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

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

> 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.

From Spring 4.1.x ( I can't remember specific version though ), you can do something like

@Value("#{${your.properties.key.name}}")
private Map<String, String> myMap;

where your.properties.key.name in your properties file should be something like

your.properties.key.name={\
    name1 : 100, \
    name2 : 200 \
}

Just make sure that you should create PropertySourcesPlaceholderConfigurer bean to make it work both in your app and if you are writing any unit test code to test your code, otherwise ${...} placeholder for the property value won't work as expected and you'll see some weird SpringEL errors.

The quickest Spring Boot based solution I can think of follows. In my particular example I am migrating data from one system to another. That is why I need a mapping for a field called priority.

First I've created the properties file (priority-migration.properties) like such:

my.prefix.priority.0:0
my.prefix.priority.10:1
my.prefix.priority.15:2
my.prefix.priority.20:2
another.prefix.foo:bar

and put it on the classpath.

Assuming you want to use the map in a spring managed bean/component, annotate your class with:

@Component
@PropertySource("classpath:/priority-migration.properties")

What you actually want in your map is of course only the key/value pairs which are prefixed with my.prefix, i.e. this part:

{
    0:0
    10:1
    15:2
    20:2
}

To achieve that you need to annotate your component with

@ConfigurationProperties("my.prefix")

and create a getter for the priority infix. The latter proved to be mandatory in my case (although the Sring Doc says it is enough to have a property priority and initialize it with a mutable value)

private final Map<Integer, Integer> priorityMap = new HashMap<>();

public Map<Integer, Integer> getPriority() {
    return priorityMap;
}

---

In the End

It looks something like this:

@Component
@ConfigurationProperties("my.prefix")
@PropertySource("classpath:/priority-migration.properties")
class PriorityProcessor {

    private final Map<Integer, Integer> priorityMap = new HashMap<>();

    public Map<Integer, Integer> getPriority() {
        return priorityMap;
    }

    public void process() {

        Integer myPriority = priorityMap.get(10)
        // use it here
    }
}

I make one solution inspired by the previous post.

Register property file in the Spring configuration:

<util:properties id="myProp" location="classpath:my.properties"/>

And I create component:

@Component("PropertyMapper")
public class PropertyMapper {

    @Autowired
    ApplicationContext applicationContext;

    public HashMap<String, Object> startWith(String qualifier, String startWith) {
        return startWith(qualifier, startWith, false);
    }

    public HashMap<String, Object> startWith(String qualifier, String startWith, boolean removeStartWith) {
        HashMap<String, Object> result = new HashMap<String, Object>();

        Object obj = applicationContext.getBean(qualifier);
        if (obj instanceof Properties) {
            Properties mobileProperties = (Properties)obj;
        
            if (mobileProperties != null) {
                for (Entry<Object, Object> e : mobileProperties.entrySet()) {
                    Object oKey = e.getKey();
                    if (oKey instanceof String) {
                        String key = (String)oKey;
                        if (((String) oKey).startsWith(startWith)) {
                            if (removeStartWith) 
                                key = key.substring(startWith.length());
                            result.put(key, e.getValue());
                        }
                    }
                }
            }
        }

        return result;
    }
}

And when I want to map all properties that begin with specifix value to HashMap, with @Value annotation:

@Service
public class MyServiceImpl implements MyService {

    @Value("#{PropertyMapper.startWith('myProp', 'service.expiration.', true)}")
    private HashMap<String, Object> portalExpirations;

Solution for pulling Map using @Value from application.yml property coded as multiline

> application.yml

other-prop: just for demo 

my-map-property-name: "{\
         key1: \"ANY String Value here\", \  
         key2: \"any number of items\" , \ 
         key3: \"Note the Last item does not have comma\" \
         }"

other-prop2: just for demo 2 

Here the value for our map property "my-map-property-name" is stored in JSON format inside a string and we have achived multiline using \ at end of line

> myJavaClass.java

import org.springframework.beans.factory.annotation.Value;

public class myJavaClass {

@Value("#{${my-map-property-name}}") 
private Map<String,String> myMap;

public void someRandomMethod (){
    if(myMap.containsKey("key1")) {
            //todo...
    } }

}

More explanation

• \ in yaml it is Used to break string into multiline

• \" is escape charater for "(quote) in yaml string

• {key:value} JSON in yaml which will be converted to Map by @Value

• #{ } it is SpEL expresion and can be used in @Value to convert json int Map or Array / list Reference

Tested in a spring boot project

Use the same variable name as the Yaml name

Eg:

private final HashMap<String, String> expiration 

instead of

private final HashMap<String, String> expirations 

Or something similar to this in properties file

org.code=0009,0008,0010
org.code.0009.channel=30,40
org.code.0008.channel=30,40
org.code.0010.channel=30,40

in Java, read org.code and then loop thru each org.code and build org.code..channel and put it into a map....