Cache readers and writers in Java caching technology

Caching technology is widely used in daily development, and there are various cache implementations in Java. Among them, the cache reader and writer is an important caching technology. This article will introduce the cache reader and writer in Java in detail.

1. What is a cache reader and writer

The cache reader and writer is an interface provided to support specific cache behavior when storing objects in the cache. Cache readers and writers provide methods for reading data from the cache and methods for writing data to the cache. Cache readers and writers ensure cache consistency and provide a common cache interface that allows developers to customize their own cache strategies.

The cache reader and writer in Java uses a pattern called CacheWriter and CacheLoader. CacheWriter provides methods to write data to the cache, while CacheLoader provides methods to read data from the cache.

2. CacheWriter interface

The CacheWriter interface is an interface used to write data to the cache. It contains a write method that receives a CacheEntry object as a parameter. A CacheEntry object represents the data to be written to the cache. The following is sample code for the CacheWriter interface:

public interface CacheWriter<K,V> {
    void write(Cache.Entry<? extends K, ? extends V> entry) throws CacheWriterException;
}

CacheWriter contains a generic type K and V, representing the types of cache keys and values. The write method receives a Cache.Entry object as a parameter, indicating that the data in the cache is to be written. Cache.Entry contains cache keys and cache values, and provides methods to get and set their values.

When writing to the cache, the CacheWriter interface provides the following methods:

Write a single cache entry: write(Cache.Entry)

Write multiple entries: writeAll( Collection>)

Delete cache entries: delete(Object)

Delete multiple entries: deleteAll(Collection

It should be noted that the write method of CacheWriter is synchronous, so it can ensure data consistency.

3. CacheLoader interface

The CacheLoader interface is an interface used to read data from the cache. It contains a load method that receives a cache key as a parameter and returns a cache value. The following is sample code for the CacheLoader interface:

public interface CacheLoader<K,V> {
    V load(K key) throws CacheLoaderException;
}

CacheLoader contains a generic type K and V, representing the types of cache keys and values. The load method receives a cache key as a parameter and returns a cache value. If the cached value is not found, the load method should return null.

Generally speaking, CacheLoader is used to automatically fill the cache. When the value corresponding to a key cannot be found in the cache, the cache will call the load method of CacheLoader to automatically load data from background data sources (such as databases, file systems, etc.) and store the data in the cache.

4. CacheWriter and CacheLoader examples

The following is the sample code of CacheWriter and CacheLoader. Here we use a simple cache based on ConcurrentHashMap:

import java.util.Map;
import javax.cache.Cache.Entry;
import javax.cache.integration.CacheLoader;
import javax.cache.integration.CacheLoaderException;
import javax.cache.integration.CacheWriter;
import javax.cache.integration.CacheWriterException;

public class SimpleCache<K, V> implements CacheWriter<K, V>, CacheLoader<K, V> {

    private Map<K, V> cache = new ConcurrentHashMap<>();

    @Override
    public void delete(Object o) throws CacheWriterException {
        cache.remove(o);
    }

    @Override
    public void deleteAll(Collection<?> collection) throws CacheWriterException {
        for(Object o : collection) {
            delete(o);
        }
    }

    @Override
    public void write(Entry<? extends K, ? extends V> entry) throws CacheWriterException {
        cache.put(entry.getKey(), entry.getValue());
    }

    @Override
    public void writeAll(Collection<? extends Entry<? extends K, ? extends V>> collection) throws CacheWriterException {
        for(Entry<? extends K, ? extends V> entry : collection) {
            write(entry);
        }
    }

    @Override
    public V load(K k) throws CacheLoaderException {
        return cache.get(k);
    }

    @Override
    public Map<K, V> loadAll(Iterable<? extends K> iterable) throws CacheLoaderException {
        throw new UnsupportedOperationException("Not implemented");
    }

    @Override
    public void loadCache(IgniteBiInClosure<K, V> biInClosure, Object... objects) throws CacheLoaderException {
        throw new UnsupportedOperationException("Not implemented");
    }
}

In this example, we use ConcurrentHashMap to implement a memory-based cache. Implemented the CacheWriter and CacheLoader interfaces, and implemented the corresponding write and load methods. When a key does not exist in the cache, the load method will return null, and the cache will call the load method of CacheLoader to load data from the background data source.

5. Summary

The cache reader and writer is an important part of Java cache technology. It provides a customizable caching interface that allows developers to customize their own caching strategies. In Java, CacheWriter and CacheLoader are one of the implementation methods of cache readers and writers. By implementing them, the function of automatically filling the cache can be realized in the application.

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