javaehcache-3

How to initialize List<> of object for ehcache?


I need to initialize the Cache which needs to contain

String in key
List<Object> in value

So i have CacheHelper class which has

public class CacheHelper {

    private CacheManager cacheManager;

    private Cache<String,List<Person>> cacheDataList;

    private static final String CACHE_PERSON="cache_key_person";


    public CacheHelper() {


    }

    public void putInCacheFromDb(){
        System.getProperties().setProperty("java -Dnet.sf.ehcache.use.classic.lru", "true");
        cacheManager= CacheManagerBuilder
                .newCacheManagerBuilder().build();
        cacheManager.init();


        cacheDataList = cacheManager
                .createCache("cacheOfPersonList", CacheConfigurationBuilder
                        .newCacheConfigurationBuilder(
                                String.class,Person.class,
                                ResourcePoolsBuilder.heap(10)).withExpiry(Expirations.timeToLiveExpiration(Duration.of(60,
                                TimeUnit.SECONDS))));


    }


    public void putInList(List<Person> personList){
        System.out.println("putting list in cache");
        cacheDataList.put(CACHE_PERSON,personList);
    }


}

But at this line of code,I am not able to conver object into list String.class,Person.class ,which needs to be String.class,List:

 cacheDataList = cacheManager
                    .createCache("cacheOfPersonList", CacheConfigurationBuilder
                            .newCacheConfigurationBuilder(
                                    String.class,Person.class,
                                    ResourcePoolsBuilder.heap(10)).withExpiry(Expirations.timeToLiveExpiration(Duration.of(60,
                                    TimeUnit.SECONDS))));

But I am getting error as:

Incompatible types. Required Cache<String, List<Person>> but 'createCache' was inferred to Cache<K, V>: Incompatible equality constraint: List<Person> and Person

I need to store List in a single key.how can I initialize it?


Solution

  • What you have won't work because you're defining the configuration builder to have a key of String and a value of Person, not a List of Person. Generics doesn't let you get the class of List so you need to implement a wrapper:

    import org.ehcache.Cache;
    import org.ehcache.CacheManager;
    import org.ehcache.config.builders.CacheConfigurationBuilder;
    import org.ehcache.config.builders.CacheManagerBuilder;
    import org.ehcache.config.builders.ResourcePoolsBuilder;
    import org.ehcache.expiry.Expirations;
    
    import java.util.ArrayList;
    import java.util.Collection;
    import java.util.List;
    import java.util.concurrent.TimeUnit;
    
    public class CacheHelper {
    
    
        private CacheManager cacheManager;
    
        private Cache<String, PersonList> cacheDataList;
    
        private static final String CACHE_PERSON = "cache_key_person";
    
        private static class Person {
            final String name;
    
            public Person(final String name) {
                this.name = name;
            }
        }
    
        private class PersonList extends ArrayList<Person> {
            public PersonList(final Collection<? extends Person> c) {
                super(c);
            }
        }
    
        public static void main(String[] args) {
    
    
            List<Person> persons = new ArrayList<>();
            persons.add(new Person("Bob"));
            persons.add(new Person("Sally"));
    
            CacheHelper helper = new CacheHelper();
            helper.putInList(persons);
            PersonList personList = helper.cacheDataList.get(CACHE_PERSON);
            for (Person p : personList) {
                System.out.println("Found " + p.name);
            }
    
        }
    
        public CacheHelper() {
            System.getProperties().setProperty("java -Dnet.sf.ehcache.use.classic.lru", "true");
            cacheManager = CacheManagerBuilder
                    .newCacheManagerBuilder().build();
            cacheManager.init();
            cacheDataList = cacheManager
                    .createCache("cacheOfPersonList", CacheConfigurationBuilder
                            .newCacheConfigurationBuilder(String.class, PersonList.class, ResourcePoolsBuilder.heap(10))
                            .withExpiry(Expirations.timeToLiveExpiration(org.ehcache.expiry.Duration.of(20, TimeUnit.SECONDS))));
        }
    
    
        public void putInList(List<Person> personList) {
            System.out.println("putting list in cache");
            cacheDataList.put(CACHE_PERSON, new PersonList(personList));
        }
    
    
    }