20
Is it posible to map like this key:value set
name1 = 100
name2 = 20
Solution 1:
You can use the SPEL json-like syntax to write a simple map or a map of list in property file.
simple.map={'KEY1': 'value1', 'KEY2': 'value3', 'KEY3': 'value5'}
map.of.list={\
'KEY1': {'value1','value2'}, \
'KEY2': {'value3','value4'}, \
'KEY3': {'value5'} \
}
I used \
for multiline property to enhance readability
Then, in Java, you can access and parse it automatically with @Value
like this.
@Value("#{${simple.map}}")
Map<String, String> simpleMap;
@Value("#{${map.of.list}}")
Map<String, List<String>> mapOfList;
Here with ${simple.map}
, @Value
gets the following String from the property file:
"{'KEY1': 'value1', 'KEY2': 'value3', 'KEY3': 'value5'}"
Then, it is evaluated as if it was inlined
@Value("#{{'KEY1': 'value1', 'KEY2': 'value3', 'KEY3': 'value5'}}")
You can learn more in the official documentation
Solution 2:
Is it possible to use Spring @Value, to map values from properties file to the HashMap?
Yes, it is. With a little help of code and Spel.
Firstly, consider this singleton Spring-bean (you should scan it):
@Component("PropertySplitter")
public class PropertySplitter {
/**
* Example: one.example.property = KEY1:VALUE1,KEY2:VALUE2
*/
public Map<String, String> map(String property) {
return this.map(property, ",");
}
/**
* Example: one.example.property = KEY1:VALUE1.1,VALUE1.2;KEY2:VALUE2.1,VALUE2.2
*/
public Map<String, List<String>> mapOfList(String property) {
Map<String, String> map = this.map(property, ";");
Map<String, List<String>> mapOfList = new HashMap<>();
for (Entry<String, String> entry : map.entrySet()) {
mapOfList.put(entry.getKey(), this.list(entry.getValue()));
}
return mapOfList;
}
/**
* Example: one.example.property = VALUE1,VALUE2,VALUE3,VALUE4
*/
public List<String> list(String property) {
return this.list(property, ",");
}
/**
* Example: one.example.property = VALUE1.1,VALUE1.2;VALUE2.1,VALUE2.2
*/
public List<List<String>> groupedList(String property) {
List<String> unGroupedList = this.list(property, ";");
List<List<String>> groupedList = new ArrayList<>();
for (String group : unGroupedList) {
groupedList.add(this.list(group));
}
return groupedList;
}
private List<String> list(String property, String splitter) {
return Splitter.on(splitter).omitEmptyStrings().trimResults().splitToList(property);
}
private Map<String, String> map(String property, String splitter) {
return Splitter.on(splitter).omitEmptyStrings().trimResults().withKeyValueSeparator(":").split(property);
}
}
Note: PropertySplitter
class uses Splitter
utility from Guava. Please refer to its documentation for further details.
Then, in some bean of yours:
@Component
public class MyBean {
@Value("#{PropertySplitter.map('${service.expiration}')}")
Map<String, String> propertyAsMap;
}
And finally, the property:
service.expiration = name1:100,name2:20
It's not exactly what you've asked, because this PropertySplitter
works with one single property that is transformed into a Map
, but I think you could either switch to this way of specifying properties, or modify the PropertySplitter
code so that it matches the more hierarchical way you desire.